STANDARD OPERATING PROCEDURE: ASYLUM MFP-3D AFM

Transcription

1 STANDARD OPERATING PROCEDURE: ASYLUM MFP-3D AFM Purpose of this Instrument: To obtain 3D surface topography at sub-nanometer scale resolution, measure contact and friction forces between surfaces in contact, measure sample conductivity and magnetic property in nano-scale region and image samples in liquid environment. Location: White Hall Room B-20B Primary Staff Contact: Dr. Weiqiang Ding Office: ESB G75D (cell) The Shared Research Facilities are operated for the benefit of all researchers. If you encounter any problems with this piece of equipment, please contact the staff member listed above immediately. There is never a penalty for asking questions. If the equipment is not behaving exactly the way it should, contact a staff member. WARNING: Directly looking into the laser beam can cause permanent eye damage or blindness. Always use a piece of paper if you want to view the beam image. NOTE: The purpose of this manual is for general measurements with the AFM. For more advanced measurements or measurements with accessories, please contact MFCF staff members or refer to the Asylum MPF-3D operation manual, which is located on the computer workbench. START UP 1. Log in your session on the FOM. Sign in on the logbook located on the corner bench. 2. Check the AFM controller box (Figure 1) at the bottom of the computer cart to ensure that it is powered up (the green LED above the Power switch is ON). 3. Open the right side door of the AFM enclosure box. Power up the Herzan TS-150 isolation table under the AFM. Press E button to enable the vibration isolation. Figure 1. AFM controller front panel [1]. 1

2 4. Open the MFP-3D software by clicking on the Stable Asylum Research MFP3D icon on the computer desktop. Wait until MFP-3D Ready is shown at the bottom of the MFP-3D software tray (Figure 2). 5. In the Master Panel, click on the Main tab and check the Imaging Mode at lower section of the tab. Select AC Mode (tapping mode) if it is not already shown. Contact a SRF staff if you need help on other operation modes. Figure 2. MFP-3D software tray PROBE MOUNTING 1. Find the tip holder assembly on the loading pedestal (Figure 3a,b) and go to step 4. Otherwise, go to next step. (a) (b) (c) Figure 3. (a) AFM tip holder assembly; (b) holder assembly in the loading pedestal; (c) Removing tip holder assembly from AFM head [1]. 2. If you could not find holder assembly on the loading pedestal, it should be attached to the AFM head. Remove the AFM head from the sample stage and lay it upside down next to the sample stage (Do not stretch the cable attached to the AFM head). 3. Remove the tip holder assembly from the AFM head by pressing the round button on the side (Figure 3c) and mount it into the loading pedestal apparatus (Figure 4A). 4. Loosen the clamp screw (the middle one, Figure 4B) with a screwdriver. 5. Check the AFM probe against the light to ensure that the cantilever is not damaged. 2

3 6. Slide the AFM probe under the tongue clamp (Figure 4B). You may need to gently lift the tongue clamp with a pair of sharp tweezers to accommodate thicker probe chips. 7. Position the probe to the center of the clear trapezoidal shaped quartz optical window (Figure 4C). 8. Tighten the clamp screw with the screwdriver until finger tight. Do NOT over tighten the screw (Figure 4E). 9. Remove the tip holder assembly from the loading apparatus and put it back into the MFP-3D head (Figure 3c). Figure 4. Proper probe loading procedure [2]. LASER ALIGNMENT 1. Flip the AFM head to its normal position and settle it on the table surface. NOTE: do not stretch or twist the cable. 2. Turn on the laser by turning the key on the front of the AFM controller 90 o clockwise to ON position (Figure 1). 2. Place the Newport infrared sensor card under the tip holder. You should see a laser spot on the card if the laser is not being blocked by anything. 3. If you can t see the laser spot, turn the thumbwheel on the right side of the AF head (labeled LDX, Figure 5) counter clockwise to move the laser spot outward along the cantilever length until the 3

