Differences

This shows you the differences between two versions of the page.

--- afm [2025/07/23 17:25] – ethanminot
+++ afm [2025/09/03 22:44] (current) – [Imaging rules of thumb] ethanminot
@@ Line 64: / Line 64: @@
 //If a tip change is needed - see the [[AFM tip change information]]//
-  - Sign into the black notebook (on the table next to the AFM)
+  - Sign into the log book (black ring binder) on the table next to the AFM.
   - Start your RELMS reservation on the [[https://relms.oregonstate.edu/facilities|RELMS website]].
   - Turn on the laser - Key switch on the AFM computer
-  - Open version 19 of the realtime AFM software (latest stable version as of April 2025).
+  - Open version 19 of the realtime AFM software (latest stable version as of July 2025).
   - Click the first option, "Template"
   - Once software loads, set AC mode in master panel
@@ Line 76: / Line 76: @@
   - Align Laser:
     * Turn on the camera - Click the lower left icon that looks like a camera.
-    * Turn on the camera light - Switch on the box which sits on top of the AFM
+    * Turn on the camera light - Switch on the box which sits on top of the AFM.
-    * Align camera on cantilever - Two knobs sticking up at the very rear of the  MFP-3D
+    * Align camera on cantilever using two knobs sticking up at the very rear of the MFP-3D tripod.
-    * Not usually needed, but you might need to focus the camera on the AFM tip - Use the the focus ring toward the rear of the MFP-3D. The ring is difficult to turn (as of April 2025).
+    * Not usually needed, but you might need to focus the camera on the AFM tip - Use the the focus ring toward the rear of the MFP-3D. The ring is difficult to turn (as of July 2025).
-    * Move laser toward the tip of the cantilever - the control wheels are labeled LDX and LDY (laser deflection x and y). They are located on the back & right side of the MFP-3D tripod. Use these controls to maximize the 'Sum' signal.
+    * Move laser toward the tip of the cantilever - the control wheels are labeled LDX and LDY (laser deflection x and y). They are located on the back & right side of the MFP-3D tripod. Use these controls to maximize the 'Sum' signal. If the laser is badly misaligned, it can be hard to locate. If you "loss" the laser spot, ask an experienced user for help.
     * Adjust the photodetector (PD) position. The control wheel for the photodetector is located on the left side of the MFP-3D tripod and is labeled PD. Set the PD 'Deflection' meter to near zero.
   - X Set AC Mode - In main tab of the master panel select 'AC Mode' in the 'Imaging Mode' pull down menu
   - Tune the AFM
     *  Open 'Tune' tab in the master panel
-    *  Set 'Target %' to -5.0 % (this setting favors repulsive mode imaging, often recommended for beginners)
+    *  Set 'Target %' to -5.0 %. This setting is a first guess at the ideal drive frequency (setting it slightly less than the resonant frequency). You may have to test different drive frequencies later if you notice "phase jumping" during imaging.
     * Click the 'Auto Tune' button and wait for tuning to finish. Software will set drive frequency.
   - Engage the tip
     * Set the I gain to 10
-    * Make the 'Set Point Voltage' about 95% of the measured amplitude signal. (The measured amplitude signal is probably 1 V right now)
+    * Make the 'Set Point Voltage' about 95% of the measured free-air amplitude signal. (The measured free-air amplitude signal is probably 1 V right now, but you need to watch this, it might be drifting.)
-    * Click 'engage' in the S&D meter and
+    * Click 'engage' in the S&D meter panel.
     * Lower the tip down towards the sample by shortening the front leg of the MFP-3D tripod. Watch the measured amplitude as you do this. Also watch the camera image. As the surface comes into focus (before the amplitude starts to drop), consider moving to a clean place on your sample (use the x-y stage coarse positioning micrometers).
-    * If you have a clean landing area for your tip, continue lowering the tip down towards the sample. The amplitude will drop as you near the surface. The computer will beep when feedback kicks in to stop the amplitude from dropping below the setpoint. Continue lowering until the Z voltage is in the middle of its range.
+    * If you have a clean landing area for your tip, continue lowering the tip down towards the sample. The amplitude will drop as you near the surface. You will also notice changes in phase. Pay attention to these "tell-tales". The computer will beep when feedback kicks in to stop the amplitude from dropping below the setpoint. Continue lowering until the Z voltage is just past the middle of its range. (If the Z-voltage is not behaving as expected, click withdraw and check the amplitude and phase).
-    * If the Z-voltage goes down instead of up, re-tune. If that doesn't fix it, you might have junk stuck to the tip.
+    * Lower the 'Set Point Voltage' click by click. The Z-voltage will increase.
-    * Lower the 'Set Point Voltage' by about 10%.
+    * When the Z-voltage is above its midpoint, use the thumb wheel to lower the tripod leg until the Z-voltage is below the midpoint.
-    * Lower the tip until the 'Z voltage' approximately in the middle of its range.
+    * Lower the 'Set Point Voltage' again, reducing it click by click. The Z-voltage will increase. Watch for a hard stop. If the Z-voltage increases past its midpoint without a hard stop, repeat the cycle of (a) thumb wheel and (b) set point voltage.
-    * Lower the 'Set Point Voltage' by about 10%. Watch for "hard stop" on the Z-voltage.
