Ionic movement during oxide growth by plasma anodization

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Abstract
Our present understanding of the mechanisms of oxide growth by anodization in oxygen plasmas is presented. Transport-number measurements and isotopic-tracer experiments are used to study ionic transport processes under high electric field (106−107 V cm−1). The results show that oxide growth can be attributed to either the sole migration of oxygen ions or the cooperative motion of cations and oxygen ions. In the first case, inversion of the order of oxygen atoms is observed by isotropic tracing, while in the second case the oxygen order is preserved. Practically all the results show that the classical treatment of migration of point defects cannot be applied to ionic movement during oxide growth by plasma anodization. A correlation is observed between cation and oxygen-ion transport, and this cooperative migration of both constituents is described in the framework of a single transport event involving the simultaneous short-range migration of oxygen ions and cations. In the case of the plasma anodization of silicides, experimental evidence is presented for ionic motion via a ‘place-exchange mechanism’ in which molecular entities exchange their positions during oxide growth. This mechanism could explain ionic migration under high fields in amorphous media when different oxides are present.

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