Nanocrystalline gamma alumina coatings by inverted cylindrical magnetron sputtering

Alumina coatings were deposited on glass, silicon and stainless steel substrates by magnetron sputtering of two cylindrical aluminum targets in argon–oxygen plasma using a mid frequency AC power supply operated at 41 kHz and 5 kW. No substrate heating was used during the deposition process. Reactive sputtering was carried out in the poisoned mode of the targets at low deposition rates of about 0.09 nm s− 1. The coatings were characterized by X-ray diffraction studies and found to be nano-crystalline, γ-phase of aluminum oxide. The coatings thickness was measured using the optical interference effects in the UV–visible spectrum of thin films deposited on glass substrates. Thin film thickness after 4 h of reactive sputtering was found to be 1.3 μm. We further studied the oxidation resistance of the alumina coatings produced on stainless steel substrates at a temperature of 400 °C. Coatings were found to be completely stable at this temperature and prevented the oxidation of underlying stainless steel substrate.