The contact potential of oxide films depended on the concentration of acid solutions. Further, when the anodic oxidation was performed under the constant current density, the film formation potential depended on the concentration of acid solutions. By comparing the contact potential and the oxide film formation potential, the following conclusions were made:(1) As the film formation potential increased in the oxalic acid, the work function of the oxide films increased.(2) If the magnitude of the steep rise in the oxidation potential was large, the work function of the oxide films became small when the sulfuric acid was used.
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