Dense oxide films have been formed anodically on p ‐ and n ‐type single‐crystal Si in connection with the electrical properties of Si surfaces. Concentrated or permit forming, but the highest voltage obtainable is less than 200 v. A solution of in N ‐methylacetamide permits forming to 560 v, and is also preferable in other respects. The field during forming is of the order corresponding to a thickness increment of about 3.8Aå/v. The ratio has been found as well from interference colors and direct weighing, as by capacitance measurements. Above an oxide thickness of 400Aå the rate‐limiting step for film growth is inside the oxide. The ionic current efficiency of film growth is very low. In methylacetamide it can be increased by addition, for example, of chloride ions or more so by fluoride ions. The oxide is an electrolytic rectifier and behaves similar to an oxide on Al or Ta. The direction of easy flow for electrons is from the Si to the electrolyte.
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Schmidt et al. (1957) studied this question.