Ellipsometric study of the anodic oxide of vanadium

The anodic oxide film formed on vanadium in an electrolyte of acetic acid, sodium borate, and a small quantity of water has been studied using ellipsometric and electrical measurements. These studies indicate that when a cathodic current is applied to a vanadium electrode upon which an anodic oxide film has been grown conversion of the anodic oxide occurs, and a new species or complex is formed on the electrode surface. Reapplication of an anodic current converts the film back to its original state. Both the refractive index and the solubility of the cathodically converted film differ from those of the anodic film. In particular, the cathodically converted film is much less soluble in water than is the anodic film. Ellipsometric data are consistent with a model in which the conversion of the film begins at the oxide/electrolyte interface and proceeds toward the metal. The results of ellipsometric studies concerning the optical anisotropy of the anodic oxide film on vanadium are also presented. These studies indicate that the anodic oxide film on vanadium behaves optically as a uniaxial negative material, both under a large applied electric field and under zero applied electric field