Influence of the size-dependent surface tension of a liquid film on a capillary force in an atomic force microscope

An adsorbed water film always exists between the sample and the probing tip of an atomic force microscope operating at atmospheric conditions. A new expression for the capillary force that acts between the tip and the thin liquid film has been obtained taking into account the size dependence of the surface tension of the liquid described by an exact solution of the Gibbs-Tolman-Koenig-Buff equation. The calculation agrees fairly well with the experimental results.