Photoacoustic and photoluminescence characterization of highly porous, polycrystalline TiO2 electrodes made by chemical synthesis

We report the effect of the application of a voltage in a concentrated elec trolyte on photoacoustic (PA) and photoluminescence (PL) spectra for the pr eparation of porous TiO2 electrodes. The intensities of the PA spectrum of the TiO2 electrode with the treatments are larger than those without the tr eatments below the band-gap region, indicating the formation of defect stat es at the surface. The modulation frequency dependence of the PA intensity of the former is different from the latter in the low-frequency region, ind icating good contact and/or the reduction of the interface states between T iO2 film and substrate. The PL spectrum of the former shows more intense si gnal intensities than the latter, indicating the increase of recombination processes by the defect states at the surface. These states might aid in th e formation of a good Schottky barrier. (C) 2000 Elsevier Science B.V. All rights reserved.