Crystal structure characterisation of filtered arc deposited alumina coatings: temperature and bias voltage

Using a filtered vacuum arc deposition device, stoichiometric aluminum oxide (Al2O3) films, with thickness ranging from 20 nm to several microns, were produced under various substrate bias voltages and temperatures. Analysis of the resulting alumina crystal structures was performed with transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Depending on the negative substrate bias voltage, the deposition temperature required to form α-Al2O3 could be reduced. A crystal phase diagram showing the effect of bias and temperature is presented. Also, preliminary hydrogen permeation measurements of these coatings deposited on thin palladium foil show a good barrier performance as compared with uncoated samples.