Theoretical study of the bias-dependent scanning tunneling microscopy images of pyridine on Ge(001)

Abstract

We have studied the electronic structure of a pyridine-adsorbed Ge(001) surface using ab initio pseudopotential calculations. Examining the projected density of states, we found that the N lone-pair state, which is the highest occupied molecular orbital, and the down-Ge dangling bond disappear in forming a dative bond. Other molecular orbitals of pyridine are found to rigidly shift downwards due to the surface potential with some degree of broadening. Such changes in the electronic structure induced by the pyridine adsorption explain well the bias dependence of the scanning tunneling microscopy images, and the simulated images are in accordance with the experimental observation.