DIFFERENCE PHOTOACOUSTIC AND DIFFERENCE REFLECTANCE SPECTRA OF THE ELECTRODE-ELECTROLYTE INTERFACE, THIN OXIDE FILMS ON GOLD AND PLATINUM

Des spectres PA ont été tracés "in situ" pour des électrodes de platine et d'or, nues ou couvertes d'oxyde. Les résultats de PA calibrée sont comparés à ceux de réflexion.PA spectra have been measured in situ of oxide-covered and oxide-free Au and Pt electrodes. The corresponding difference PA spectra are given. Intensity-calibrated PA data are compared with reflectivity data of these systems

Photoelectrochemically induced periodical deposition patterns of platinum on p InP. Part 2 kinetic model

A kinetic model is presented which rationalizes the previous observation of spatially periodical platinum deposition induced photocathodically by a moving laser spot on p InP. The model is similar to that of the Liesegang phenomenon. It includes the following processes nucleation of ad atoms, growth of nuclei, formation of a depletion zone, limitation of mass transport by diffusion, shift of the photocathodic reaction zone along with the moving laser spot. Computer simulations of the model equations reproduce the experimentally found periodical platinum deposition and demonstrate the spatiotemporal evolution of the number of nuclei, the deposition peaks and the corresponding hexacloro platinate IV concentration profile. The influence of the model parameters is discusse

Imaging UV photoactivity and photocatalysis of TiO2 films

Differently prepared thin layers of TiO2 were scanned with a UV laser to produce images of photoactivity. Flame oxidized, galvanically oxidized, sputtered and Sol Gel prepared layers were compared by determining images of UV induced photocurrent under otherwise constant conditions. Significant differences were found between the samples, both with respect to distribution and intensity of photoactivity. Also within the same sample, variations in photoactivity of up to one order of magnitude was found, which partially could be traced back to characteristic features of the preparation technique. The UV photoactivity of TiO2 layers was shown to depend on the preparation procedure and the duration of photoelectrochemical activity. The developed technique is discussed as a strategy for optimizing photoactivity of TiO2 layers. By locally immobilizing oxidants e.g. methanol, chlorophenol within a deposited porous sodium silicate layer, enhanced photooxidation activity can be identified in form of patches of increased photocurrent density. In this way the technique will allow minimal approaches to photooxidation and detoxification of chemicals. The described UV imaging techniques can be developed as a useful tool for optimizing photocatalytic layers for solar detoxification and surface cleanin