The scanning microscope for semiconductor characterization (SMSC): electrolyte electroreflectance and photovoltage imaging study of the electrochemical activation of RuS2 photoelectrodes for oxygen evolution

The photoelectrochemical behaviour of the oxygen evolving n-RuS2 \ H2SO4 in terface was investigated with the help of the scanning microscope for semic onductor characterization. Electrolyte electroreflectance and photovoltage digital images were obtained as a function of the pretreatment of the RuS2 surface (polishing and electrochemical etching). Polishing gives rise to an inhomogeneous, scarcely photoactive surface, while electrochemical etching destroys the damaged overlayer generated by polishing, leaving an inhomoge neous, highly photoactive surface in contact with the electrolyte. In gener al, more photoactive zones are characterized by a higher electrolyte electr oreflectance signal (EER-s) generated at the interfacial hydroxide layer, a nd a smaller signal coming from the space charge layer. According to the ob served influence of the donor concentration on the EER-s signal amplitude, the contrast observed in the EER-s image was attributed to lateral heteroge neities in the donor concentration. The difficulty of modulating the electr ic field in the hydroxide layer at relatively high frequencies was attribut ed to the low relaxation time constant of surface states involved in the EE R-s signal. The fact that at low light modulation frequencies those zones w ith the highest EER-s amplitude also show the highest photovoltage indicate s that the photovoltage intensity depends on the time constant. (C) 1998 El sevier Science S.A. All rights reserved.