Kazuhisa Azumi1, Toshiaki Ohtsuka1 and Norio Sato1
1Electrochemistry Laboratory, Faculty of Engineering, Hokkaido University, Sapporo
The electronic properties of the passive films formed on iron in pH6.5 borate solution were investigated by measuring the transient photocurrent. An anodic spike-like photocurrent followed by a small steady one was observed after switching on the illumination onto the passive electrode. Another spike-like current was also observed in the reverse direction after switching off the illumination. The charges and time constants of decay of the spike-like current and the steady state photocurrent were measured as a function of film formation potential and measurement potential. A simulation was made to explain the transient behaviour of the photocurrent by assuming an equivalent circuit with the generation of a photo-induced free carrier pair in the n-type passive film. From the simulation the transient photocurrent behaviour can be explained from the relations among the thickness of the passive film, the recombination rate of the photo-induced free carrier in the film, the density of surface states, and the redox system in the solution which can energetically exchange the hole or electron with the electrode.
iron, passive film, transient photocurrent, semiconductive properties, surface states, experiments simulation analysis
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