Unusual effects noticed in previous force microscopy data are explained by a model based on work-function anisotropies and their associated patch charges. Measurable forces between macroscopic bodies can be due to the interaction of patch charges, with important consequences in the fields of surface forces, contact mechanics, adhesion, Schottky barriers, and the surface properties of insulators.

• Received 22 January 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.144