Lattice-scale imaging of mica and clay (001) surfaces by atomic force microscopy using net attractive forces

The force between a sample and the tip during an AFM experiment consists of both attractive and repulsive components. In air, attraction is a combination of capillary adhesion from adsorbed water and attraction from van der Waals and Coulombic interactions. Opposing these attractive components is the repulsive force resulting from overlap of electron orbitais at the point of tip-sample contact. If the tip is very sharp, this Pauli-exclusion force is localized enough to obtain atomic- and lattice-scale resolution. In air, repulsive contact is present even while scanning with a net attractive force, as indicated by atomic- or lattice-scale resolution in the attractive-imaging mode. In this paper, we present lattice-scale images of mica and clay (001) surfaces that were obtained in air with a net attractive force on the cantilever. These images demonstrate that contact forces at the point of tip-sample contact oppose the capillary forces acting on the AFM tip in air.