Surface states on chemically modified TiO 2 electrodes

Abstract

When the surface of TiO 2 is modified with alkysilanes, impedance and photocurrent measurements indicate that surface states are being introduced at the semiconductor-electrolyte interface. These states, which act as effective recombination centers for light-generated carriers. have a broad Gaussian distribution with a maximum near the bottom of the conduction band. The width of this distribution varies linearly with surface coverage. A model based on slow reorganization of the solvent molecules can account for the Gaussian distribution, but not for the variation of the values of reorganization energy obtained under certain experimental conditions. An alternative model is presented which is based on the formation of a surface state band through overlap of the orbitals of randomly distributed surface adsorbants. This model is then extended to account for observations concerning the mechanism of hole transfer on an unmodified semiconductor-electrolyte interface.