Numerical calculation of the potential distribution on the Si(111)-7 × 7 surface for scanning tunneling potentiometry

Abstract

Scanning tunneling potentiometry enables us to obtain electrochemical potential distribution of the sample surface in sub-nanometer-scale spatial resolution, and provides information on electrical resistances at the surface and local defects on it. In order to evaluate the influence of the conductance through the substrate in the measurements, we performed numerical simulation using a resistance network model that consists of a conductive surface layer with one resistive site at the center, representing the metallic surface states of the Si(111)7 × 7 surface and its single height step, respectively. The calculated results demonstrate that the substrate conductance modifies the surface potential distribution, in particular around the electrodes attached at the sides of the surface layer, and reduces the amount of the potential drop at the step and the potential gradient on the terrace nearby. In spite of the modification, however, the ratio of the conductivity of the step to that of the terrace estimated from the potential profile, is not affected by the substrate conductance as far as a low-doped substrate (103 Ω · cm or larger) is used in the case of the Si(111)7 × 7 surface.