Electronic structure and catalytic properties of oxide semiconductors modified with fine metal particles

Abstract

The morphology of metal nanophase formed on the surface of wide-bandgap semiconductor oxides via the contact, photocatalytic, or photoelectrochemical deposition is substantially dependent on concentration, bulk distribution, and energy characteristics of donor defects in the semiconductor substrate. The generation of electronic surface states in a forbidden zone of the semiconductor by the deposition of metal nanoparticles is the major factor determining the efficiency of electron exchange between metal particles and semiconductor bulk and the efficiency of electrocatalytic process as a whole. According to the electrolyte electroref- lectance spectroscopic measurements, Ag, Pd, and Pt nanoparticles induce the «shallow» (with respect to the c-band edge) surface states in the forbidden zone of Ti02, which provide near-unimpeded electron exchange between metal particles and semiconductor c-band. As the size of metal particles increases, the surface state levels in Ti02 become more «deep» in relation to the edge of c-band. Thus the modification of the energy structure of surface states, e.g. by depositing metal nanophase of definite morphology or using the successive deposition of different metals opens the fresh opportunities in exerting an effective control over the electrocatalytic, photocatalytic, and photoelectrochemical properties of metal-loaded semiconductors.