Conductivity and Surface Electronic State of Resistive Passivation Oxide Films on Metals

研究了金属表面钝化氧化膜的表面电子态，以了解膜的耐腐蚀性。钝化氧化膜的电阻率可能与表面态的能量位置和密度有很大关系。利用椭偏仪和阻抗技术研究了紫外光照射下钛和铁表面钝化膜的变化，发现紫外光可能通过空穴激发产生新的表面态，建立了一套可以测量紫外光照射下金属表面钝化氧化膜的椭偏测量系统。利用椭偏仪测量了钝化膜在紫外光照射下的变化。钛钝化膜的变化依赖于溶液的pH值：当溶液pH高于2时，钛钝化膜的折射率降低，膜增厚。这种观察意味着氧化膜变成了水合的形式。在pH为1的酸性溶液中，最初观察到同样的现象，然而，在长时间的紫外光照射下，薄膜变薄。紫外光照射产生的空穴诱导了新的电子表面态，进而导致氧化物的水化。这些反应取决于溶液的pH值。从阻抗测量可以看出，电容随着紫外光的照射而变化。电容的变化对应于膜表面状态的产生、膜的水化和光诱导溶解，对于铁表面的钝化膜，也进行了类似的测量。虽然薄膜太薄，不能详细讨论钝化氧化膜的变化，但在紫外光照射下观察到了氧化膜的水化。

Surface electronic states of passivatlon oxide films on metals have been investigated for understanding the corrosion resistivity of the films. The resistivity of the passivation oxide films may be greatly connected with the energy position and density of the surface state. In this investigation, the change of the passivation films on titanium and iron was examined by ellipsometry and impedance during the ultra-violet (uv) light irradiation which may induces new surface states through the hole excitation.An ellipsometric measurement system has been developed In which the passivation oxide films on metals can be measured under uv light irradiation. By using the ellipsometer, the changes of the passivation films was measured with the simultaneous uv light Irradiation. The change of titanium passivation films depends on solution pH : Above pH 2, decrease of refractive index of the film and thickening of the film are observed. This observation means that the oxide film changes to a hydrous form. At an acidic solution of pH 1, same observation is Initially seen, however, the thinning of the film takes place during prolonged uv light irradiation. The hole generation by the uv light irradiation induces new electronic surface states and then hydration of the oxide. This reactions depend on solution pH values. From impedance measurement, it is seen that the electric capacitance changes with the uv light irradiation. The capacitance change corresponds to generation of the surface state on the film, hydration of the film, and light-Induced dissolution, For the passivation film on Iron, similar measurement was done. Although the film Is too thin to discuss the change of the passivation oxide films In detail, the hydration of the oxide films was observed with the uv light irradiation.