A PHOTOELECTROCHEMICAL IMPEDANCE SPECTROSCOPIC STUDY OF PASSIVE METALS

The photoelectrochemical impedance of passive metals is recorded in order to explore coupling between the electronic and ionic defect structures of passive oxide films. Square-wave modulated uv irradiation is used and the concomitant modulated photocurrents are measured from which a photoelectrochemical impedance can be derived by a frequency response analyzer. Since square-wave excitation is used, the applicability of linear response theory was explicitly certified by three independent procedures. At present, two metals have been investigated, ie tungsten and zirconium. The photoelectrochemical impedance of passive WO3 films can be explained by assuming a surface recombination mechanism. For ZrO2 films, diffusion of charge carriers are responsible for the observed low-frequency photocurrent response.