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--- afm [2025/09/03 22:41] – [Imaging rules of thumb] ethanminot
+++ afm [2025/09/03 22:44] (current) – [Imaging rules of thumb] ethanminot
@@ Line 129: / Line 129: @@
 **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.
+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 (the 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 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.
+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.
-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.
+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.
-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.
+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.
 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.