SEMICONDUCTOR PROPERTIES OF THE PASSIVE FILM FORMED ON Ni201 IN NEUTRAL SOLUTION

Abstract

The semiconductor properties of the passive film on Ni201 formed by anodic passivation in pH=8.4 buffer solution and the oxide film on Ni201 formed by thermally grown in air at 500℃ were investigated by photoelectrochemical response and Mott-Schottky response analysis.The Mott-Schottky plots for both the passive film and the thermal oxide film on Ni201 demonstrated that the two films exhibited p-type semiconductors with different values of flat band potential:0.40 V for the passive film and 0.15 V for the thermally grown NiO.The photocurrent spectra of the passive film on Ni201 were derived into two peaks for inner NiO and outer Ni(OH)_2 layers,respectively.The band gap energy E_g for the inner NiO was 2.8 eV and the E_g for outer Ni(OH)_2 was 1.6 eV,respectively.The E_g of the inner NiO of the passive film on Ni201(2.8 eV) was closed to that of the thermally grown oxide of Ni201(2.4 eV),indicating that the inner NiO in the passive film is crystalline structure.An electronic energy band model of both p-type semiconductors of inner NiO and outer Ni(OH)_2 layers was proposed to explain the photocurrent and Mott-Schottky plots for the passive film on Ni201.