Theory of scanning tunneling microscopy of Ge(111)-(2×2)

Abstract

A scattering theory of scanning tunneling microscopy (STM) of the (2×2) reconstructed Ge(111) surface is presented. Probing the occupied surface states close to the valence band maximum (negative sample bias) in constant height mode leads to maxima of the tunnel current above the adatoms and the rest atoms. At low positive sample bias, probing the unoccupied surface states, the adatoms appear as pronounced maxima. Upon increasing the positive sample voltage the rest atoms become also pronounced. The STM appearance of the Ge(111)-(2×2) surface depends upon the tip-sample distance and the magnitude of the applied voltage. The effect of the barrier height and the bearing of the interaction between the tunnel tip and the sample surface on the imaging properties are emphasized.