Preface. The information in this document is subject to change without notice and does not represent a commitment on the part of NT-MDT.

Transcription

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2 Preface The information in this document is subject to change without notice and does not represent a commitment on the part of NT-MDT. Please note: Some components described in this manual may be optional. The delivery volume depends on the ordered configuration. Please note: Product names mentioned herein may also be trademarks and/or registered trademarks of their respective companies. Attention: Please read the information below and safety regulations issue before using the instrument Laser Warning Logotype and Aperture Label - This label is located on the head. Certification Label - This label is located on the head. Attention Label - This label is located on the back panel of electronics block. Related Manuals General information Instruction Manual Reference Manual Surface Objects Analysis with the Help of «GRAIN ANALYSIS» tool Copyright No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, for any purpose without the express written permission of NT-MDT.

3 Table of contents I Table of contents Chapter 1. What is SPM Solver P47H* Functions and Performance Capabilities of SPM Solver P47H Functions of SPM Solver P47H Measurement Capabilities of SPM Solver P47H Measurement and Influence Methods and Modes Implemented in SPM Solver P47H Functional Parameters of SPM Solver P47H Technical parameters of Solver P47H Brief description of the unit s design Measurement heads Scanner module The vibroprotection system The electronic module Preparing the microscope and PC Installing the scanner module onto the vibroprotection system Connecting the Scanning Probe Microscope (SPM) Installing the interface card into PC (when sold without PC) Software installation (when sold without PC) Turning the unit on and off Operation conditions Safty regulations Requirements to computer and operational system Requirements to operation room Chapter 2. General concepts and brief description of microscope operation in AFM modes Main components, general principle of microscope operation and main components interaction scheme The atomic force microscope probe Piezoelectric scanner Optical system for cantilever deflections detection General concepts of AFM Mode operations Forces acting between the cantilever tip and the sample Atomic Force Microscope modes and main techniques of Atomic Force Microscopy General concepts of the unit s operation in contact mode General concepts of the unit s operation in the mode of Contact Atomic Force Microscopy Feed-back Loop Schematic in the contact mode Advantages and disadvantages of Contact Mode AFM General concepts of the modes using vibration techniques Vibration and Modulation Techniques of Atomic Force Microscopy General concepts of the unit s operation in the mode of Semi-Contact Atomic Force Microscopy Feedback loop in the semi-contact mode Controlling the SPM and the main parameters determining the unit s operation Graphic Interface for SPM Control Main program window SPM Control block diagram Lock-In Amplifier and Phase Detector Control block diagram Scanning Parameters Control Window Main parameters determining SPM s operation * Under development

4 II Solver P47H SPM Instruction Manual Chapter 3. Preparing the microscope, SPM head, probe and sample Main operations to be performed to prepare the microscope for operation Turning the unit on, the control program start up Choice of cantilever Installing the cantilever Installing the cantilever in SPM heads SFC050, SFC050SEMI, SFC090, SFC090SEMI Installing the cantilever in SPM heads SFC050L, SFC090L Cantilever holder for operation in air Cantilever holder for operation in fluid Installing the cantilevers into holders Installing the cantilever holder into the SPM head Removing the cantilever holder Replacing the cantilever Adjusting the laser and photodiode Turning on the laser and the photodiode indicator Laser adjustment Visual observation mirror Adjusting the laser with the naked eye Adjusting the photodiode using the photodiode indicator Fine laser adjustment using the photodiode indicator Adjusting the laser and photodiode using program oscilloscopes Special features and differences of the laser and photodiode adjustment for SPM heads SFC050L, SFC090L with an installed cantilever holder for operation in liquid media Preparing and installing samples Installing small size samples Installing large size samples Some recommendations about sample preparation Installing the SPM head Installing the SPM head on the sample approach module Checking parallelism between the SPM head base plane and sample plane Initial sample approach to the probe Hanging the approach module with the installed head on the anti-vibration suspension Addition (Moving the sample using the control program) Attachment 1. Installation of a sample and installation of the SPM head when the head is used as the Stand Alone Microscope Installation of samples on the surface of the base (operation in a mode of the Stand Alone microscope) Installation of the SPM head (operation in a mode of the Stand Alone microscope) Attachment 2. Closed liquid cell General Information Requirements to the sample Design Liquid cell operation Installing the sample and assembling the cell Installing the cell Installing the measurement beak Preliminary adjustment of the optical system Installing the head Fine adjustment of the optical system Contact mode Semi-contact mode Withdrawal from the surface

5 Table of contents 3.10 Attachment 3. High temperature stage Design Specifications Measurement head design features High temperature heating stage design Getting ready for operation Installing and connecting the thermal stage Installing a sample Installing a cantilever Thermal stage operation Control software features Setting and control of temperature What is special about using an AFM with a high temperature stage Temperature calibration Chapter 4. Contact Atomic Force Microscopy Initial State. Main Stages and Operations of the Contact Mode Initial State Main Stages and Operations of the Contact Mode Configuration of the Program Main Window Program Oscilloscope (Application of Signals, Starting and Stopping of Measurement, Scaling) Preparation of the SPM control block diagram for the Contact Mode Operation Checking of the switches positions Applying the DFL signal to the feedback input «FB In» Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter Initial level of the DFL signal and Set Point Parameter Setting Up the DFL Signal Initial Level Adjustment of the DFL Signal Initial Level Using the indicator of the photodiode signals Adjustment of the DFL Signal Initial Level Using the Program Oscilloscope Setting the Set Point Parameter Value Automatic approach of the sample to the probe Enabling the automatic approach of the sample to the probe Windows «Approach», «Probe», «Mover» Continuing the automatic approaching of the probe to the sample Selection of the Feedback Gain Factor A Manual approach of the probe to the sample A Enabling the Feedback A Procedure of manual approach of the Probe to the Sample A Selection of the Feedback Gain Factor Setting Scanning Parameters Scanning Parameters Control Window The procedure to Set the Scanning Parameters Scanning Velocity The Scanning Area, Step and Number of Scan Points Scanning Mode The Scanner Non-Linear Travel Correction (NLCor button) Measurement Channels: Application of Signal, Setting Scan Direction The ADC Preamplifier Gain Factor, Low-Pass Filter The Drawing, Show Scan Lines, Scope Data, Line Strobe, AutoScale and Save To NT.MDT Buttons The Subtraction Procedure (Subtract button, Exc Hi button) Parameters for Scanning Grid-Type Test Sample III

6 IV Solver P47H SPM Instruction Manual 4.6 Scanning Start of Scanning The Scanning Control Line Optimization of Scanning Parameters Saving the Acquired Data Switching from the Contact to Semi-Contact Mode Switching off the Microscope Lateral Force Microscopy Introduction Signal Related with the Cantilever Torsion Deformation Preparation of the Unit for Operation in the Lateral Force Measurement Mode Applying the Lateral F Signal to the Measurement Channel B Input Setting the Scanning Direction Switching the SPM Window into the Two-Window Mode The Unit Operation in the Lateral Force Microscopy Mode Force Imaging in the Contact Mode Introduction Preparation of the Unit for the Force Imaging Application of the DFL Signal to the Input of the Measuring Channel A Setting zero value for the feedback gain factor (FB Gain) The Unit Operation in the Force Imaging Mode The Mode of the Feedback Error Signal Registration Chapter 5. Semi-contact atomic force microscopy Initial condition, main stages and operations of semi-contact microscopy Initial condition Main stages and operations of semi-contact microscopy Configuration of the main program window Connecting signals to program oscilloscopes Preparation of the SPM control block diagram for semi-contact Mode Operation Checking of the switches positions Applying the MAG signal to the feedback input Setting the cantilever working frequency and oscillation amplitude Determining the resonance frequency cantilever, setting the working frequency The working frequency, the resonance frequency, the cantilever piezodriver generator Self-acting determination of the cantilever resonant frequency and self-acting installation of the working frequency Procedure of measuring the frequency response of the cantilever s oscillation amplitude Manual (non-automatic) setting the working frequency Selecting and setting the cantilever oscillation amplitude Setting the initial level of the MAG signal Approaching the sample to the probe, selecting and setting a working point Automatic approaching of the sample to the probe Setting the initial Set Point value Enabling the automatic approach Windows «Approach», «Probe», «Mover» Initial Stage of the sample automatic approaching to the probe Continuing the automatic approaching A Manual approach of the probe to the sample A Setting the initial Set Point value A Enabling the feedback A Starting manual approaching the probe to the sample A Continuing the manual approach procedure

7 Table of contents Selecting the Set point value Rough estimate of the cantilever oscillation amplitude value Selecting the feedback gain factor Setting the scanning parameters Scanning parameters control window The procedure to Set the Scanning Parameters Scanning Velocity The Scanning Area, Step and Number of Scan Points Scanning Mode The Scanner Non-Linear Travel Correction Measurement Channels: Application of Signal, Setting Scan Direction The ADC Preamplifier Gain Factor, Low-Pass Filter The Drawing, Show Lines, Scope Data, Line Strob, AutoScale and Save To NT. MDT Buttons Subtracting procedure (Subtract button, Exc Hi button) Scanning parameters for a test grid-type sample Scanning Scanning start Direct Scanning Control Line Selecting the optimal scanning parameters Saving the acquired data Switching from semi-contact to contact mode Turning the microscope off Phase Imaging Introduction Signals related to the probe oscillation phase Preparing the unit for phase imaging (Required conditions and operations) Applying a phase signal to the measurement channel input Adjusting the phase signal Operation in the Phase Imaging mode Features and differences of the semi-contact mode in fluid medium Chapter 6. Spectroscopy mode Measuring the relationship between the FB signal and the distance between the probe and the sample. Calibrating the cantilever oscillation amplitude Opening the spectroscopy mode control window Setting the measured relationship (FB(z) relationship) Selecting the measurement mode, setting the argument changing range and other parameters Selecting the measurement mode Setting the argument measurement range Minimum limit for the probe approach to the surface (limit, (na)) Setting the number of points plotted on the Z axis where the FB(z) relationship will be measured Buttons «Smooth», «Repeat», «& Back» Starting the measurement mode, saving the acquired data Viewing the spectroscopy data Calibrating the cantilever oscillation amplitude Chapter 7. Multi-pass operation mode of the unit About Multi-pass operation mode Adjustment and control in Multi-pass operation mode States of the unit and switching between them in SPM control block diagram V

8 VI Solver P47H SPM Instruction Manual Multi-pass Mode Menu Multi-pass Mode Setup Measurement Channels Control Block diagram, Signal and Dir buttons How to activate the Single-pass mode? Special cases in Single-pass mode How to activate Multi-pass mode of the unit?

9 Chapter 2. General concepts and brief description of microscope operation 2-1 Chapter 2. General concepts and brief description of microscope operation in AFM modes Contents Contents Chapter 2. General concepts and brief description of microscope operation in AFM modes Main components, general principle of microscope operation and main components interaction scheme The atomic force microscope probe Piezoelectric scanner Optical system for cantilever deflections detection General concepts of AFM Mode operations Forces acting between the cantilever tip and the sample Atomic Force Microscope modes and main techniques of Atomic Force Microscopy General concepts of the unit s operation in contact mode General concepts of the unit s operation in the mode of Contact Atomic Force Microscopy Feed-back Loop Schematic in the contact mode Advantages and disadvantages of Contact Mode AFM General concepts of the modes using vibration techniques Vibration and Modulation Techniques of Atomic Force Microscopy General concepts of the unit s operation in the mode of Semi-Contact Atomic Force Microscopy Feedback loop in the semi-contact mode Controlling the SPM and the main parameters determining the unit s operation Graphic Interface for SPM Control Main program window SPM Control block diagram Lock-In Amplifier and Phase Detector Control block diagram Scanning Parameters Control Window Main parameters determining SPM s operation

10 2-2 Solver P47H SPM Instruction Manual Chapter 2. General concepts and brief description of microscope operation in AFM modes 2.1 Main components, general principle of microscope operation and main components interaction scheme One of the main components of Solver P47H is an SPM head that is a universal, multifunctional scanning probe microscope. The main SPM components are probe, probe deviation registration system, piezo scanner, scanner control system. SPM head main components interaction scheme is typical for an atomic force microscope (Fig ). Fig The operation of an atomic force microscope is based on the sample surface probing by a sharp probe, which is essentially a sharp tip located at the free end of a flexible cantilever plate attached to the scanner. The probe tip interacting with the sample surface scans the surface by means of the scanner. The interaction force between the tip and the sample surface causes the change of cantilever mechanical state, for example, it causes the cantilever plate to deflect. During scanning the detection system measures the probe deflection (or any other interaction parameter) from the initial value and sends to the scanner control system a signal proportional to the deflection value. The control system moves the probe by means of the scanner perpendicular to the surface to bring the parameter back to its original value. Simultaneously the probe displacement value is saved in the PC memory and interpreted as the sample topography The atomic force microscope probe Cantilever type probes are used in the atomic force microscope. This probe consists of a flexible cantilever, a sharp tip and a substrate. The cantilever is a beam with one end fixed and other free. The sharp needle is on the free end of cantilever. The cantilever is fixed on a solid substrate inserted in a probe holder situated on scanner. 2.1 Main components, general principle of microscope operation and main components interaction scheme

11 Chapter 2. General concepts and brief description of microscope operation The point usually has a radius of curvature less than 10 nm and length from 3 to 15 microns. The smaller is the radius of curvature the greater resolution can be obtained. Most of cantilevers have a triangular (V-type) or rectangular form. As a rule cantilevers are in the range of micron of length. The cantilevers are made of silicon and silicon nitride. The cantilever s important parameters are the spring constant (rigidity) and the resonance frequency. The spring constant value is determined by geometrical dimensions and by cantilever s material and is in the range of 0.01 to 100 N/m. Usually there are two or several different cantilevers with points on one base (substrate). The data of cantilevers produced by NT-MDT firm are given below as an example. 2-3 Cantilever type A B Min Typical Max Min Typical Max Cantilever length (l), µm Cantilever width (w), µm Cantilever thickness, µm *Resonant frequency, khz *Force constant, N/m Tip Parameters: curvature radius - below 10 nm; tip height - 7 microns; vertex angle ; conductive. 2.1 Main components, general principle of microscope operation and main components interaction scheme

12 2-4 Solver P47H SPM Instruction Manual Piezoelectric scanner The scanner controls two independent movements of the cantilever: scanning along the sample surface (in X, Y plane) and movement perpendicular to the surface (along the Z-axis). The scanner is made of piezoelectric material that expands or shrinks depending upon the sign of electrical voltage applied to it and proportionally to its value. SPM head can utilize two scanner modifications with certain design variations and different maximum scanning area capabilities: 50-micron and 90-micron. Scanner consists of 2 different diameter piezotubes one of which is inserted into the other. The lower end of the large tube is attached to the SPM head, with the upper attached to the smaller diameter tube. The lower end of the latter is fixed to the cantilever holder. The smaller diameter piezoelectric tube scans in the plane parallel to the sample surface (X, Y), as for the larger diameter tube, it makes it possible for the cantilever to move perpendicular to the surface (along the Z-axis) Optical system for cantilever deflections detection The unit features an optical system for the cantilever deflection detection that can detect any angular deflection of the cantilever to an accuracy of less than 0.1", that gives vertical resolution of 0.05 nm. The detection system consists of a light source, a position sensitive photodetector and an optical system (Fig ). Fig The light source is a semi-conductor laser (λ=670 nm, P = 0.9 mw). The position sensitive photodetector is a four-segment photodiode. The optical system consists of a focusing lens, two mirrors, mirrored surface of the cantilever and a magnifying glass. The laser beam is focused by the lens into a 50 mkm wide elliptic spot on the reverse side of the cantilever in the vicinity of the tip. The light reflected from the cantilever falls on the four-segment photodiode. Any deflections of the cantilever results in the shifting of the laser spot with respect to the segments (a, b, c, d) of the photodiode, which, in its turn, results in changes of electrical signals (A, B, C, D), arriving from those segments. Signals are preprocessed (amplified, appended and deducted) and three signals arrive at the output of the detection system: 1) «VER.DFL» - signal proportional to vertical cantilever deviation. VER.DFL is a difference signal between the upper and lower halves of the photodiode (Fig ): «VER.DFL»=(A+B) - (C+D). This signal is equal to: «VER.DFL» «DFL». 2.1 Main components, general principle of microscope operation and main components interaction scheme

13 Chapter 2. General concepts and brief description of microscope operation 2-5 2) «LAT.DFL» - signal proportional to lateral cantilever deviation. The detection system is able to register also the twisting deformation of the cantilever that can be caused by lateral forces. The twisting deformation deflects the reflected beam sideways. The signal «LAT. DFL» is a difference signal between the left and right halves of the photodiode (Fig ): «LAT. DFL» = (A+C) - (B+D). This signal can be identically represented as: «LAT.DFL» «LF» «LATERAL F» 3) «LASER» - signal proportional to the intensity of the light falling upon the cantilever. «LASER» is a total signal from all four segments of the photodiode «LASER»=A+B+C+D. This signal is used for the laser adjustment. Fig During scanning the laser beam spot does not move with respect to the cantilever although the cantilever is attached to the mobile part of the head and the laser is fixed on its stationary part. This can be achieved by using a unique optical tracking system. 2.2 General concepts of AFM Mode operations Forces acting between the cantilever tip and the sample When the cantilever tip approaches the sample surface Van der Waals Forces start acting upon it (Fig ). Fig General concepts of AFM Mode operations

14 2-6 Solver P47H SPM Instruction Manual They are sufficiently far-ranging and are felt at the distance of a few tens of angstroms. Then at the distance of several angstroms repulsive force starts acting. In humid air a water layer is present on the sample surface. The capillary force arises that holds the tip in contact with the surface and increases the minimum achievable interaction force. Electrostatic interaction between the probe and the sample may appear rather often. This can be both attraction and repulsion. Van der Waals attraction forces, capillary, electrostatic and repulsion forces at the point where the tip touches the sample and forces acting upon the tip from the deformed cantilever compensate each other in equilibrium Atomic Force Microscope modes and main techniques of Atomic Force Microscopy The physical principle of the atomic force microscope operation is based on interaction between the probe tip and the surface. Based on the type and degree of this interaction the atomic force microscope modes can be broken down into: 1) contact; 2) non-contact and 3) semi-contact, which is a transition mode between the contact and non-contact modes. In the contact mode the probe tip is in direct contact with the sample surface during scanning. Accordingly, in the non-contact mode the probe tip is not in direct contact with the sample surface and in the semi-contact mode this contact is partial. Non-contact and semi-contact modes of the atomic force microscope operation have been developed based modulation techniques. There are three methods of topography measurement using an atomic force microscope: contact atomic force microscopy measuring surface topography in contact mode; non-contact atomic force microscopy measuring surface topography in non-contact mode based on the use of vibration technique; semi-contact atomic force microscopy, also known as similar intermittent contact atomic force microscopy, i.e. measuring surface topography using vibration technique when the oscillating probe tip taps slightly on the sample surface. Operation in contact atomic force microscopy and in semi-contact atomic force microscopy modes is the basis for other techniques in atomic force microscopy. For this reason below we will consider the general concepts of the unit s operation in contact and semi-contact microscopy modes. 2.3 General concepts of the unit s operation in contact mode In contact mode the cantilever is in direct contact with the sample surface and the operation is based on its repulsion from the surface. Repulsion force F acting upon the cantilever is related to the cantilever deviation value x under Hooke s law: F = -kx, where k is spring constant. The spring constant value for different cantilevers usually vary from 0.01 to several N/m. In our unit the vertical cantilever deviation value is measured by means of the optical registration system and converted into electrical signal DFL. In contact mode the DFL signal is used as a parameter characterizing the interaction force between the tip and the surface. There is a linear relationship between the DFL value and the force. The microscope operation in the mode of maintaining constant interaction force between the tip and the surface sample, i.e. maintaining a certain specified DFL signal level, is the base for measuring surface topography as well as for measuring local rigidity, local viscosity and local friction force. 2.3 General concepts of the unit s operation in contact mode

15 Chapter 2. General concepts and brief description of microscope operation 2-7 In contact mode the DFL signal is used as a feedback signal that is applied to the input of the tracking system General concepts of the unit s operation in the mode of Contact Atomic Force Microscopy Contact Force Microscopy is surface topography measurement in the contact mode. Let us consider briefly the unit s operation when measuring surface topography in the contact mode. Let us mention one more time that topography measurement is carried out in the constant force maintenance mode, which is achieved by maintaining the DFL signal at the same level. This signal is used as a feedback signal. In the beginning (prior to scanning), the operator approaches the sample to the probe to a distance at which the cantilever tip begins to interact with the surface. The operator sets an initial value for DFL by setting an appropriate Set Point parameter. By doing so he sets a specified cantilever deviation value in the approached state and, accordingly, a specified value interaction for the force interacting between the tip and the surface, since the DFL signal is linearly related to the force acting upon the cantilever. The DFL value is set and maintained at a specified level, equal to the Set Point value, by the feedback system. Please note one more time that the DFL signal in the contact mode is a feedback signal and when the feedback system is activated this signal is maintained equal to the Set Point parameter set by the operator. The feedback loop schematic and a brief description of the feedback system operation are given below (2.3.2). During scanning the cantilever deviation value changes in every point due to the surface topography. Accordingly, the current value of the DFL signal changes in relation to the Set Point level. This deviation from the Set Point value, with the feedback system, activated is perceived as an error signal. In every point of the surface the feedback system, with the help of the scanner, moves the probe perpendicular to the surface in such a way that the current DFL value is brought back to the Set Point level, i.e. the cantilever deviation is brought back to its original value. Simultaneously a signal proportional to the scanner vertical displacement is sent to the adjustable gain ratio amplifier. After the amplifier the signal is applied to the analog-digital converter and then via an interface card it is recorded in the computer memory thus generating a topographic image of the sample surface Feed-back Loop Schematic in the contact mode A Feed-back Loop Schematic in the contact mode is shown in Fig The «DFL» (in the contact mode) at the detection system output is compared with the «Set point» signal (preset by the operator) and the difference signal («DFL»- «Set point») is sent to the integrator s input. The difference signal is perceived as an error signal, it is amplified and integrated to allow its correct processing by the piezoscanner constant shifting system. The signal from the integrator is sent to the high voltage amplifier, and then to the piezoscanner to compensate for the error. The feedback function maintains the error signal in the proximity of the given level («Set point»). The accuracy of the integrated feedback used here depends on the loop gain factor. High-speed feedback is required to achieve maximum scanning speeds. To increase the speed of the signal processing by the feedback it is advisable to set the maximum loop gain factor. 2.3 General concepts of the unit s operation in contact mode

16 2-8 Solver P47H SPM Instruction Manual However, if the gain factor is too high the generation threshold can be reached. Operation at values close to the generation threshold is characterized by excessive fluctuations affecting accuracy. On the other hand, when the gain actors are too low it also reduces the measurement accuracy. Therefore, there exists an optimum gain factor for each probe-sample system ensuring the maximum accuracy of the feedback operation and data accuracy. Fig Several parameters determine the proper value for the gain factor. Depending upon the cantilever used with the rest of the parameters being the same the gain factor can vary several times. The gain factor changes in inverse proportion to the cantilever length and, therefore, the shorter is the cantilever, the higher is the gain factor. Besides, the gain factor can significantly change depending upon the cantilever alignment. The operator can adjust the general loop gain factor by changing the FB Gain value in the integrator s amplifier Advantages and disadvantages of Contact Mode AFM Advantages of Contact Mode AFM: 1) High scanning speeds. 2) Only in contact mode it is possible to achieve atomic grid resolution. 3) Possibility to measure local hardness 4) Possibility to measure local friction. 2.4 General concepts of the modes using vibration techniques

17 Chapter 2. General concepts and brief description of microscope operation 2-9 Disadvantages of Contact Mode AFM: 1) When exploring soft samples (like polymers, biological samples, Langmuir-Blodgett films etc.) they can be destroyed because the probe scanning tip is in direct contact with the surface. 2) Possible existence of substantial capillary forces imposed by a liquid adsorption layer can decrease the resolution. 3) Possible lateral forces can distort the image. 2.4 General concepts of the modes using vibration techniques Vibration and Modulation Techniques of Atomic Force Microscopy A big stride in the development of atomic force microscopy was made by the introduction of various techniques using vibration or modulation of the probe or of the sample. One of the vibration techniques is the semi-contact mode, non-contact mode and local hardness mode. The main advantages of certain vibration techniques are as follows: 1) decrease of interaction forces, in particular, lateral ones between the probe and the surface; 2) use of resonance properties of the system, which significantly improves sensibility of the system compared to static measurement; 3) possibility to register differential parameters maintaining constant average values; 4) decrease of noise level with frequency dependence of 1/f (where f is frequency) by shifting the signal spectrum into the high frequency range General concepts of the unit s operation in the mode of Semi- Contact Atomic Force Microscopy One of the most common vibration techniques is the Semi-Contact microscopy also known as similar intermittent-contact atomic force microscopy. In semi-contact mode the scanning is done by the cantilever oscillating near the sample surface. The particular feature of this mode is that the oscillating tip is so close to the surface that it even slightly knocks on the sample surface during the scanning and contacts it in the lowest point of its amplitude. At the same time, during the most of its oscillation period the cantilever does not touch the surface and their interaction level is relatively low. Only when the tip approaches the surface and till its arrival into the repelling potential zone (Fig ), the interaction increases sharply and in this impact the cantilever looses the excess energy it has accumulated during the rest of the oscillation period. Depending upon the type of interaction the phase deviation there may be changes in the main oscillation harmonic with regard to the exciting signal, as well as in the amplitude and phase of higher harmonics. The cantilever oscillates vertically at its resonance frequency and close to it. The value of the cantilever oscillation amplitude is approximately within the range between 1 nm and 100 nm. Mechanical oscillations of the cantilever are excited by the piezodriver that has a direct contact with the cantilever substrate. The laser beam of the detection system is reflected from the vertically oscillating cantilever. The cantilever oscillations cause oscillating movement of the laser spot with regard to the positionsensitive photodiode of the detection system (with regard to the upper and lower halves of the 2.4 General concepts of the modes using vibration techniques

18 2-10 Solver P47H SPM Instruction Manual photodiode). This results in variable electric signal at the cantilever oscillation frequency whose amplitude is proportional to the oscillation amplitude of the cantilever tip. In the case of our SPM this signal is the variable component of the «DFL» signal at the cantilever oscillation frequency. The detection system registers the cantilever oscillation amplitude and converts it into an electrical signal as a variable component of the «DFL» signal. Then the variable component of the «DFL» signal is processed: it is filtered, amplified and detected. In order to increase the unit s sensitivity and resolution the variable signal is processed: it is filtered, amplified and converted into a constant electrical signal. In our SPM head there are several processing modes for the variable signal and any of those can be selected at the operator s option. The variable electrical signal can be applied to the input of: 1) Lock-In amplifier, 2) RMS detector, 3) Phase detector. The Lock-In amplifier forms three electrical signals at its output: 1) «MAG» equal to the «DFL» variable signal amplitude at the modulation frequency; 2) «MAG*sin» proportional to the product of the variable signal amplitude at the modulation frequency and the cantilever oscillation phase deviation sine with regard to the reference signal; 3) «MAG*cos» proportional to the product of the variable signal amplitude at the modulation frequency and the cantilever oscillation phase deviation cosine with regard to the reference signal; The cantilever oscillation phase shift value with respect to the reference signal consists of the sum of the cantilever oscillation phase displacement value with respect to the reference signal and the phase displacement between the exciting and reference signals (precision is determined by the hardware factor). The root-mean-square detector (RMS detector) forms at its output the «RMS» signal proportional to the root-mean-square value of the variable «DFL» signal for the entire frequency range of the detector. The Phase Detector forms the «Phase 1» signal. The deviation of the Phase 1 signal is proportional to the phase deviation of the cantilever oscillation phase displacement with regard to the exciting signal. The Phase 1 signal consists of the sum of the cantilever oscillation phase displacement value with respect to the exciting signal and the phase displacement between the exciting and reference signals (precision is determined by the hardware factor). Any of the above mentioned signals can be included in the feedback loop. The cantilever oscillation amplitude is used in the semi-contact mode as a parameter characterizing the interaction between the tip and the sample surface. The microscope operation in the constant oscillation amplitude maintenance mode is the basis for the surface topography measurement. 2.4 General concepts of the modes using vibration techniques

19 Chapter 2. General concepts and brief description of microscope operation The constant oscillation amplitude is maintained by maintaining the same level of the signal proportional to the oscillation amplitude. Such signals, which are proportional to the oscillation amplitude, are MAG and RMS. Any of them can be used as a feedback signal for topography measurement. However, it is preferable to use the MAG signal as in this case it is possible to achieve a lower noise level and, therefore, obtain a higher resolution due to the use of synchronous detection. The selection is done by the operator by including a proper signal in the feedback loop in the graphic interface of the unit s software control. Let us consider briefly the unit s operation when measuring surface topography in the semi-contact mode. As it was mentioned above, topography is measured in the constant oscillation amplitude maintenance mode, which is achieved by maintaining the MAG (or RMS) signal at a constant level. It is assumed that this signal (MAG) has been selected as a feedback signal. The general operation scheme is similar to the operation in the contact mode. Prior to scanning the operator approaches the sample to the probe to a distance at which the cantilever tip begins to interact with the surface. The operator sets an initial value for MAG by setting an appropriate Set Point parameter. By doing so he sets a specified cantilever oscillation amplitude value in the approached state and, accordingly, a specified value interaction between the tip and the surface. The MAG value is set and maintained at a specified level, equal to the Set Point value, by the feedback system. Please note one more time that the MAG signal in the semi-contact mode is a feedback signal and when the feedback system is activated this signal is maintained equal to the Set Point parameter set by the operator. The feedback loop schematic and a brief description of the feedback system operation are given below (item 2.4.3). During scanning the value of the cantilever oscillation amplitude will be changed in every point due to the surface topography. Accordingly, the current value of the MAG signal changes in relation to the Set Point level. This deviation from the Set Point value, with the feedback system, activated is perceived as an error signal. In every point of the surface the feedback system, with the help of the scanner, moves the probe perpendicular to the surface in such a way that the current MAG value is brought back to the Set Point level, i.e. the cantilever oscillation amplitude is brought back to its original value. Simultaneously a signal proportional to the scanner vertical displacement is sent to the adjustable gain ratio amplifier. After the amplifier the signal is applied to the analog-digital converter and then via an interface card it is recorded in the computer memory thus generating a topographic image of the sample surface General concepts of the modes using vibration techniques

20 2-12 Solver P47H SPM Instruction Manual Feedback loop in the semi-contact mode The feedback loop layout is shown in Fig Fig As opposed to the contact mode, the constant cantilever oscillation amplitude is maintained during scanning, the oscillation amplitude in this case being a tip-surface interaction parameter. This is achieved by maintaining a specified level of the MAG (or RMS) signal that is used as the feedback signal. Otherwise, the feedback system operation is similar to the contact mode (item 2.3.2). 2.5 Controlling the SPM and the main parameters determining the unit s operation Graphic Interface for SPM Control Control is performed by means of a graphic interface, its main components are as follows: Main program window containing direct control line, SPM window, toolbar; SPM control block diagram; Lock-In Amplifier and Phase Detector control block diagram; Scanning Parameters Control Window The program has context-sensitive help. If you want to get information about any object (window, menu, button etc.) place the cursor on the unknown object and press F1. As a result, a window will be displayed containing information on this object. 2.5 Controlling the SPM and the main parameters determining the unit s operation

21 Chapter 2. General concepts and brief description of microscope operation Main program window The main program window (Fig ) is displayed after the start of smena.exe: 2-13 Fig The main components of the program main window are: direct control line, SPM window and toolbar. The upper direct control line (Fig ) is used for on-line check and control of several parameters. Fig The toolbar (Fig ) is located on the left-hand side of the main window, it contains several buttons providing direct access to certain commands and functions. The SPM window (Fig ) is the main window for the unit s control, observation and data processing. Fig Fig Controlling the SPM and the main parameters determining the unit s operation

22 2-14 Solver P47H SPM Instruction Manual To open the SPM control block diagram, the Lock-In Amplifier and Phase Detector Control block diagram or Scanning Parameters Control Windows (SCAN) click on the Operation button in the second row of the Main Window and select Scanning in the displayed menu (Fig ). Fig This will display the Scanning window. Choosing SCAN, SPM or Lock-in in the upper row of this window will open, respectively, the Scanning Parameters Control Windows (SCAN), the SPM Control block diagram (Fig ) or the Lock-In Amplifier and Phase Detector Control block diagram (Fig ). In addition to that there is an easier way to open the SPM Control block diagram and the Lock-In Amplifier and Phase Detector Control block diagram. This can be done by pressing the button in the SPM window menu (Fig ) SPM Control block diagram The SPM Control block diagram (Fig ) lets you select and set the unit s operation mode (contact, semi-contact, non-contact etc.), enable and disable the feedback, select and include in the feedback loop one of the signals characterizing the interaction between the probe and the sample («MAG», «RMS», «DFL» («VER.DFL») etc), select and set the «Set point» value, the feedback coefficient «FB Gain», as well as some other parameters. Fig Fig To change the value of a parameter or to set another parameter, just place the cursor on the required element of the control block diagram and press the left mouse button or Enter. Then set the necessary value in the displayed window or select the required parameter. 2.5 Controlling the SPM and the main parameters determining the unit s operation