+    * After you achieve a hard stop, disengage the tip by clicking 'withdraw' in the S&D meter
-    * Disengage the tip by clicking 'withdraw' in the S&D meter
+  - Close AFM Hood gentle (don't bump the machine).
-  - Close AFM Hood
+  - Check the Amplitude and Phase of the cantilever vibration. Re-tune if needed.
   - Set image details in the main tab
-  - Scan the sample, clicking 'frame up' or 'frame down' will start a scan
+  - Scan the sample. Clicking 'frame up' or 'frame down' will start a scan
+  - Observe the quality of the scan. Look for phase jumps. Look for parachuting. Look for the tip loosing contact with the surface. If needed, you can change the set-point amplitude during an image. The Set-point should be low enough that the tip stays in contact with the surface. However, don't make the set-point too low. The ideal set-point amplitude is typically about two clicks away from loosing contact with the surface.
@@ Line 105: / Line 106: @@
   - Click 'Stop!!!' button to stop the current scan and withdraw the tip
   - Open AFM Hood
-  - Manually retract tip from sample - Give the front thumbwheel a few clockwise twists
+  - Manually retract tip from sample - turn the front thumbwheel in the "up" direction. Watch the camera feed and the tip amplitude to ensure you aren't inadvertently crashing the tip into the sample.
-  - Turn off laser - Key on the AFM computer
+  - Turn off laser - Key on the AFM controller.
-  - Turn off camera light - Switch on the box sitting on top of the AFM
+  - Turn off camera light - Switch on the box sitting on top of the AFM enclosure.
-  - Place MFP-3D onto its shelf holder
+  - Place MFP-3D tripod onto its shelf holder
   - Remove sample
-  - Close software and log out
+  - Close the AFM Hood to keep dust out of the machine.
+  - Close software.
+  - Sign out of the Log Book.
+  - End the reservation in RELMS.
   - Leave controller and PC running unless expecting a power outage
 ===== Imaging rules of thumb =====
-It is easiest to get a good image on a small scan area (~ 2 micron). Starting from the default settings you can fine tune the image and then start increasing the scan size. Good settings will minimize ringing and reduce shadows while keeping the scan rate reasonably fast.
+It is easiest to get a good image on a small scan area (~ 2 micron). A small scan also facilitates verification of tip sharpness. Starting from the default settings you can fine tune the image and then start increasing the scan size. Good settings will minimize ringing and reduce shadows while keeping the scan rate reasonably fast.
 **Beginner settings**
-  *Scan size 2 micron (look at a random small feature on a flat background to verify the sharpness of the tip)
+  *Scan size 4 micron (look at a random small feature on a flat background to verify the sharpness of the tip)
-  *Scan rate < 15 micron / s
+  *Scan rate < 15 micron/s
   *Integral gain 10
   *Free amplitude 1 V (corresponds to a cantilever motion of ~ 100 nm)
   *Set-point amplitude 0.75 V
-Sometimes the image is improved by lowering the set-point amplitude a few clicks. For example, this might fix parachuting.
+**Adjustments to these settings**
+When you withdraw from the surface, check the free-air amplitude is the same as you when you first tuned the tip. If **free-air amplitude has drifted**, you can manually change the drive amplitude.
+Sometimes the image is improved by withdrawing and re-running the autotune procedure (**resonant frequency might have changed**). The autotune procedure will make changes to both the drive amplitude and drive frequency.
+Sometimes the image is improved by lowering the set-point amplitude a few clicks. For example, this might fix **parachuting**. Minor changes to set-point amplitude can be made in real time, during imaging.
-Sometimes the image is improved by withdrawing and re-running the autotune procedure (the resonant frequency might have changed).
+Another thing to try is a slower **scan rate**. The price you pay is scan time. However, I've found that you actually save time (and headache) by taking a single high quality slow scan rather than a bunch of quick ones with little parameter adjustments in between. I find that adjusting the rate so that the scan speed is <10 micron/sec works well in nearly all cases.
-When you withdraw from the surface, check the free air amplitude is the same as you when you first tuned the tip.
+If you notice **phase jumping** (a jump from below 90 degree to above 90 degrees), you should try adjusting the drive frequency. Make test images with different values of drive frequency such that the free-air phase is 70 degrees, 80 degrees, 100 degree and 110 degrees. To make these test images, you'll need to maintain a constant free-air amplitude by simultaneously adjusting drive amplitude. By doing this, you are searching for imaging parameters for which the cantilever oscillations are most stable.
-Another thing to try is a slower scan rate. The price you pay is scan time. However, I've found that you actually save time (and headache) by taking a single high quality slow scan rather than a bunch of quick ones with little parameter adjustments in between. I find that adjusting the rate so that the scan speed is <10 micron/sec works well in nearly all cases.
+It’s hard to predict a priori whether the best images will be acquired with phase below 90, or above 90. The best imaging regime for a given day depends on tip sharpness, cantilever stiffness, the sample’s mechanical/adhesive properties, the material and coating of the tip, and the humidity in the room. These factors modify the functional form of long-range van der Waals forces, the electrostatic forces, the way the tip indents the sample, and the capillary forces related to the water meniscus. A nonlinear tip–sample force with respect of tip-sample separation leads to bistabilities, and these bistabilities cause the phase jumps which mess up the AFM image.
 **Using nanotubes as a diagnostic tool**