2. Other Artifacts

Sample Drift

Sample drift means that your sample is moving as you try to scan it in the AFM.
This artifact occurs in any type of SPM, or indeed any microscopy, but is much more serious in high resolution techniques like SEM, TEM and AFM than optical microscopy. It's known as "drift", because, in general, we see the sample moving slowly, in one direction (or expanding or contracting). You can generally recognize this as a "distortion" of the image, which changes when you change the slow scan direction. beginning of the image, and then the image will start to appear more normal over time. The effect will be particularly pronounced if you move to a new place within your scan range.
See the example below.

Two AFM images showing effects of sample drift

In the example above, the two images of the same cluster of bacteria are not identical because the sample is moving while it is being scanned. It is typical of this effect that you will get different images when scanning in different directions.

How to avoid it.
The best thing to do, is to stop your sample from moving. The way to do this depends on why it's moving.

Is it thermal expansion?
-then keep the temperature constant, turn off external sources of heat(lights), and wait for it to stop moving.
It's usually worth trying to fix the sample down better. The other way to overcome (or at least to reduce) the distortion is to scan quickly.