23 Chapter 2. General concepts and brief description of microscope operation Lock-In Amplifier and Phase Detector Control block diagram The Lock-In Amplifier and Phase Detector Control block diagram (Fig ) is used to control the Lock-In Amplifier and Phase Detector parameters Scanning Parameters Control Window In the scanning Parameters Control Window (Fig ) you can set and change such scanning parameters as scanning speed, step and direction, number of scan points along the X and Y axis; enable and disable channels (A, B, C, D), each of which generates the image for one of the selected signals. Simultaneously you can run up to four channels. Below you will find signals whose images can be generated in any of the indicated channels: Height DFL ( VER.DFL) Lateral F ( LF LAT.DFL) MAG MAG*sin MAG*cos RMS Phase1 Phase2 Calc Phase FB-out Bias V Calc Mag Snap Back BV probe Current Ex1 Ex2 HvX HvY Ex3 T o 1 Fig Main parameters determining SPM s operation Three most general parameters can be identified: Set point probe and surface interaction parameter, maintained via feedback during scanning; FB Gain integrator gain coefficient included in the general feedback loop coefficient and Velocity scanning speed. These parameters should normally be set and selected in any operation mode, besides, they are very important for the quality of the acquired image. 2.5 Controlling the SPM and the main parameters determining the unit s operation

24 2-16 Solver P47H SPM Instruction Manual The main parameters can be arbitrarily divided into several groups: 1) Parameters determining interaction between the probe and the sample surface; 2) Feedback loop parameters; 3) Scanning parameters; 4) Parameters of various devices, components and parts of the unit. The main parameters determining interaction between the probe and the sample surface are the following signals: «DFL», proportional to the probe deflection from the sample surface; «Lat. DFL», proportional to the value of the cantilever twisting deformation; «MAG», proportional to the probe oscillation amplitude at the cantilever modulation frequency in the modulation mode (semi-contact, non-contact mode); «RMS», proportional to the root-mean-square value of the probe oscillations in the entire frequency range of the RMS detector in the modulation mode (semi-contact, non-contact); «MAG*sin», proportional to the product of the variable signal amplitude at the modulation frequency and the cantilever oscillation phase deviation sine with regard to the reference signal; «MAG*cos», proportional to the product of the variable signal amplitude at the modulation frequency and the cantilever oscillation phase deviation cosine with regard to the reference signal; «Phase 1», proportional to the phase deviation of the cantilever oscillations with regard to the reference signal. The main parameters of the feedback loop are the following: «FB Gain» - gain coefficient of the Integrator in the feedback loop; «Gain» - Lock-In Amplifier gain coefficient (for operation in modulation modes using the Lock-In Amplifier) The main scanning parameters are the following: «Velocity» - probe scanning speed; «Step» - scanning step; «NX», «NY» - number of points along X and Y axis accordingly; parameters determining the scanning direction: «+X+», «+Y+»; «-X+», «-Y+»; «+X-», «+Y-»; «-X-», «-Y-»; «...» - scanning angle. A letter corresponds to the quick scanning axis, for instance, «+X+» means that quick scanning will be done along the X - axis and slow scanning will be therefore done along the Y - axis. The + sign before the letter means that quick scanning is done in the positive direction. The + sign after the letter means that slow scanning is done in the positive direction. 2.5 Controlling the SPM and the main parameters determining the unit s operation

25 Chapter 2. General concepts and brief description of microscope operation Parameters of various devices, components and parts of the unit This type of parameters includes adjustable gain and division factors in various amplifiers and dividers, adjustable filter parameters, various calibration factors etc. In particular, this group includes parameters of the cantilever piezodriver generator determining the excitation of the cantilever oscillations in modulation modes: F oscillation frequency, v amplitude of exciting voltage applied to the piezodriver Controlling the SPM and the main parameters determining the unit s operation

26 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-1 Chapter 3. Preparing the microscope, SPM head, probe and sample Contents Contents Chapter 3. Preparing the microscope, SPM head, probe and sample Main operations to be performed to prepare the microscope for operation Turning the unit on, the control program start up Choice of cantilever Installing the cantilever Installing the cantilever in SPM heads SFC050, SFC050SEMI, SFC090, SFC090SEMI Installing the cantilever in SPM heads SFC050L, SFC090L Cantilever holder for operation in air Cantilever holder for operation in fluid Installing the cantilevers into holders Installing the cantilever holder into the SPM head Removing the cantilever holder Replacing the cantilever Adjusting the laser and photodiode Turning on the laser and the photodiode indicator Laser adjustment Visual observation mirror Adjusting the laser with the naked eye Adjusting the photodiode using the photodiode indicator Fine laser adjustment using the photodiode indicator Adjusting the laser and photodiode using program oscilloscopes Special features and differences of the laser and photodiode adjustment for SPM heads SFC050L, SFC090L with an installed cantilever holder for operation in liquid media Preparing and installing samples Installing small size samples Installing large size samples Some recommendations about sample preparation Installing the SPM head Installing the SPM head on the sample approach module Checking parallelism between the SPM head base plane and sample plane Initial sample approach to the probe Hanging the approach module with the installed head on the anti-vibration suspension Addition (Moving the sample using the control program) Attachment 1. Installation of a sample and installation of the SPM head when the head is used as the Stand Alone Microscope Installation of samples on the surface of the base (operation in a mode of the Stand Alone microscope) Installation of the SPM head (operation in a mode of the Stand Alone microscope) Attachment 2. Closed liquid cell General Information Requirements to the sample

27 3-2 Solver P47H SPM Instruction Manual Design Liquid cell operation Installing the sample and assembling the cell Installing the cell Installing the measurement beak Preliminary adjustment of the optical system Installing the head Fine adjustment of the optical system Contact mode Semi-contact mode Withdrawal from the surface Attachment 3. High temperature stage Design Specifications Measurement head design features High temperature heating stage design Getting ready for operation Installing and connecting the thermal stage Installing a sample Installing a cantilever Thermal stage operation Control software features Setting and control of temperature What is special about using an AFM with a high temperature stage Temperature calibration

28 Chapter 3. Preparing the microscope, SPM head, probe and sample Chapter 3. Preparing the microscope, SPM head, probe and sample In the present section a general preparation of the microscope for operation in the atomic force microscopy mode is under consideration. The general preparation of the microscope includes operations that need to be performed when preparing for operation in any of the modes of atomic force microscopy. 3.1 Main operations to be performed to prepare the microscope for operation The preparation of the unit for operation in atomic force microscopy mode can be divided into the following main steps: 1) turning the unit on, the control program start up; 2) preparing the probe (cantilever selection and installation); 3) adjusting the laser and the photodiode (aiming the laser beam on the cantilever, setting the maximum value for the LASER signal, zero values for VER.DFL and LAT.DFL signals); 4) preparation and installation of the sample; 5) installing the SPM head on the sample approach module (installation, alignment check, initial sample approach, hanging on anti-vibration suspension). Description of these operations is given below. The SPM Head Smena used as a component of the unit may be of two types. The first type of SPM heads (there are five versions: SFC050, SFC050SEMI, SFC090, SFC090SEMI, SFC050H) can operate in air. The second type of SPM heads (two versions: SFC050L, SFC090L) has two changeable cantilever holders and can operate both in air and liquid. Accordingly, probe preparation procedures (cantilever installation), laser and photodiode adjustment are somewhat different. Except of operation in the main mode (operation in the composition of the device), the SPM head also may work in the mode of Stand Alone microscope. Accordingly, procedures of installation of a sample and installation of the SPM head in these cases also differ. 3.2 Turning the unit on, the control program start up To turn the unit on the following has to be done: 1) turn on the SPM controller with switch located on the controller; 2) start the SPM control program up, use smena.exe file for the start up. 3.3 Choice of cantilever The choice of cantilever depends on the task and on the sample to be analysed. For measurement of topography of a rigid sample in contact mode, if it is not necessary to obtain atomic resolution, it is recommended to use short triangular cantilevers of microns long. It allows avoiding the «geometric» generation, due to friction force. It usually doesn t appear if the cantilever is up to 150 microns long. For operating in contact mode when it is necessary to obtain the atomic resolution it is better to use longer cantilevers about 200 microns long. It also concerns a case, when it is necessary to work in the lateral force mode and in the topography measurement mode simultaneously or sequentially. Besides, for measurement of lateral forces it is recommended to use rectangular cantilevers Choice of cantilever

29 3-4 Solver P47H SPM Instruction Manual When operating in contact mode with soft samples it is better to use long cantilevers, having small rigidity to reduce the effect of the cantilever on the sample. Usually to achieve the minimally possible interacting force ( N) it is enough to use cantilevers that are microns long and have rigidity of about N/m (when working in open air). Cantilevers used for semi-contact mode usually have resonance frequency higher than 80 khz. Short cantilevers usually have such resonance frequency. For electrostatic forces microscopy, depending upon the task, it is necessary to use conductive cantilevers of a different type: high alloy silicon or with conductive coating (W 2 C, TiN, TiO, W, Cr). For capacitance microscopy it is better to use cantilevers, which have a rather large curvature radius of the tip and rigidity of the beam of several N/m to ensure high sensitivity of the device. It can be used high alloy silicon cantilevers, but it is better to use cantilevers with conductive coating. For the surface potential microscopy it is necessary to use conductive cantilevers with a relatively small resonance frequency for operation in non-contact mode. To analyse the surface electrical properties of the samples using the spread resistance measurement technique it is necessary to use cantilevers with a conductive coating made of W 2 C, TiN, TiO, W, Cr. For magnetic force microscopy when analysing magnetic samples it is necessary to use cantilevers coated with magnetic - sensing coating (for example, Co or Ni). 3.4 Installing the cantilever Since the cantilever installation procedure is different for different SPM head types, item describes this operation for the first type of SPM heads (SFC050, SFC050SEMI, SFC090, SFC090SEMI), which are designed for operation in air only. Accordingly item contains a description of this operation for the second type of SPM heads (SFC050L, SFC090L), which are designed for operation in both air and liquid media Installing the cantilever in SPM heads SFC050, SFC050SEMI, SFC090, SFC090SEMI To install or replace the cantilever do the following steps. 1) Take the SPM head, turn it over and place on a table in the upside down position (Fig ). Fig Fig ) Open (lift) the cantilever holder clip. To do it, rotate the lever downward into its open position with a sharp forceps (Fig , Fig ). The lever is trapezoid-shaped and it is located on a side of the mounting stage. 3.4 Installing the cantilever

30 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-5 Fig Attention! The clamping spring should be lifted only by rotating the lever. Do not bend it with forceps or you hand as this can result in irreversible deformation. Attention! The cantilever holder is attached to the scanner and excessive force applied to the holder may result in damage to the scanner. 3) Select the working side of the cantilever chip depending upon the type of cantilever you are going to use. 4) Take the cantilever from the box with the forceps making sure that the working side will be closer to you during the installation. Do not turn the cantilever over since the cantilevers are placed in the box (Fig ) with their tips pointing upwards. Fig Fig ) Take the cantilever to the holder and place it on the left side of the working area (Fig , Fig , Fig ). The working area is located in the corner of the stage under the holder clip. 6) Move the cantilever to the working area with the forceps (Fig ) as shown schematic in Fig The cantilever on the working area is shown in Fig Installing the cantilever

31 3-6 Solver P47H SPM Instruction Manual Fig Fig ) After the installation of the cantilever onto the working area close (push down) the holder clip to hold the cantilever in position. To do it, turn the lever into the closed position with the forceps (Fig ). Fig Fig ) Invert the SPM head in working position (Fig ). Fig Installing the cantilever in SPM heads SFC050L, SFC090L As indicated above this type of SPM heads (SFC050L, SFC090L) has two changeable holders, one of which allows operating in air medium and the other in liquid medium. 3.4 Installing the cantilever

32 Chapter 3. Preparing the microscope, SPM head, probe and sample Cantilever holder for operation in air Cantilever holder for operation in air is shown in Fig The main components of the holder are schematically shown in Fig It consists of platform 1, beak 2, clamping spring 3 combined with lever 6. The clamping spring is attached with screw 4. Two electrical contacts 5 pass through the platform to supply modulating voltage to the piezo-transmitter built in the beak. Four ferromagnetic elements are glued to the platform bottom to ensure magnetic adhesion to the scanner tube on the measuring head. 3-7 Fig Fig Cantilever holder for operation in fluid Cantilever holder for operation in fluid is shown in Fig The main components of the holder are schematically shown in Fig It consists of platform 1, glass prism 2 glued to platform 1 with epoxy adhesive, detachable clamping spring 3. The spring is fixed on the holder with pin 4. The piezo-transmitter for operation in semi-contact mode is located inside the prism. Two electrical contacts 5 pass through the platform to supply modulating voltage to the piezo-transmitter. Fig Fig The glass prism makes it possible to put the cantilever into fluid to the depth of up to 6 mm and conduct measurements in fluid. The spring installation and removal procedure for the prism washing is shown in Fig and Fig To remove the spring hold it by its prominent part and lift it over fixing pin 4 and move it in the direction of the arrow (Fig ). To install the spring pick it up carefully with forceps in the bend area 1 (Fig ) and push until it stops into the guiding holes at the end of the platform. 3.4 Installing the cantilever

33 3-8 Solver P47H SPM Instruction Manual Fig Fig Installing the cantilevers into holders A cantilever is first installed into the holder and then the holder is installed into the SPM head. To avoid damaging prominent contacts when installing cantilevers into holders use the special supplied support. It has two holes and a fixing rotating lock. At installation of the holder on a support electric contacts should enter into holes of a support. Installing the cantilever into an air type holder (Fig ) 1) Place the cantilever holder on the support (Fig ) so that the electrical contacts enter the holes provided in the support. When installing the cantilever into an air type holder, lock 2 on the support does not have to be closed. 2) Lift the spring slightly pressing lever 4 and put the cantilever on the break 5 under spring (Fig , Fig ). The length of the prominent part of the cantilever substrate should be about 1 mm. 3) Then release the spring. Fig Fig Installing the cantilever into the liquid type holder (Fig ) 1) Place the cantilever holder on the support 3 (Fig ) so that the electrical contacts enter the holes provided in the support. 2) Close lock 2, fixing the holder on the support. 3.4 Installing the cantilever

34 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-9 Fig Fig ) Lift the spring. To lift the spring you can insert screwdriver 1 between the spring and the glass prism as shown in Fig and pull back the spring. You can also use a special key shown in Fig The key has a bent shape, the bent end is inserted between the prism and the prism. When you push the other end of the key, the spring is pulled back (Fig ). Fig Fig ) Place the cantilever on the prism under the spring (Fig ). The length of the cantilever substrate part salient above the polished surface of the prism should be about 0.8 mm i.e. the edge of the cantilever substrate should be above the middle of the polished facet of the prism. 5) Release the spring. 6) Open lock 2 on the support and take the holder with installed cantilever out Installing the cantilever holder into the SPM head The cantilever holder is installed onto the SPM head in the turned-over position of the head. Take the holder with the installed cantilever to the mounting place on the head. The holder must be turned to 45 0 relative to its working position and the marking point on its platform must be aligned with the INSERT arrow on the head dial (Fig and Fig ). 3.4 Installing the cantilever

35 3-10 Solver P47H SPM Instruction Manual Fig Fig Caution! Do not low the holder onto the mounting place if it is not turned to 45 0 i.e. if the marking point on the holder and the INSERT arrow are not aligned. Otherwise it can cause damage to the contacts and mirror in the measuring head. If the marking point and the INSERT arrow are aligned, low the holder into its mounting place. Make sure that the mounting ring on the holder platform bottom enters into the scanning tube. The holder will stand on the magnetic fixture evenly without any misalignment. After installing the holder onto the mounting place of the SPM head turn the holder platform clockwise until the marking point on the platform with the OPERATION arrow on the head dial (Fig and Fig ). This is the working position of the holder where all measurements are taken. In this position the force pressing holder against the scanner tube is maximal. Fig Fig Removing the cantilever holder To remove the cantilever holder turn to 45 0 it clockwise so that the marking point on the platform is aligned with the REMOVE arrow on the head dial (Fig and Fig ). After that remove the holder. Fig Fig Installing the cantilever

36 Chapter 3. Preparing the microscope, SPM head, probe and sample Caution! Do not remove the holder from the head if it is not turned to 45 0 i.e. if the marking point on the holder and the REMOVE arrow are not aligned. Otherwise it can cause damage to the contacts and mirror in the SPM head. Removal and installation of the liquid type holder are done in a similar way Replacing the cantilever To replace the cantilever it is imperative to remove the holder from the SPM head and replace it in accordance with the above instructions on the cantilever installation procedure. Caution! Do not change the cantilever in the holder installed on the SPM head. 3.5 Adjusting the laser and photodiode The purpose of adjusting the laser and photodiode is: 1) to aim the laser beam on the cantilever end and 2) to set the photodiode with regard to the beam reflected from the cantilever in such a way that the beam falls into the central part of the photodiode. The laser and photodiode adjustment procedure can be divided into 4 steps: 1) turning on the laser and the photodiode indicator; 2) aiming the laser beam to the cantilever end; 3) adjusting the photodiode with regard to the laser beam (setting the maximum value for the LASER signal, zero values for VER.DFL and LAT.DFL signals); 4) fine adjustment of the laser beam using the readings on the photodiode indicator. Below you will find a detailed description of every operation mentioned above. As it was indicated above there are two types of SPM heads: SPM heads for operation on air medium (SFC050, SFC050SEMI, SFC090, SFC090SEMI, SFC050H) and SPM heads with changeable cantilever holders designed for operation in air and liquid media (SFC050L, SFC090L). Laser and photodiode adjustment procedures included in this section (items ) cover SPM heads, designed for operation in air medium i.e. SPM heads SFC050, SFC050SEMI, SFC090, SFC090SEMI, SFC050H as well as SPM heads SFC050L, SFC090L with installed changeable holder for operation in air medium. Item addresses briefly special features and differences of the laser and photodiode adjustment for SPM heads SFC050L, SFC090L with installed cantilever holder for operation in liquid media Turning on the laser and the photodiode indicator Turn on the laser. To turn on the laser use the button in the upper row (Fig ) Fig Caution! Be careful! Avoid direct contact between the laser beam and your eyes! (The safety category of the laser provides for safe contact between the laser beam and the eye during a period of time corresponding to a normal human reaction to irritation (about 0.25 sec.). This time is enough for a person to blink and turn away. Extended exposure can result in short-term eyesight disturbance.) Turn on the digital photodiode signal indicator. To do it press the button in the upper row of the program window (Fig ). This button is located next to the laser turn-on button. 3.5 Adjusting the laser and photodiode

37 3-12 Solver P47H SPM Instruction Manual This will display the photodiode signal indicator window (Fig ). It consists of the table and the indicator of the laser spot position. The table displays the current values of the photodiode signals. The indicator of the laser spot position shows the position of the laser spot with respect to the photodiode segments. Fig The displayed signals have the following meanings: LASER - total signal that comes from all four segments of the photodiode and therefore is proportional to the intensity of the laser radiation reflected from the cantilever. VER.DFL - difference signal between the upper and lower halves of the photodiode, the identical labeling of this signal is DFL ( i.e. VER.DFLºDFL). LAT.DFL - difference signal between the left and right halves of the photodiode, the identical labeling of this signal is LF (i.e. LAT.DFLºLF). Note: In older versions of the control program the LAT.DFL signal could be described as «Lateral», «HOR.DFL», «LF», «LATERAL F» Laser adjustment The laser beam is focused in a point located in the same plane as the cantilever attached to the scanner. The size of the focused laser spot in this plane is approx. 50 microns. The laser beam can be moved in the cantilever plane in 2 directions using alignment knobs 1 and 2 in the upper part of the head (Fig ). The range of the laser spot movement is approx. 2 mm x 2 mm (Fig ). The purpose of the laser adjustment is to aim the laser spot by moving it with alignment knobs 1 and 2 on the cantilever end as shown in Fig Adjusting the laser and photodiode

38 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-13 Fig Fig When adjusting the laser you can observe the probe and the adjacent area with the naked eye. In addition to that during adjustment you can use an image of the passed-through laser beam on a screen using as such a sheet of paper Visual observation mirror The unit is equipped with a special mirror for visual observation of the probe (cantilever) and of the studied sample. The mirror is located on the SPM head next to the probe holder. Observation is done through an opening in the cylinder scanner tip in the direction of the axis forming an approx. 30 degrees angle with the horizontal plane (sample plane) (Fig , Fig ). Fig Fig Adjusting the laser with the naked eye For a novice user adjustment with the naked eye is a rather difficult task as even the cantilever substrate that is near 1.5 mm big can be hardly seen, much less the cantilever itself, which is practically invisible. However, experience shows that after some training adjustment with the naked eye is not only quite feasible but is probably the easiest and the most convenient method. The laser adjustment can be divided into 2 steps: first aiming the laser beam on the cantilever (find the cantilever with the laser spot); second -aiming the laser beam on the cantilever end. The following guidelines should be used when performing adjustments with the naked eye. 3.5 Adjusting the laser and photodiode

39 3-14 Solver P47H SPM Instruction Manual First adjustment step - aiming the laser beam on the cantilever First, try to determine where the laser spot is located. Use the image of the passed-through laser beam on the screen. To do it take the SPM head and lift it approx cm above a sheet of white paper, using the latter as a screen (Fig ). Three cases are possible: 1) the laser beam passes through the SPM head freely, this is associated with an undistorted image of the laser spot on the screen; 2) the image of the laser beam is not present on the screen, which means that the beam falls onto the cantilever substrate or the cantilever holder; 3) a distorted image of the laser beam can be seen, which means that the beam partially touches an edge or the cantilever. Fig Fig If the image of the laser beam is not present on the screen look closely at the visible part of the probe (visible part of the cantilever substrate) through the observation mirror (Fig , Fig ) and the area of the cantilever holder adjacent to it. The laser spot can be seen (by its scattering) if the beam falls onto the cantilever holder or its edge, the cantilever substrate edges or the cantilever (spot positions 1, 2, 3, 5, 6 in Fig ). If the laser beam passes through the head freely try to aim it on the cantilever holder edge by rotating alignment knob 2 (Fig ). This knob allows moving the laser beam in the direction perpendicular to the cantilever holder edge (Fig ). When knob 2 is rotated in the clockwise direction the laser beam is moved away from the cantilever holder, when it is rotated in the counterclockwise direction the laser beam is moved towards the cantilever holder. If knob 2 is rotated in the counterclockwise direction until it stops the laser spot will be somewhere on the cantilever holder. Then, if you have managed to detect the laser beam and it is located, for instance, on the probe holder (Fig ) we can recommend the following procedure for aiming the laser beam on the cantilever end: probe holder substrate edge substrate edge with cantilever cantilever cantilever end. By rotating knobs 1 and 2 place the laser beam on the substrate edge where the cantilever is located (position 3 in Fig ). Using knob 2 slightly move the laser spot in the direction perpendicular to the edge so that it slightly touches the substrate edge (position 4 in Fig ). You can also observe the image of the beam that has passed through the head on the screen. In case of movement (using knob 2) in the 3.5 Adjusting the laser and photodiode

40 Chapter 3. Preparing the microscope, SPM head, probe and sample direction perpendicular to the front side of the substrate (perpendicular to the holder edge) the image of the beam on the screen will demonstrate when the edge of the substrate starts crossing the laser beam. Then, rotate knob 1 to move the spot along the front edge of the substrate. Simultaneously it is necessary to observe attentively to the cantilever substrate and to the image of passed beam on the paper screen. Since the cantilever is small in size a slight rotation of the knob will be sufficient to miss the cantilever. Therefore you need to rotate the knob very slowly. One rotation of knob displaces the cantilever with respect to laser beam on 350 microns, while the cantilever dimension in the transversal direction can be for different cantilevers from 20 to 400 microns. If you have started the movement along the edge not from a corner but from somewhere in the middle and you cannot detect the cantilever after reaching the edge, you need to reverse the movement direction. As soon as the cantilever starts crossing the laser beam (position 5 in Fig ), you will see it by scattering. Visually it will look like the appearance of a bright spot near the front edge of the cantilever substrate. Then you will need to perform the next adjustment step, that is, aim the laser spot at the cantilever end (position 6 in Fig ). For novice users this is the most difficult step in the laser adjustment procedure. The difficulty is that visually both case 6, when the laser spot is precisely aimed at the cantilever end and case 5, when the laser spot is on one of the cantilever beams, look identical. In both cases all you can see is a small bright spot. However, the image of the passed-through laser beam spot on the paper screen located over the head will be completely different. This laser beam image on screen can be used to aim the laser beam at the cantilever end. Second laser adjustment step aiming the laser beam on the cantilever end If the cantilever does not cross the laser beam the paper screen will show a relatively homogenous extended-shape spot (Fig ) Fig Fig As soon as the cantilever starts crossing the laser beam moving along the front edge of the substrate (as you rotate knob 1) the homogenous shape of the spot on the paper screen will be distorted. The type of distortion in the image on the screen can be different, for example as on Fig If you continue to move the laser beam in the same direction (by rotating knob 1) the cantilever will pass through the laser beam zone and exit this zone on the other side. As soon as the cantilever exits the beam zone the spot image distortion on the paper screen will disappear. Therefore, there are two positions of knob 1 - within the range between them distortion of the passed-through beam image can be observed also within the same range the cantilever crosses the laser beam. You need to set knob 1 approx. between these two positions i.e. approx. in the middle of the range where distortion of the passed-through beam image can be observed (Fig ). 3.5 Adjusting the laser and photodiode

41 3-16 Solver P47H SPM Instruction Manual Fig Please note that the type of distortions depends on the location on the cantilever where the beam falls, cantilever position with regard to the beam, cantilever size and shape. Case of triangular cantilever There is a very important detail from adjustment standpoint. The thing is that when the beam falls onto the cantilever end the image of the passed-through beam on the screen (distorted image) is approximately identical, at least for triangular cantilevers, regardless of their sizes. Let s assume that you have positioned the laser beam using knob 1 approx. in the middle of distortion range. After that you can start moving the cantilever perpendicular to the front side of the substrate using knob 2. At first you should try to rotate it counter-clockwise to make the beam move away from the cantilever. If you rotate knob 2 to a too large degree you may exit the distortion area on the image of the passed-through beam. In this case you can return to the distortion area by rotating the knob backwards. Without exiting the distortion area on the image of the passed-through beam you need to find such a position of knob 2 in which the image of the passed-through beam will look similar to the image shown in Fig The image of the passed-through beam shown in Fig is associated with a case when the laser spot is aimed on a triangular form cantilever end. Fig Fig Case of rectangular cantilever In case of a rectangular cantilever the image of the passed-through beam on the screen must look differently approx. as shown in Fig However, in this case the presence of the right image is not a sufficient prove yet of the correct adjustment. The image shown in Fig can be observed if the center of the laser beam is located on the longitudinal axis of the cantilever regardless of the cantilever end position it can be next to the cantilever end or rather far from it. 3.5 Adjusting the laser and photodiode

42 Chapter 3. Preparing the microscope, SPM head, probe and sample The image similar to Fig indicates that using knob 1 in the transversal direction you have managed to position the laser beam approx. in the center of the rectangular cantilever. This should be taken into account also after you have managed to make the necessary adjustment in the transversal direction using knob 1, try to position the spot on the very end using knob 2 that allows moving the laser beam along the longitudinal axis of the cantilever Adjusting the photodiode using the photodiode indicator After adjusting the laser beam on the cantilever you can start adjusting the photodiode position with regard to the laser beam reflected from the cantilever. During adjustment you need to position the photodiode with regard to the laser beam in such a way that when reflected from the cantilever it would fall onto the central part illuminating all four photodiode segments in a similar way. The photodiode movement is done using two alignment knobs 3 and 4 located on the SPM head (Fig ). Knob 4 moves the photodiode in vertical direction with regard to the cantilever plane and knob 3 moves it in the lateral direction. Photodiode signals can be monitored using the photodiode signal indicator. As it was mentioned above (item 3.5.1), the photodiode signal indicator is turned on by pressing the button in the upper row of the program window. This will display the photodiode signal indicator window (Fig ) Fig Fig Using photodiode alignment knobs 4 (VER. DFL) and 3 (LAT.DFL) (Fig ), you need to set the maximum possible value for the total signal LASER, as for the VER.DFL (DFL) and LAT.DFL (LF) signal values they need to be set into zero positions (Fig ). At the same time, VER.DFL and LAT.DFL signals appearing when knobs 4 («VER. DFL») and 3 («LAT.DFL») are rotated in both directions with regard to the zero position must change their signs. If any of these signals is reduced to zero when an appropriate knob is rotated without changing its sign, you need to rotate this knob in the opposite direction until you find a position where the signal will change its sign. Note.The photodiode can be adjusted using program oscilloscopes. Use of program oscilloscopes for photodiode signals monitoring is described below in item Adjusting the laser and photodiode

43 3-18 Solver P47H SPM Instruction Manual Fine laser adjustment using the photodiode indicator After aiming the laser on the cantilever end and adjusting the photodiode perform fine adjustment of the laser on the cantilever end based on the total photodiode signal. To do it use laser alignment knobs 1 and 2 to set the maximum value for the total photodiode signal (LASER). Caution! The laser spot must remain on the cantilever end! Adjusting the laser and photodiode using program oscilloscopes The laser and the photodiode can be also adjusted using the program oscilloscopes. In this case the signals from the photodiode are controlled by the program oscilloscopes. For adjustment set the program oscilloscopes up for the measurement of DFL and LF signals (DFL VER.DFL, LF LAT.DFL). A specific signal is connected to the oscilloscope by pressing the second button in the oscilloscope menu (Fig ) Fig and by choosing then the necessary signal in the displayed menu. For example the signal DFL in Fig and LF in Fig : Fig Fig The measuring process can be turned on using the button (the third button from the left in the oscilloscope menu). After the measurement process start it is possible that the signal on the oscilloscope screen will not be displayed because the axis have not been scaled properly. The measured signal may not fall within the scale range set up along the vertical or horizontal axis. Below you will find a short description of the axis scaling procedure (for details see item ). To adjust the oscilloscope scale place the cursor on the oscilloscope field and press simultaneously «Shift» and left mouse button and move the mouse in the required direction. Moving downwards (upwards) compresses (expands) axis Y, moving to the left (to the right) compresses (expands) axis X. If you press the left mouse button only (without pressing Shift) the mouse movement will cause the set range to move along the axis without changing the axis scale. For scaling you can also use the Scale button in the oscilloscope menu. Turning the photodiode setting knobs 4 (VER.DFL DFL) and 3 (LAT.DFL LF) (Fig ) obtain any non-zero signal on oscilloscopes (Fig ). 3.5 Adjusting the laser and photodiode

44 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-19 Fig Fig Then, rotating knob 3 set a zero signal on the LF oscilloscope and on the DFL oscilloscope set the maximum possible module signal using knob 4 (Fig ). Then, rotating knob 3 set a zero signal on the LF oscilloscope and set a zero signal in the DFL window using knob 4. It is possible that in the course of this procedure the signal in the LF window may slightly deviate from its zero value, in this case reset it to zero using knob 3. Then set a zero value of the DFL signal using knob 4. In order to obtain zero values of the DFL and LF signals you may have to repeat these operations several times. Fig Fig Make sure that rotation of photodiode alignment knobs 4 and 3 in one and another direction causes the values of the signals on the DFL and LF oscilloscopes to deviate both in the positive and negative directions (Fig , Fig ). The zero value of the signals DFL and LF corresponds to the reflected laser beam position in the center of the photodiode. 3.5 Adjusting the laser and photodiode

45 3-20 Solver P47H SPM Instruction Manual Special features and differences of the laser and photodiode adjustment for SPM heads SFC050L, SFC090L with an installed cantilever holder for operation in liquid media The following laser adjustment procedure can be recommended for an SPM head with an installed liquid type holder. First aiming the laser beam on the cantilever in air by lifting the SPM head slightly (Fig ) and viewing the image of the passing laser beam spot on a screen by means of the laser adjustment knobs 1,2 (Fig ) similar to the adjustment procedure for the SPM head for operation in air (item 3.5.2). Fig Fig Then you will need to use some simple tools: a Petri dish, two identical supports having 5-10 cm in height and a sheet of white paper. Take the Petri dish and place it on the supports (Fig ). Supports should be installed on the white sheet of paper that will function as a screen. Pour some distilled water into the Petri dish. Fig Fig Adjusting the laser and photodiode

