Examination of the geometry of long-range tip-sample interaction in atomic force microscopy

A simple method for the in situ determination of the effective large-scale curvature of the atomic force microscope (AFM) imaging tip is presented. In the method, the interaction between a spherical particle of known radius and a planar surface, both coated with an adsorbed surfactant bilayer, in aqueous solution is measured. This standard interaction is then compared with the measurements of the force of interaction between AFM tips and planar surfaces possessing the same adsorbed surfactant bilayers in aqueous solution. The probable effects of both geometrical simplifications and surface roughness are considered in the discussion of the method. The range from 100 to 400 nm is found to cover most of the effective radii (R_eff) for the commonly used microfabricated silicon nitride tips.