4 spot appears. If no spot can be seen on the IR card, charge the IR card for a few seconds under the fluorescent light. Figure 5. AFM head with various alignment thumbwheels labeled [2]. 4. Turn the laser adjustment thumbwheel on the right side (labeled LDX, Figure 5) clockwise until the laser spot disappears (moves back onto the AFM chip) (Figure 6 step #1). Note that the laser spot will also not be visible on the IR card if it is outside the transparent quartz window. 5. Turn the LDX thumbwheel counter clockwise until the laser spot re-appear (Figure 6 step #2). 6. Turn the laser adjustment thumbwheel on the back side of the AFM head (labeled LDY, Figure 6) (Figure 6 step #3) while monitoring the laser spot on the IR card. The laser spot intensity will be temporarily reduced when it crosses the cantilever beam and the SUM reading on the Signal and Deflection Meter (Figure 7) will increase significantly. Reverse the direction if the laser spot completely disappears (goes beyond the transparent window). NOTE: Keep turning the thumbwheel forward beyond the limit will damage the LDY thumbwheel. 7. Maximize the SUM reading by adjusting both LDX and LDY thumbwheels (Figure 6 step #4). Figure 6. Laser alignment pattern [2]. 4

5 PHOTODECTOR (PD) ALIGNMENT 1. Check the Deflection voltage signal in the Signal and Deflection (S&D) meter (Figure 7). It may show Red (positive) or Blue (negative) if the voltage is not zero. 2. If the Deflection value is negative (blue), turn the PD adjustment thumbwheel (Figure 5) counter clock-wise (CCW) to get to around 0 V. If the Deflection value is red (positive), turn the PD thumbwheel clockwise (CW) to get around 0 V. Figure 7. Signal and Deflection meter [2]. SAMPLE MOUNTING 1. Attach your sample to a piece of glass slide with sticky tab, super glue, epoxy or vacuum grease. Contact MFCF staff if you need to measure in fluids. 2. Mount the sample slide at the center of the sample stage. 3. Secure the sample slide to the stage with the two small magnet blocks on both sides (Figure 8). Figure 8. Sample stage and sample positioning [1]. AFM HEAD MOUNTING 1. Lift the AFM head with two hands. Place the two back legs into the divots on the AFM baseplates first (Figure 9A). 5

6 Figure 9. Mount the AFM head onto the base plate [2]. 2. Move thumbs under the front of the AFM head (Figure 9B). Slowly lower the AFM head down towards the stage while continually monitoring the tip-sample separation to avoid tip crash (Figure 9B). 3. If the tip appears to crash to sample, lift the head back and adjust the front leg height to increase the tip-sample separation. Repeat the process. 4. Adjust sample position with respect to the cantilever tip with the adjustment knobs on the right side of the base plate (Figure 8). 5. Power up the Herzan active vibration isolation system under the AFM stage. ALIGNMENT CHECK WITH VIDEO CAMERA 1. Turn on the light source for the video camera. The black switch knob is located on the right corner of the AFM computer cart. 2. Load the video camera window by clicking the camera icon at the bottom of the AFM software window. Select the S-video input in the Source pull-down menu in the video window. 3. Adjust the image brightness with the light source switch knob. 4. Adjust the two camera translation knobs at the back of the AFM head (Figure 5) to position the AFM cantilever probe in the middle of the video screen. 5. Focus the camera on the cantilever probe with the camera focus ring (Figure 5) at the back of the AFM head. Turn the ring clockwise to focus down and counter-clockwise to focus up. 6. Check and ensure that the laser spot is positioned on the cantilever beam. If not, adjust the LDX, LDY laser positioning thumbwheels to position the laser spot onto the cantilever beam and maximize the SUM reading. 7. Adjust the focus ring clockwise to focus on the sample surface. 8. Find the area of interest on sample surface by adjusting the scanner adjustment knobs on the right side of the sample stage (Figure 8). 9. Position the area of interest under the AFM probe. 6

7 FRQUENCY TUNING IN AC (TAPPING) MODE 1. In software program Master Panel, select the Tune tab (Figure 10). 2. Set Target Amplitude to 1.0 V. 3. Set Target Percent to 5.0 %. 4. The default auto tune frequency range (50 khz to 400 khz) covers most drive frequencies of common cantilevers. Adjust the frequency range if the expected cantilever resonance frequency is out of the range. 5. Click on Auto Tune button to start the frequency sweep. 6. A frequency/phase response curve will show up if auto tune finishes successfully (Figure 11a). The Drive Frequency will be automatically updated in the Master Panel. 7. Check the S&D meter reading (Figure 11b). The Amplitude value should be close to the set Target Amplitude of 1.0 V. (a) Figure 10. Auto tune tab [2]. (b) Figure 11. (a) Cantilever frequency auto tune result. (b) S&D meter after auto tune (before tip engagement) [2]. 8. If you encounter Auto Tune failure, the laser may not be properly aligned. Repeat the laser alignment process. 7