46 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-21 Take the SPM head in your hands and hold it above the Petri dish. Then move the SPM head down so that the tip of the prism of the cantilever holder with the cantilever is inserted into the liquid (Fig ). The paper screen will show the image of the passed-through laser beam. Since the cantilever has been placed in liquid and refractive index of air and liquid are different, the laser beam will slightly move away from the cantilever end and some fine-tuning will be required. While observing the image of the passed-through laser beam on the paper screen and using the laser adjustment knobs 1,2 (Fig ) aim the laser beam on the cantilever end. Usually, for finetuning of the laser it is necessary to turn the laser adjustment knobs on degrees counterclockwise. (The laser beam is aimed similar as described above for operation in air medium (item 3.5.2) by means of the laser adjustment knobs 1 and 2, Fig ). After the laser beam has been aimed onto the cantilever in liquid medium, the photodiode is adjusted by means of adjustment knobs 3,4 (Fig ) as described above for operation in air medium (item 3.5.3). After the laser and the photodiode have been adjusted the SPM head can be placed for the time being on a table and after the next operation (preparation and installation of the sample) the SPM head is installed on the carriage of the approaching module. The optical system adjustment will not change if you don t touch the adjustment knobs. 3.6 Preparing and installing samples The unit can be used to study samples with linear dimensions in plane up to 100 mm and the thickness of up to 15 mm Installing small size samples Small sample (less than mm) should be fixed on a special adapter substrate, then install this adapter substrate on the holder stage with the sample already attached to it. As an adapter substrate it is normally recommended to use the standard SU001 substrate (Fig ) manufactured and supplied by NT-MDT. The substrate is made of polycrystalline sapphire and its size is 24x19x0.5 mm. It is possible to use any other similar type substrate with the thickness of 0.5 mm as an adapter substrate. To attach samples to the adapter substrate you can use double-sided adhesive tape. Fig Fig A special sample holder is available for small sample installation (Fig ), its base is made of magnetic material. The sample holder is installed on the magnetic holder (Fig ) of a stage for sample positioning (Fig ). This configuration allows rotation of the sample holder with respect to the vertical axis at any angle, which supports any required orientation of the sample in plane X, Y. 3.6 Preparing and installing samples

47 3-22 Solver P47H SPM Instruction Manual Fig Fig When installing the adapter substrate into the holder insert it into the holder on the respective side under the spring clips on the side of 2 balls (Fig ) in such a way that the clips press the upper surface of the substrate from above and the bottom surface of the substrate is on the three ball supports (Fig ). Fig Fig Samples that are bigger than mm but smaller than mm should be attached to the special SU002 substrate manufactured and supplied by NT-MDT. Also it may be used SU001 substrate with pasted adapter plate, having the thickness near 2 mm. The width of adapter plate must be smaller than the distance between the spring clips of the holder and the thickness of adapter plate must be lager than the height of the spring clips Installing large size samples Samples with linear sizes above 20 mm and less than 100 mm can be installed directly onto the stage for positioning. You can also use a sufficiently large parallel-sided adapter plate. You can attach the sample to this plate that you can install on the stage. This plate can be also used to attach small linear size samples Some recommendations about sample preparation Very even surfaces are used to study objects of submicron sizes such as thin films with defects, biological objects, films containing incorporated objects. Laminated materials, such as highly orientated pyrolytic graphite (HOPG), mica, are best suitable for this purpose. As for metallic substrates, gold or platinum are most frequently used. Smooth (but not atomically flat) surfaces for investigating and deposition various substances are obtained by vacuum deposition of gold or platinum onto other substrates. The surface of noble metals stay suitable for use over long time. 3.6 Preparing and installing samples

48 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-23 Let us take the example of graphite to explain the preparation of a sample. Take a HOPG plate not bigger than 10x15 mm and not more than 3 mm thick, for example HOPG plate supplied by NT-MDT. Take a standard SU001 substrate. Cut off a piece of double-sided adhesive tape slightly larger than the sample. Stick a piece of adhesive tape on the substrate, smooth it out with the pointed forceps to prevent any air-bubles from forming between the substrate and the adhesive tape. Put the sample - a graphite plate - over the adhesive tape and carefully press it down with the forceps in several places (but not there where investigation is to be done). Adhesive tape is used to obtain a clean and smooth graphite surface. Stick a piece of adhesive tape that is slightly larger than the graphite over the graphite surface and smooth it out to prevent airbubbles from forming under the tape. Then take the tape off together with the upper graphite layer. The graphite molecular layers have a slight inclination with respect to the outer surface. Therefore after the tape is taken off the smoothness of the surface at various sides of the sample will be different. Note the side where the surface is smooth after the tape is taken off and in future take the tape off from this side. Preparation of a sample on a mica substrate is similar. In order to achieve a fresh chip of mica you can pick up the upper layer using a thin blade and then remove it with forceps. 3.7 Installing the SPM head When performing this operation you need to: 1) Install the SPM head on the sample approach module; 2) Check the parallelism between the SPM head base plane and the sample plane; 3) Approach the sample to the probe at approx mm; 4) Hang the approach module with the installed head onto the anti-vibration suspension Installing the SPM head on the sample approach module Prior to installing the head you need to estimate the future distance between the probe and the sample surface after the head installation and make sure that this distance will be sufficient (at least 1-2 mm) to avoid the damage to the probe and the sample surface. Otherwise, i.e. if you see that this distance will not be sufficient to avoid damage you will have to move the sample down to a sufficient distance prior to installation. The easiest way to move the sample is to use the manual approach knob located at the bottom of the approach module (Fig ). The sample can be moved downwards by rotating the knob in the clockwise direction (if you face the knob). Besides, the sample can be moved using the SPM control software, for details see item Fig Fig Installing the SPM head

49 3-24 Solver P47H SPM Instruction Manual The SPM head should be installed to support platforms of the sample approach module with support screws (Fig , Fig ), in such a way that the front legs (legs with lock nuts) of the head get into support platforms having a hole and a riffle. Fig Fig Checking parallelism between the SPM head base plane and sample plane In order to decrease undesired tilt during scanning the SPM head base plane must be parallel with the sample holder base plane. (Assuming that the studied sample is parallel-sided and the sample surface plane is parallel to the holder base plane). To check the parallelism between the SPM head base plane and the sample holder base plane you can use a regular ruler. With the ruler you need to measure the distance between the SPM head base and the approach module plane near each of the three support legs, for instance, as it is shown in Fig Distances in these points should be set equal by adjusting the length of the support legs as precisely as allowed by the ruler you are using. With a regular ruler these distances can be adjusted to the nearest 0.5 mm which is absolutely sufficient Initial sample approach to the probe The easiest way to do the initial approach is to conduct it manually using the above mentioned manual approach knob (Fig ). Let us remind you that the knob rotation in the counterclockwise direction moves the sample upwards (if you face the knob). While observing from one side approach the sample to the probe to a distance of mm (Fig ). Note. If necessary the sample can be moved with the help of the step-motor using the SPM control program. For details on this procedure see item «3.7.5 Addition» below. 3.7 Installing the SPM head

50 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-25 Fig Fig Hanging the approach module with the installed head on the anti-vibration suspension Prior to hanging check the laser and the photodiode adjustment using the photodiode indicator and, if necessary, do some fine-tuning as required. Remove the approach module from its supports by lifting it slightly and rotating it, then hang it onto anti-vibration suspension (Fig ). Using the bracket adjustment knobs position the approach module horizontally. Now you can proceed with operation in any of the AFM modes Addition (Moving the sample using the control program) To move the sample using the step-motor, open the Approach window. To open the Approach window press the Operation button in the SPM window menu (Fig ) and then select in activated menu the Approach label (Fig ). Fig Fig Fig The Approach window also can be opened by pressing the button the bottom (Fig )., which is on the toolbar at Select the Mover label in the opened Approach window and the Mover window (Fig ) will be opened. 3.7 Installing the SPM head

51 3-26 Solver P47H SPM Instruction Manual Fig Fig Fig The sample can be moved away from the probe (downwards) using the «Until ESC» button, under the «Backward» header (Fig ). When this button is pressed the step-motor turns on and the mobile cylinder of the sample approach module with the attached sample starts moving from the probe. To stop the movement, press the ESC key. Accordingly, to move the sample towards the probe you need to use the «Until ESC» button, under the «Forward» header (Fig ). To stop the movement, press the ESC key. When using the above mentioned button for the sample movement it is important not to mix up the «Until ESC» button associated with Fig. ckward» header that controls movement away from the probe, with a similar button «Until ESC» associated with the «Forward» header that controls movement towards the probe. When moving the sample away from the probe you can specify a certain distance over which the sample needs to be moved. For instance, you need to move the sample 3 mm downwards (i.e. move the sample away from the probe). In this case in the Mover window you should click on the indicator button located near the Remote button (Fig , Fig ). In the displayed regulator window (Fig ) specify the required value - in our example this is 3 mm. The input of the value is done by pressing the left mouse button (Fig ). Fig Fig Fig After specifying the required value for the sample downward movement, click on the Remote button (Fig ). This turns on the step-motor and the mobile cylinder with the holder and the sample starts moving downwards (away from the probe). Fig Fig After the sample has been moved downward to a preset value the step motor position indicator WAY (Fig ) will indicate displacement value (in microns). 3.8 Attachment 1. INSTALLATION OF A SAMPLE AND INSTALLATION OF THE SPM HEAD WHEN THE

52 Chapter 3. Preparing the microscope, SPM head, probe and sample 3.8 Attachment 1. Installation of a sample and installation of the SPM head when the head is used as the Stand Alone Microscope As it was mentioned above the SPM head can be used as an independent AFM microscope and can work in a mode of the Stand Alone microscope. At working of the SPM head in a mode of the Stand Alone microscope the SPM head is installed directly on the sample if the sizes of the last exceed distance between the support legs of the SPM head. If the sizes of the sample there are less than distance between the support legs of the SPM head the sample is installed on some surface, enough flat and solid, which carries out function of the base, and already on this surface the SPM head is installed. In the elementary case as the base the surface of a table may be used Installation of samples on the surface of the base (operation in a mode of the Stand Alone microscope) At installation a sample should be 1) It is rigidly enough fixed on the surface of the base and 2) It is located so that the upper surface of a sample was parallel the surface of the base. At installation of a sample it is possible to be guided by the following recommendations: If the sample is massive enough, it is possible to put the sample directly on the horizontal surface of the base. It is desirable to fix the sample inflexibly enough on the surface of the base, if the sample: a) has the small sizes, b) is rather light, c) is too thin and may bend. Quite sufficient fixing is provided with gluing the sample by means of a double-sided adhesive tape. There is no necessity to paste the sample by all side (because if the sample is pasted by all side, it will be rather difficult to remove the sample after the ending of measuring). If the sample is rather large (has in a horizontal plane the sizes about mm), it is enough to paste the sample in three places, in other words to provide three points of support. Importantly, so as one of support point was in that place in that you are going to make AFM measuring. f the sample has the small sizes (has in a horizontal plane the sizes less than mm) and is inflexibly enough (not pliable) such sample can be pasted on two parallel narrow streaks of a double-sided adhesive tape that are located on a distance slightly smaller than width of the sample. In this case the sample will be easily removed after completion of works. If the sample has small sizes and is too thin (pliable) it is better to paste the sample on some adapter substrate and already to set this substrate on the surface of the base Installation of the SPM head (operation in a mode of the Stand Alone microscope) The SPM head has three support legs on which it is installed above the sample. Two legs are identical (front legs). The third leg (a back leg) has from above the adjusting handle. The length of all three legs can be adjusted. The height of the probe relative to the surface of the base (and, accordingly, the d.8 nce between the probe and the sample) is adjusted by means of changing the length of the legs Attachment 1. Installation of a sample and installation of the SPM head when the head is used as the

53 3-28 Solver P47H SPM Instruction Manual Prior to installing the SPM head the length of the back leg has to be adjusted thus that cantilever does not touch the sample to prevent its damage. The major task at carrying out the procedure of installing the SPM head is to adjust and to establish correctly the length of the legs of the SPM head. For this purpose it is necessary to adjust the length of legs so that a) The distance between the probe and the sample was about mm (to avoid casual damage of the probe and scanner), and so as b) Subsequently, after carrying out the procedure of the approach of the probe to the sample the plane of the SPM head was parallel to the surface of the sample. Viewing procedure of adjusting the length of legs, it is necessary to make the following important note. Depending on character of prospective AFM-researches, it is necessary to mark out two extreme cases: a) the case when a small tilting of the SPM head plane relative to the plane of the sample is not important, b) the case when it is important so as the tilting was minimum (for example, at the big field of scanning). In the first case it is enough to install the length of legs simply by eye. For many types of measurements it is quite enough. Accordingly, at the same time should be remembered that after installation between the probe and the sample there should be a sufficient distance to not damage the probe, the scanner and the sample. In the second case when it is important that the tilting was minimum, the regulation of the legs length is necessary to make more carefully. For this case we shall consider sense of the above-mentioned requirements in more detail. Let us assume that procedure of installing the SPM head is executed (Fig ). After procedure of installing the SPM head will be executed, the procedure of approaching the probe to the sample will be carried out further. Fig Attachment 1. Installation of a sample and installation of the SPM head when the head is used as the

54 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-29 The specified procedure, i.e. the procedure of approaching, is carried out manually, by means of rotating the handle of the back leg (the handle of approaching) ( * ). ( * ) The note. Except the case when the SPM head is completed with the motorized approach leg (LGM01), which allows to make the automated approaching. At rotating of the handle (counter-clockwise) the length of the back leg will decrease. As a result of it, the SPM head plane will be rotated concerning the spin axis, which coincides with the direct line that is situated in the plane of the base and passed through the points of support of the front legs. Accordingly, simultaneously with rotational displacement of the SPM head plane there is an approach of the probe to the sample. The approach process will end by touching of the sample by the probe (by cantilever tip). The case when at the moment of touching by the probe of the sample, the SPM head plane and the plane of the surface of the sample will be parallel (it is supposed, that the surface of the sample and the surface of the base are parallel) will be ideal. Thus, at the SPM head installation the plane of the SPM head should have a small tilting with respect to the plane of the base (Fig ) and subsequently this small tilting should be compensated at completion of the subsequent approach procedure. The legs length determines the value of tilting. Therefore at the SPM head installation the adjustment of legs should be such that a) the front legs had the same length and b) so that the difference of lengths of the back leg and front leg (digitized from the SPM head plane) was approximately three times more than distance between the sample and the probe. Schematically it is explained in Fig The relation shown in Fig (h back -h front 3h probe ) is connected by that fact that the distance from the rotation axis (the straight line passing through the support points of the front legs) up to the back leg approximately three times is more than distance from the rotation axis up to the probe. At adjustment of the legs length for measurement it is possible to use usual ruler. Use of a good usual ruler provides the installing the distances with accuracy of 0,5 mm that is quite sufficient. 3.9 Attachment 2. Closed liquid cell General Information The closed liquid cell (MP1LC) is designed for measuring samples using scanning probe microscopy methods in fluids. This cell is used in combination with the scanning probe heads for operation in liquids like SFC050L or SFC090L; this allows performing the measurements of: topography using contact and semi-contact microscopy, lateral forces; local hardness and viscosity; phase contrast Requirements to the sample The studied sample are held in place on a sapphire substrate using spring clips or glued onto the titanium base. The glue should be selected according to the type of the liquid used. The user can employ any other substrates if it is possible to place them into this cell. The height of the sample glued to the substrate must not be more than 2 mm. 3.9 Attachment 2. Closed liquid cell

55 3-30 Solver P47H SPM Instruction Manual Design General view of the assembled closed liquid cell is shown in Fig Fig Fig The cell is supplied with (Fig ) cantilever holder with a silastic membrane (1), device (2) for installing the cantilever holder onto the head, platform for the liquid cell (3). The cell consists of the following parts (Fig ): titanium base (4), polycrystalline sapphire substrate (5) with clips (6) for sample installation, fluoroplastic ring with silastic O-ring seal (7), titanium threaded ring (8) for fixing fluoroplastic ring (7) on base (4), flange with levers (9) for clamping cantilever holder and membrane, two nipples with tubes for fluid feed and removal (10, Fig ). Fig Fig Fluid is fed into the cell from a special fluoroplastic cup, medical syringe or any other suitable container. The volume of the cell is 2-5 ml depending upon the sample. 3.9 Attachment 2. Closed liquid cell

56 Chapter 3. Preparing the microscope, SPM head, probe and sample Liquid cell operation Installing the sample and assembling the cell The sample can be attached with double-sided adhesive tape, glue insoluble in this medium, or installed using spring clips 6 (Fig ) directly onto substrate 5 (Fig ). Or you can first place the sample onto a special sapphire substrate and then attach it to the big substrate (Fig ). Fig Fig Place the substrate with the sample onto the titanium base. Make sure the substrate is installed with its seats between pins (Fig ). Place the fluoroplastic ring with rubber seal 7 (Fig ) on top of the substrate so that the base pins enter in appropriate openings on the ring (Fig ). Put part 9 (Fig ) onto the fluoroplastic ring and threaded titanium ring 8 (Fig ) on top of it, then screw it evenly (Fig ). Fig Fig Attachment 2. Closed liquid cell

57 3-32 Solver P47H SPM Instruction Manual Installing the cell Replace the standard platform with magnetic sample holder (Fig ) with a platform for liquid cell installation (Fig ) Fig Fig Install the cell onto the platform (Fig ) Connect tubes (Fig ) Fig Fig Pull aside the two handles designed for.9 mping the membrane to the cell (Fig ) 3.9 Attachment 2. Closed liquid cell Fig

58 Chapter 3. Preparing the microscope, SPM head, probe and sample Installing the measurement beak The cantilever holder (Fig ) for operation with the liquid cell is provided with an additional silastic membrane as opposed to a regular holder Fig A fluoroplastic cap is provided to protect it from damage during installation of the holder onto the scanning head (detail 2, Fig ). Place the cantilever holder into the cap (Fig ), approach the holder with a pre-installed cantilever to its seat on the head holding the membrane with your fingers as shown in Fig , Fig Make sure the holder is rotated by 45 relative to its working position and the marker on its platform matches the INSERT arrow on the head dial. If the marker and the INSERT arrow match place the holder onto its seat. The seat ring located on the bottom side of the holder platform must enter into the scanner tube. The holder will land onto its seat evenly without any misalignment. Fig Fig After installing the holder on the head seat rotate the holder cap 45 clock-wise until the marker on the platform matches the OPERATION arrow on the head dial (Fig ). This is the working position of the holder in which all measurements are carried out. In this position the force pressing the holder against the scanner tube is maximum. 3.9 Attachment 2. Closed liquid cell

59 3-34 Solver P47H SPM Instruction Manual Remove the cap. Fig Fig Install the cantilever into the holder (Fig ). Fig Preliminary adjustment of the optical system First of all aim the laser beam at the cantilever in air, by lifting the head slightly and using the spot of the passed-through laser beam and the cantilever shadow (see the Manual, item 3.5.2). Since the laser beam path will be different in liquid and air you probably won t see the signal in the photodiode window. Fine adjustment of the system is done the head is installed onto the base and the cell is filled with solution Installing the head Set the required length for the head legs. Shift the liquid cell installed on the approaching base into its extreme position (manually or using the step motor). Carefully place the head above the cell and using the positioning screws adjust the cell position so that the membrane can easily enter into the cell (Fig ). 3.9 Attachment 2. Closed liquid cell

60 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-35 Fig Fig Carefully approach the cell manually to the membrane (try to make sure they are both at approximately the same level and the membrane can easily enter into the cell). Be careful do not break the cantilever! Clamp the membrane to the cell using the two knobs on the cell (Fig ) Fine adjustment of the optical system Fill the cell with the working solution. Open the photodiode signal measurement window. Rotate the laser alignment knobs counter-clockwise. Laser signal must appear. If the Laser signal does not appear, try to twist slightly knobs of adjustment of the photodiode. After appearing of the Laser signal adjust the signals Laser, VER.DFL and LAT.DFL in the usual way (as at adjusting on air, item 3.5.3, 3.5.4) Contact mode Approach to the sample surface is done in the same way as with the regular unit (see User s Manual, chapter 4) Semi-contact mode For operation in semi-contact mode in liquid first of all approach the sample in contact mode. Then turn off the feedback and after applying voltage to the piezo-transmitter Probe (using the control circuit diagram in the program) scan the cantilever oscillation amplitude in the frequency band from 60 to khz. In the oscilloscope window you will see a curve with multiple resonance peaks as opposed to operation in air. Select a band khz wide containing the highest resonance peaks. Scan this band. Then turn on the feedback (DFL must remain your DFL signal). This will press the cantilever to the surface. Check it the color scanner advance bar does not fill the frame completely. Press and hold Shift and click F-Scan one more time. In doing so you will scan the set frequency range one more time but the oscilloscope window will continue displaying the previous scan data. Compare the data of both scans one with the free cantilever and one with the cantilever pressed to the surface. Some of the resonance peaks would decrease significantly, others practically would not change and some of them would even grow. 3.9 Attachment 2. Closed liquid cell

61 3-36 Solver P47H SPM Instruction Manual For operation in the semi-contact mode you can choose any peak whose amplitude has decreased in the pressed down condition. Select the peak whose amplitude in the pressed down condition has decreased most significantly. Turn off the feedback again, apply the selected frequency, switch the feedback signal to MAG and set the SP value slightly higher than the current amplitude value. Turn on the feedback and while decreasing the SP value switch over to operation in semi-contact mode. Note: During withdrawal from the surface the MAG signal can decrease at the selected frequency and you won t be able to use this signal for a second approach. If the MAG signal does not decrease during withdrawal compared to the disabled feedback level, this signal can be used for a second approach Withdrawal from the surface Be careful when withdrawing from the sample! Withdraw the sample from the head at mm. Pull the handles on the cell aside and free the membrane. Withdraw the sample at 3-5 mm and Remove the head Attachment 3. High temperature stage Design Specifications Sample size from 5x5 mm Heating stage size 15x17 mm Temperature range from room temperature to 300 C Temperature measurement precision 1 C (on the stage surface) Temperature maintenance accuracy 0.5 C Temperature sensor thermal couple Z2-K-2M (IEC), chrome-alumel thermal couple Temperature measurement rate about 25 seconds up to 100 C, not more than 150 seconds up 300 C Heating element power consumption 50 W Voltage 25 V (via the controller) Measurement head design features Measurement head Smena SFC050H (Fig ) is used for operation with the high temperature stage. Compared to standard measurement head Smena SFC050, this head has a high temperature protection on the bottom cover. For this reason the cantilever holder and the front legs have been modified. The rest of the head design remains the same. There is no provision for applying voltage to the cantilever or measure the current passing through the cantilever Attachment 3. High temperature stage

62 Chapter 3. Preparing the microscope, SPM head, probe and sample 3-37 Fig Fig High temperature heating stage design The high temperature stage consists of a heating element with a built-in temperature sensor and a heat sink (Fig ). Wires from the heating element and the temperat.8 sensor in one cable are connected to a special port of the controller. The sample is pressed against the heating element with two clips. The thermal stage is designed for installation on mover MP001. Sapphire plates can be seen on the bottom of the thermal stage, the stage bears upon the balls of mover MP001 with these plates Getting ready for operation Installing and connecting the thermal stage To install the thermal stage into mover MP001 remove the standard insert from the mover (Fig ). The insert is held in place inside the mover by means of two microscrews and a spring plate. To remove the insert pull it horizontally towards the spring plate, then lift the opposite edge slightly and carefully release the spring plate. Fig Fig Then put the high temperature stage back (Fig ). First unscrew the microscrews until they stop. Pay attention to the orientation of the stage the flat platforms must be positioned in front of the spring plate and of the front screw, the platform with a groove must be in front of the right screw. The cable from the thermal stage goes to the rear flat support for the measurement head Attachment 3. High temperature stage

63 3-38 Solver P47H SPM Instruction Manual Install the sapphire platform in front of the spring plate and push it almost parallel. Lower the opposite edge and place appropriate platforms in front of the miscroscrews. Rotate the screws to place the stage into an average position. Fig Connect the thermal stage cable to the controller. A special socket for the thermal stage is located in the bottom part of the rear cover. Attention! The cable can be connected only with the power supply turned off. Attention! If the thermal stage is connected, launch the program before turning on the unit Installing a sample To install a sample lift the black lever on the thermal stage (Fig ). Place the sample under lifted clips. Lower the lever to fix the sample in place. Use forceps to install a.9 ple dirt on the sample and the stage may soot the cantilever. Fig Fig Installing a cantilever To install a cantilever turn the measurement head upside down (Fig ). Move the cantilever adjustment lever into the O.10 osition. Place the cantilever under the lifted spring. Move the lever into the CLOSE position. The cantilever adjustment is done in the usual way Attachment 3. High temperature stage

64 Chapter 3. Preparing the microscope, SPM head, probe and sample Thermal stage operation Control software features Fig All the features of the control software for the high temperature stage are present in the special T window and in the scanning parameters menu. To set and control temperature open the scanning parameters window and go to the T window Setting and control of temperature To set the required temperature click T( C)= and set the required value. To turn on the heating click ON. The current temperature is displayed on the left in red. The relationship between the current temperature and time can be observed on the built-in oscilloscope (in window A or B) via input T300. If the set temperature is below the current one, the heater is turned off until the set temperature is reached. Be careful during heating the temperature may exceed the set value for a short time by up to 5 C in the range between C and by 2-3 C in the range between C (Fig ). Fig Attachment 3. High temperature stage

65 3-40 Solver P47H SPM Instruction Manual What is special about using an AFM with a high temperature stage When working with a high temperature stage it is preferable to use cantilevers without additional reflective coating. As the reflective coating and the cantilever material have different thermal expansion coefficient this results into cantilever beam bending during heating. This leads in its turn to changes in the DFL signal. This is especially important when using «soft» cantilevers in the contact mode. In case of substantial deviation the value of DFL can be adjusted with photodiode adjustment screw. The most preferable is the operation in the semi-contact mode. Besides the beam bending, heating also results into expansion of the thermal stage itself, reduction of the resonance frequency and the cantilever oscillation amplitude. Make sure that prior to every temperature increase on the sample the probe is moved at least 1 mm away ( Approach Remote ). The scanner range (2 micrometers) is sufficient to compensate for thermal expansion only if increasing the temperature by 5 C. Wait for 5-10 minutes. Check the resonance frequency and the cantilever oscillation amplitude. Approach the probe to the sample again. During minutes after heating up to the specified temperature and approaching you may observe sufficient drift along the Z-axis. If you cannot wait until the end of stabilization keep checking the scanner position on the colored ruler in the upper portion of the screen, and try to set a small duration for scanning (for example, by decreasing the number of scanning points). When preparing the sample keep it clean organic contamination may soot the cantilever during its burning. Also make sure that the studied samples do not contain substances that may produce soot if heated up to 300 C. If deposited on the cantilever they may reduce the Laser signal. Prior to heating a new sample note the value of the Laser signal. Prior to reducing the temperature you don t have to move the sample away from the cantilever. But you will have to check the frequency, the cantilever amplitude and the approach to the sample each time Temperature calibration The high temperature stage has been calibrated by the manufacturer. If necessary you can adjust the calibration within a small range using the coefficients K0 and Kr (Fig ), where: K0 absolute displacement; Kr inclination of the thermal couple calibration curve. Changes may result in a small difference between the set temperature and the sensor readings. If significant correction is required contact the manufacturer. If you use a large sample the power consumption of the heater can be increased by increasing the Ksamp parameter Attachment 3. High temperature stage

66 Chapter 4. Contact Atomic Force Microscopy 4-1 Chapter 4. Contact Atomic Force Microscopy Contents Contents Chapter 4. Contact Atomic Force Microscopy Initial State. Main Stages and Operations of the Contact Mode Initial State Main Stages and Operations of the Contact Mode Configuration of the Program Main Window Program Oscilloscope (Application of Signals, Starting and Stopping of Measurement, Scaling) Preparation of the SPM control block diagram for the Contact Mode Operation Checking of the switches positions Applying the DFL signal to the feedback input «FB In» Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter Initial level of the DFL signal and Set Point Parameter Setting Up the DFL Signal Initial Level Adjustment of the DFL Signal Initial Level Using the indicator of the photodiode signals Adjustment of the DFL Signal Initial Level Using the Program Oscilloscope Setting the Set Point Parameter Value Automatic approach of the sample to the probe Enabling the automatic approach of the sample to the probe Windows «Approach», «Probe», «Mover» Continuing the automatic approaching of the probe to the sample Selection of the Feedback Gain Factor A Manual approach of the probe to the sample A Enabling the Feedback A Procedure of manual approach of the Probe to the Sample A Selection of the Feedback Gain Factor Setting Scanning Parameters Scanning Parameters Control Window The procedure to Set the Scanning Parameters Scanning Velocity The Scanning Area, Step and Number of Scan Points Scanning Mode The Scanner Non-Linear Travel Correction (NLCor button) Measurement Channels: Application of Signal, Setting Scan Direction The ADC Preamplifier Gain Factor, Low-Pass Filter The Drawing, Show Scan Lines, Scope Data, Line Strobe, AutoScale and Save To NT.MDT Buttons The Subtraction Procedure (Subtract button, Exc Hi button) Parameters for Scanning Grid-Type Test Sample Scanning Start of Scanning The Scanning Control Line Optimization of Scanning Parameters

67 4-2 Solver P47H SPM Instruction Manual 4.7 Saving the Acquired Data Switching from the Contact to Semi-Contact Mode Switching off the Microscope Lateral Force Microscopy Introduction Signal Related with the Cantilever Torsion Deformation Preparation of the Unit for Operation in the Lateral Force Measurement Mode Applying the Lateral F Signal to the Measurement Channel B Input Setting the Scanning Direction Switching the SPM Window into the Two-Window Mode The Unit Operation in the Lateral Force Microscopy Mode Force Imaging in the Contact Mode Introduction Preparation of the Unit for the Force Imaging Application of the DFL Signal to the Input of the Measuring Channel A Setting zero value for the feedback gain factor (FB Gain) The Unit Operation in the Force Imaging Mode The Mode of the Feedback Error Signal Registration

68 Chapter 4. Contact Atomic Force Microscopy Chapter 4. Contact Atomic Force Microscopy This chapter describes operation of the unit in the mode of contact atomic force microscopy. «Contact Atomic Force Microscopy» stands for contact measuring of surface topography. The unit contact mode operation when measuring surface topography serves as a basis for the unit operation in other contact techniques, such as lateral force mode, force imaging, adhesion force imaging, local rigidity and viscosity imaging (in combination with modulation methods). 4.1 Initial State. Main Stages and Operations of the Contact Mode Initial State The microscope is on; The program has been started, the display shows the program main window; The cantilever is set up, The laser and photodiode adjustment completed; The sample installed; The SPM head is installed on the approach module, the preliminary approach of a sample to the probe is executed Main Stages and Operations of the Contact Mode Operation in the contact mode may be divided into the following basic stages and operations: 1. Preparation of the SPM control block diagram for the contact mode, which includes: applying the DFL signal to the feedback input and switching operations in the SPM control block diagram required for operation in the contact mode. 2. Selection and adjustment of the initial DFL signal level and Set Point parameter value. 3. Approaching the sample to the probe: 1) Approach procedure 2) Setting the feedback gain factor 4. Check and adjustment of scanning parameters 5. Scanning 6. Saving the acquired information. 7. Switching to other modes. 8. Unit switch-off. A more detailed description of the above principal stages and operations is given below. It is assumed, that the program main window configuration is used. The configuration is briefly described below, prior to description of principal operations Initial State. Main Stages and Operations of the Contact Mode

69 4-4 Solver P47H SPM Instruction Manual Configuration of the Program Main Window It is recommended that the program main window configuration shown in Fig be set up. Under this configuration, the left part of the program main window is occupied by the SPM window, which, while scanning, will be imaging the signal applied to the channel A input. Fig At the left margin of the main window, there is a tool bar to control the unit similarly to the SPM window menu. In the right part of the main window, there are two built-in oscilloscopes. The FB feedback signal is applied to the input of one of the oscilloscopes; the other oscilloscope is provided with an input for viewing 2D «Ext» data Program Oscilloscope (Application of Signals, Starting and Stopping of Measurement, Scaling) To be able to use the oscilloscope, it is necessary, as a minimum, to know how to apply the necessary signal to the oscilloscope, how to start and to stop the process the measurement of the selected signal, and how to perform the adjustment of the oscilloscope axes scale. These issues will be briefly discussed below. In more detail, the program oscilloscope operation will be described in the Item 5 of «Program Control Description». 1) Applying Signals to the Program Oscilloscope Application of the necessary signal to the oscilloscope is performed with the second button from the left in the oscilloscope menu; when clicked, this button displays the available signals menu. To apply the necessary signal, click the appropriate button in the opened menu. E.g., clicking the FB button would apply the FB signal (Fig ) the «Ext» button would apply the Ext signal (Fig ). Fig Fig Initial State. Main Stages and Operations of the Contact Mode

