Interpreting Scanning Tunneling and Atomic Force Microscopy Images

Abstract

In scanning tunneling microscopy (STM) and atomic force microscopy (AFM) studies, one eventually faces the question of how to interpret the observed images epecially when they are in atomic or molecular resolution. In the STM studies of metallic samples, the tip-sample electron transfer typically involves the energy levels of the sample lying in the vicinity of the Fermi level ef. To a first approximation, the STM image is described by the spatial variation of the partial electron density ρ(r0, ef) of the sample [1]. In contact-mode AFM measurements, in which the tip-sample repulsive force is probed, all electrons of the sample atoms are involved in the repulsive interactions with the tip. Therefore, the AFM image is described by the spatial variation of the total electron density ρ(r0) of the sample.