8 PROBE ENGAGEMENT There are two ways to engage the tip to sample surface: Hard Engage and Soft Engage. The hard engage is quick but may result in minor tip wear. In soft engage, the tip engages at the lowest force possible and is suite able for expensive, super sharp tip or functionalized tip. Figure 12. A qualitative conceptual amplitude voltage vs. distance for AC mode imaging [2]. HARD ENGAGEMENT 1. Click the Main tab in Master Panel (Figure 13). 2. Select a Set Point voltage that is around 20% off the free air amplitude voltage. (E.g., if the free air amplitude is 1.0 V, the Set Point voltage should be 0.8 V). 3. Choose an Integral Gain of 8 to Choose a Scan Rate of 1 Hz. 5. Click the Engage button on the S&D meter (Figure 11b). Monitor the Z Voltage reading, which should be 150 V. Figure 13. Main tab in Master 6. Slowly turn the thumbwheel on the front of the AFM head Control for scan parameters [2]. counterclockwise to lower the tip towards sample surface. When the Amplitude Voltage decrease to the selected Set Point voltage, there is a concomitant chime sound (if the speaker is on). 7. Further turn the thumbwheel and monitor the Z Voltage, which should decrease. Stop when the Z Voltage drops to 70V. 8. The AFM tip is now stationary on the surface (not scanning). SOFT ENGAGEMENT 1. Select a Set Point voltage that is around 5% off the free air amplitude voltage. (E.g., if the free air amplitude is 1.0V, the Set Point voltage should be 0.95 V). 8

9 2. Click Engage button on the S&D meter (Figure 11b). 3. Slowly turn the thumbwheel on the front of the AFM counterclockwise to lower the tip towards sample surface while monitoring the amplitude voltage on S&D meter. Stop when the amplitude voltage equals the Set Point voltage. 4. Further turn the thumbwheel to set the Z Voltage to 30-50V (halfway blue). 5. Activate the radio label for the Set Point voltage on the Main tab (See Figure 13). 6. Slowly turn the big Hamster wheel on the front of the controller (Figure 1) to increase the force (i.e., decrease the Set Point value). The Z voltage will move to more positive voltage value (more red). Continue turning the wheel until you notice that Z voltage will no longer move to more positive value. At this point, the tip is engaged on the surface at the lowest possible Set Point force. 7. The AFM tip is now stationary on the surface (not scanning). SCANNING 1. Click the Do Scan button, or Frame up or Frame Down button on the Main tab of the Mater Panel to start scanning (Figure 13). 2. Set proper channel for image observation: Ht (Height) Am (Amplitude), Ph (Phase), ZS (Z sensor). 3. Check the Trace and Retrace fast scan lines below each image channel to see if they follow each other well. 4. If you use the Soft Engage, decrease the Set Point voltage value to increase the force applied to the sample. NOTE: Do not set the Set Point voltage lower than 50% of the free air amplitude voltage. 5. Slightly increase the Drive Amplitude in the Main tab and monitor the improvement. 6. Adjust the Integral Gain in the Main tab to better track the surface. Increase the Integral Gain until high frequency noise shows up in the trace/retrace lines. Decrease the Integral Gain until the noise disappears. 7. Select a proper Scan Rate for image acquisition. After adjusting the Scan Rate, click Frame Up or Frame Down buttons to initiate the newly entered scan rate. SAVING IMAGES 1. Select proper Scan Points and Scan Lines in the Main tab of the Master Panel. Use 128x128 or 256x256 for rough scan, 512x512 for data acquisition. 2. Adjust Image Z scale: Click Auto check box in top left corner of the image channel tabs. Click the Fix button on the left of the Data Scale section. 3. Select Real Time Flattening by choose the Line or Masked Line in the Live Flatten pull-down menu. 9