70 Chapter 4. Contact Atomic Force Microscopy 2) Starting and Stopping the Measurements Clicking the button (third left) starts (or stops) the process of measuring the signal applied to the oscilloscope input. 3) Setting the Oscilloscope Display Range Upon switching on the oscilloscope, there may be no signal on the oscilloscope screen resulting from a faulty scaling of the oscilloscope. The signal being measured may miss the interval range established along the oscilloscope vertical axis because the signal value exceeds the established interval, i.e. the established scale range is too extended along the signal axis, or the interval set in the oscilloscope is significantly shifted with respect to the signal being measured. The easiest way for setting the oscilloscope display range is as follows: Compression and Extension of the Oscilloscope Axes Scales To compress the scale along the Y axis (signal axis) of the oscilloscope: 1) place the mouse cursor within the oscilloscope field (Fig ), 2) simultaneously press Shift and the mouse left key, move the mouse vertically downward. This will result in the axis compression (Fig ) The extension of the axis may be performed in a similar way, but the mouse is to be moved upward. The extension (and compression) along the horizontal axis can be effected likewise by moving the mouse across to the right (left). 4-5 Fig Fig A simultaneous movement of the mouse vertically and horizontally changes the scale in both axes, accordingly, with the mouse left key + Shift key pressed. Shifting the Scale Range along the Oscilloscope Axes To move the set up range along an axis without any changes to the scale: 1) place the mouse cursor within the oscilloscope field (Fig ), 2) press the mouse left key, and move the mouse in the desired direction. This will result in a shift of the active range without changing the scale (Fig , the result of a vertical move). The mouse travel upward (downward) causes shifting of the interval up (down) the Y axis (the signal axis), horizontal travelling results in shifting along the X axis. Accordingly, a simultaneous movement of the mouse both vertically and horizontally causes shifts of the established active ranges along both axes. 4.1 Initial State. Main Stages and Operations of the Contact Mode

71 4-6 Solver P47H SPM Instruction Manual Fig Fig Axes scaling can also be performed using the Scale button in the oscilloscope menu (fifth left). 4.2 Preparation of the SPM control block diagram for the Contact Mode Operation Open the SPM control block diagram, for example, by pressing the button in the SPM window menu (in this configuration it will be in the second line of the program main window). Check and set the correct positions of the switches and apply the DFL signal to the feedback input (Fig ). Fig Checking of the switches positions 1) The «I» switch must be in its off position, i.e. the feedback loop is opened (Fig ). Fig Fig ) The switch applying the exciting voltage to the cantilever piezodriver must be in its off position (off position is shown in Fig ). 4.2 Preparation of the SPM control block diagram for the Contact Mode Operation

72 Chapter 4. Contact Atomic Force Microscopy Applying the DFL signal to the feedback input «FB In» To apply the DFL signal to the feedback input, place the cursor on the FB In button (Fig shows the state when the FB input receives the MAG signal), press it to open the signal selection menu (Fig ). Following the selection of the DFL signal (Fig ) and pressing the mouse left key (or the Enter button), the DFL signal will be applied to the feedback input (Fig 4.2-7). Fig Fig Fig Fig There is an easier way to apply the signal (DFL in our case) to the feedback input. To do it press the FB signal selection button on the direct control line (Fig , Fig ), this button is located between the buttons FB and SP. (Fig , Fig show the state when the DFL signal is already applied). Then, similarly to the case discussed above, apply the DFL signal. Fig Fig The text on this button corresponds to the signal applied to the feedback input. 4.3 Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter Initial level of the DFL signal and Set Point Parameter The cantilever deflection in the direction perpendicular to the sample surface causes the light spot to move relative to the upper and lower halves of the photodiode. This results in a change of the DFL signal, as the latter equals the residual signal between the upper and lower halves of the photodiode. The amount of change of the DFL signal is proportional to the amount of deflection of the free end of the cantilever, with the cantilever deflection, in its turn, being proportional to the force acting on the cantilever tip. The initial level of the DFL signal conforms to the DFL signal when the cantilever is sufficiently far from the surface and does not interact with it. The value of the DFL signal initial level is dependent upon the photodiode positioning relative the light spot. As a result of this, the light spot is distributed between the upper and lower parts of the photodiode. The DFL signal zero value corresponds to the laser spot position midst the upper and lower halves of the photodiode, and the spot area is distributed between them equally. Using alignment knob 4 (Fig ), the DFL signal initial level value may be regulated by moving the photodiode vertically relative to the laser beam reflected from the cantilever. 4.3 Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter

73 4-8 Solver P47H SPM Instruction Manual Fig Prior to the approach procedure, i.e. in the initial state, when the probe is far enough from the surface and does not interact with it, it s necessary to set the initial level of the DFL signal using the above mentioned knob in order to adjust the photodiode position (knob 4 in Fig ). Recommendations on selection of the DFL signal initial level value will be discussed below along with recommendations on the Set Point parameter. When the probe is approached sufficiently close to the surface, the cantilever tip begins to interact with the surface. The deviation value of the DFL signal from the initial level, i.e. the difference between the current value of the DFL signal and the initial level of the DFL signal, will just define the degree of the interaction between the probe and the sample. The larger the deviation of the DFL signal from its initial level, the stronger the interaction, the stronger the force acting on the free end of the cantilever, and the stronger its deflection from the initial state. An increasing of the DFL signal (with respect to its initial level) corresponds to the cantilever deflection in the positive direction from the surface, i.e. to the action of a repulsive force to the cantilever tip. And vice versa, a decrease of the DFL signal compared to its initial level corresponds to the action of the attracting force on the cantilever tip. The DFL signal s correlation with the distance between the probe and the surface can be plotted as a curve shown in Fig The curve shape shown in the picture is typical for ordinary, most often used cantilevers, e.g. silicon ones, which are sufficiently hydrophilic, i.e. water wettable. In this case, when measuring in the air, a thin layer of liquid forms between the cantilever tip and the surface resulting in additional capillary forces. (In case of hydrophobic cantilevers, the curve has a different shape). Fig Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter

74 Chapter 4. Contact Atomic Force Microscopy The DFL signal maximum value, as well as its changes, can not exceed the Laser signal value equaling the cumulative signal from all the photodiode segments. The Set Point parameter defines the DFL signal level (i.e. the FB signal level), which must be maintained by the tracking system when using the feedback. The Set Point parameter value is selected and set by the operator. The Set Point parameter value should exceed the DFL signal initial level. This corresponds to a situation when the Set Point level must cross the DFL(z) curve, e.g. as it is shown in Fig Otherwise the tracking system will fail to establish the DFL signal level equal to the set up Set Point value. The greater the difference between the set up Set Point value and the initial level of the DFL signal, the greater the difference between the DFL signal value maintained by the tracking system and the initial DFL signal level, the greater the cantilever deflection, the greater the force of interaction between the cantilever tip and the surface. And, accordingly, vice versa, the smaller the difference between the Set Point value and the initial level of the DFL signal, the weaker the interaction of the cantilever and the surface. Thus, changing the Set Point parameter with respect to the DFL signal initial level, it s possible to change and set a definite level of interaction force between the probe and the surface. And correspondingly, surface topography images at specified levels of interaction between the probe and the surface may be obtained. If the set up difference between the Set Point value and the initial DFL level is too big, which corresponds to a significant strength of interaction of the cantilever tip and the surface, than, when scanning, it might cause both the probe and the survey surface destruction. With a too small difference between the Set Point and the DFL initial level, corresponding to the operation mode maintaining a weak interaction between the cantilever tip and the surface, the tracking system operation may be unstable. At the initial exploration stage it can be recommended to set a medium level of the interaction intensity corresponding to the difference between the Set Point value and the DFL initial level of one to two na. As for the procedure to select and set up the DFL signal initial level and the Set Point parameter value, the following operations algorithm may be recommended, though generally, it is not mandatory and not the only one correct. First, you decide on the value of the acting force, i.e. on the difference between the Set Point and the DFL initial level, to be used when scanning the surface. Upon deciding on the difference between the Set Point and the DFL initial level, it s necessary to set the value of the initial DFL signal level. The DFL signal initial level is adjusted to a negative value equaling in its module the assumed Set Point and DFL initial level difference, that was selected for the surface scanning. After that, the Set Point parameter is to be set up approximately at the zero value. When scanning, the feedback system will be maintaining the DFL signal value equal to that of the Set Point parameter, i.e. somewhat close to zero. In this case a lower noise level is ensured, and besides, the work is being performed in the middle of the linear range of the recording system. Suppose you select to set up the difference (Set Point - DFL initial level) equal to 1.5 na. After that, set the DFL initial level at -1.5 na, and the Set Point parameter at zero Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter

75 4-10 Solver P47H SPM Instruction Manual Setting Up the DFL Signal Initial Level The DFL signal value can be observed with the help of the indicator of the photodiode signals, which can be switched on by pressing the button in the program upper line. It is, apparently, the most simple and convenient way. Besides, the DFL signal value can be observed with the help of the program oscilloscope adjusted to measure the FB signal, as well as using the digital FB signal indicator. The digital FB signal indicator is located in the SPM control block diagram below the «FB In» feedback signal selection button (Fig ). Fig Adjustment of the DFL Signal Initial Level Using the indicator of the photodiode signals 1) Turn on the photodiode signal indicator by pressing the button in the upper row of the program window. This will display the photodiode signal indicator window (Fig ). It consists of the table and the indicator of the laser spot position. The table displays the current values of the photodiode signals. The indicator of the laser spot position shows the position of the laser spot with respect to the photodiode segments. 2) Watching the FB signal level in the photodiode signal indicator and using knob 4 (the photodiode vertical move knob, Fig ), set the required DFL signal value (of approximately -1.5 na in our example, Fig ). Let s remind, that DFL = VER DFL. Fig Fig Adjustment of the DFL Signal Initial Level Using the Program Oscilloscope 1) Turn on one of the program oscilloscopes to measuring the FB signal (had it not been already done). 2) Watching the FB signal level in the oscilloscope (Fig ), set the required DFL signal value (of approximately -1.5 na in our example) using knob 4 (the photodiode vertical move knob, Fig ). 4.3 Selection and Adjustment of the Initial DFL Signal Level and Value of the Set Point Parameter

76 Chapter 4. Contact Atomic Force Microscopy 4-11 Fig Setting the Set Point Parameter Value If you want to set up the difference (Set Point - DFL signal initial level) at 1.5 na and have set the DFL initial level at -1.5 na, than the Set Point parameter value to be set should be zero. To set up the Set Point parameter: 1) Open the SPM control block diagram by clicking the button in the SPM window menu (in the second line of the program main window). 2) Press the SPoint button (Fig ), and set the necessary value in the displayed regulator window (Fig , Fig ). Fig Fig Fig In the example shown in the above figures, the DFL signal initial level is -1.5 na, and the SPoint parameter, after the adjustment, equals na. The SPoint parameter regulator window can also be opened by pressing the SP button in the upper line of the program main window. 4.4 Automatic approach of the sample to the probe Note 1. Prior to starting the approach procedure pay attention to the set value for the feedback gain ration (parameter FB Gain). The FB Gain value should not be too low (not less than 1). The set value for this parameter is displayed in the FB Gain button in the SPM control diagram as well as in the «FBg» button in the upper line of the main program window. Accordingly, pressing any of these buttons display the regulator window where you can change the GB Gain value. After performing the above operations i.e. setting an initial level for the DFL signal and the SPoint parameter you can start approaching the sample to the probe. The unit utilizes automatic approach of the sample to the probe. The approach is done by means of a step motor that moves the sample holder with the sample attached to it relative to the probe. 4.4 Automatic approach of the sample to the probe

77 4-12 Solver P47H SPM Instruction Manual Note 2. In addition to the automatic approach of the probe to the sample it is possible to approach the probe manually. The manual approach is used when the SPM head is used as a stand-alone SPM. However, if required the manual approach can also be used when SPM head is operated as a part of P47H. The procedure for manual approach is described below after the description of the main procedure (automatic approach procedure) in item 5.5.1A Enabling the automatic approach of the sample to the probe In order to begin the automatic approach operation, open the Approach window. To open the Approach window press the Operation button first in the SPM window menu (Fig ) and then Approach in the displayed menu (Fig ). Fig Fig Fig The Approach window can be also opened by pressing the button located in the very bottom of the toolbar (Fig ). Choose the Probe tab in the displayed Approach window; this will open the Probe window shown in Fig The subsequent pressing of the button «Landing» in this window turns on the step motor of the approach mechanism. Below you can find a detailed description of the Approach, Probe and Mover windows. Fig Automatic approach of the sample to the probe

78 Chapter 4. Contact Atomic Force Microscopy Windows «Approach», «Probe», «Mover» As mentioned above, at pressing the Approach button or the Approach tab the window shown in Fig will be open. The upper left part of this window contains as a matter of fact the Approach window. In which the «Probe» or «Mover» or «Laser Adjust» window is mapped. It is determined by what tab is selected in the menu «Approach». In Fig the «Probe» tab was selected. The upper right part contains the photodiode indicator. The bottom part contains a program oscilloscope. If to switch off the button in the menu of a window «Approach» (Fig ) the photodiode indicator and an oscilloscope will be closed and there will be opened only the Approach window (Fig ) Fig The «Probe», «Mover» windows (Fig , Fig ) contain the Landing button, several indicator buttons, including the Rate indicator button. The indicator buttons display the current values of appropriate parameters. Pressing such a button will display a regulator window where you can, if necessary, change the value of a specified parameter. Fig Fig Buttons Landing, Rate, Fine, Exit, and the indicator of the step motor relative position Way are common for all tabs of the Approach menu and not only for the Probe tab (Fig , Fig ). The Landing button (Fig , Fig ) starts the automatic approach procedure. When this button is pressed the step drive starts operating. Fig Fig The Rate indicator button is located near the Landing button (Fig , Fig ). This button is used for setting up the approaching rate. The velocity here is expressed in some relative units. The maximum velocity corresponds to 20 units. The rate scale is not linear. For instance, the rate decrease from 20 units to 19 units means that the real sample travel velocity is smaller by a factor than the original one. 4.4 Automatic approach of the sample to the probe

79 4-14 Solver P47H SPM Instruction Manual For operation in the contact mode it is recommended to set the approaching rate in the range between 17 and 19 units. To change the approaching rate press Rate and set the required value in the displayed regulator window (Fig ). If the approach rate is too high there might be a situation when the tracking system will not be able to stop the sample when required. This is due to the fact that during movement the mechanical system is subjected to deformations and mechanical strains that have extended relaxation times. For this reason after the step motor is stopped some residual travel of the sample takes place that is due to the relaxation of the above mentioned mechanical strains. This residual travel can exceed the possible travel range of the piezoelectric scanner and in this connection the tracking system cannot maintain the specified FB signal level. When the approaching rate is decreased, mechanical strains and the residual travel distance go down. Therefore at a certain approach rate the residual travel distance becomes lower than the possible travel range of the piezoelectric scanner. The upper row (Fig ) of the Probe window contains buttons SetPoint, FB Gain and Bais (v). The indicator button SetPoint displays the Set Point parameter value that we specified earlier when performing operations under item In our example (in Fig ) this value is equal to na. Therefore, the indicator button FB Gain will display the feedback gain factor (FB Gain) specified earlier. The bottom part of the Approach window contains a program oscilloscope. Apply the FB signal to the oscilloscope input using the first button in the oscilloscope menu and start the signal measurement process by pressing the GO button (second button in the oscilloscope menu). For more details on the program oscilloscope operation see item above in this chapter where there are instructions regarding signal application to the oscilloscope input, axis ranging etc. This oscilloscope can be used to observe changes in the FB signal during approaching. Fig shows a state at the oscilloscope input where the FB signal is applied and the measurement process for this signal is activated. As it is shown in Fig , the oscilloscope window displays the FB signal whose level is -1.5 na. The signal level is also displayed in the FB signal indicator (Fig , Fig ), which is located near the feedback selection button (in our case this signal is DFL). 4.4 Automatic approach of the sample to the probe Fig Continuing the automatic approaching of the probe to the sample As it was indicated above, start automatic approaching by pressing the Landing button (Fig , Fig ). This will turn on the step motor that will move the sample towards the probe. Simultaneously the feedback is automatically turned on. As a result of the feedback operation the piezoelectric scanner (and the probe with it) will be put forward on its maximum length in the direction of the sample (along axis Z). In its initial position the probe tip is located at a sufficient distance from the sample (about 1 mm) compared to the maximum possible scanner travel (about 3 microns) along axis Z. Although the tip of the probe approaches to the sample as a result of a complete scanner extension, the distance between the tip and the sample is still large enough to avoid any kind of interaction. Therefore the current FB signal level does not change; the difference between the FB and Set Point levels remains large.

80 Chapter 4. Contact Atomic Force Microscopy The scanner extension is displayed on the analog indicator located on upper row of the main program window (Fig ) between the photodiode indicator start button and the FB button (Fig ) Fig The degree of extension is represented by the length of the color bar, which is green during operation in contact mode. Fig Fig When the scanner is fully extended the green bar fills the entire indicator (Fig ). When approaching watch the changes in the FB signal in the FB oscilloscope window and the state of the scanner extension indicator. Fig shows how the FB signal normally changes over time in the course of the cantilever approaching to the surface. Increase in time corresponds to approach to the surface. Fig At first the signal value does not change when the cantilever is approached since the probe is sufficiently far from the surface. Then, after the probe is close enough to the surface interaction between the tip and surface begins. Further, a sudden jump is observed generally on the FB signal dependency (Fig ), which corresponds to the operation start of the tracking system maintaining the FB signal at a constant level equal to the Set Point value. In this case the length of the green scanner extension bar reduces and it stops somewhere in the middle of the indicator (Fig ). The Probe window displays the message OK. This means that the automatic approach has been successfully performed. Fig Fig This very important approach operation can be described in more detail as follows. Certain smooth variations of the FB signal are possible in immediate proximity to the surface, which is due to a deviation of the cantilever free end, typically in the direction of the sample surface under attractive force, after that the cantilever touches the surface with its tip. Further approaching results in the FB signal increase, because after touching the surface the cantilever free end will be moved with the sample, while the second cantilever end is fixed on the scanner. As a result, the cantilever bends, and its end with the tip deflects from its initial state. This deflection is measured by a detection system. The increasing of the DFL signal (FB signal) is proportional to the cantilever deflection. 4.4 Automatic approach of the sample to the probe

81 4-16 Solver P47H SPM Instruction Manual When the FB signal reaches the value of SPoint the tracking system starts maintaining this level of FB signal using the Z-drive of the scanner and the step motor stops. The step motor is stopped when the Z-drive of the scanner reaches approximately the mid-position of its extension range. This moment, when the FB signal reaches the level of the Spoint parameter, will be immediately registered by the scanner advance indicator. Two situations are possible here: 1) the green bar (scanner advance) decreases and stays in an intermediate position on the indicator (Fig ), and 2) the green bar shrinks to zero (Fig ). The first case indicates a successful completion of the approach resulting in the normal operation condition of the tracking system. The green bar intermediate position on the indicator corresponds to an intermediate position of the scanner between the extreme states. In this case the tracking system has been able to compensate the difference between the current FB level and the SPoint value by moving the scanner, and furthermore, it can still maintain the FB signal level equal to the SPoint, as the scanner is within the range of the possible advance interval. In the second case we skip the working point because of a too rapid approach of the sample to the probe. In that way, after passing the Spoint and engine stop the sample moves too far due residual mechanical strains in the mechanic system, which exceeds the maximum range of the scanner advance. The tracking system, trying to set the FB signal value equal to the SPoint level, drives the probe away from the sample as far as its range allows, i.e. fully retracts the scanner, but this shift is insufficient to compensate the FB signal change, which has exceeded the SPoint value. Then, the step motor starts again automatically this time it will be moving the sample away from the probe. At a certain point the current FB level must go down below the SPoint value. Accordingly, the tracking system will advance the scanner again, which must be reflected on the scanner advance bar that will fill the entire length of the indicator. Typically, after moving the sample away from the probe the step motor will stop and the window will display the message OK as the tracking system has not performed its task. In this case you need to reduce the approach velocity as indicated in item above and restart the approach procedure by pressing the Landing button. Upon a successful completion of the automatic approach the mechanical system should switched into the backlash mode. To do it, go to the Mover tab in the Approach menu, this will display the Mover window (Fig ). In this window press several times (4-6) the button «Backward One Step» (Fig ). After each press the step motor will make one step back. 4.4 Automatic approach of the sample to the probe Fig Fig

82 4.4.3 Selection of the Feedback Gain Factor Chapter 4. Contact Atomic Force Microscopy Upon completion of the probe approach, the feedback gain factor should be selected. On the one hand, the larger the gain factor, the quicker the processing of the unbalance signal by the feedback system, and the greater scanning velocity is allowed. However, with a too high feedback factor, the feedback system operation becomes unstable and generation starts. Therefore, it is recommended that firstly, after the approaching is completed, the generation threshold be determined by increasing the feedback factor. Then set up the operation value equaling to 0.5 to 0.7 of the threshold level. The procedure to select the feedback gain factor is as follows Open the SPM control block diagram by pressing the button in the second line of the program main window. Open the window with the FB Gain regulator by pressing the FB Gain button (Fig , Fig ). When increasing the FB Gain value, watch the FB signal level in the program oscilloscope. Determine the FB Gain factor value when the generation starts. The generation point will be marked by a sharp increase in the variable component of the FB signal (Fig ) Fig Fig The operation level of the FB gain factor should be set up at 0.5 to 0.7 of the FB Gain factor threshold value when the FB signal generation begins. Fig Automatic approach of the sample to the probe

83 4-18 Solver P47H SPM Instruction Manual 4.4A Manual approach of the probe to the sample As it was mentioned above in addition to the automatic approach of the sample to the probe it is possible to approach the probe manually. The manual approach is used when the SPM head is used as a stand-alone SPM. However, if necessary the manual approach can be used for the SPM head operation as a part of P47H in the main mode. In this case it is supposed, that preliminary preparation of the SPM head is carried out (the plane of the SPM head base and the plane of a sample are established in parallel, the necessary length of the SPM head legs is established, adjustment of the laser and the photo diode is carried out, the SPM head is established above a sample, the necessary switching in the SPM control block diagram and other operations on preparation for work in a contact mode are executed). The manual approach procedure of a probe to a sample can be divided into the following operations: 1) turning on the feedback, 2) manual approach of a probe, 3) setting the feedback gain factor. A more detailed description of these operations is given below A Enabling the Feedback Having established the Set Point initial value (according to item 4.3.3), enable the feedback. Feedback can be enabled either by pressing the FB button in the upper line of the program main window (Fig A), or in the SPM control block diagram by closing the feedback loop with the «I» switch. Fig A After the feedback is enabled, the piezoscanner (along with the probe) will move maximally along the Z axis towards the sample. In its initial position, the probe is far enough from the sample (about 1 mm) as compared to the maximum possible travel of the piezoscanner (about 3 microns) along the Z axis. Though, as a result of the full advance of the scanner, the probe approaches the sample, the gap between the probe and the sample still remains too large for any interaction to occur between them. Hence the active FB signal level does not change, and the difference between the FB and Set Point levels remains significant. The scanner advance is registered by the analog indicator of the scanner extension located in the upper line of the program main window (Fig A) between the photodiode indicator switch button and the FB button (Fig A). The extent of the advance is indicated with the length of the color line, which is green when the operation is in the contact mode. Fig A Fig A When the scanner is fully extended, the green line fills in the indicator (Fig A). 4.4A Manual approach of the probe to the sample

84 Chapter 4. Contact Atomic Force Microscopy 4.4.2A Procedure of manual approach of the Probe to the Sample 4-19 Note. Prior to starting the approaching, check the set up value of the feedback factor (the FB Gain Parameter). The FB Gain value should not be too low (no less than 1). The established value of this parameter will be shown on the FB Gain button in the SPM control block diagram, as well as on the FBg button in the upper line of the program main window. Correspondingly, pressing any of these buttons would open the appropriate regulator window to change the FB Gain value. Upon enabling the feedback and the scanner s advance towards the sample, you can start approaching the probe to the sample. The approaching is to be performed manually, using the handle of the approach screw (Fig A). The approach screw is one of three leg supports of the SPM head and is provided, unlike the other two, with a handle. Fig A Fig A Turning the approach handle allows movement of the SPM head, along with the probe, relative to the sample in the vertical direction. The rotation direction defines the direction of the movement. While approaching, the handle is to be rotated counterclockwise. A 360-degree turn of the approach handle moves the probe for approximately 120 microns. During approach while turning the approach handle, watch the signal change in the FB oscilloscope window, and the status of the scanner extension indicator. Fig A demonstrates a standard time-dependent change of the FB signal while approaching the cantilever to the surface. An increase in time corresponds to approaching to the surface. Initially, with the approaching of the cantilever, the signal value does not change, as the probe is sufficiently far from the surface. Then, with the probe sufficiently close to the surface, an interaction between the tip and the surface begins. A sudden jump is observed generally on the FB signal dependency (Fig ), which corresponds to the beginning of interaction and to the operation start of the tracking system. 4.4A Manual approach of the probe to the sample

85 4-20 Solver P47H SPM Instruction Manual The approach screw rotation must be stopped as soon as interaction of the tip with the surface will begin and, as a result of work of the tracking system, the level of the «FB» signal will achieve the level of the «SPoint» parameter value. The moment, when the FB signal reaches the level of the SPoint parameter, will be immediately registered by the scanner extension indicator. Here two cases are possible: 1) the green line (scanner advance) decreases and stays in an intermediate position on the indicator (Fig A), and 2) the green line shrinks to zero (Fig A). Fig A Fig A The first case indicates a successful completion of the manual approach resulting in the normal operation condition of the tracking system. The green line intermediate position on the indicator corresponds to an intermediate position of the scanner between the extreme positions. In this case the tracking system has managed to compensate the difference between the current FB level and the SPoint value by moving the scanner, and furthermore, it can maintain the FB signal level equal to the SPoint, as the scanner is within the range of the possible advance interval. In the second case we skip the Set point because of a too rapid approach of the probe to the sample. In that way, after passing the SPoint, we inertially move the probe for a too large distance, which exceeds the maximum range of the scanner advance. The tracking system, trying to set the FB signal value equal to the SPoint level, drives the probe away from the sample surface for its possible maximum distance, i.e. fully pulls the scanner in, but this shift is insufficient to compensate the FB signal change, which has exceeded the SPoint value. If the second situation occurs, it s necessary to slightly turn the screw backward (clockwise) to move the probe somewhat away from the sample. With this, the current signal level must decrease and to attain the SPoint level. Respectively, the tracking system will start its operation the scanner must advance (this will be displayed on the scanner status indicator as an emerged and building-up green line). And if the first case is successfully effected, i.e. the green line on the indicator is in the intermediate position, the approach procedure may be considered as completed. Otherwise, in case of the scanner s full advance (the green line fills the whole of the indicator), the procedure of approaching the probe to the surface should be started anew by slowly turning the screw counterclockwise A Selection of the Feedback Gain Factor Upon completion of the probe approach, the feedback gain factor should be selected. This procedure is completely similar to item Selection of the Feedback Factor which above mentioned in section 4.4 Automatic approach of the probe to the sample. 4.4A Manual approach of the probe to the sample

86 4.5 Setting Scanning Parameters Scanning Parameters Control Window Chapter 4. Contact Atomic Force Microscopy To set up the scanning parameters, open the scanning parameters control window (Fig ) Fig Fig To open the scanning parameters window, press in sequence: 1) The Operation button in the SPM window menu, 2) Scanning in the displayed menu, and 3) SCAN in the header of the displayed window. The scanning parameter control window may also be opened by pressing the button on the tool bar in its Scan section that is used to control the scanning parameters (Fig ) followed by pressing SCAN in the header of the displayed window. (The tool bar is located at the left-hand side of the program main window) The procedure to Set the Scanning Parameters The procedure of setting parameters in the scanning parameter control window is uniform for all elements of the control graphical interface. To set the parameters, select and press the desired button. As a result, the signals or states menu, or the regulator window will be displayed. For instance, if you need to change the scan step, press the indicator button Step (Fig ), set the necessary value in the displayed regulator window (Fig ), and then click the mouse left button to fix the value. Fig Fig Or suppose that it s necessary to switch the A channel to measuring the Height signal. Press the channel A signal selection button (Fig ), choose the Height signal in the displayed signal menu (Fig ), and fix it by pressing the mouse left key (Fig ). 4.5 Setting Scanning Parameters

87 4-22 Solver P47H SPM Instruction Manual Scanning Velocity Fig Fig Fig The scanning velocity is a parameter significantly affecting the quality of the acquired images. The scan velocity is set up using the «Vel» button (Fig ), displaying the current velocity value. Velocity measurement units are displayed on the button on the right. This button can be used to change the Velocity measurement units - you can choose between Angstrom/sec and microns/sec. To set up the required unit of measure place the mouse pointer on the right corner of the button (Fig ) and press the left mouse button. This will display two buttons (Fig ) that are used for selecting the required units of measure. Fig Fig Fig To the right of the button displaying the velocity measurement unit there is an indicator displaying the line scanning frequency (Fig , 4.5-9), corresponding to the selected scanning velocity. To change the scanning velocity press «Vel» and set the required value in the displayed regulator window. The available velocity regulation range depends upon the scan area range. The greater the area, the higher the upper velocity value. An initial scan velocity to be recommended is the value when scanning of one line can be completed within approximately sec., i.e. the line scanning frequency will be Hz. Selecting the optimal scan velocity depends upon the surface peculiarities of the studied sample, the scan area, and the external conditions. A surface with a smooth relief can be scanned at a higher velocity than a rough relief surface with notable differences in height. Velocity can be regulated directly during the scan process, adjusting and trying values to select the optimal one. This procedure will be detailed below in item Setting Scanning Parameters

88 Chapter 4. Contact Atomic Force Microscopy The Scanning Area, Step and Number of Scan Points The maximum scanning area of the SPM head is 50 x 50 microns or 90 x 90 microns (depending upon the scanner model). The scanning area can be set up using the Area button in the lower line of the scanning parameter control window (Fig ), and using the similar Area button located on the tool bar, in its part called «Scan» that is designed to control the scanning parameters (Fig ). Fig Fig In this case, if the scan area is changed, the scan step will be also changed automatically. And on the contrary, when changing the scan step, with the scan point size being stated, the scan area changes. The value of the scanning step is set up with the Step indicator button (Fig , )) displaying the current value of the scanning step. The unit of measure is angstrom, which is displayed on the indicator to the right of the Step button. Further to the right there is an indicator displaying the size of the scanning area (in microns), corresponding to the specified step and number of points along axis X, Y. Fig Fig The number of scanning points along axis X and Y is specified accordingly as «NX=...» «NY=...», as shown in Fig With button 2^N enabled (Fig ) the scan side dimensions are automatically reduced down to the nearest number of the type 2 in N power. If button 2^N is disabled you can specify any number of scanning points along both axis in the range of provided that this number multiplied by the scanning step does not exceed the maximum size of the scanning area. Otherwise, the maximum number of points will be limited by a value equal to the ratio of the maximum size of the scanning area and the specified scanning step. In case no data on the sample surface are available, it is advisable to start scanning with a minor area, say, microns by microns. Depending upon the results of scanning a small area, better values can be selected and set up for such parameters as the work point size, scan velocity, feedback factor. Than the scan area can be expanded to the medium dimensions of approximately microns. After the preparatory operations have been completed, the probe has been approached to the sample, the set point has been selected it is recommended to check if the scanning range along axis Z is sufficient for operation on the selected area of the surface. 4.5 Setting Scanning Parameters

89 4-24 Solver P47H SPM Instruction Manual After approaching and during the parameters setting the probe was located in the center of the selected area, however in the other parts of the selected area, especially in its corners high relief or big slope can result in a situation where the scanner range along axis Z will not be sufficient. It is possible to check with the scanning area selection tool (Area). If you specify the scanning area using this tool with the Moving option enabled, the probe will move with scanning area selection frame. Fig In order to check the scanning range, moving slowly (which is very important), place the frame center in turns in every corner of the planned scanning area while watching the color scanner advance indicator along axis Z. If during the movement of the frame over the selected area the color bar always stays in the working range this means that the scanning range is sufficient for all points. If the color bar extends to its entire length in an area of the planned scanning field, the topography won t be read for this area in the course of scanning (due to general sample inclination or very deep hole in this location). The most dangerous situation is when the color bar disappears completely. This means that the scanner has been retracted completely trying to maintain close to the specified Set point value but its range is not sufficient because of a general slope or a particularly high protuberance. In this case the tip can touch the surface, which can lead to its blunting. If during such inspection of the planned scanning field the color bar is reduced to 1/6 1/8 of its length limit the scanning field so that this area is not included Scanning Mode The scanning mode is to be set up with the second button in the lower line of the scan parameter control window (Fig ). Fig Set up the One Scan mode as shown in the above picture. Under the One Scan mode, a single scan run of a selected area will be performed. In addition to the above mentioned mode, the following scanning modes are available: Many Scans multiple scanning of a selected area, which will be recurring until interrupted by pressing ESC; NxN Scans shifted scanning; Move Scans - scanning with a shift in a preset direction. These special modes are detailed in the program description. 4.5 Setting Scanning Parameters

