In Situ studies of the determination of surface states at the semiconductor/solution interface

Abstract

The presence of surface states at the p-type semiconductor/solution interface was examined by the use of three independent techniques: Scanning Tunneling Microscope (STM), Sub Band-Gap Photocurrent (SBGP) Spectroscopy, and impedance spectroscopy. STM was proven to be a valuable technique in the determination of surface states in the semiconductor/solution interface. Here, a model was developed to characterize the electron tunneling process between the tip and the semiconductor. The effect of an oxide film on the electrode surface was considered. On the other hand, investigations using SBGP spectroscopy in the IR region considerably increased the resolvability of the energy range in which surface states can be determined. A surface state band was located at about 0.3 eV above the top of the valency band at the surface of the semiconductor. This band of surface states was induced in the oxide/solution interface. The dependence of both the energy position and density of surface states on the electrode potential and electrolyte strongly suggests that surface states were induced by adsorption of H atoms (an intermediate on the H, evolution reaction) on the electrode surface. Comparison between the dependence of both the H coverage and the density of surface states with the electrode potential supports the concept that surface states arise as a consequence of H adsorption.