Transmission electron microscopy and X-ray diffraction analysis of alumina coating by alternate-current inverted magnetron-sputtering technique

Thin films of alumina were deposited by alternate-current inverted magnetron sputtering at 350 °C on stainless steel substrates. Chromium oxide was used as a template layer because it can be deposited at low temperatures and has a low lattice mismatch with alpha alumina. X-ray diffraction and selected area electron diffraction results showed that pure alpha alumina coatings could be grown at 6 kW and 0.5 % partial pressure of oxygen. Cross-sectional transmission electron microscopy analysis showed a crystalline layer of alumina on top of the chromium oxide layer. Pure alpha alumina could be grown if deposited for 2 h. Layers with mixed phases of alpha and gamma alumina were obtained with other deposition parameters.