Properties of alumina films prepared by metal-organic chemical vapour deposition at atmospheric pressure in the presence of small amounts of water

Thin alumina films were deposited on stainless steel, type AISI 304. The deposition process was carried out in nitrogen with low partial pressures of water (0-2.6 x 10 -2 kPa (0-0.20 mmHg)) by metal-organic chemical vapour deposition (MOCVD) with aluminium-tri-sec-butoxide (ATSB) as the precursor. Also results are presented regarding the alumina deposition in the presence of small amounts of 2-butanol. The film properties, including the protection of the underlying substrate against aggressive gas compounds such as sulphur at high temperatures, the chemical composition, the microstructure, and the refractive index were investigated as a function of the water vapour pressure. In contrast with the results of stress reduction in silica films by the addition of small amounts of water to the deposition process, no significant effect on the internal stress in alumina films was found. TEM analysis showed that extremely fine grains of ~A1203/A10(OH) were formed, in agreement with the refractive index. Only an increase of the OH groups was found if water was added to the process, which also was the only impurity in the oxide film. Carbon was not detected.