Anodic Oxidation of Tungsten in Non‐Aqueous Electrolyte I . Optical Anisotropy of the Oxide Film

Ellipsometry is used to study the optical properties of the oxide film grown on tungsten by anodization in acetic acid electrolyte. The tungsten substrate was found to have refractive index 0=4.080 and extinction coefficient N=3.205 at a wavelength of 632.8 nm. At an anodizing current density of 172 μA/cm 2 the field in the oxide is 5.38 MV/cm. With the anodizing field applied, the index of refraction of the film in the field direction is O 2 =2.062 and transverse to the field is N x =2.176