Abstract
The photopotential vs. time curves and photoelectric polarization curves of copper oxide films formed by high temperature oxidation were measured in Na2SO4 solutions of various pHs. Particular attention was given to the difference in these curves between CuO(outer)/Cu2O(inner) film and Cu2O single film. The signs of photopotentials for the CuO/Cu2O films were independent of solution pH, and were positive. On the contrary, those of the Cu2O film varied, depending on the pH region of the solution, that is, the signs observed in the solutions at pH2∼5 were positive, whereas those at pH5∼12 were negative. A relatively large photocurrent of the CuO/Cu2O film was observed as a cathodic current, while the anodic photocurrent of the film was hardly observable. In contrast, both anodic and cathodic photocurrents were observed for the Cu2O film. It was found that in the solutions of pH2∼12, flat-band potentials of the CuO/Cu2O films were higher than those of the Cu2O films. It was observed for both oxide films that the relative height between the flat-band potential and the rest potential determines the sign of photopotential. Such a difference in photoelectrochemical behavior between the two films was explained in terms of the energy-band model in the vicinity of the oxide surface.
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