The Concentration of Mobile Ions in Insulating Oxide Films During Growth

The high field model had to be modified for the anodic growth of amorphous oxide films (Al, Nb, and Ta). Mobile ions are only formed at the interfaces and migrate through the film. Simulations based on this assumption show a very similar shape of current-potential curves compared to the experimental results. The simulations use only one free parameter, the charge density rho. All other parameters, such as i(0) and beta, were taken from the experiments. The formation of amorphous oxides is independent of the crystallographic orientation of the metal substrate. For the crystalline oxide films on Zr the oxide kinetics differ from grain to grain. This requires localized measurements on single grains. Such experiments were carried out with a new device, the droplet cell. Examples of the potentiodynamic and the capacity measurements are presented.