The influence of capillary effect on atomic force microscopy measurements

The study is focused on capillary phenomena that arise from the indentation of the AFM cantilever probe into a liquid film on the sample surface. We propose a new method to obtain an equation describing the geometry of the interface of three phases (liquid, air and probe) with consideration for capillary actions. It is shown that gravitational forces cannot be neglected at the nanoscale. The opening angles of the probe and the depths of AFM probe indentation into the liquid are analyzed, evidencing that the radius of curvature of the liquid boundary near the probe is much larger than that of the atomic force microscope probe. It has been found that, at the moment of contact with the liquid, the probe immediately dives into the liquid to a depth which is much larger than the nanoscale dimensions. The situation is explored where the surface layer is a thin liquid film of restricted volume, the liquid is gathered near the probe, and the dry surface area appears far away from the probe.