Chemical dependence of the multiple-tip effect in scanning tunneling microscopy

Abstract

Simultaneous imaging by multiple atomic tips in scanning tunneling microscopy has the effect of superimposing displaced images, which for a two-atom tip may appear as a doubling of atoms. In this paper we present spectroscopic images where the doubling is voltage dependent. We interpret this effect by proposing a tunneling tip with two protruding chemically different atoms. The relative contribution of each atom to the total current is proportional to the atoms’ local density of states that can participate in tunneling. If the two protruding tip atoms are chemically different, then the contribution of each tip, and thus the doubling of the image, can be voltage dependent.