FREQUENTLY ASKED QUESTIONS ABOUT ATOMIC FORCE MICROSCOPY (AFM FAQ)

AFM Artifacts

by Peter Eaton

1. Tip Effects
Dirty or Contaminated Tips

If the tip is dirty or contaminated (often with parts of the sample sticking to it), you can get
strange repeating shapes in the image. Sometimes it is obvious, sometimes it is not. In the example below there are
two images of the same sample, one taken with a clean tip, and one with a badly contaminated tip.
Using a sample you already know can help you diagnose this problem.



In the example above, the image on the right was scanned using a very badly contaminated tip, the one on the left with a
clean tip, but the sample is the same!

This shows the drastic effects than can occur when the tip is dirty.
How to avoid it.

Change the tip. Once a tip is broken, you must change it. If it is contamination, you might be able to clean it.
But most often, even in this case, you will have to change to a new tip.

Note that the image above is of a sample of BOPP film (Biaxially Oriented PolyPropylene). The use of this sample in
tip characterization, and even to clean the tip has been discussed by Nie et al in:
H.-Y. Nie, M. J. Walzak, and N. S. Mcintyre,
"Use of biaxially oriented polypropylene film for evaluating and cleaning contaminated atomic force microscopy probe tips:
an application to blind reconstruction," Review of Scientific Instruments, vol. 73, pp. 3831-3836, 2002.

However, you could use any well-known sample to characterise the state of your tip. The advantage of BOPP is that
it is also possible to clean the tip by performing indentation into the sample. In principle you could use
other samples for this. Again, it should be remembered that you will likely NEVER return to the pristine state of a new tip.


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This document was written by, and is maintained by Peter Eaton (peter.eaton@fc.up.pt)
Reproduction or distribution not allowed without my permission.
Please feel free to email me comments / questions / answers.
Document updated on 19th March 2007.