90 Chapter 4. Contact Atomic Force Microscopy The Scanner Non-Linear Travel Correction (NLCor button) Enabling and disabling of the scanner s non-linear travel correction is performed with the NLCor button (Fig ). This button is to be in the ON position, as shown in the picture below. Fig Fig Measurement Channels: Application of Signal, Setting Scan Direction The unit has four measuring channels, a certain signal can be applied to each of them, and when scanning, data for imaging of the applied signals will be produced. The measurement channels A, B, C and D must be set in positions shown in Fig As follows from the above Fig , the Height signal is applied to the input of the measurement channel A, the selected scan direction (Dir) is +X+. The remaining channels (B, C, and D) are off. The Dir button of each measurement channel is activated only if the channel is on. If a channel is off the setting in the Dir button of this channel is not important. When scanning, the height image data (the Height signal) will be displayed in the SPM window of the image channel A. The letter «X» means that the high velocity scanning will be performed along the X axis, the symbol «+» in front of the X letter means that the high velocity scanning will occur in the positive direction, and the «+» symbol following the «X» letter means that the low velocity scanning (Y axis scanning) will also be effected in the positive direction. It should be mentioned that Channel A is a special channel as compared to the other ones: the scan direction is set up through this channel. In other channels, only the direction of the signal reading can be established. Note This section addresses only the minimum of measurement channels buttons functions required for operation in the topography measurement mode. For more details on the measurement channels buttons functions see Chapter 7 addressing the multi-pass mode The ADC Preamplifier Gain Factor, Low-Pass Filter Values for such parameters as the ADC preamplifier gain factor (Gain), low-pass filter cutoff frequency (LPass (khz), and the number of measurements at each point (Average) are recommended as shown in Fig Fig The Gain factor = 1 corresponds to the most «rough» ADC sensitivity. If the height signal change is insignificant, the gain factor may be increased (by switching to the «10» or «100» position). With increasing gain factor, the signal is being measured at a minor step, but in this case the ADC signal measuring interval shrinks. With a high sensitivity, the measured signal happens to be in excess of the ADC measured interval in some zones of the scan area, which will result in trimming of the signal in these zones. 4.5 Setting Scanning Parameters

91 4-26 Solver P47H SPM Instruction Manual The low-pass filter is used for eliminating the high-frequency noise. The recommended cutoff frequency to be set up is 2 to 4 khz. Increasing the number of measurements in each point (Average) slows down the scanning velocity, especially for small fields (under 1 micron) but improves the quality of the result. Note, that the preamplifier and the low-pass filter are available only in the A and C channel circuits, and, respectively, are absent in the B and D channel circuits The Drawing, Show Scan Lines, Scope Data, Line Strobe, AutoScale and Save To NT.MDT Buttons The Drawing, Show Scan Lines and Scope Data buttons (Fig ) are directly related to the scan process, they enable or disable imaging of the respective signals while scanning the sample. Fig These buttons must be set in positions shown in Fig , with the Scope Data button off, and the Drawing, Show Scan Lines buttons on. The Drawing button enables or disables imaging of signals arriving from the respective measurement channels (Channel A, or Channels A and B, and so on) in the SPM window. When the button is disabled, the image being scanned will not be displayed in the SPM window. The Show Scan Lines button enables and disables imaging of the Channel A signal image profile along the scanning line in the Ext oscilloscope. When scanning, switching of the Ext oscilloscope to signals from other channels can be done using the direct control line (section 4.6.2). The Scope Data button enables and disables signal imaging in other program oscilloscopes while scanning. Thus, if this button is disabled, the oscilloscopes will not be working during scanning even if they are on. The button is recommended to be set into the off position. In this case signals applied to the oscilloscopes will not be measured while scanning. This allows reducing the noise caused by the ADC switching, as well as a more economical use of the unit. The Line Strobe button enables and disables the application of the pulse signal to the external output in the scanning start of each line for external equipment synchronization with the scanning process. The AutoScale button enables and disables the automatic scaling of a signal displayed at scanning in the Ext oscilloscope. The Save To NT. MDT button enables and disables the automatic saving of obtained data in NT. MDT file The Subtraction Procedure (Subtract button, Exc Hi button) The Subtract button (Fig ) effects enabling and disabling of the subtraction procedure. It has the following positions (Fig ): None, Plane, 1st-Slope, 2nd-Slope, 3rd-Slope and 4th- Slope. 4.5 Setting Scanning Parameters

92 Chapter 4. Contact Atomic Force Microscopy 4-27 Fig Fig None - corresponds to the «disabled» status Plane - immediately upon completion of a scan run, the operation of plane subtraction will be performed 1st-Slope - after scanning each line, the first order curve subtraction is performed 2nd-Slope - after scanning each line, the second order curve subtraction is performed 3rd-Slope - after scanning each line, the third order curve subtraction is performed 4th-Slope - after scanning each line, the fourth order curve subtraction is performed If the «Exc Hi» button is switched off, at performance of the subtraction procedure, when the deducted curve or plane is calculated, all scanned points of the surface are taken into account. If the «Exc Hi» button is switched on, at performance of the subtraction procedure, when the deducted curve or plane is calculated the points of the surface areas containing spikes and pins are excluded Parameters for Scanning Grid-Type Test Sample The following parameters are recommended for scanning a grid-type test sample: FB - DFL ; Vel um/s NX x NY x 256 ; Step... - maximal ; NLCorr - on ; Channels: A - «Height», «Dir» - «+X+» ; B - off ; C - off ; D - off ; «Gain» - 1 ; «Lpass» - 4 khz, (1 khz to 4 khz); «Average» - 1 ; «Drawing» - on ; «Show Scan Lines» - on ; «Scope Data» - off ; «Subtract» - none ; 4.5 Setting Scanning Parameters

93 4-28 Solver P47H SPM Instruction Manual «SP» - depending upon the results of approaching, (approximately 1-2 na more than the DFL initial level). «FB Gain» - depending upon the approach outcome. Select the single scan run mode (One Scan). 4.6 Scanning Start of Scanning After the preparatory operations, the probe approach to the sample, the Set point selection, and scanning parameters setup are completed, a sample surface scanning may be initiated. Scanning is started by pressing the RUN button located on the tool bar, in its part called Scan that is designed to control scanning parameters (Fig ), or using the similar RUN button in the lower line of the scanning parameters control window (Fig ). Fig Fig After that, a line-by-line scanning of the sample surface by the probe starts. Simultaneously, a line-by-line displaying of the topography (height) image of the surface being scanned will start in the Channel A window. Correspondingly, if the SPM window is in the position to display two channels (A and B), then the Channel B window will display the signal applied to the Channel B input. The unit control during the scanning process is possible via the (menu) line of the direct control while scanning The Scanning Control Line Upon initiation of scanning, the upper menu is replaced with a new line. This is the scanning control line (Fig ). Fig The unit control during scanning can be effected only using this line. The scanning control line allows changing the main parameters while scanning: scan velocity, feedback gain factor, set point value, the size and position of the scan area, as well as some other operations. The scanning control line consists of buttons, each of which is designated for a special parameter or a special function. The first three buttons, and are for changing, respectively, the velocity, the feedback gain factor, and the set point value. Each of them is provided with a digital indicator to display the current value of the parameter corresponding to that button. At the scanning start, the first button is highlighted, which indicates that it is on. The desired button can be highlighted with the «right» and «left» keyboard keys that move the highlighted position along the line. 4.6 Scanning

94 Chapter 4. Contact Atomic Force Microscopy The value of the parameter corresponding to the marked (switched on) button can be decreased or increased using the «down» and «up» keyboard keys. The,,,,, buttons switch on after having been marked, with the following pressing the Enter key The The button restarts scanning. button allows changing the size and position of the scan area. The button initiates the procedure of subtracting the plane slope. The parameters of the plane being subtracted are determined for the area, which has already been scanned by the moment of switching the button on. From now on the parameters of this particular plane will be subtracted from the whole data set. The button stops the slow axis scanning with the quick axis scanning being continued and performed along the same line. When switched on, the button keeps flashing periodically to show it is on. To switch off this button, press the Enter key again. With the button on, all other buttons of the line can be used. This operation mode can be utilized to select the optimal parameters, say, of scanning velocity Optimization of Scanning Parameters The main parameters significantly impacting the quality of the acquired surface images are scanning velocity, Set point value (SP), feedback gain factor (FB Gain), the probe oscillation amplitude. The first three parameters (scanning velocity, SP and FB Gain) can be regulated directly while scanning by selecting the optimal value using the respective buttons in the scanning control line (Item 4.6.2). Scanning velocity The selection of the optimal scan velocity value depends upon the properties of the studied object, scan area size, external conditions. The surface with a smooth relief can be scanned with a higher velocity than the surface with a rougher topography and significant differences in height. The scanning velocity should be decreased if no proper images can be acquired because of a mound or a pit slope in the scan direction. Feedback gain factor The operational value of the FB gain factor should be established at the level of of the FB Gain factor threshold value, when the FB signal generation starts. The procedure for selection of the feedback gain factor is described in Item Saving the Acquired Data Upon completion of a sample surface scanning, the acquired data of the surface image will be stored in the random-access memory. Each scan of the surface produces a separate image. And if, only Channel A displaying was enabled when scanning in the SPM window, in addition to the measuring Channel A, other measuring channels were also turned on, than images corresponding to the data of the other active channels will be formed in the memory in addition to the Channel A data image. Images are numbered in order of their acquisition. Data corresponding to spectroscopy (Section 6.1) are also available as a separate image. 4.7 Saving the Acquired Data

95 4-30 Solver P47H SPM Instruction Manual To record the obtained data on the hard disk, place the cursor on the File button in the SPM window menu (Fig ), click Save in the displayed menu (Fig ), and record the data as a file Fig Fig under an arbitrary name with the *.MDT extension (Fig ). Fig Accordingly, the Open option of the same menu (Fig ) allows opening of the earlier recorded files. 4.8 Switching from the Contact to Semi-Contact Mode To switch over from the contact to semi-contact mode, effect the operations described below following the semi-contact mode operating instructions (Chapter 5): 1) Disable the feedback; 2) Enable the cantilever modulation; 3) Apply a new signal (MAG signal) to the feedback input, determine and set the resonance frequency if this has not been done already, set the initial value for the new feedback signal (MAG signal); 4) Set the SP value relative to the current value of the new FB signal (MAG signal); 5) Enable the feedback; 6) Continue operation in the semi-contact mode. 4.9 Switching off the Microscope To switch off the microscope: 1) Remove the sample away from the probe approximately 2-4 mm. To perform this operation: open the «Mover» (figure 4.9-1) window (the step motor control window) by subsequently opening: «Operation» - «Approach» - «Mover», set the value of «Remote» at 2-4 mm (figure 4.9-2) and press the Remote button. 4.9 Switching off the Microscope

96 Chapter 4. Contact Atomic Force Microscopy 4-31 Fig Fig ) Disable feedback by pressing the FB button in the upper line of the program main window (fifth right, Fig ); Fig ) Switch off the laser by pressing the button in the upper line of the program main window (forth left, Fig ); the button is red in color when on, and black when off; 4) De-energize the microscope with the «Power» toggle switch on the electronics block; 5) Exit the control program pressing the Exit button in the menu (Fig ) which is displayed when the cursor is placed on the Main button in the left corner of the program main window (Fig ). Fig Fig Exiting the program is also possible using the F10 function key (after closing all displayed menus with the Esc button because the F10 key is functional only with the menus closed) Lateral Force Microscopy Introduction SPM head can measure the distribution of the local friction force over the sample surface. In accordance with the established concepts and understanding, this method is called Lateral Force Microscopy. The physical basics of the method are as follows. When scanning in the contact mode, besides the cantilever s deflection in the normal direction, an additional torsion deformation of the cantilever occurs (Fig ). It is caused by the moment of forces acting on the tip. With minor deflections, the angle of torsion is proportional to the side (lateral) force. The cantilever s torsion is measured by the microscope optical recording system Lateral Force Microscopy

97 4-32 Solver P47H SPM Instruction Manual Fig Fig For measuring the lateral forces, the unit functions in the constant force maintenance mode, i.e. the same way as when measuring topography in the contact mode. When moving over a flat surface with zones of different friction factors, the angle of torsion will be changing in every new zone (Fig ). This allows measuring of the local friction force. If the surface is not absolutely flat, such an interpretation is impossible. Nevertheless, this type of measuring allows obtaining images with clearly seen minor relief details and facilitates their search. In addition, the lateral force measuring mode easily provides the atomic resolution on mica and some other laminar materials Signal Related with the Cantilever Torsion Deformation As stated above (Section 2.1.3), the optical registration system forms a LAT.DFL electric signal (with the identical Lateral F and LF symbols), which changes in proportion with changing of the cantilever torsional deformation. This signal is used for obtaining images of the local force of friction against the sample surface Preparation of the Unit for Operation in the Lateral Force Measurement Mode The unit s operation in the mode of lateral force measurement actually is an additional option for Contact Atomic Force Microscopy (contact topography). Imaging of the local friction force distribution is performed simultaneously with contact topography measurements. The necessary condition for the operation in the lateral force microscopy mode is the preliminarily preparation for the contact topography mode operation (contact AFM) as described above in the earlier sections of this Chapter 4. On completion of the unit preparation for the contact topography, and after obtaining a high-quality topography imaging, the lateral force imaging can be performed. To perform that, the following additional steps are necessary: 1) Apply the Lateral F signal to the measuring Channel B input. 2) Set the Channel A scan orientation in the X axis direction (if it has not been already done). 3) Switch the SPM window into the two-window mode for the topography to be displayed in one (A) window, and the lateral force (Lateral F) signal image to be displayed in the other (B) window during the follow-up scanning Lateral Force Microscopy

98 Chapter 4. Contact Atomic Force Microscopy Applying the Lateral F Signal to the Measurement Channel B Input To apply the Lateral F signal to the input of the measuring channel B: 1) Open the scan parameter control window (Fig ) 4-33 with the button on the tool bar (in its segment, called Scan that controls the scanning parameters), Fig , and pressing subsequently SCAN in the title of the displayed window (Fig ). The tool bar is located on the left-hand side of the program main window. Fig Fig The scanning parameter control window can also be opened by clicking sequentially the following buttons: 1) Operation in the SPM window menu, 2) Scanning in the displayed menu, and 3) SCAN in the header of the displayed window. 2) Press the Channel B signal selection button (Fig ), select the Lateral F signal in the displayed menu (Fig ). Fig Fig Fig As a result, the Lateral F signal must be applied to the Channel B input as shown in Fig Similarly, using the Dir button of Channel B, set up the signal reading direction for this channel, as shown in Fig Lateral Force Microscopy

99 4-34 Solver P47H SPM Instruction Manual Fig Fig Fig Setting the Scanning Direction Setting of the scanning direction should be performed in Channel A. Set up the +X+ direction in the Dir button of Channel A as shown in Fig In this case scanning will be performed in the direction perpendicular to the cantilever s longitudinal axis as shown in Fig Switching the SPM Window into the Two-Window Mode To switch the SPM window into the two-window mode, press the line (Fig ). button in the window lower Fig This will result in splitting the SPM window into two windows, A and B (Fig ). Fig When scanning, the surface topography (Height signal) will be displayed in Window A, and the Lateral F signal will be displayed in the B Window Lateral Force Microscopy

100 Chapter 4. Contact Atomic Force Microscopy The Unit Operation in the Lateral Force Microscopy Mode The unit further operation in the lateral force imaging mode is identical with the operation in the contact topography mode. If all the above preparatory procedures are completed, scanning can be commenced as per the recommendations and directions stated in Chapter 4 sections describing the unit operation in the contact microscopy (topography) mode. As an example, the below Fig shows a surface topography image and a Lateral F signal image acquired simultaneously when scanning the same sample sector. Fig The sample is a monolayer Langmuir film applied onto a smooth silicon surface. The monolayer Langmuir film consists of a mixture of two surface-active compounds, a polymer with a perfluorine radical (-C 7 F 15 ), and a diazobenzene derivative with an aliphatic radical (-C 18 H 37 ). In the hybrid Langmuir layer these compounds form two phases. The phases are characterized by different heights, as evident from the left picture, corresponding to the topography. The evident difference in the phases height is approximately 1 nm, which is in conformity with the known molecular thickness of the individual component layers. According to these data based on the knowledge of the molecular size of the components being used, and on X-ray structure surveys, the «higher» areas must belong to the diazobenzene derivative phase (they are lighter in color in the picture). The right-hand picture corresponds to the lateral force signal image. Apparently, areas corresponding to different phases have different friction factors. And it may be stated that areas corresponding to the polymer monolayer phase have a higher friction factor than areas of diazobenzene derivative monolayer phase. The latter statement arises from the fact that the Lateral F signal has a greater value in areas corresponding to the polymer monolayer phase as compared to areas corresponding to the diazobenzene phase. And Lateral F signal changes are in proportion with the lateral force acting on the cantilever tip and causing the torsion deformation of the latter. The following important fact should be emphasized here. To correctly interpret the Lateral F signal imaging data, it is important to verify the sign correlation of the Lateral F signal change value and the torsion deformation change value, as they can be both equal and opposite in sign. In the first case, an increase in the lateral force causing an increase in torsion deformation will be registered as an increase of the Lateral F signal value, and the second case is vice versa. It can be verified by the form of the «drop» occurring at the initial moment of scanning each line for the Lateral F signal Lateral Force Microscopy

101 4-36 Solver P47H SPM Instruction Manual This information is already available in the acquired Lateral F signal image. To use it, it is sufficient to observe several cross-section profiles (in the scanning direction) of the Lateral F signal image at the initial moment of scanning, i.e. near the left image border if the scanning has been performed in the positive direction of the X axis. As an example, two X axis cross sections of the Lateral F signal image presented in Fig are displayed in Fig and The initial portions of the displayed curves correspond to an increase in the torsion deformation value, as supposedly, at the initial moment the cantilever is still, and there is no deformation, but then the cantilever starts moving, and a torsion deformation with the positive sign arises. Accordingly, at the initial portions of the shown curves you can observe an increase of the Lateral F signal. Hence, it can be assumed that in the cited example the torsion deformation and the Lateral F signal change have the same signs. For this reason, regarding the above Lateral F signal image of Fig , the conclusion could be drawn that the friction factor at the areas corresponding to the higher Lateral F signal value is greater than the friction factor at the areas corresponding to the lower Lateral F signal value. Fig Fig Accordingly, had the «drop» observed at the scanning initial moment been reverse, i.e. had the Lateral F signal some value at the start (at the zero moment), and had it been decreasing to some level after the scan start, than the torsion deformation and the Lateral F signal change would have had opposite signs Force Imaging in the Contact Mode Introduction The method of Force Imaging in the contact mode implies acquiring force images resulting from scanning of a surface in the contact mode with a fixed height level (with a fixed Z value scanner s coordinates). Application of feedback in SPM operation results in increased noise levels, partial loss of information on the surface topography, and a certain restriction of the scanning velocity. Sometimes it is helpful to use the scanning mode with the feedback being off, the piezoscanner s Z axis position fixed, and the immediate photodiode error signal related to the cantilever s deflection (DFL signal ) used as the signal to be registered. This is the continuous operation mode (Z = constant). In this case the force pressing the cantilever to the surface changes during scanning. But if the sample is sufficiently hard, the resulting image will reflect the surface topography fairly well Force Imaging in the Contact Mode

102 Chapter 4. Contact Atomic Force Microscopy 4-37 The dynamics of the surface tracking in this mode are restricted by the cantilever s frequency properties, and not by those of the feedback. The cantilevers resonance frequencies are significantly higher than the distinctive feedback frequency measuring up to only few kilohertz. This allows scanning at higher velocities. If the cantilever dependence on the distance between the probe and the sample (i.e. the DFL signal dependence on the Z coordinate) has been determined, than this dependence can be used to convert the registered photocurrent (the DFL signal) into linear dimensions. However, it should be kept in mind that in case of considerable deflections from the zero position, the DFL signal dependence on the probe deflection becomes non-linear. The approximate range of the linearity depends upon the cantilever: the shorter the cantilever, the narrower the range. Besides, if the elasticity constant and the geometrical dimensions of the cantilever being used are known, the image of the cantilever deflection signal can be calculated into the image of the local force acting on the cantilever. The force imaging method (i.e. measuring the DFL signal with the scanner Z-coordinate value fixed) may be used in combination with the multi-pass method and semi-contact and non-contact modes, though such occasions deserve a special attention and are discussed in the sections devoted to the multi-pass method Preparation of the Unit for the Force Imaging The requirement for the Force Imaging with the unit is for it to be prepared beforehand for the operation in the contact topography mode (contact AFM) as discussed in the above sections of this Chapter 4. Upon completion of the preparation of the unit for operation in the contact topography mode and acquisition of a surface topographic image, the operator may proceed with acquiring the force images. To do it, perform the following steps: 1) Apply the DFL signal to the input of the measuring Channel A. 2) Reduce the feedback gain factor FB Gain to zero Application of the DFL Signal to the Input of the Measuring Channel A To apply the DFL signal to the input of the measuring Channel A: 1) Open the scan parameter control window (Fig ) Fig Fig Force Imaging in the Contact Mode

103 4-38 Solver P47H SPM Instruction Manual by pressing the button in the tool bar s part called «Scan» that is designated to control the scanning parameters (Fig ), and a subsequent clicking of SCAN in the header of the displayed window (Fig ). The toolbar is at the left side of the program main window. The scan parameter control window can also be opened by successively pressing buttons 1) «Operation» in the SPM window menu, 2) «Scanning» in the displayed menu, and 3) «SCAN» in the header of the displayed window. 2) Press the signal selection button of Channel A (Fig ), and select the DFL signal (Fig ) in the displayed menu (Fig ). Fig Fig Fig Fig As a result, the DFL signal will be applied to the input of the measurement Channel A (Fig ) instead of the earlier (contact topography mode) applied signal «Height» Setting zero value for the feedback gain factor (FB Gain) To set up the zero value for the feedback gain factor (FB Gain), open the SPM control block diagram with the button in the SPM window menu. Then press the FB Gain button (Fig ), and using the displayed regulator window set the value for the feedback gain factor close to zero (approximately 0.001) Force Imaging in the Contact Mode Fig Thus we actually disable the feedback. Meanwhile, the scanner s coordinate Z is locked in position where it was when the gain factor was decreased. The probe remains in the working point position established earlier for the contact mode. For operation in the force imaging mode, the feedback must not be disabled with the switches designed for that (the «I» switch in the SPM block diagram and the FB switch button in the direct control line), as in this case in addition to disabling the feedback, the scanner automatically retracts along the Z-coordinate, thus moving the probe away from the surface The Unit Operation in the Force Imaging Mode On completion of the above-mentioned preparatory operations, scanning can be started in the same way as in the contact topography mode. While scanning, the DFL signal image will be displayed in Window A, the signal changes are proportional to the cantilever s deflections (i.e. changes of height), and the cantilever s deflections are in proportion with changes of the force acting on the cantilever.

104 Chapter 4. Contact Atomic Force Microscopy The DFL signal is a current signal, and is measured in na. But it can be recalculated and represented in the length units provided the proper calculation factor is known, this factor reflects the cantilever linear motion relation with the current signal changes. It can be determined from the DFL signal dependence on the distance between the probe and the sample The Mode of the Feedback Error Signal Registration The feedback error signal (the DFL signal), emerging when scanning in the contact topography mode, contains some additional information about the topography. It can be utilized for achieving a more precise recovery of the relief. Additionally, this mode can be considered as intermediate between the mode of constant force and constant height, if the feedback gain factor (i.e. the feedback processing speed) is adjusted for the system to be able to trace subtle changes of the relief and to be too slow to trace the steep changes. Then, when the probe travels over minor irregularities, scanning will be carried out with an almost constant piezoscanner length. As a result, the slow changes of the relief will hardly show up on the images, and the steep changes will appear in high contrast. This may be helpful in finding minor irregularities on large areas against major sloping relief features. The necessary condition for operation in the feedback error signal registration mode is for the unit to be prepared beforehand for the operation in the contact topography mode (contact AFM) as discussed in the above sections of this Chapter 4. Upon completion of the unit preparation for operation in the contact topography mode and after acquiring a surface topographic image, the operator may proceed with operation in the feedback error signal registration mode. The following additional operations are to be performed: 1) Apply the DFL signal to the Channel B input. 2) Reduce the feedback gain factor to such a value that would enable the feedback system to trace subtle relief changes and to be too slow to trace the steep changes (the required gain factor value to be determined experimentally while scanning). 3) Switch the SPM window into the two-window mode to display the topography in one (A) window, and the feedback error signal image (of the DFL signal) in the other (B) window during subsequent scanning. The procedures of applying signals to the measuring channels, feedback gain factor adjustment, and switching the SPM window into the two-window mode are described above in the previous sections 4.10, Then the unit operation, and scanning in particular, is performed similarly to that in the contact topography mode The Mode of the Feedback Error Signal Registration

105 Chapter 5. Semi-Contact Atomic Force Microscopy 5-1 Chapter 5. Semi-Contact Atomic Force Microscopy Contents Contents Chapter 5. Semi-contact atomic force microscopy Initial condition, main stages and operations of semi-contact microscopy Initial condition Main stages and operations of semi-contact microscopy Configuration of the main program window Connecting signals to program oscilloscopes Preparation of the SPM control block diagram for semi-contact Mode Operation Checking of the switches positions Applying the MAG signal to the feedback input Setting the cantilever working frequency and oscillation amplitude Determining the resonance frequency cantilever, setting the working frequency The working frequency, the resonance frequency, the cantilever piezodriver generator Self-acting determination of the cantilever resonant frequency and self-acting installation of the working frequency Procedure of measuring the frequency response of the cantilever s oscillation amplitude Manual (non-automatic) setting the working frequency Selecting and setting the cantilever oscillation amplitude Setting the initial level of the MAG signal Approaching the sample to the probe, selecting and setting a working point Automatic approaching of the sample to the probe Setting the initial Set Point value Enabling the automatic approach Windows «Approach», «Probe», «Mover» Initial Stage of the sample automatic approaching to the probe Continuing the automatic approaching A Manual approach of the probe to the sample A Setting the initial Set Point value A Enabling the feedback A Starting manual approaching the probe to the sample A Continuing the manual approach procedure Selecting the Set point value Rough estimate of the cantilever oscillation amplitude value Selecting the feedback gain factor Setting the scanning parameters Scanning parameters control window The procedure to Set the Scanning Parameters Scanning Velocity The Scanning Area, Step and Number of Scan Points Scanning Mode The Scanner Non-Linear Travel Correction Measurement Channels: Application of Signal, Setting Scan Direction The ADC Preamplifier Gain Factor, Low-Pass Filter The Drawing, Show Lines, Scope Data, Line Strob, AutoScale and Save To NT. MDT Buttons Subtracting procedure (Subtract button, Exc Hi button) Scanning parameters for a test grid-type sample

106 5-2 Solver P47H SPM Instruction Manual 5.7 Scanning Scanning start Direct Scanning Control Line Selecting the optimal scanning parameters Saving the acquired data Switching from semi-contact to contact mode Turning the microscope off Phase Imaging Introduction Signals related to the probe oscillation phase Preparing the unit for phase imaging (Required conditions and operations) Applying a phase signal to the measurement channel input Adjusting the phase signal Operation in the Phase Imaging mode Features and differences of the semi-contact mode in fluid medium

107 Chapter 5. Semi-Contact Atomic Force Microscopy Chapter 5. Semi-contact atomic force microscopy This chapter covers the unit s operation in the semi-contact atomic force microscopy mode. Semicontact atomic force microscopy, also known as similar intermittent-contact atomic force microscopy, is measurement of surface topography in the semi-contact mode. The unit s operation in the mode of measurement of surface topography in the semi-contact mode is the basis of the unit s operation in other techniques using the probe modulation. The present chapter contains the description of procedures of the semi-contact mode by operation in air medium. Features and differences of the semi-contact mode in fluid medium briefly are considered in section Initial condition, main stages and operations of semi-contact microscopy Initial condition The microscope is turned on; The program is running, the monitor displays the main program window; the cantilever is installed; The laser and photodiode adjustment completed; The sample installed; The SPM head is installed on the approach module, the preliminary approach of a sample to the probe is executed Main stages and operations of semi-contact microscopy Operation in the semi-contact mode can be divided into the following stages and operations. 1. Preparation of the SPM control block diagram for the semi-contact mode, which includes: Applying the MAG signal to the feedback input and switching operations in the SPM control block diagram required for operation in semi-contact mode. 2. Setting the cantilever working frequency and oscillation amplitude. 3) Determining and setting the cantilever working frequency. 4) Selecting and setting the cantilever oscillation amplitude. 3. Selecting and setting the initial level of the MAG signal. 4. Approaching the sample to the probe. 1) Approaching procedure. 2) Selecting a working value for the Set Point parameter. 3) Selecting the feedback gain factor. 4. Setting the scanning parameters. 5) Scanning mode. 6) Scanning speed. 7) Dimensions of the scanning area, step and number of scanning points 8) Correction of non-linearity Initial condition, main stages and operations of semi-contact microscopy

108 5-4 Solver P47H SPM Instruction Manual 9) Measurement channels: setting signals and scanning direction. 10) Other parameters. 11. Scanning. 12) Scanning start. 13) Scanning direct control line. 14) Selecting optimum scanning parameters. 7. Saving the acquired data. 8. Switching to other modes. 9. Turning the unit off. Below you will find a detailed description of the above stages and operations. It is assumed that you are using the main window configuration that is given below before the description of the main operations Configuration of the main program window To facilitate the set-up and subsequent operation it is recommended to use the configuration of the main program window in Fig Fig In the presented configuration the left part of the window is occupied by the SPM window that will display during the scanning the image of the signal applied to input A. This window can be easily split in two windows (using the button window). in the left corner of the SPM 5.1 Initial condition, main stages and operations of semi-contact microscopy

109 Chapter 5. Semi-Contact Atomic Force Microscopy Each of these windows will display the scanning data of channels A and B accordingly (Fig ). 5-5 Fig Two built-in oscilloscopes are located in the right part of the main window. The feedback signal FB is applied to the input of them (upper), the other is provided with the Ext input for viewing twodimensional data. A toolbar enabling the unit control similar to the SPM window menu is located on the left-hand side of the main window. You can set up various configurations for the main program window. Some prefer the main window configuration where the SPM window is located in the lower half of the screen, at the same time they split the window in two to display channels A and B (Fig ). Fig Initial condition, main stages and operations of semi-contact microscopy

110 5-6 Solver P47H SPM Instruction Manual You can select and install the desired configuration using the button in the top left corner of the SPM window or the Window button that appears in the place of the Main button when the cursor is placed on the Main button (Fig ). Fig If you have changed the configuration and wish to save it for future operation, you can proceed as follows. Place your mouse pointer on the Main button. This will display a new upper line (Fig ). Press the Options button in this line, this will display the menu (Fig ). Fig To save the configuration press Save (Fig ), the configuration will be saved in the configuration file smena.opt. This file is automatically loaded each time the program is started. Using the Save as command you can save the configuration in any *.opt file that can be loaded using the Load command in the same menu (Fig ) Connecting signals to program oscilloscopes A specific signal can be connected to an oscilloscope as follows. Press the second button from the left in the oscilloscope menu; this will display the menu of possible signals. Select the necessary signal and after pressing the left mouse button the selected signal is applied to the oscilloscope input, for example, FB on Fig or Ext on Fig Fig Fig With the button (third from the left) the measurement process of the signal applied to the oscilloscope input can be enabled (or disabled). After the measurement process start it is possible that the signal on the oscilloscope screen will not be displayed because the axis have not been scaled properly. The measured signal may not fall within the scale range set up along the vertical or horizontal axis. Below you will find a short description of the axis scaling procedure (for details see item ). 5.1 Initial condition, main stages and operations of semi-contact microscopy

111 Chapter 5. Semi-Contact Atomic Force Microscopy To adjust the oscilloscope scale place the cursor on the oscilloscope field and press simultaneously Shift + left mouse button and move the mouse in the required direction. If you press the left mouse button only (without pressing Shift) the mouse movement will cause the set range to move along the axis without changing the axis scale. For scaling you can also use the Scale button in the oscilloscope menu. 5.2 Preparation of the SPM control block diagram for semicontact Mode Operation Open the SPM control block diagram, for example, by pressing the button in the SPM window menu (in this configuration it will be in the second line of the program main window). Check and set the correct positions of the switches and enable the required signals (Fig ). 5-7 Fig Checking of the switches positions 1) Switch I must be off i.e. the feedback loop is open (Fig ). Fig Fig Fig ) The switch providing excitatory voltage for the piezodriver of the cantilever must be set in the Probe position (Fig ). 3) If you use a cantilever with resonance frequency over 50 khz activate the button «Hi» of the input switch of the preliminary amplifier of the Lock-IN and RMS detector (Fig ). If this is not the case activate the button Low. The reason for this is that the preliminary amplifier has two 5.2 Preparation of the SPM control block diagram for semi-contact Mode Operation

