Dynamic effects on force measurements. I. Viscous drag on the atomic forcemicroscope cantilever

When the atomic force microscope (AFM) is used for force measurements, the driving speed typically does not exceed a few microns per second. However, it is possible to perform the AFM force experiment at much higher speed. In this article, theoretical calculations and experimental measurements are u sed to show that in such a dynamic regime the AFM cantilever can be signifi cantly deflected due to viscous drag force. This suggests that in general t he force balance used in a surface force apparatus does not apply to the dy namic force measurements with an AFM. We develop a number of models that ca n be used to estimate the deflection caused by viscous drag on a cantilever in various experimental situations. As a result, the conditions when this effect can be minimized or even suppressed are specified. This opens up a n umber of new possibilities to apply the standard AFM technique for studying dynamic phenomena in a thin gap. (C) 2001 American Institute of Physics.