Structural analysis of alumina films produced by two-step electrochemical oxidation

The structure and properties of Al2O3 films produced by two-step anodization (the first step is anodization of Al in oxalic acid electrolyte, the second in boric acid electrolyte) have been studied. It has been shown that the films are amorphous, dense-like, about 5 X 10(-6) m thick with excellent dielectric properties (breakdown voltage is about 3.5 kV, i.e. breakdown field is about 7 X 10(8) V/m). The short-range order of these alumina films is analogous to that of porous alumina formed at the first step of the process. It has been observed that there is an increase in the fraction of fourfold coordination of Al ions for the films produced by a two-step process as compared to that in dense alumina formed only in boric acid electrolyte. (C) 2000 Published by Elsevier Science S.A. All rights reserved.