112 5-8 Solver P47H SPM Instruction Manual inputs: high and low frequency. The first is used at frequencies over 50 khz and the second at frequencies under 50 khz accordingly. The buttons «Hi» and «Low» are used to select the appropriate input, one of them must turned on. 4) The switch at the lock-in amplifier input and switch at the phase detector input must be in position d as it is shown in the control block diagram and Fig , Fig Fig Fig Fig ) The harmonic number switch of the Lock-IN amplifier input must be in position 1 as it is shown in Fig Applying the MAG signal to the feedback input To connect the signal to the feedback input press FB In in the SPM control block diagram (Fig ). The text on the button corresponds to the signal currently applied at the feedback input. In the example shown this signal is MAG. After the button is pressed the signal selection menu will be displayed (Fig ). After you select the MAG signal in the menu (Fig ) this signal will be set at the feedback input. Fig Fig Fig There is an easier way to apply the required signal to the feedback input. To do it press the FB signal selection button on the direct control line (Fig , Fig ), this button is located between the buttons FB and SP. Fig (Fig and Fig show a state when the MAG signal has already been selected since the text on the button corresponds to the set-up signal). Fig The required signal can be set up in a way similar to the one described above, i.e. by picking up a signal from the displayed menu. 5.2 Preparation of the SPM control block diagram for semi-contact Mode Operation

113 Chapter 5. Semi-Contact Atomic Force Microscopy About selection of feedback signal In the semi-contact mode the measure of interaction between the probe and the sample surface is a signal proportional to the probe oscillation amplitude. The MAG signal (signal after the lock-in amplifier) and RMS (signal after the RMS detector) are such signals in SPM Head. Any of them can be used as a feedback signal. The use of the MAG signal is preferred since it implies the use of synchronous detection, which results in a reduced noise level. 5.3 Setting the cantilever working frequency and oscillation amplitude Determining the resonance frequency cantilever, setting the working frequency The working frequency, the resonance frequency, the cantilever piezodriver generator The working frequency exciting the cantilever oscillations in the semi-contact mode is usually equal or close to the cantilever resonance frequency. Different cantilevers have different resonance frequency of mechanical oscillations. Resonance frequency is a parameter indicated in the technical specifications of a cantilever. However, for operation in semi-contact mode you need to know the exact value of the resonance frequency and technical specifications don t provide such accuracy. The specifications only indicate the interval where you should look for the resonance peak value. Therefore after replacing a cantilever it is necessary to determine its resonance frequency. The resonance frequency is determined by measuring the frequency dependence of the cantilever s mechanical oscillations. The cantilever mechanical oscillations are excited with the help of a piezodriver that contacts directly the cantilever s substrate. As for the piezodriver itself its mechanical oscillations are excited by alternating voltage that is applied to it and comes from the piezodriver generator via the amplifying and dividing stage. The cantilever piezodriver generator operates in two modes: 1) generation of alternating voltage with a specific amplitude and fixed frequency whose values are set by the operator. 2) generation of alternating voltage scanning the frequency within the given range. The first mode is the main mode and it is used in the semi-contact and other modulation modes. The second mode is ancillary and it is used for measuring the frequency dependence of the cantilever s oscillation amplitude in order to determine the cantilever s resonance frequency. The generator s frequency can be regulated within the range from 0 Hz to 2 MHz, the voltage at the generator s output can be regulated within the range between 0 and 1 Volt. In device the procedure of search of a cantilever resonant frequency and of installation of working frequency is automated. At execution of this procedure automatically the cantilever resonant frequency will be determined and also automatically the working frequency (equal to resonant) will be installed. In addition you can carry out the measuring of the frequency dependence of the cantilever oscillations amplitude, then from the obtained dependence you can determine the value of the resonance frequency and set the working frequency manually Setting the cantilever working frequency and oscillation amplitude

114 5-10 Solver P47H SPM Instruction Manual The procedures of self-acting installation of the working frequency, and also of measuring the frequency dependence of the cantilever vibration amplitude and of manual installation of the working frequency are described below. It is necessary to note, that except of the frequency dependence of a cantilever vibration amplitude, it is possible the measuring of the frequency dependences of some other signals and quantities (for example, cantilever oscillation phases) Self-acting determination of the cantilever resonant frequency and self-acting installation of the working frequency For a self-acting finding of the cantilever resonant frequency and self-acting installation of the working frequency, it is necessary to execute the following operations. 1) Open the SPM control block diagram by pressing the button in the SPM window. 2) Press the SEARCH button (Fig ), this button runs procedure. Fig Fig As a result of performance of this procedure the frequency dependence of the MAG signal will be measured (in our case the MAG signal is proportional to the cantilever vibration amplitude), the cantilever resonant frequency will be defined and the working frequency (that equals to resonant frequency) will be set automatically. On the Ext oscilloscope the maximum of the resonance curve (Fig ) will be displayed. On the indicator of the khz button (the button of installation of the working frequency) the value that equals to the resonant frequency (Fig ) will be automatically set. Fig Fig It can be tested if to press the khz button. At pressing this button the regulator window (Fig ) will be opened, and on the resonance curve the line - finder will appear. The standing of this line - finder will coincide with the standing of the resonance maximum (Fig ). 5.3 Setting the cantilever working frequency and oscillation amplitude

115 Chapter 5. Semi-Contact Atomic Force Microscopy 5-11 Fig Procedure of measuring the frequency response of the cantilever s oscillation amplitude 1) Open the SPM control block diagram by pressing the button in the SPM window. The generator s parameters are controlled in the following section of the SPM control block diagram (Fig ). Fig Three buttons in the third row counting from the bottom are used to set the following: «KHz» - alternating voltage frequency at the generator s output; «(V)» - alternating voltage amplitude; «Phase» - phase of alternating voltage with respect to the reference signal. The buttons to the left and to the right of F (second row from the bottom in Fig ) are used to set the minimum (Min) and the maximum (Max) scanning range in terms of frequency. The buttons in generator control line (Fig ) have the following functions: Fig The first button F-SCAN starts frequency scanning when measuring frequency dependence; The second button in the row sets the signal whose frequency dependence will be measured (in our case the signal MAG is enabled); The last button «Numb...» - sets the number of points within the frequency range where generation will take place in the course of frequency scanning. 2) Set the lowest and highest range limits within which the cantilever s frequency is assumed to be located. To do it, press the button setting the lowest value of the range (Fig ). In the displayed regulator window (Fig ) set the corresponding value of the lowest limit. 5.3 Setting the cantilever working frequency and oscillation amplitude

116 5-12 Solver P47H SPM Instruction Manual Fig Fig Then, set the upper limit of the range in the same way. 3) Turn on the frequency scanning of the cantilever driver generator. To do it press F-SCAN in the generator controlling line. After scanning the Ext oscilloscope will display the frequency dependence of the selected signal (Fig ), in our case it will the MAG signal. Fig Fig The indicated dependence shows that certain frequency is associated with resonance. If the scanning range is big enough the curve can have several peaks. In order to determine precisely the resonance frequency position it is necessary to decrease the scanning range. For this purpose it is necessary to press the button - indicator, which corresponds to the lower edge of the scanning interval. At pressing together with opening of the regulator window the line - finder will appear on the resonance curve in the window of oscilloscope Ext. The standing of this line - finder corresponds to current value of the lower edge of the scanning interval. Establish necessary value of the lower edge of the interval (Fig ) by moving the line. Next establish by similar way the upper edge of the scanning interval (Fig ) and repeat the frequency scanning. The scanning results in a more detailed curve of the resonance peak (Fig ). 5.3 Setting the cantilever working frequency and oscillation amplitude

117 Chapter 5. Semi-Contact Atomic Force Microscopy 5-13 Fig Fig The cantilever resonance frequency is determined out of the position of the maximum on the resonance curve displayed at the Ext oscilloscope. To do it press the Vie button in the oscilloscope control line and shift the frequency value with your mouse pointer to determine the frequency value corresponding to the highest position on the resonance curve (Fig ). Fig Manual (non-automatic) setting the working frequency After determining the resonance frequency of the cantilever set the working frequency of the cantilever driver generator. Normally in the semi-contact mode the generator working frequency is set equal to the cantilever resonance frequency or close to it. To set the working frequency press the khz button (Fig ) and set the required value in the displayed regulator window (Fig ). Fig Fig Establishing the working frequency, it is convenient to observe the current value of frequency by means of position of the line - finder on the resonant curve in the oscilloscope Ext (Fig , Fig ). 5.3 Setting the cantilever working frequency and oscillation amplitude

118 5-14 Solver P47H SPM Instruction Manual Fig Fig Selecting and setting the cantilever oscillation amplitude The cantilever oscillation amplitude is controlled by the alternating voltage value that is applied to the cantilever piezodriver from the generator via the amplifying and dividing stage. To set the working value of the generator voltage press the (v) button (Fig ) in the generator controlling block and set the required value in the regulator window (Fig ). Fig Fig Voltage from the generator s output is applied after the Probe switch to the amplifying and dividing stage that can be set in one of three positions using the buttons. Therefore, depending upon the position of the switch the resulting voltage is decreased to 1/10 remains unchanged or increases 10 times. At the initial measurement stage the voltage applied to the cantilever piezodriver should be set to approx volt. Comments on selecting the value for cantilever oscillation amplitude. The cantilever oscillation amplitude is one of the parameters that can considerably influence the quality of the received surface images. In order to achieve a higher resolution and ensure a softer impact on the sample it is desirable to use small amplitude of the cantilever oscillations. However, at small oscillation amplitude the cantilever can possibly stick to the sample as a result of capillary forces or for some other reasons (for instance, strong adhesion, electrostatic interaction etc.). Therefore the oscillation amplitude has to be increased. The optimum amplitude value depends on the nature and physical properties of the explored sample, measurement conditions and the cantilever s parameters. What is actually measured is a certain signal proportional to the cantilever oscillation amplitude. Based on the changes of this signal we can see the relative changes of the oscillation amplitude. We will know the real oscillation amplitude value if the signal is calibrated i.e. if the proportionality constant is found between the amplitude and the signal. This relation can be determined by measuring the dependence of the signal from the distance between the probe and the surface. The procedure for measuring this dependence is described below in chapter Setting the cantilever working frequency and oscillation amplitude

119 Chapter 5. Semi-Contact Atomic Force Microscopy 5.4 Setting the initial level of the MAG signal In the semi-contact mode the cantilever mechanical oscillation amplitude is a parameter characterizing the interaction between the probe and the surface. In our microscope the MAG signal (or RMS) is used as the signal proportional to the cantilever oscillation amplitude when measuring the surface topography. The MAG signal is proportional to the mechanical oscillation amplitude, the repeater amplifying ratio and the lock-in amplifier gain ratio. Therefore, the signal level can be adjusted by changing the cantilever oscillation amplitude, the repeater amplifying ratio (two values 1 and 10) and the lock-in amplifier gain ratio (Gain). The RMS signal is proportional to the mechanical oscillation amplitude and the repeater amplifying ratio. Therefore, the signal level can be adjusted by changing the cantilever oscillation amplitude, the repeater amplifying ratio (two values 1 and 10). The MAG signal is a current signal and it is expressed in nanoamperes. It is recommended to set a value within na as the initial MAG signal value. The value of the signal selected as the feedback signal (FB signal) can be observed with the help of a program oscilloscope turned on to measure the FB signal as well as using the FB signal digital indicator. The FB signal digital indicator is located in the SPM control block diagram under the feedback signal selection button «FB In» (Fig ) and consists of the digital indicator itself and of a nearby button determining the indicator operation mode (Fig ) Fig Fig The digital FB signal indicator features two modes of operation. In the first mode it displays the FB signal in na and in the second operation mode the displayed signal is calibrated in angstroms i.e. it practically shows the cantilever oscillation amplitude. To switch between the modes it is necessary to press a corner of the button or simply to hold the button in the pressed condition some time and to select the necessary button in the displayed window (Fig ). Please note that the indicator operation in the cantilever oscillation amplitude display mode is possible only the cantilever in use has been previously calibrated and the proportionality constant K, linking the oscillation amplitude and the FB signal (MAG signal) has been determined. The K constant can be determined by measuring the dependence between the FB signal and the distance between the probe and the sample surface that is described below in section 6.1 If, as a result of execution of the mentioned procedure, the value K1=Dz/DFB (z) was determined the value of factor K can be defined as K=K1*Gain, where Gain is the current value of the gain factor of the Lock-IN amplifier. Thus if the value of the K constant is known you can press the «K=» button (Fig ) and set its value. Only in this case you can use the FB signal indicator in the cantilever oscillation amplitude display mode. The MAG signal can be adjusted by changing the Gain value of the lock-in amplifier as follows: 1) Enable the measurement of the FB signal in one of the program oscilloscopes (if this has not been done already). The signal level can be monitored using the program oscilloscope. 5.4 Setting the initial level of the MAG signal

120 5-16 Solver P47H SPM Instruction Manual 2) Open the SPM control block diagram by pressing the button in the SPM window (second line of the main window). 3) Press the Gain button (Fig ) in the lock-in amplifier control block diagram. Fig Fig ) Watching the signal level in the FB oscilloscope set in the displayed regulator window the required value of the lock-in amplifier control block diagram (Fig ). The MAG signal adjustment by changing of the cantilever oscillation amplitude can be done by changing the value of the exciting voltage applied to the cantilever piezodriver. The voltage adjustment procedure is described above in item The MAG signal level can be monitored during the changing of the voltage at the cantilever piezodriver generator at the oscilloscope in a way similar to the above-mentioned adjustment done by changing the gain factor of the lock-in amplifier. 5.5 Approaching the sample to the probe, selecting and setting a working point After setting the initial level of the MAG signal it is necessary to approach the sample to the probe. In our case MAG is a feedback signal FB as the signal we applied earlier to the feedback input (in item 5.1.2) was the MAG signal. For this reason the phrases «MAG signal» and «FB signal» will have below the same meaning. Note Prior to approaching check the set up value for the feedback factor (FB Gain parameter). The FB Gain value should not be too low (not less than 1). The set up value for this parameter is displayed on the FB Gain button in the SPM control block diagram, as well as on the FBg button in the upper line of the main program window. Pressing any of these buttons will display a regulator window where you can change the FB Gain value. The unit utilizes automatic approach of the sample to the probe. The approach is done by means of a step motor that moves the sample holder with the sample attached to it relative to the probe. Note In addition to the automatic approach of the probe to the sample it is possible to approach the probe manually. The manual approach is used when the SPM head is used as a stand-alone SPM. However, if required the manual approach can also be used when SPM head is operated as a part of P47H. The procedure for manual approach is described below after the description of the main procedure (automatic approach procedure) in item 5.5.1A Automatic approaching of the sample to the probe The automatic approach operation can be broken down into the following steps: 1) Setting an initial value for Set Point. 2) Preparing and enabling the automatic approach operation. 5.5 Approaching the sample to the probe, selecting and setting a working point

121 Chapter 5. Semi-Contact Atomic Force Microscopy 3) Initial stage of the automatic approach operation. 4) Continuing the automatic approach operation. Below you can find a detailed description of these steps Setting the initial Set Point value Set the initial Set Point value approx. 50% lower than the initial MAG signal level (signal FB). To set the required value of Set Point: 1) Open the SPM control block diagram by pressing the button in the SPM window menu (in the second line of the main program window). 2) Press the SPoint button (Fig ) and set the required value in the displayed regulator window (Fig ). For example, if the signal level is 14 na set the SPoint value at approx. 7-8 na. Fig Fig The regulator window can be also opened by pressing the SP button in the upper line of the program main window ore the Setpoint button in the Probe window Enabling the automatic approach In order to begin the automatic approach operation, open the Approach window. To open the Approach window press the Operation button first in the SPM window menu (Fig ) and then Approach in the displayed menu (Fig ). Fig Fig Fig The Approach window can be also opened by pressing the button located in the very bottom of the toolbar (Fig ). Choose the Probe tab in the displayed Approach window; this will open the Probe window shown in Fig Then, start the automatic approach process using the Landing button provided the required value for the Set Point parameter has been set up in accordance with item above and preparation for approaching has been completed. Below you can find a detailed description of the approaching preparation, description of the buttons required for approaching as well as other components of the Approach and Probe windows. 5.5 Approaching the sample to the probe, selecting and setting a working point

122 5-18 Solver P47H SPM Instruction Manual Fig Windows «Approach», «Probe», «Mover» As mentioned above, at pressing the Approach button or the Approach tab the window shown in Fig will be open. The upper left part of this window contains as a matter of fact the Approach window. In which the «Probe» or «Mover» or «Laser Adjust» window is mapped. It is determined by what tab is selected in the menu «Approach». In Fig the «Probe» tab was selected. The upper right part contains the photodiode indicator. The bottom part contains a program oscilloscope. If to switch off the button in the menu of a window «Approach» (Fig ) the photodiode indicator and an oscilloscope will be closed and there will be opened only the Approach window (Fig ). Fig The «Probe», «Mover» windows (Fig , Fig ) contain the Landing button, several indicator buttons, including the Rate indicator button. The indicator buttons display the current values of appropriate parameters. Pressing such a button will display a regulator window where you can, if necessary, change the value of a specified parameter. 5.5 Approaching the sample to the probe, selecting and setting a working point

123 Chapter 5. Semi-Contact Atomic Force Microscopy 5-19 Fig Fig Buttons Landing, Rate, Fine, Exit, and the indicator of the step motor relative position Way are common for all tabs of the Approach menu and not only for the Probe tab (Fig , Fig ). The Landing button (Fig , Fig ) starts the automatic approach procedure. When this button is pressed the step drive starts operating. Fig Fig The Rate indicator button is located near the Landing button (Fig , Fig ). This button is used for setting up the approaching rate. The velocity here is expressed in some relative units. The maximum velocity corresponds to 20 units. The rate scale is not linear. For instance, the rate decrease from 20 units to 19 units means that the real sample travel velocity is smaller by a factor than the original one. To change the approaching rate press Rate and set the required value in the displayed regulator window (Fig ). If the approach rate is too high there might be a situation when the tracking system will not be able to stop the sample when required. This is due to the fact that during movement the mechanical system is subjected to deformations and mechanical strains that have extended relaxation times. For this reason after the step motor is stopped some residual travel of the sample takes place that is due to the relaxation of the above mentioned mechanical strains. This residual travel can exceed the possible travel range of the piezoelectric scanner and in this connection the tracking system cannot maintain the specified FB signal level. When the approaching rate is decreased, mechanical strains and the residual travel distance go down. Therefore at a certain approach rate the residual travel distance becomes lower than the possible travel range of the piezoelectric scanner. In order to avoid the above difficulties the unit features an automatic approaching control system, which, in particular, reduces the approach velocity when the probe starts interacting with the surface. In the semi-contact mode an optimum operation of the approaching system is ensured with the Fine button in the on position. This button is located near the Rate button (Fig ). In this case (with the Fine button in the on position) the velocity changes taking into account the FB signal derivative, the step motor is stopped in such a way that the scanner is positioned near the middle of its advance range and the step motor is switched in the backlash mode etc. 5.5 Approaching the sample to the probe, selecting and setting a working point

124 5-20 Solver P47H SPM Instruction Manual The following recommendations can be given regarding the velocity and way of approaching in the semi-contact mode: 1) It is recommended to perform the approaching with the Fine button in its on position, as it is shown in Fig ; 2) The initial approach velocity in the semi-contact mode (with the Fine button in its on position) must be set at its maximum i.e. equal to 20 units. The upper row (Fig ) of the Probe windows contains buttons Set Point, FB Gain è Bais (v). The indicator button Set Point displays the Set Point parameter value that we specified earlier when performing operations under item Therefore, the indicator button FB Gain will display the feedback gain factor (FB Gain) specified earlier. The bottom part of the Approach window contains a program oscilloscope. Apply the FB signal to the oscilloscope input using the first button in the oscilloscope menu and start the signal measurement process by pressing the GO button (second button in the oscilloscope menu). For more details on the program oscilloscope operation see item above in this chapter where there are instructions regarding signal application to the oscilloscope input, axis ranging etc. This oscilloscope can be used to observe changes in the FB signal during approaching. Fig shows a state at the oscilloscope input where the FB signal is applied and the measurement process for this signal is activated. The signal level is also displayed in the FB signal indicator (Fig , Fig ), which is located near the feedback signal selection button (in our case this signal is MAG). Fig Initial Stage of the sample automatic approaching to the probe If the initial value for Set Point has been set up as described in item above you can start the approaching operation. As it was indicated above, start automatic approaching by pressing the Landing button (Fig , Fig ). This will turn on the step motor that will move the sample towards the probe. Simultaneously the feedback is automatically turned on. As a result of the feedback operation the piezoelectric scanner (and the probe with it) will be put forward on its maximum length in the direction of the sample (along axis Z). In its initial position the probe tip is located at a sufficient distance from the sample (about 1 mm) compared to the maximum possible scanner travel (about 3 microns) along axis Z. Although the tip approaches to the sample as a result of a complete scanner extension, the distance between the tip and the sample is still large enough to avoid any kind of interaction. Therefore the current FB signal level does not change; the difference between the FB and Set Point levels remains large. The scanner extension is displayed on the analog indicator located upper row of the main program window between the photodiode indicator star button and the FB button (Fig ). The degree of extension is represented by the length of the color bar, which is red during operation in semi-contact mode. Fig Fig Approaching the sample to the probe, selecting and setting a working point

125 Chapter 5. Semi-Contact Atomic Force Microscopy When the scanner is fully extended the red bar fills the entire indicator (Fig ). When approaching watch the changes in the FB signal in the FB oscilloscope window and the state of the scanner extension indicator. Fig shows how the FB signal (i.e. the cantilever oscillation amplitude) normally changes over time in the course of the cantilever approaching to the surface. Increase in time corresponds to approach to the surface. Initially the signal value does not change Fig Then, when the cantilever is close enough to the surface the cantilever oscillation amplitude begins decreasing and accordingly the current value of the FB signal is also going down. The first portion of the relationship between the FB signal and distance to the surface (i.e. oscillation amplitude distance to the surface), where the oscillation amplitude begins decreasing with the distance reduction, is not related to interaction between the tip and the surface but it is due to a damping action of air layer between the cantilever beam and the surface. This portion is very extended and unstable. During further approach the oscillation amplitude will be going down and at a certain point there will be a portion where the oscillation amplitude will go down in a more sudden fashion. This second portion corresponds to the interaction start between the probe tip and the surface. You should immediately note the point when the current FB goes down to the SPoint value on the scanner extension indicator. Two situations are possible here: 1) the red bar (of the scanner extension indicator) decreases and stays in an intermediate position on the indicator (Fig ); and 2) the red bar shrinks to zero (Fig ). Let s consider both cases in detail. Fig Fig The first case indicates a successful completion of the approach initial step resulting in the normal operation condition of the tracking system. The red bar intermediate position on the indicator corresponds to an intermediate position of the scanner between the extreme states. In this case the tracking system has been able to compensate the difference between the current FB level and the SPoint value by moving the scanner, and furthermore, it can still maintain the FB signal level equal to the SPoint, as the scanner is within the range of the possible advance interval. The above Fig shows the first situation where the tracking system upon successful completion of the initial approach stage is maintaining the FB signal level equal to the set-up SPoint value (equal to 8 na in the Figure). 5.5 Approaching the sample to the probe, selecting and setting a working point

126 5-22 Solver P47H SPM Instruction Manual This first situation has to be implemented in order to continue the approaching procedure. Generally, if the approach is being done with the Fine button in its on position, the automatic approach control system is operating properly, the first situation occurs. However, if the automatic approach control system does not operate properly or for some other reasons, the second situation can occur. In the second case we skip the Set Point because of a too rapid approach of the sample to the probe. In that way, after passing the Set Point and engine stop the sample holder (with the sample) moves too far due residual mechanical strains in the system, which exceeds the maximum range of the scanner advance. The tracking system, trying to set the FB signal value equal to the SPoint level, drives the probe away from the sample surface as far as its range allows, i.e. fully retracts the scanner, but this shift is insufficient to compensate the FB signal change, which has exceeded the SPoint value. Then, the step motor starts again automatically this time it will be moving the probe away from the sample. The current FB level will start growing and at a certain point it will exceed the SPoint value. Accordingly, the tracking system will advance the scanner again, which must be reflected on the scanner extension indicator where the red bar that will appear and start growing. If in doing so the control system manages to implement the first situation (perform the initial approaching stage successfully) i.e. stop the step motor in such a position where the scanner will be close to the middle of its range (the red advance bar will near its intermediate position on the indicator) you will be able to carry on with the approach procedure. Otherwise, the control system will withdraw the probe from the sample on a distance where there is no interaction, the scanner will fully advance (the read bar will fill the indicator) and the step motor will be turned off. In this case try to repeat the approach operation by pressing the Landing button one more time. Let us assume that you have managed to perform successful approaching at the specified value of SPoint i.e. you managed to establish a state where the tracking system maintains the FB signals equal to the specified value of Spoint, and the scanner is positioned within the possible advance range. The red bar will reach an intermediate position on the extension indicator. After that you can continue the approaching procedure Continuing the automatic approaching Further it is necessary to make attempt to reduce the value of the «SPoint» parameter. The decreasing of the «SPoint» value you can carry out by means of the regulator window that is opened by pressing the Set Point button in the Probe window (Fig ), or the SP button in the upper line of the program main window, or the SPoint button in the SPM control block diagram. Here two cases are possible: 1) at decreasing of the «SPoint» value the red bar (of the scanner extension indicator) practically does not grow, 2) at decreasing of «SPoint» value the length of the red bar will increase and the red line completely fills the indicator. Realization of the first case (i.e. case when at decreasing of the «SPoint» value the red bar does not grow) corresponds to completion of the approach procedure. That fact that the red scanner advance bar stops growing when we try to decrease the SPoint level means that we have finally approached the probe close enough to the surface. The cantilever tip starts striking the surface and if you approach it any further its oscillation amplitude will be limited because of its touch with the surface. Thus, if the first case takes place the procedure of approach is completed and further it is necessary to proceed to execution of item Approaching the sample to the probe, selecting and setting a working point

127 Chapter 5. Semi-Contact Atomic Force Microscopy 5-23 The second case means that the procedure of approach is not completed. If the second case takes place then, you need to decrease the SPoint value to such a level when the red scanner advance bar extends to its extreme right position. The SPoint value at which the red bar reaches its extreme position must be set as the new SPoint level. Then start the automatic approach operation again by pressing the Landing button this time for the new SPoint level. Accordingly, the approach (for the new SPoint level) is considered successful if it was possible to achieve a state when the red bar is in a middle position. After that the SPoint level decrease procedure and the following automatic approach at each new SPoint level should be repeated until such a point when the red bar stops increasing sharply when you try to decrease the SPoint level, i.e. when the first case will take place. If you have carried out the approaching with the Fine button in its off position, the mechanical system should be switched into the backlash mode upon successful completion of the approaching operation. To do it go to the Mover tab in the Approach menu, this will display the Mover window (Fig ). In this window press several times (5-10) the button «Backward One Step» (Fig ). Fig Fig In this case the step motor will make one step backwards with each press. In case of approaching with the Fine button in its on position, the mechanical system will be switched into the backlash mode automatically upon successful completion of the approaching operation. Then go to item The following item 5.5.1A below addresses the probe manual approach operation A Manual approach of the probe to the sample As it was mentioned above in addition to the automatic approach of the probe to the sample it is possible to approach the probe manually. The manual approach is used when the SPM head is used as a stand-alone SPM. However, if necessary the manual approach can be used for the SPM head operation as a part of P47H in the main mode. In this case it is supposed, that preliminary preparation of the SPM head is carried out (the plane of the SPM head base and the plane of a sample are established in parallel, the necessary length of the SPM head legs is established, adjustment of the laser and the photo diode is carried out, the SPM head is established above a sample, the necessary switching in the SPM control block diagram and other operations on preparation for work in a semi-contact mode are executed). The manual approach procedure of a probe to a sample can be divided into the following operations: 1) Setting the initial Set Point value, 2) Turning on the feedback, 5.5 Approaching the sample to the probe, selecting and setting a working point

128 5-24 Solver P47H SPM Instruction Manual 3) Initial stage of the manual approach operation, 4) Continuing the manual approach operation. A more detailed description of these operations is given below A Setting the initial Set Point value This procedure is completely similar to procedure of setting the initial value of «Set Point» parameter in case of the automatic approach, which above mentioned in item Setting the initial Set Point value A Enabling the feedback After setting the initial Set Point value enable the feedback. The feedback is enabled either by pressing the FB button (Fig A) in the upper line of the main program window or by closing the feedback loop using the I toggle switch in the SPM control block diagram. Fig A After the feedback is enabled the piezoscanner (and the probe) will advance over the maximum distance along axis Z towards the sample. In its initial state the probe is located at a considerable distance away from the probe (about 1 mm) compared to the maximum possible travel of the piezoscanner (about 3 microns) along axis Z. Therefore, although the probe approaches to the sample as a result of the complete advance of the scanner the distance between the probe and the sample is still too big for any kind of interaction, for this reason the FB signal level does not change, the difference between the levels of FB and Set Point remains considerable. The scanner advance is indicated by the readings of the analog scanner extension indicator that is located in the upper line of the main program window between the photodiode indicator switch and the FB button (Fig A). The extent of the advance is shown by the length of the red bar. Fig A Fig A When the scanner is fully advanced the red bar completely fills the indicator (Fig A) A Starting manual approaching the probe to the sample After enabling the feedback and advancing the scanner to the sample you can start approaching the probe to the sample. The approaching is to be performed manually, using the approach screw (Fig A). The approach screw is one of three leg supports of the SPM head and is provided, unlike the other two, with a handle. Fig A Fig A 5.5 Approaching the sample to the probe, selecting and setting a working point

129 Chapter 5. Semi-Contact Atomic Force Microscopy 5-25 By rotating this handle you can move the SPM head and the probe relative to the sample in the vertical direction. The rotation direction determines the movement direction. During approach the screw should be rotated counter-clockwise. The rotation of the screw to 360 degrees moves the probe by approx. 120 microns. When approaching rotate the screw and watch the signal changes in the oscilloscope window FB and the scanner extension indicator. Fig A shows how the FB signal (i.e. cantilever oscillation amplitude) typically changes over time during approach of the cantilever to the surface. Increase in time corresponds to approach to the surface. At first, the cantilever approach does not change the signal value. Then when the probe moves much closer to the sample the cantilever oscillation amplitude begins decreasing and the current value of the FB signal goes down accordingly. Starting from this moment you should rotate the screw slower watching the scanner extension indicator. The first portion of the relationship between the FB signal and distance to the surface (i.e. oscillation amplitude distance to the surface), where the oscillation amplitude begins decreasing with the distance reduction, is not related to interaction between the tip and the surface but it is due to a damping action of air layer between the cantilever beam and the surface. This portion is very extended and unstable. When the cantilever is further approached the oscillation amplitude continues to decrease and at a certain moment there will be a section where the oscillation amplitude will decrease in more sudden fashion. This second section corresponds to the beginning of interaction between the probe tip and the surface. As soon as the level of the current signal FB decreases to reach the level of the SPoint value stop rotating the approach screw. We will immediately note this on the scanner extension indicator. Here there will be two possible cases: 1) the red bar (of the scanner extension indicator) goes back to zero (Fig A), 2) the red bar decreases to a certain intermediary position (Fig A). Fig A Fig A In the first case we miss the Set Point due to an extremely fast approach of the probe to the sample. At the same time, after passing the SPoint we mechanically move the probe to a distance bigger than the maximum scanner advance range. The tracking system trying to set the FB signal level equal to the SPoint level moves the probe as far as possible away from the sample surface i.e. completely retracts the scanner but this movement is not sufficient to compensate the change in the FB signal whose value has gone below the SPoint level. If the first case has taken place it is necessary to rotate the approach screw slightly in the opposite direction (clockwise), in order to move the probe away from the sample. This should cause the current level of the signal to go up and reach the SPoint level. The tracking system will start operating accordingly, the scanner will advance, which will be reflected on the scanner indicator as appearance and growth of the red bar. If, in doing so, you could implement the second option, i.e. the red advance bar stops at an intermediary position in the indicator you can continue the approaching procedure. 5.5 Approaching the sample to the probe, selecting and setting a working point

