Dear Hamid Akbari Moayyer,

If you are going to do your experiments in liquid medium, the capillary forces will not influence to results. For experiments on air with very soft materials, it is possible to have some artefacts from meniscus (capillary) forces. That effect will be depend on a humidity.

There is a very good book about force measuring with AFM:

"Force measurements with the atomic force microscope: Technique, interpretation and applications"

H.-J. Butt, B. Cappella,M. Kappl

http://tid.uio.no/~dansh/pdf/author/butt_AFM.pdf

Good luck!

Thank you Mr. Korneev

I know humidity has much effect on adhesion force when detaching tip and sample from each other but I don't know about the effect in indentation test.

If I want to do my experiments on relatively low vacuum, will capillary force eliminate?

If your sample is not extremely soft, the capillary forces don't have a serious effect for indentation experiments. Those forces are more important for experiments with detachment of a tip from surface. In this case it is possible to skip an influence of those force by analysis of force-distance curves - just discard "nonspecific" area on the detachment curve.

Don't worry about the capillary forces - they a not very important problem for indentation experiments. There are some more important problems: geometry of a tip, contamination of the tip when measuring, heterogeneity of a surface, etc.

If it is possible, visualize the probe's tip by electron microscopy after experiments - it is very useful for interpretation of the indentation curves.

Good luck!         

Thank you so much Mr. Korneev.