10 4. Give a proper filename for you image in the Base Name section at the bottom of the Master Panel. 5. Click the Save Images checkbox. Use Browse to choose an image folder. 6. Check the Save Status section to see if it will save current scan. 7. If you want to save a screen shot of one of the windows, you can make it the front window, and go to menu File -> save Graphics Select the desirable format and size. IMAGE ANALYSIS 1. In top menu, select AFM Analysis > Browse Saved Data to locate the saved images. 2. Open the chosen image file by placing the cursor over the image thumbnail and double clicking the mouse button. The image will open in the Display Window. Flattening/PlaneFit 1. Click the M button on the upper right corner of the image display window to open the Modify Panel. 2. Select the Flatten Tab (Figure 14). Set a Flatten Order to 0 in the pull-down menu, and select the All radio button underneath. 3. Click the Flatten button and the image will be flattened. 4. Select the Planefit Tab (Figure 14). 5. Set the Planefit Order to 1 in the pull-down menu. Select the All radio button. 6. Click the XY button to planefit the image in the X-Y plane with respect to Z. Figure 14. (left) Flatten tab and (right) Planefit tab [2]. 10

11 Roughness 1. Click the A button on the top right corner of the Display window to open the Analyze Panel. 2. Open the Roughness tab on the Analyze Panel (Figure 15). 3. The data present in the Roughness tab is the most recent image. 4. Click the Export Roughness button at the bottom to create a text file of the data. 5. Refer to Section in Operation manual for roughness measurement on masked image. Section Analysis 1. Click the A button in the upper right corner of the Display window to open the Analyze Panel. 2. Open the Section tab in Analyze Panel. 3. Select Line from the Mode pull-down menu. 4. Click the Draw button. 5. Move cursor over to image and draw a line on the feature of interest. A section plot will appear. 6. If needed, place cursors on the curve to measure points on the line. Figure 15. Roughness tab. 7. If the curve is not leveled, perform a 1 st order XY plane fit. Refer to Section B in operation manual for leveling the line sections. 8. Click the Export Roughness button at the bottom to create a text file of the data. For other image analysis procedures, please refer to the Chapter 7 in the Procedural Operation Manualette located on the corner workbench. SHUT DOWN 1. Click the Stop!!! button in the Master Panel to withdraw the tip. The S&D meter Z Voltage will read 0.0 V. 2. Turn the front thumbwheel clockwise to retract the tip from sample surface. Turning the thumbwheel in the wrong direction will cause tip and sample damage. 3. Turn off the power of the Herzan TS-150 active vibration isolation system. 4. Turn off the laser by switching the key on the AFM controller counter clockwise to OFF position. 5. Turn off camera fiber optics light (switch on the AFM computer table). 6. Remove the AFM head from sample stage. Set it upside down on the table. NOTE: Do NOT stretch the cable. 11

12 7. Remove the tip holder assembly from the AFM head and place it into the loading apparatus. 8. Loosen the middle screw and remove AFM tip from the holder. 9. Tighten the middle screw until finger tight. Leave the holder assembly on the loading apparatus. 10. Remove sample from the sample stage. 11. Set the AFM head (without tip holder assembly) back onto the sample stage. 12. Sign out on the FOM and sign out on the log book. Report any problem in the log off window on the FOM and in the note section of the log book. 13. Clean up the work area before leaving the room. REFERENCES 1. MFP-3D TM Atomic Force Microscope Installation and Operation Manual, Asylum Research Inc., Dr. Ryan Fuierer, Procedural Operation Manualette, Beta Version 10, September

13 EMERGENCY PROCEDURES If a user ever has a problem or an uncertainty should ASK someone who knows and can help. There are no penalties for asking for help but there may be for not reporting damage to the equipment that may delay or prevent others from working. If, at any time, the user needs to contact someone for help, call or locate the following staff of the Materials Fabrication and Characterization Facility (MFCF): Weiqiang Ding Office: ESB G75D Phone: (304) cell Harley Hart Office: White Hall 409 Phone: (412) cell If no one is available and the AFM is not acting as expected, the user should do the following: Shut down the AFM controller Shut down the computer Then, if possible, the user should stay with the AFM while trying to contact the above individuals. If it becomes necessary to leave the instrument then the user should leave a large, legible note on both the AFM and at least one of the above individuals offices, stating: The problem, describing what happened and steps taken When it occurred date and time User name and phone number If a dangerous situation is evident (smoke, fire, sparks, etc.), the user should press the power button on the power strip beside the AFM optical table or unplug the power strip to turn OFF power to the entire AFM system and notify the proper emergency personnel. If turning off the power would be unsafe in the user s estimation, the user should leave the facility and contact emergency personnel immediately. 13