130 5-26 Solver P47H SPM Instruction Manual Otherwise, i.e. in case of complete scanner advance (the red bar fills the indicator), you need to restart approaching the probe to the surface slowly rotating the screw counter clockwise. Let us discuss in particular the possibility of the cantilever break during its approach. In reality this situation is rather rare but nevertheless it happens now and then. If the first case takes place and you try to move the probe away from the sample, the red scanner advance bar is not displayed on the indicator. This means that the cantilever broke down, the FB signal disappears from the display. The SPoint value becomes higher than the FB signal because the latter is simply not present. Therefore the feedback system will maintain the scanner in its fully retracted position. In this case move the probe (or what is left from it) and exchange cantilever. The second case corresponds to a successful completion of the manual approach operation, which results in normal functioning of the tracking system. The intermediary position of the red bar on the indicator corresponds to the intermediary position of the scanner between two extreme states. In this case the tracking system managed to compensate the difference between the current FB level and the SPoint value by moving the scanner and at the same time it can maintain the FB signal level equal to SPoint as the scanner is within the possible advance range. This second case needs to be implemented to continue the approach. Let us assume that the probe has been approached successfully at the set SPoint level, i.e. we could establish a state in which the tracking system maintains the FB signal level equal to the SPoint value and the scanner is located within the possible advance range. The red bar in the scanner extension indicator is in a middle position. After that you can continue the approach procedure A Continuing the manual approach procedure Further it is necessary to make attempt to reduce the value of the «SPoint» parameter. The decreasing of the «SPoint» value you can carry out by means of the regulator window that is opened by pressing the SP button in the upper line of the program main window, or the SPoint button in the SPM control block diagram, or the Set Point button in the Probe window. Here two cases are possible: 1) at decreasing of the «SPoint» value the red bar (of the scanner extension indicator) practically does not grow, 2) at decreasing of «SPoint» value the length of the red bar will increase and the red line completely fills the indicator. Realization of the first case (i.e. case when at decreasing of the «SPoint» value the red bar does not grow) corresponds to completion of the approach procedure. That fact that the red scanner advance bar stops growing when we try to decrease the SPoint level means that we have finally approached the probe close enough to the surface. The cantilever tip starts striking the surface and if you approach it any further its oscillation amplitude will be limited because of its touch with the surface. Thus, if the first case takes place the procedure of approach is completed and further it is necessary to proceed to execution of item The second case means that the procedure of approach is not completed. If the second case takes place then, you need to decrease the SPoint value to such a level when the red scanner advance bar extends to its extreme right position. The SPoint value at which the red bar reaches its extreme position must be set as the new SPoint level. Then, approach the probe manually using the approach screw according to the procedure described above (item ), this time for the new SPoint level. Accordingly, the approach for the new SPoint level is considered successful if it was possible to achieve a state when the red bar is in a middle position. 5.5 Approaching the sample to the probe, selecting and setting a working point

131 Chapter 5. Semi-Contact Atomic Force Microscopy 5-27 After that the SPoint level decrease procedure and the following manual approach at each new SPoint level should be repeated until such a point when the red bar stops increasing sharply when you try to decrease the SPoint level, i.e. when the first case will take place Selecting the Set point value The relationship between the cantilever oscillation amplitude (signal proportional to it) and the distance has the shape shown on Fig Fig If we consider this relationship we can notice a certain point where the character of the relationship changes. When the distance changes the amplitude changes very slowly above this point and very fast below this point. Please note that every SPoint value set by us corresponds to the certain oscillation amplitude (or rather to the signal proportional to the oscillation amplitude), since the feedback maintains the signal equal to the set SPoint level. The SPoint value at which the red scanner advance bar stops growing sharply when you try to decrease the SPoint value is in fact the characteristic point on the curve of relationship between the oscillation amplitude and the distance between the probe and the surface. At this point the probe starts striking the surface and the more we decrease the SPoint value, the stronger it strikes and the more the oscillation amplitude is limited. The SPoints values starting from the level of the characteristic point and below correspond to the semi-contact mode. Within this range you can pick up a SPoint value to use as a working point for semi-contact mode operation. The choice of an optimum point depends on the properties of the studied object as well as on other factors, and it is best to select it experimentally. As the initial Set point level we can recommend a SPoint value of approx of the characteristic point level. Then during scanning you can select a better value Rough estimate of the cantilever oscillation amplitude value After determining the characteristic point i.e. the value of SPoint at which the red scanner advance bar stops growing sharply when you try to decrease the SPoint value, you can make a rough estimate of the cantilever oscillation amplitude. To do it you need to remember the value of coordinate Z at which the SPoint value is equal to the value of the characteristic point, then decrease the value to one half and based on the readings of the coordinate Z indicator determine the change of coordinate Z. This change of coordinate Z is equal to approx. one half of the cantilever oscillation amplitude. 5.5 Approaching the sample to the probe, selecting and setting a working point

132 5-28 Solver P47H SPM Instruction Manual In order to determine the constant of proportionality between the oscillation amplitude and the measured signal more precisely, it is necessary to measure the relationship between the FB signal and the distance between the probe and the sample. The measurement procedure for this relationship is described below in section Selecting the feedback gain factor After approaching the sample and setting the set point we need to select a value for the feedback gain factor. The selection procedure for the feedback gain factor is as follows: Open the SPM control block diagram by pressing the button in the second line of the main program window. Open the FB Gain regulator window by pressing the FB Gain button (Fig , Fig ). Increasing the FB Gain value watch the FB signal level at the program oscilloscope. Fig Fig Determine the value of the FB Gain factor at which generation starts. The start of generation can be determined by a sharp increase of the variable component of the FB signal (Fig ). As a working value of the FB Gain factor it is recommended to set a value equal to of the FB Gain factor value at which the generation of the FB signal starts. Fig Approaching the sample to the probe, selecting and setting a working point

133 Chapter 5. Semi-Contact Atomic Force Microscopy 5.6 Setting the scanning parameters Scanning parameters control window To set up the scanning parameters, open the scanning parameters control window (Fig ) Fig Fig To open the scanning parameters window, press in sequence: 1) The Operation button in the SPM window menu, 2) Scanning in the displayed menu, and 3) SCAN in the header of the displayed window. The scanning parameter control window may also be opened by pressing the button on the tool bar in its Scan section that is used to control the scanning parameters (Fig ) followed by pressing SCAN in the header of the displayed window. (The tool bar is located at the left-hand side of the program main window) The procedure to Set the Scanning Parameters The procedure of setting parameters in the scanning parameter control window is uniform for all elements of the control graphical interface. To set the parameters, select and press the desired button. As a result, the signals or states menu, or the regulator window will be displayed. For instance, if you need to change the scan step, press the indicator button Step (Fig ), set the necessary value in the displayed regulator window (Fig ), and then click the mouse left button to fix the value. Fig Fig Or suppose that it s necessary to switch the A channel to measuring the Height signal. Press the channel A signal selection button (Fig ), choose the Height signal in the displayed signal menu (Fig ), and fix it by pressing the mouse left key (Fig ). 5.6 Setting the scanning parameters

134 5-30 Solver P47H SPM Instruction Manual Scanning Velocity Fig Fig Fig The scanning velocity is a parameter significantly affecting the quality of the acquired images. The scan velocity is set up using the «Vel» button (Fig ), displaying the current velocity value. Velocity measurement units are displayed on the button on the right. This button can be used to change the Velocity measurement units - you can choose between Angstrom/sec and microns/sec. To set up the required unit of measure place the mouse pointer on the right corner of the button (Fig ) and press the left mouse button (one may also simply to press the button and to hold it in the pressed condition some time). This will display two buttons (Fig ) that are used for selecting the required units of measure. Fig Fig Fig To the right of the button displaying the velocity measurement unit there is an indicator displaying the line scanning frequency (Fig , Fig ), corresponding to the selected scanning velocity. To change the scanning velocity press «Vel» and set the required value in the displayed regulator window. The available velocity regulation range depends upon the scan area range. The greater the area, the higher the upper velocity value. An initial scan velocity to be recommended is the value when scanning of one line can be completed within approximately sec., i.e. the line scanning frequency will be Hz. Selecting the optimal scan velocity depends upon the surface peculiarities of the studied sample, the scan area, and the external conditions. A surface with a smooth relief can be scanned at a higher velocity than a rough relief surface with notable differences in height. Velocity can be regulated directly during the scan process, adjusting and trying values to select the optimal one. This procedure will be detailed below in item Setting the scanning parameters

135 Chapter 5. Semi-Contact Atomic Force Microscopy The Scanning Area, Step and Number of Scan Points The maximum scanning area of the SPM head is 50 x 50 microns or 90 x 90 microns (depending upon the scanner model). The scanning area can be set up using the Area button in the lower line of the scanning parameter control window (Fig ), and using the similar Area button located on the tool bar, in its part called «Scan» that is designed to control the scanning parameters (Fig ). Fig Fig In this case, if the scan area is changed, the scan step will be also changed automatically. And on the contrary, when changing the scan step, with the scan point size being stated, the scan area changes. The value of the scanning step is set up with the Step indicator button (Fig , Fig )) displaying the current value of the scanning step. The unit of measure is angstrom, which is displayed on the indicator to the right of the Step button. Further to the right there is an indicator displaying the size of the scanning area (in microns), corresponding to the specified step and number of points along axis X, Y. Fig Fig The number of scanning points along axis X and Y is specified accordingly as «NX=...» «NY=...», as shown in Fig With button 2^N enabled (Fig ) the scan side dimensions are automatically reduced down to the nearest number of the type 2 in N power. If button 2^N is disabled you can specify any number of scanning points along both axis in the range of provided that this number multiplied by the scanning step does not exceed the maximum size of the scanning area. Otherwise, the maximum number of points will be limited by a value equal to the ratio of the maximum size of the scanning area and the specified scanning step. In case no data on the sample surface are available, it is advisable to start scanning with a minor area, say, microns by microns. Depending upon the results of scanning a small area, better values can be selected and set up for such parameters as the Set point value, scan velocity, feedback factor. Than the scan area can be expanded to the medium dimensions of approximately microns. After the preparatory operations have been completed, the probe has been approached to the sample, the Set point has been selected it is recommended to check if the scanning range along axis Z is sufficient for operation on the selected area of the surface. 5.6 Setting the scanning parameters

136 5-32 Solver P47H SPM Instruction Manual After approaching and during the parameters setting the probe was located in the center of the selected area, however in the other parts of the selected area, especially in its corners high relief or big slope can result in a situation where the scanner range along axis Z will not be sufficient. It is possible to check with the scanning area selection tool (Area). If you specify the scanning area using this tool with the Moving option enabled, the probe will move with scanning area selection frame. Fig In order to check the scanning range, moving slowly (which is very important), place the frame center in turns in every corner of the planned scanning area while watching the color scanner advance indicator along axis Z. If during the movement of the frame over the selected area the color bar always stays in the working range this means that the scanning range is sufficient for all points. If the color bar extends to its entire length in an area of the planned scanning field, the topography won t be read for this area in the course of scanning (due to general sample inclination or very deep hole in this location). The most dangerous situation is when the color bar disappears completely. This means that the scanner has been retracted completely trying to maintain close to the specified Set point value but its range is not sufficient because of a general slope or a particularly high protuberance. In this case the tip can touch the surface, which can lead to its blunting. If during such inspection of the planned scanning field the color bar is reduced to 1/6 1/8 of its length limit the scanning field so that this area is not included Scanning Mode The scanning mode is to be set up with the second button in the lower line of the scan parameter control window (Fig ). Fig Set up the One Scan mode as shown in the above picture. Under the One Scan mode, a single scan run of a selected area will be performed. In addition to the above mentioned mode, the following scanning modes are available: Many Scans multiple scanning of a selected area, which will be recurring until interrupted by pressing ESC; NxN Scans shifted scanning; Move Scans - scanning with a shift in a preset direction. These special modes are detailed in the program description The Scanner Non-Linear Travel Correction Enabling and disabling of the scanner s non-linear travel correction is performed with the NLCor button (Fig ). This button is to be in the ON position, as shown in the picture below. 5.6 Setting the scanning parameters

137 Chapter 5. Semi-Contact Atomic Force Microscopy 5-33 Fig Fig Measurement Channels: Application of Signal, Setting Scan Direction The unit has four measuring channels, a certain signal can be applied to each of them, and when scanning, data for imaging of the applied signals will be produced. The measurement channels A, B, C and D must be set in positions shown in Fig As follows from the above Fig , the Height signal is applied to the input of the measurement channel A, the selected scan direction (Dir) is +X+. The remaining channels (B, C, and D) are off. The Dir button of each measurement channel is activated only if the channel is on. If a channel is off the setting in the Dir button of this channel is not important. When scanning, the height image data (the Height signal) will be displayed in the SPM window of the image channel A. The letter «X» means that the high velocity scanning will be performed along the X axis, the symbol «+» in front of the X letter means that the high velocity scanning will occur in the positive direction, and the «+» symbol following the «X» letter means that the low velocity scanning (Y axis scanning) will also be effected in the positive direction. It should be mentioned that Channel A is a special channel as compared to the other ones: the scan direction is set up through this channel. In other channels, only the direction of the signal reading can be established. Note This section addresses only the minimum of measurement channels buttons functions required for operation in the topography measurement mode. For more details on the measurement channels buttons functions see Chapter 7 addressing the multi-pass mode The ADC Preamplifier Gain Factor, Low-Pass Filter Values for such parameters as the ADC preamplifier gain factor (Gain), low-pass filter cutoff frequency (LPass (khz), and the number of measurements at each point (Average) are recommended as shown in Fig Fig The Gain factor = 1 corresponds to the most «rough» ADC sensitivity. If the height signal change is insignificant, the gain factor may be increased (by switching to the «10» or «100» position). With increasing gain factor, the signal is being measured at a minor step, but in this case the ADC signal measuring interval shrinks. With a high sensitivity, the measured signal happens to be in excess of the ADC measured interval in some zones of the scan area, which will result in trimming of the signal in these zones. The low-pass filter is used for eliminating the high-frequency noise. The recommended cutoff frequency to be set up is 2 to 4 khz. 5.6 Setting the scanning parameters

138 5-34 Solver P47H SPM Instruction Manual Increasing the number of measurements in each point (Average) slows down the scanning velocity, especially for small fields (under 1 micron) but improves the quality of the result. Note, that the preamplifier and the low-pass filter are available only in the A and C channel circuits, and, respectively, are absent in the B and D channel circuits The Drawing, Show Lines, Scope Data, Line Strob, AutoScale and Save To NT. MDT Buttons The Drawing, Show Lines and Scope Data buttons (Fig ) are directly related to the scan process, they enable or disable imaging of the respective signals while scanning the sample. Fig These buttons must be set in positions shown in Fig , with the Scope Data button off, and the Drawing, Show Lines buttons on. The Drawing button enables or disables imaging of signals arriving from the respective measurement channels (Channel A, or Channels A and B, and so on) in the SPM window. When the button is disabled, the image being scanned will not be displayed in the SPM window. The Show Lines button enables and disables imaging of the Channel A signal image profile along the scanning line in the Ext oscilloscope. When scanning, switching of the Ext oscilloscope to signals from other channels can be done using the direct control line (section 5.7.2). The Scope Data button enables and disables signal imaging in other program oscilloscopes while scanning. Thus, if this button is disabled, the oscilloscopes will not be working during scanning even if they are on. The button is recommended to be set into the off position. In this case signals applied to the oscilloscopes will not be measured while scanning. This allows reducing the noise caused by the ADC switching, as well as a more economical use of the unit. The Line Strobe button enables and disables the application of the pulse signal to the external output in the scanning start of each line for external equipment synchronization with the scanning process. The AutoScale button enables and disables the automatic scaling of a signal displayed at scanning in the Ext oscilloscope. The Save To NT. MDT button enables and disables the automatic saving of obtained data in NT. MDT file Subtracting procedure (Subtract button, Exc Hi button) The Subtract button (Fig ) effects enabling and disabling of the subtraction procedure. It has the following positions (Fig ): None, Plane, 1st-Slope, 2nd-Slope, 3rd-Slope and 4th-Slope. 5.6 Setting the scanning parameters Fig Fig

139 Chapter 5. Semi-Contact Atomic Force Microscopy 5-35 «None» - corresponds to the «disabled» status; «Plane» - immediately upon completion of a scan run, the operation of plane subtraction will be performed; «1st-Slope» - after scanning each line, the first order curve slope subtraction is performed; «2nd-Slope» - after scanning each line, the second order curve subtraction is performed; 3rd-Slope - after scanning each line, the third order curve subtraction is performed; 4th-Slope - after scanning each line, the fourth order curve subtraction is performed. If the «Exc Hi» button is switched off, at performance of the subtraction procedure, when the deducted curve or plane is calculated, all scanned points of the surface are taken into account. If the «Exc Hi» button is switched on, at performance of the subtraction procedure, when the deducted curve or plane is calculated the points of the surface areas containing spikes and pins are excluded Scanning parameters for a test grid-type sample It is recommended to set the following parameters to scan a test grid-type sample: «FB» - «Mag» ; «Vel...» - 50 um/s ; «NX x NY» x 256 ; «Step...» - maximum ; «NL Corr» - on ; Channels: A - «Height», «Dir» - «+X+» ; B - «Phase 1», «Dir» - ; C - off ; D - off ; «Gain» - 1 ; «Lpass» - 4 khz ; «Average» - 1 ; «Drawing» - on ; «Show Lines» - on ; «Scope Data» - on ; «Subtract» - none ; «SP» - based on the approaching results; «FB Gain» - based on the approaching results. Select the one-pass scanning mode One Scan. 5.6 Setting the scanning parameters

140 5-36 Solver P47H SPM Instruction Manual 5.7 Scanning Scanning start After the preparatory operations are complete, the probe is approached to the sample, the Set point is selected and the scanning parameters are set you can start scanning the sample surface. The scanning is started by pressing the RUN button on the toolbar that is located under the Scan header and controls the scanning parameters (Fig ), or by pressing the similar function RUN button in the bottom line of the scanning parameters control window (Fig ). Fig Fig After that the probe starts scanning the sample surface line by line. At the same time the relief (height) image of the scanned surface will start appearing line by line in the A channel window. Therefore, if the SPM window is switched to display both channels A and B, the B channel window will display the image of the signal applied at the B channel input. In our case this is the phase signal (Phase 1). During scanning the unit can be controlled via the direct scanning control line (menu) Direct Scanning Control Line When the scanning is started a new line appears in place of the upper menu this is the direct scanning control line (Fig ). Fig The unit control during scanning can be effected only using this line. It allows changing the main parameters in the course of scanning: scanning speed, feedback gain factor, Set point value, the size and location of the scanning area and execute some other functions. The scanning control line consists of buttons, each of which is designated for a special parameter or a special function. The first three buttons, and, are used to change the scanning speed, feedback gain factor, Set point value, accordingly. Each of these buttons has a digital indicator displaying the current value of the corresponding parameter. At the scanning start, the first button is highlighted, which indicates that it is on. The desired button can be highlighted with the «right» and «left» keyboard keys that move the highlighted position along the line. The value of the parameter corresponding to the marked (switched on) button can be decreased or increased using the «down» and «up» keyboard keys. The,,,,, buttons switch on after having been marked, with the following pressing the Enter key. The button The button is used to restart scanning. is used to change the size and location of the scanning area. 5.7 Scanning

141 Chapter 5. Semi-Contact Atomic Force Microscopy 5-37 The button turns on the plane slope subtracting procedure. The parameters of the subtracted plane are determined for the area that has already been scanned when the button is turned on. After the parameters of this very plane will subtract from the entire data array. The button is used to stop the slow axis scanning, the fast axis scanning will continue and it will be done along the same line. When the button is enabled it starts blinking periodically, which indicates that it is in its on position. To disable it press the Enter key one more time. With the button in its on position you can use all the other buttons of the line. This mode can be used to select the optimal parameters, for example, the scanning velocity Selecting the optimal scanning parameters The main parameters, which are very important for the quality of the acquired surface image are the scanning velocity, value of the Set point SP, feedback gain factor FB Gain, and the cantilever oscillation amplitude. The first three parameters i.e. the scanning velocity, SP and FB Gain can be adjusted during scanning by selecting their optimal values with appropriate buttons in the scanning control line (item 5.7.2). Scanning velocity The optimum scanning velocity value depends on the surface properties of the studied object, the size of the scanning area, external conditions. A flat topography surface can be scanned at a higher velocity than a surface with rough topography and considerable height differences. The scanning velocity should be decreased when a hill or a recess slope is not imaged in the scanning direction. With soft materials you can experience plucks on the scan image in the scanning direction on surface hills. In this case it is recommended to decrease the scanning velocity as well as to increase the SP in order to decrease the sample surface impact. FB Gain factor As a working value of the FB Gain factor it is recommended to set a value equal to of the FB Gain factor value at which the generation of the FB signal starts. The selection of the gain.12 r value is described in item Sometimes, during the probe approach to the surface the feedback system becomes unstable and falls into a «generation» mode that cannot be corrected by decreasing the FB Gain factor. This type of instability is due to the «sticking» effect. This instability can be eliminated by increasing the cantilever oscillation amplitude. To do this disable the feedback, increase the cantilever oscillation amplitude and the SP parameter value by approximately 30% and then enable the feedback again. 5.8 Saving the acquired data After the sample surface scanning completion the acquired data are kept in the random-access memory. A separate image corresponds to every surface scan. Please note that if only the A channel was displayed in the SPM window but the measurement of other channels was enabled in addition to the A channel, images corresponding to the data from the other enabled channels will be generated. The image numbers correspond to the sequence of their acquisition. Spectroscopy data (section 6.1) also exist as a separate image. 5.8 Saving the acquired data

142 5-38 Solver P47H SPM Instruction Manual To save the acquired data on the hard drive you need to place the cursor on the File button in the SPM window menu (Fig ). Fig Fig In the displayed menu press Save (Fig ) and save as an arbitrary name file with *.MDT extension (Fig ). Fig Using the Open command (Fig ) in the same menu you can pull up previously saved files. 5.9 Switching from semi-contact to contact mode In order to switch from the semi-contact mode to the contact mode you need to execute the following operations: 1) Disable the feedback; 2) Disable the cantilever modulation; 3) Apply a new signal to the feedback input (DFL signal), determine the current value for this signal (using the FB oscilloscope); 4) Set the SP value with regard to the current value of the new FB signal (DFL signal); 5) Enable the feedback; 6) Continue operation in the contact mode; 5.10 Turning the microscope off To turn off the microscope: 1) Remove the sample away from the probe approximately 2-4 mm. To perform this operation: Open the «Mover» (Fig ) window (the step motor control window) by subsequently opening: «Operation» - «Approach» - «Mover», Set the value of «Remote» at 2-4 mm (Fig ) and press the Remote button Turning the microscope off

143 Chapter 5. Semi-Contact Atomic Force Microscopy 5-39 Fig Fig ) Disable the feedback by pressing the FB button that is located in the upper line of the main program window (fifth from the right, Fig ); Fig ) Turn off the laser by pressing the button that is located in the upper line of the main program window (fourth from the left, Fig ), the button is red in the on position and black in the off position; 4) Turn off the power using the power toggle switch on the electronic block; 5) Exit the controlling program by pressing the Exit button in the menu (Fig ), which is displayed when the cursor is placed on the Main button in the left-hand corner of the program window (Fig ). Fig Fig You can also exit the program by pressing F10 (after closing all open menus using the Esc button since F10 operates only with the menus closed) Phase Imaging Introduction In semi-contact and non-contact modes the surface is scanned by an oscillating probe tip, the oscillation of which is excited by the cantilever piezodriver. The tip oscillation amplitude and oscillation phase with regard to the exciting voltage (piezodriver generator voltage) are the parameters depending from the value of interaction between the oscillating tip and the surface. Based on experience, the oscillation phase is more sensitive, compared to the amplitude, to changes in interaction between the probe and the sample surface, in particular to changes related to local variations in surface adhesion and viscoelasticity. Acquiring a phase signal image simultaneously with a surface topography image provides some additional information on the surface structure details. This method is called Phase Imaging. In case of a smooth surface the Phase Imaging technique provides contrasting images of the surface structure details related to local variations in surface adhesion and viscoelasticity Phase Imaging

144 Phase Imaging Solver P47H SPM Instruction Manual The unit supports phase imaging as well as imaging signals related to the probe oscillation phase both 1) simultaneously with the surface topography measurement and 2) sequentially as a result of alternation in line-by-line surface topography measurement and subsequent phase signal measurement. The latter case is described in sections covering double-pass technique, magnetic force microscopy and electrical force microscopy. This section describes the first case when the phase signal imaging (or imaging of probe oscillation phase related signals) is done simultaneously with surface topography measurement in semi-contact or non-contact mode. The feedback signal in this case is a signal proportional to the cantilever oscillation amplitude (MAG or RMS) Signals related to the probe oscillation phase In SPM head the initial signal corresponding to the probe oscillations is the variable component of the DFL signal. After it s processing by the Lock-IN amplifier and the phase detector the following signals are generated, they are related to the probe oscillation amplitude with regard to the exciting voltage: 1) «Phase 1» - signal corresponding to the sum of phase displacements: phase displacement between the cantilever oscillation phase and the exciting signal phase, phase displacement between the exciting and the reference signals (precision is determined by the hardware factor). This signal comes from the phase detector output. 2) «MAG*sin» is a signal proportional to the product of the variable signal amplitude at the modulation frequency and the cantilever oscillation phase deviation sine with regard to the reference signal. Accordingly the cantilever oscillation phase shift value with respect to the reference signal consists of the sum of the exciting signal phase displacement value with respect to the reference signal and the cantilever oscillation phase displacement with respect to the exciting signal (precision is determined by the hardware factor). This signal comes from the Lock-IN amplifier output. 3) «MAG*cos» proportional to the product of the variable signal amplitude at the modulation frequency and the cantilever oscillation phase deviation cosine with regard to the reference signal. This signal comes from the Lock-IN amplifier output. 4) «Calc. Phase» - signal corresponding to the phase displacement between the cantilever oscillation phase and the reference signal. This signal is calculated by computer on the base of the MAG*sin signal and the MAG*cos signal. Any of these signals can be used for imaging. When the Phase 1 signal is used this will the image of the phase measured in angle degrees accordingly. When the MAG*cos (MAG*sin) signal is used this will the image of a signal proportional to the phase sine (cosine). These signals have the lowest noise level. It is recommended to use the Phase 1 signal for Phase Imaging, however, when it is necessary to achieve the highest possible sensitivity and resolution, we can recommend to use the signals MAG*sin or MAG*cos since they have lower noise level Preparing the unit for phase imaging (Required conditions and operations) The required condition for phase imaging is that the unit must be prepared for operation in semicontact topography (semi-contact AFM) as described in section 5 of this manual. After the unit is ready for operation in semi-contact AFM proceed with the following two operations: 1) Apply the selected signal (Phase 1 or MAG*cos or MAG*sin) to the input of measurement channel B.

145 2) Properly adjust the selected signal. Chapter 5. Semi-Contact Atomic Force Microscopy Applying a phase signal to the measurement channel input To apply a signal (for example, Phase 1): 1) Open the scanning parameters control window (Fig ) Fig Fig by pressing the button on the tool bar that is located under the Scan header and controls the scanning parameters (Fig ), then press SCAN in the header of the displayed window (Fig ). (The toolbar is located to the left of the main program window.) The scanning parameters control window can be also opened by pressing in sequence the following buttons: 1) Operation in the SPM window menu; 2) Scanning in the displayed menu and 3) SCAN in the header of the displayed window. 2) Press the signal selection button for channel B (Fig ), in the displayed menu (Fig ) and select Phase 1 (Fig ). Fig Fig Fig This will set the Phase 1 signal for the input of Channel B as it shown in Fig In a similar way, using the Dir. button set the direction of signal measuring for Channel B, as shown in Fig Phase Imaging

146 5-42 Solver P47H SPM Instruction Manual Fig If you have selected the signal MAG*sin (or MAG*cos), their setting is done in a similar fashion Adjusting the phase signal Adjustment is done with a program oscilloscope. A brief of the oscilloscope operation is given in item of this chapter (for more details see item ). Adjustment consists of two operations: 1) applying a phase signal to the program oscilloscope input, 2) setting an initial level for the phase signal. 1) Applying a phase signal to the program oscilloscope input A phase signal (Phase 1, MAG*Sin, MAG*Cos) is applied to the program oscilloscope input in two steps. This is due to the fact that these signals are not included in the main signals menu (the second button in the oscilloscope menu). However, the main signals menu provides for connection of two additional oscilloscope inputs («A» and «B»), where you can apply additional signals. The following sequence of operations must carried out to enable the phase signal (for example, Phase 1): a) Press the Opt button in the oscilloscope menu (the third button on the right, Fig ). Fig b) Select the Signal tab in the displayed menu (Fig ) and press the signal selection button (Fig ). Fig Fig This will display the signal selection menu where you need to choose one of the additional inputs, for instance, «A» (Fig ) Phase Imaging

147 Chapter 5. Semi-Contact Atomic Force Microscopy 5-43 Fig Fig c) After you select «A» the additional signal selection button will appear near the signal selection button (Fig ), pressing this button will display the additional signal selection menu (Fig ). Fig Fig After Phase 1 is selected in the additional signal menu this signal will be applied to the additional input A (Fig ) and to the oscilloscope input. The signals MAG*Sin, MAG*Cos or other signals that are not present in the main menu are connected in a similar way. You can enable (disable) the measurement of the relationship between the set up signal and time by pressing the GO button (the third button on the left in the oscilloscope menu). 2) Setting an initial level for the phase signal The initial level for the Phase 1 signal (as well as for signals MAG*Sin, MAG*Cos) can be adjusted by changing the phase of the piezodriver generator voltage (Phase parameter). To do it, open the SPM control block diagram using the button in the SPM window menu. Then press the Phase button (Fig ) and using the displayed regulator window set up the initial level for the signal Phase 1 (as well as for signals MAG*Sin, MAG*Cos) Phase Imaging

148 5-44 Solver P47H SPM Instruction Manual Fig Fig When the Phase parameter changes from 0 to 360 degrees the Phase 1 signal changes between 0 and 180 degrees. Using an oscilloscope registering the time dependence of Phase 1 it is possible to obtain a quality relationship between Phase 1 and the Phase parameter as a result of a smooth change in the Phase parameter from 0 to 360 degrees. This will result in a curve shaped approximately as shown in Fig Based on the acquired graph (Fig ) the following can be said about the initial level of the Phase 1 signal. Do not set the Phase 1 value close to the limits of the possible range i.e. close to zero and 180 degrees. In Fig these points are shown as 1 and 2. It is recommended to set up the initial level for the Phase 1 signal approximately in the middle of this signal variation range i.e. between angle degrees. Accordingly, the Phase 1 level is set by adjusting the generator voltage phase (Phase parameter). In the case of the signals MAG*Sin, MAG*Cos, set their initial level at zero by adjusting the generator voltage phase (Phase parameter) Operation in the Phase Imaging mode Phase imaging mode is similar to operation in the semi-contact topography mode. The difference is that a phase signal is additionally applied to the measurement Channel B input and adjusted. Also, two windows, A and B, are installed in the SPM window, they will display topography data and phase related signal data during scanning. If all the above preparations have been carried out you can proceed with scanning in accordance with the recommendations and instructions given section of Chapter 5 covering operation in semicontact microscopy mode (topography). To demonstrate the effectiveness of Phase Imaging in surface structure details contrasting the following picture are provided as an example. They show surface topography and phase signal images or images of phase related signal acquired for two different polymer samples. Fig shows topography and Phase 1 signal images obtained during simultaneous scanning of the surface of a polybutyleneperephtalate-polytetrametholene oxide copolymer. This polymer has a lamellar structure typical for spherulites. The topography image shows a spherulite and the phase image contains the spherulite lamellar structure where it can be seen that lamellas are perpendicular to the surface Phase Imaging

149 Chapter 5. Semi-Contact Atomic Force Microscopy 5-45 Fig Accordingly Fig shows topography and MAG*Sin signal images acquired when scanning another polymer sample surface (polyethylene oxide). In this case spherulites also have a lamellar structure. The phase signal image (MAG*Sin) also shows a lamellar structure but as opposed to the previous example lamellas are positioned at an angle to the surface. Fig Features and differences of the semi-contact mode in fluid medium For the SPM head with a fluid type holder approach to the surface should be done only in the contact mode and very carefully, as the DFL feedback signal changes very quickly when the cantilever tip touches the surface. For operation in the semi-contact mode in fluid, first it is necessary to approach the sample in the contact mode. Then turn off the feedback and after applying voltage from the generator to the piezo-transmitter Probe (using the operation software) scan the cantilever oscillation amplitude in the frequency range between 60 and khz. In the oscilloscope window you will see a curve with many resonance peaks as opposed to air operation. Select a khz wide section where the resonance peaks are higher. Scan this section. Then turn on the feedback (DFL must still be your feedback signal). Holding the Shift key press F-Scan one more time. In doing so you scan the selected range one more time, but the oscilloscope window continues to display the previous scan data Features and differences of the semi-contact mode in fluid medium

