In order to investigate the oxidation process of evaporated Bi thin films, the time dependence of X-ray diffraction during the process was studied for the various oxidation conditions.
It was found that the diffraction intensity is proportional to the square root of oxidation time for a slow oxidation condition showing that the oxidation is controled by a diffusion process. However, it tends to saturate at the end of the oxidation. In the case of a fast oxidation, the saturation appears at much earlier time such as several ten seconds.
Bi
2O
3 film during the oxidation has a cubic structure which stands for a metastable phase (β'-phase). After a complete oxidation, the film begins to change to α-phase which has been known a low temperature stable phase.
All films as well as Bi films are found to be almost complete polycrystalline except a week (111) orientational growth.
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