150 5-46 Solver P47H SPM Instruction Manual Compare the data from the two scans with free cantilever and with cantilever pressed against the surface. Some of the resonance peaks dropped very significantly and some went up. For operation in the semi-contact mode you can select any peak whose amplitude decreases in the pressed down condition. Select a peak whose amplitude decreases in the pressed down condition at the heaviest. Turn off the feedback again, set the selected frequency, switch the feedback signal to MAG and set the SP value somewhat higher that the current amplitude value. Turn on the feedback and decreasing the SP value switch to operation in the semi-contact mode. Stability of the feedback and the noise level are different for different peaks Keep trying. For soft cantilevers scan the amplitude in the low range 5-90 khz, make sure you press the LOW frequency filter button. Note: When moving away from the surface the MAG signal at the selected frequency can decrease and you will not be able to use this signal at the second approach. If when the MAG signal does not decrease compared to the enabled feedback level at the selected frequency when you move away from the surface, you will be able to use this signal at the second approach Features and differences of the semi-contact mode in fluid medium

151 Chapter 6. Spectroscopy mode 6-1 Chapter 6. Spectroscopy mode Contents Contents Chapter 6. Spectroscopy mode Measuring the relationship between the FB signal and the distance between the probe and the sample. Calibrating the cantilever oscillation amplitude Opening the spectroscopy mode control window Setting the measured relationship (FB(z) relationship) Selecting the measurement mode, setting the argument changing range and other parameters Selecting the measurement mode Setting the argument measurement range Minimum limit for the probe approach to the surface (limit, (na)) Setting the number of points plotted on the Z axis where the FB(z) relationship will be measured Buttons «Smooth», «Repeat», «& Back» Starting the measurement mode, saving the acquired data Viewing the spectroscopy data Calibrating the cantilever oscillation amplitude

152 6-2 Solver P47H SPM Instruction Manual Chapter 6. Spectroscopy mode SPM has a special operation mode called spectroscopy mode, in which it is possible to measure relationships between various signals/values and distances between the probe and the sample, SP value and applied voltage. In particular, in the spectroscopy mode it is possible to acquire relationship between the FB (feedback) signal and the distance between the probe and the sample FB(z). Below, we will explain in detail the operation of the unit in the spectroscopy mode by considering an example of measuring the FB(z) relationship. The operation of the unit is similar when measuring other relationships. 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample. Calibrating the cantilever oscillation amplitude In the semi-contact mode the FB signal is proportional to the cantilever oscillation amplitude. Therefore, using the measured relationship between the FB signal and the distance between the probe and the sample it is possible to calibrate the cantilever oscillation amplitude. You can measure the relationship between the FB signal and the distance between the probe and the sample after: 1) The probe is approached to the sample, 2) At least one scan has been performed. The measurement of the relationship between the FB signal and the distance between the probe and the sample (or any other relationship acquired in the spectroscopy mode) can be divided into the following sequential operations: 1) Opening the spectroscopy mode control window; 2) Setting the measured relationship (FB(z) relationship in this case); 3) Selecting the measurement mode, setting the argument measurement range and other parameters; 4) Starting the measurement mode, saving the acquired data; 5) Viewing the spectroscopy data Opening the spectroscopy mode control window The spectroscopy mode control window (spectroscopy window) can by opened by pressing Operation in the SPM window menu (Fig ) and Spectroscopy in the opened menu (Fig ), or Fig Fig Measuring the relationship between the FB signal and the distance between the probe and the sample

153 Chapter 6. Spectroscopy mode 6-3 by pressing the button located on the part of the toolbar controlling the spectroscopy mode (Fig ). This will display the spectroscopy window (Fig ). Fig Fig Setting the measured relationship (FB(z) relationship) To set the FB(z) measurement mode: a) Select (z) in the argument menu (Fig ); Fig Fig b) Set the FB signal using the function selection button (Fig ). The setting is done by pressing the button and then selecting the FBinp signal in the displayed menu of available signals (Fig ). Fig Measuring the relationship between the FB signal and the distance between the probe and the sample

154 6-4 Solver P47H SPM Instruction Manual Selecting the measurement mode, setting the argument changing range and other parameters Selecting the measurement mode Set the measurement mode in the selected point. To do it press the button measurement mode selection line (Fig ). in the Fig The selection of the above mode means that the FB(z) will be measured once in the selected point belonging to the surface area that has been scanned last. The data acquired in this case are available for viewing and saving only in the program oscilloscope window. In addition to the above there are four other possible measurement modes that can be set using buttons,, and. If you select x50 the FB(z) relationship will be measured in sequence 50 times in the same surface point. In the Line mode a series of sequential measurements of the set relationship is carried out in the surface points located on the selected line portion. In the Grid mode a series of sequential measurements of the set relationship is carried out in points the selected grid. The number of points in the grid is set using the left and right arrow buttons or corresponding mouse movements. The results of all measurements are displayed at the end of the operation in the form of a threedimensional chart where the argument is plotted on the X axis (in our case this is z) and the measurement point number is plotted on the Y axis, the color spectrum represents the signal strength, in our case this is the FB signal. In the All mode the measurement of the relationship is carried out in each point of the scan area. The results of measurements are retained in the form of a four-dimensional data array. The data are displayed as a succession of the thee-dimensional charts or as the succession of the relationships, each of which is related with the specific point of the scan area Setting the argument measurement range As mentioned above, measurement is performed after the approach is done and a working point is selected. This means that in the initial state the tracking system maintains a certain specified level of the FB signal and the probe is located at a certain distance from the surface, this distance corresponding to the specified level of the FB signal. This initial probe position relative to the surface is taken as a datum, i.e. it is considered a zero value for the argument (z) for the measured relationship of signal FB(z). Changes of the argument correspond to perpendicular movement with respect to the surface. The positive direction of axis Z corresponds to withdrawal from the sample surface. The range within which the relationship will be measured is set with regard to the datum (zero value) using two buttons that set the lower From and upper To limits of the range, accordingly (Fig. 1-9). Fig Measuring the relationship between the FB signal and the distance between the probe and the sample

155 Chapter 6. Spectroscopy mode 6-5 Note 1. In older versions of the control program the lower and upper limits of the argument measurement can be shown accordingly as «Forw» and «Back» or «Down» or «Up». In this case the buttons determining the lower and upper range limits look as shown in Figures 6.1-9A, 6.1-9B. Fig A Fig B The lower limit corresponds to the point of the range that is the closest to the surface and the upper limit corresponds to the point that is the most distant to the surface. The lower limit of the range can be changed within the range between angstroms and 0, and the upper range between 0 and angstroms. To change the lower limit of the range you need to press the appropriate button (Fig ) and set the required value in the opened controller window (Fig ). Fig Fig The upper limit of the range is changed and set in a similar way (Figures , ). Fig Fig Minimum limit for the probe approach to the surface (limit, (na)) For measurement of the FB(z) relationship the unit provides for possible limitation of the maximum cantilever deviation to prevent its damage. This limitation is provided since the situation described below might take place when measuring the FB(z) relationship. In the initial state the probe is in the initial point from where the distance is read when the relationship is being measured. The initial point is located at a certain distance from the sample surface. This distance is unknown. The value modulus of the movement range lower limit ( From value modulus) corresponds to the probe travel from the initial point to the sample surface. If the travel is set as too big it may exceed the initial distance between the probe and the surface. When the relationship is measured the scanner will start moving the cantilever towards the sample. The free end of the cantilever will travel the distance equal to the distance between the probe and the surface. Any further travel of the probe and of the free cantilever end will be limited by the sample surface. The cantilever will start bending since the scanner will continue approaching the free cantilever end and will move over a distance equal to the difference between the set travel and the initial distance between the probe and the surface. If the difference the set probe travel towards the sample (lower limit modulus) and the initial distance between the probe and the sample is too big this can result in damage to the cantilever. To avoid it the unit is provided with possible limitation of the probe travel towards the sample. In semi-contact mode the travel distance is controlled via the MAG signal value, which is proportional to the cantilever deviation. When the cantilever is approached to the surface, its oscillation amplitude is reduced and the MAG signal is reduced accordingly. 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample

156 6-6 Solver P47H SPM Instruction Manual To limit the travel set the parameter «MIN» Limit, (na) (Fig ), that sets the lower limit for the possible MAG signal range (FB signal). Fig As soon as the MAG signal is reduced to reach the set value «MIN» Limit, (na), when approaching the surface, any further approach of the probe to the sample is prohibited. To set up and enable the travel limitation based on the MAG signal do the following: 1) Turn on the small button on the left (Fig ), actually this very button enables or disables the limitation system. 2) Turn on the «MIN» button (Fig ), (if the previous operation has not been carried out the MIN and MAX buttons are not active). Fig Fig ) Set the required value for the parameter «MIN» Limit, (na). The value of the parameter «MIN» Limit, (na) (minimum possible MAG signal value) is set by the indicator button located to the right of Limit, (na) (Fig ). Pressing this button will display the controller window (Fig ), where you can set the minimum value for the MAG signal. Fig Fig For proper operation of the limitation system the MIN parameter value must be above zero and lower than the SP parameter. It is recommended to set it within an approximate range of +0.5 na +1 na Setting the number of points plotted on the Z axis where the FB(z) relationship will be measured The number of points plotted on the Z axis where the FB(z) relationship will be measured is set using the button. To change the number of points press this button (Fig ) and set the required value in the opened controller window (Fig ). Fig Fig The button is used to set the number of the FB(z) value measurements in every argument point. After carrying out the required number of measurements the measured value is averaged and the resulting average value is considered to be the FB(z) value for this argument point (z). To change the number of measurements press the button (Fig ) and set the required value in the opened controller window (Fig ). 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample

157 Chapter 6. Spectroscopy mode 6-7 Fig Fig The number of measurements can be changed within the range from 1 to Buttons «Smooth», «Repeat», «& Back» These buttons (Fig ) turn on and off the following: «Smooth» - smoothing the resulting curve based on three points; «Repeat» - in this mode relationship measurement is repeated until it is stopped by pressing the Esc key; «& Back» - relationship measurement mode in the forward (withdrawing from the sample) and reverse directions, this results in two curves. Fig In Fig the buttons are shown in their enabled positions Starting the measurement mode, saving the acquired data To start the measurement mode press the RUN button located in the bottom line of the spectroscopy window (Fig ), or the RUN button located on the part of the toolbar controlling the spectroscopy mode (Fig ). Fig Fig After that the SPM window displays the image of the last scan. In place of the SPM window menu there appears a line displaying the coordinates of point where the cursor is located (Fig ). Fig Moving the cursor within the scan image you can select any point where it is intended to measure the FB(z) relationship. 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample

158 6-8 Solver P47H SPM Instruction Manual The measurement process is started by pressing the left mouse button, the cursor disappears for the time of measurement. The cursor appears again after the measurement is complete, the point where the relationship has been measured is marked (Fig ), the program oscilloscope EXT displays the measured FB(z) relationship (Fig ). Fig Fig The relationship is measured as follows. The probe is moved from its initial position to a point corresponding to the upper range limit i.e. the furthest point from the surface. Then the relationship is measured starting from this point by approaching the probe to the surface step by step and measuring the signal value in each point. Accordingly, the step size depends on the range (difference between the upper and the lower limits) and the set number of points. If the protection system is enabled and if the signal value decreases below the set limit the approaching stops and the probe is returned in the initial position. If the & Back button is enabled the relationship is measured also during the return pass of the probe i.e. during its withdrawal from the surface. In this case the probe is moved to the upper limit point and then is returned to its initial position. To save the measured FB(z) relationship press the PUT button (Fig ). Fig In this case the spectroscopy data are added to the random-access memory to the data of previously taken images, they will be saved with them when the saving is performed. Then you can repeat the relationship measurement process in other points, don t forget press the PUT button after each measurement to save the acquired data. The measurement process described above covers the one point measurement mode. In the other modes the measurement process and saving are carried out in a similar way. The differences are that, for example, in the Line mode you need to set the initial and the final points of a line portion where points will be subjected to a series of sequential measurements. In the Grid mode you need to set the number of points in the grid. Similarly, after completing the measurement process you need to add the acquired spectroscopy data to the main data array using the PUT button to save them. 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample

159 Chapter 6. Spectroscopy mode In addition to that, in these cases (Line, Grid) the data are plotted in a separate image in the form of a three-dimensional chart, where the argument is plotted on the X curve (in our case it is z), the measurement point number is plotted on the Y axis, the color spectrum or color density represent the signal strength (Fig ). 6-9 Fig The FB(z) relationship displayed in the EXT oscilloscope window can be also saved in a *.dat or *.os file. To do it press the Fil button in the EXT oscilloscope menu (Fig ), Fig Fig in the opened menu press the Save button (Fig ) and save as a file Fig Fig with *.os extension (Fig ) or in ASCII format as a file with *.dat extension (Fig ). You can select the file format by pressing the Opt button in the oscilloscope menu (Fig ), then select File (Fig ) and specify the appropriate format by enabling *.os or *.dat ( Fig ). Fig Fig Fig Measuring the relationship between the FB signal and the distance between the probe and the sample

160 6-10 Solver P47H SPM Instruction Manual Viewing the spectroscopy data To view the spectroscopy data open the spectroscopy window (Fig ) and press the Look button located in the bottom line of the window (Fig ). Fig This will display in SPM window the Spectroscopy data view menu in place of the control line (Fig ). Fig When you press the View button the cursor automatically moves to the initial point on the surface scan image where the FB(z) was measured, at the same time the EXT oscilloscope window displays the relationship corresponding to this point (Fig ). Fig If the one point measurement mode was used to acquire the spectroscopy data, use the «>>» button to view the relationship measured in the next single point (if it exists). Accordingly, to move to the previous point use the «<<» button. If the spectroscopy data were acquired in the mode of measuring a series of relationships along a specified line portion (Line mode) or in points of a specified grid (Grid mode), the cursor can be sequentially moved over surface points where measurement was done moving the mouse in the horizontal direction or using the left and right arrow buttons. For every point where measurement was done the EXT oscilloscope window will display the relationship corresponding to this point. When the Spec button is pressed the SPM window displays, instead of a scan image, the spectroscopy data array in the form of a three-dimensional chart, where the argument is plotted on the X curve, the measurement point number is plotted on the Y axis, the color spectrum or color density represent the signal strength (Fig ). Fig Measuring the relationship between the FB signal and the distance between the probe and the sample

161 Chapter 6. Spectroscopy mode 6-11 In this case the View and All buttons operate in a similar, the only difference being that the cursor moves the image of spectroscopy data Calibrating the cantilever oscillation amplitude The FB signal is a signal proportional to the cantilever mechanical oscillation amplitude. If the signal is calibrated, i.e. the proportionality factor between the oscillation amplitude and the FB signal is found, it will be possible to know the real value of the cantilever oscillation amplitude. The FB signal can be calibrated based on the relationship between the FB signal and distance between the probe and the sample surface. The possibility of calibration is based on the following assumption. In the semi-contact mode the probe already starts knocking on the sample surface, when the probe is further approached to the surface the oscillation amplitude becomes limited. It is assumed that the value of the oscillation amplitude decrease is equal to the travel of the probe to the surface ( z): amplitude = z (1) This assumption is true if the system Q-factor is sufficiently high and if the sample is absolutely solid. FB signal calibrating example Suppose the FB signal relationship has been measured and it is displayed in the window of the program EXT oscilloscope (Fig ). Fig Fig Press the long narrow button located along the right border of the oscilloscope window (Fig ). This will display a data field to the right of the oscilloscope (Fig ). The short narrow button located under the long narrow button controls the width of the data field (Fig ). Turn on the mode of viewing the coordinates of the FB(z) curve points by pressing the View button in the oscilloscope menu (Fig ). Fig The cursor moves along the FB(z) curve, the menu appearing in the top of the oscilloscope window displays the point coordinates, Y corresponds to function, i.e. FB(z) and X corresponds to the argument i.e. z (Fig ). 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample

162 6-12 Solver P47H SPM Instruction Manual Fig Fig Choose a point on the curve from a portion corresponding to the semi-contact mode, press the left mouse button, this will mark the selected point (Fig ). In the same way select and mark the second point (Fig ). The data field displays the values X and Y that correspond to the change in argument ( z) and change in a function ( FB(z)) between the selected points (Fig ). Fig The proportionality factor linking the cantilever (probe) mechanical oscillation amplitude and feedback signal as the following relationship: K= z / FB(z) = X / Y (2) Accordingly, the probe mechanical oscillation amplitude will be determined from the relationship: Amplitude [Å] =K * (FB signal[na]) (3) In the case of our example X = 81.3 Å, Y= 1.83 na, therefore K=81.3/1.83=44.4 [Å/ na]. Accordingly, the probe mechanical oscillation amplitude will be determined from the relationship: Amplitude [Å] = 44.4* (FB signal [na]). If you set the resulting value of the K factor in the FB signal indicator, the latter will be displaying the absolute value of the cantilever oscillation amplitude in angstroms when operating in the oscillation amplitude indication mode (item 5.1.4). 6.1 Measuring the relationship between the FB signal and the distance between the probe and the sample

163 Chapter 7. Multi-pass operation mode of the unit 7-1 Chapter 7. Multi-pass operation mode of the unit Contents Contents Chapter 7. Multi-pass operation mode of the unit About Multi-pass operation mode Adjustment and control in Multi-pass operation mode States of the unit and switching between them in SPM control block diagram Multi-pass Mode Menu Multi-pass Mode Setup Measurement Channels Control Block diagram, Signal and Dir buttons How to activate the Single-pass mode? Special cases in Single-pass mode How to activate Multi-pass mode of the unit?

164 7-2 Solver P47H SPM Instruction Manual Chapter 7. Multi-pass operation mode of the unit This section addresses general issues of multi-pass operation mode structure and organization in the unit as well as possibilities to implement multi-pass techniques on its basis. 7.1 About Multi-pass operation mode One of the unit s important features is its possibility to operate in Multi-pass mode. Electronic hardware and software of the unit provide for high flexibility and allows setting up various configurations of double, triple and four-pass techniques. For instance, the unit supports traditional double-pass techniques using the double-pass mode, such as Magnetic Force Microscopy, Electrostatic Force Microscopy, Surface Potential Microscopy, Scanning Capacitance Microscopy. In the ordinary single-pass mode topography or any other value is acquired as a result of line-by-line scanning of the sample surface within certain specified scanning parameters. In the Multi-pass mode each line is scanned a specified number of times: twice in double-pass mode, three times in triple-pass mode etc. Please note an important detail each type of scanning is associated with certain scanning parameters and conditions that can be different for various passes. Our unit supports in Multi-pass mode the following: 1) Multiple scanning of each line (from one to four times depending upon the specified setting); 2) Measurement of various values and signals at each scanning; 3) Each line scanning can be done in various scanning modes (contact, semi-contact, non-contact), under various scanning conditions and parameters; 4) Topography data measured at the first pass can be taken into account and furthermore the probe movement at each following pass will be done at a specified height taking into account topography measured at the first pass. The simplest type of multi-pass mode is the double-pass one. As an example, we will consider two different schemes of double-pass techniques based on double-pass mode of the unit operation. In the double-pass mode each line is scanned twice. We will consider the following scheme as a possible double-pass technique scheme. For instance, at the first pass each line topography is measured in the contact mode, at the second pass it is possible to measure a different signal (different value). This can be the DFL signal, which is proportional to the force acting upon the cantilever. Additionally, the surface relief measured at the first pass can be taken into account. The second pass can be done with disabled feedback. The probe can be maintained at a specified constant height with respect to each local surface point. Two images can be obtained as a result of scanning: topography image and image of the signal proportional to the force acting upon the probe at a certain fixed distance from the surface. If the surface has magnetic properties and the probe is magnetic, the DFL signal image will correspond to the image of magnetic force acting upon the probe at a certain fixed distance from the surface. Here is a second example of a possible double-pass technique scheme based on double-pass operation mode. At the first pass of each line topography can be measured in semi-contact mode, the second pass can be used to measure the phase signal. Also, as in the previous example, the scanning at the second pass can be done with disabled feedback at a specified constant height with respect to each local surface point taking into account the surface relief measured at the first pass. In this case the scanning will give you a topography image and a phase signal image acquired under constant height (relative to the surface) probe scanning conditions. If the surface has magnetic properties and the probe is magnetic, the phase signal image will correspond to the image of the resulting magnetic force acting upon the probe at a certain fixed distance from the surface. Accordingly, you can also config. other double-pass schemes based on the double-pass mode. In our unit you can config. also triple and four-pass operation modes. This means that each line will be scanned three times (in case of triple-pass mode) or four times (in case of four-pass mode). Each pass is used to measure a certain value under certain conditions. Topography data measured at the first pass (if the first pass has been used to measure topography) can be taken into account at the following passes. In our unit regular single-pass mode can be considered as a particular case of multi-pass mode where the number of each line scanning passes has been set up equal to one. 7.1 About Multi-pass operation mode

165 Chapter 7. Multi-pass operation mode of the unit 7.2 Adjustment and control in Multi-pass operation mode Adjust and control in multi-pass operation mode is done using 1) the SPM control block diagram; 2) the Multi-pass mode menu and 3) measurement channels menu States of the unit and switching between them in SPM control block diagram The unit can be configured for four various states. In each given moment the unit can be in one of these four states. The main state is the first state. At the software loading the first state is activated by default. A certain setting of the unit corresponds to a certain state: a certain operation mode (contact, semi-contact, non-contact), probe and sample interaction parameters, feedback loops, scanning parameters, measurement channels parameters, parameters of amplifiers and other elements in the unit. The SPM control block diagram (Fig ) contains four state selection buttons (Fig ), numbered accordingly as 1, 2, 3 and 4. By default, Button «1» is the «On» position when the program is loaded. This means that the unit is in the first state and all SPM control block diagram parameters correspond to this first state. The first state parameters are normally used for single-pass operation, however, any other state can be also used for single-pass operation. If the «2» button is activated the unit will switch into the second state with a set of parameters corresponding to the second state. This second state of parameters can be either different from or equal to the first state parameters. 7-3 Fig Fig Similarly, when buttons «3» and «4» are pressed the unit will be switched into the third and fourth state. Accordingly, the user can change and define the required parameter values for various states. If any of the setup parameters have been changed in any of the states and you want to save the changes, this can be done by saving the setup configuration parameters either in the main parameter file smena.opt, or in another *.opt file. Each time the program is started it loads the setup configuration parameters saved in the file smena.opt. If it is necessary to use a configuration saved in different *.opt file you need to load the appropriate file containing the required setup configuration parameters. 7.2 Adjustment and control in Multi-pass operation mode

166 7-4 Solver P47H SPM Instruction Manual The possibility of quick and easy switching between any of the four available states by simply pressing an appropriate state button facilitates the operation of the unit even in the ordinary singlepass mode. In other words, if the unit is set up in the regular single-pass mode you can switch it into any of the four states by pressing an appropriate button and operate in the single-pass mode using the setup parameters corresponding to this state. For instance, if in the first state the unit is set up for operation in contact mode, you can switch from semi-contact to contact mode by simply pressing button «2» and continue operation in contact mode Multi-pass Mode Menu In order to open the multi-pass mode menu press the Operation button in the SPM window and choose Scanning in the displayed Scanning window, then press tab = = =>. This will display the multi-pass mode menu (Fig ). Fig Fig The multi-pass mode menu actually represents a short protocol of the setup parameters condition in the SPM control block diagram. The buttons in this menu allow changing appropriate parameters and the scheme condition. The bottom part of the menu (Fig ) contains the state selection line (Fig ), the buttons of which (buttons «1-st PASS», «2-nd PASS», «3-rd PASS», «4-th PASS») are completely identical to the state selection buttons in the SPM control block diagram (buttons «1», «2», «3», «4»). If a state selection button is activated in the SPM control block diagram, for example, «2», its corresponding button, i.e. «2-nd PASS» will be automatically activated in the state selection line. And vice versa, if a state selection button is activated in the state selection line, its corresponding button will be automatically activated in the SPM control block diagram. There is a button «=1st» in the state selection line that is identical with a similar button in the SPM control block diagram. This button can be used to set up parameters for the second, third and fourth states equal to the first state parameters. To do it you need to press first the appropriate state button in the state selection line or in the SPM control block diagram and then press «=1st». 7.2 Adjustment and control in Multi-pass operation mode

167 Chapter 7. Multi-pass operation mode of the unit In addition to the buttons with the same functions as the SPM control block diagram buttons the multi-pass menu has a number of additional buttons, which are not present in the SPM control block diagram. In particular the indicator button «Z». This button is used when it is necessary to scan at subsequent passes at a specified given height with respect to the surface. In such cases this button is used to specify the probe vertical displacement value with respect to the first pass taking into account the surface relief measured during the first scanning Multi-pass Mode Setup Measurement Channels Control Block diagram, Signal and Dir buttons The required multi-pass mode configuration is set up in the measurement channels control block diagram (Fig ), which is located in the scanning parameters control window (Fig ). 7-5 Fig Fig The unit has four measurement channels A, B, C and D, each of them can have a certain signal applied to it and scanning will result into applied signals image data generation. Each channel is provided with two indicator buttons in the Measurement Channels control block diagram (Fig ): «Signal» and «Dir». The Signal button is used to apply certain signals to the appropriate channel inputs. Channel A is a dedicated channel with respect to the other channels. First, a signal is always applied to this channel input. Second, Channel A is used to specify the scanning direction. The scanning direction is specified using the Dir button of this channel. The signal reading direction specified for this channel matches the scanning direction. Actions and functions of the Dir button in Channels B, C and D differ from action and functions of the corresponding button in Channel A. First, the Dir buttons in these channels (channels B, C and D) are activated only if a signal is applied to the channel input. If the channel is disabled i.e. the Signal button of this channel is in the Off position, the setting in the Dir button does not mean anything since this channel Dir button is not activated. 7.2 Adjustment and control in Multi-pass operation mode

168 7-6 Solver P47H SPM Instruction Manual Second, Dir buttons for channels B, C and D are used to specify the signal reading direction in these channels (with respect to channel A). Third, the Dir buttons for channels B, C and D are to specify the scanning mode type: single-pass or multi-pass How to activate the Single-pass mode? If none of the Dir buttons for channels B, C, D is set in a position with a double arrow, the unit is in the single-pass mode. This would be the case when the activated Dir buttons for channels B, C, D are in single arrow positions or when channels B, C, D are disabled. In the single-pass mode scanning results into reading in channel A the signal specified for this channel. Please note that a signal will be always read in channel A as this channel is always activated as opposed to channels B, C, D that can be enabled or disabled. In the single-pass mode scanning is done within parameters of the state activated in the SPM control block diagram. For instance, if Button 1 (Fig ) is activated, scanning will be performed within the setup parameters corresponding to State 1. Accordingly, if Button 2 is activated (Fig ), scanning will be done within the setup parameters corresponding to State 2; if Button 3 is activated (Fig ), within the setup parameters corresponding to State 3; if Button 4 is activated (Fig ), within the setup parameters corresponding to State 4. Fig Fig Fig Fig If you use any combinations of the states with a single arrow displayed in Buttons Dir for channels B, C, D scanning will be performed within the setup parameters corresponding to the activated state (button number activated in the SPM control block diagram). Each line scanning consists of two parts: forward movement and backward movement. Accordingly, signals can be measured both during the forward movement and backward movement. The signal reading direction is indicated by arrows in the Dir buttons for channels B, C, D. There are two AD converters used for signal reading. The first AD converter supports channels A and C, the second AD converter supports channels B and D, accordingly. In case of movement in one direction (forward or backward) it is possible to read only two signals simultaneously. Channel A is a dedicated one and the scanning and reading directions in it always match (i.e. reading in this channel is always done in the forward scanning direction). Therefore, simultaneous reading in the forward direction is possible either in channels A and B or A and D. Accordingly, in the backward direction reading can be done either in channels C and D or C and B. 7.2 Adjustment and control in Multi-pass operation mode

169 Chapter 7. Multi-pass operation mode of the unit Special cases in Single-pass mode There are several special cases when the unit is in the single-pass mode (i.e. when no «double arrow» states are displayed in activated Dir buttons for channels B, C, D), and still it has to make two passes when scanning each line, i.e. operate as in the multi-pass mode. However, the second pass scanning is done within the same parameters as the first pass. The presence of special cases is due to the fact that it is possible to specify the same signal reading directions for 2 channels supported by the same AD converter - for instance, for channels A and C, as it is shown in Fig or for channels B and D, as it is shown in Fig The unit cannot read signals in those channels simultaneously with the same AD converter. This problem can be resolved with a second scanning pass. In this case, for channels A and C the channel A signal is read during the first pass scanning and the channel C signal is read at the second pass scanning. Channels B and D will be handled in a similar way. 7-7 Fig Fig How to activate Multi-pass mode of the unit? If at least one of the activated Dir buttons for channels B, C and D is in a position displaying a double line arrow (for instance, «= =2=>» or «<= 2==»), the unit switches over to the multi-pass mode. In this case the first pass will be always used to measure the signal specified for Channel A, the scanning mode and the scanning parameters will correspond to state 1 of the unit setup parameters. The state activated in the SPM control block diagram (what button is activated in the SPM control block diagram) has no meaning at all. The second pass will measure the signal in the channel where the Dir button is set in the position displaying a double arrow. The scanning in this case will be done in the mode and within the scanning parameters corresponding to the activated state (number displayed on the double arrow). Channels are prioritized as follows: B, C, D. That means that if the double arrow is displayed in the Dir buttons for channels B, C, D and all channels are activated, the second pass will measure the signal in channel B, the third will measure the signal in channel C and the fourth in channel D. If double arrows are displayed in activated buttons for channels C and D, the second pass will measure the signal in channel C, the third will measure the signal in channel D. The following should be said regarding the number displayed on the double arrow. The number on the double arrow does not indicate the pass number but the state number of the unit parameters setting within which the scanning corresponding to this pass will be done. The direction of the double arrow indicates the signal reading direction with regard to the first pass. If the arrow goes from left to right (= = =>), reading will be done in the same direction (i.e. as the forward direction of this pass), if the arrow goes from right to left (< = ==), the signal will be read during the backward movement of this pass. However, it is not recommended to measure the signal during the backward movement (< = ==) immediately after topography measurement as the unit may not have had enough time to switch to other parameters. 7.2 Adjustment and control in Multi-pass operation mode

170 7-8 Solver P47H SPM Instruction Manual To make it clear let us consider several examples corresponding to various configurations of the multi-pass mode. Example 1 (Fig ) Fig The settings in this example are as follows: Channel A: «Signal»= «Height», «Dir»= «+X+». This channel will be used to measure height, the specified fast scanning direction is the positive direction along axis X, slow scanning will be done along axis Y in the positive direction, accordingly. You can set any other available scanning direction. The signal reading directions in the other channels will set up with regard to this scanning direction specified for Channel A. Channel B: «Signal»= «Phase 1», «Dir» = «= =2=>». This means that Channel B will be active at the second pass of the probe and this channel will be used to measure the Phase 1 signal. The second pass of the probe will be done within the unit setting parameters specified for state 2. The Phase 1 signal reading direction is determined by the double arrow direction «= =2=>» and it will be the same as at the first pass. If you reverse the direction of the double arrow «<= 2==», the signal will be read during the backward movement of the probe (with regard to the first pass). Channel C: «Signal»= «DFL», «Dir» = «= =3=>». This means that Channel C will be active at the third pass of the probe. This channel will be used to measure the DFL signal. The third pass of the probe will be done within the unit setting parameters specified for state 3. Similarly to the previous channel, the DFL signal reading direction is determined by the double arrow direction «= =3=>» and it will be the same as at the first pass. If you reverse the direction of the double arrow «<= 3==», the signal will be read during the backward movement of the probe (with regard to the first pass). Channel D: «Signal»= «Off». This means that this channel is disabled. If a channel is disabled, the indication displayed in the Dir button has no meaning. Example 2 (Fig ) Fig Adjustment and control in Multi-pass operation mode

171 Chapter 7. Multi-pass operation mode of the unit Signal Height is applied to the input of Channel A. Channels B, C, D are disabled. Although the Dir buttons for channels B, C, D are set in positions corresponding to the multi-passage mode (= =2=>, = =3=> and = =4=>), the unit will operate in the single-pass mode. Reason being that the Dir button is activated only if a signal is applied to the channel input. Example 3 (Fig ) 7-9 Fig Channel A: «Signal»= «Height» - height measurement; «Dir»= «+X+», i.e. the specified fast scanning direction is the positive direction along axis X, slow scanning will be done along axis Y in the positive direction, accordingly. Channel B: «Signal»= «Off». This means that this channel is disabled and the indication displayed in the Dir button has no meaning. Channel C: «Signal»= «DFL», «Dir» = «= =3=>». This means that Channel C will be active at the second pass of the probe. This channel will be used to measure the DFL signal. The second pass of the probe will be done within the unit setting parameters specified for state 3. The DFL signal reading direction is determined by the double arrow direction «= =3=>» and it will be the same as at the first pass. Channel D: «Signal»= «Off». This means that this channel is disabled and the indication displayed in the Dir button has no meaning. 7.2 Adjustment and control in Multi-pass operation mode