Protective Alumina Coatings by Low Temperature Metalorganic Chemical Vapour Deposition

Alumina thin films were processed by MOCVD from aluminium tri-iso-propoxide, with N2 as a carrier gas, occasional addition of water in the gas phase, deposition temperature in the range 350-700°C, total pressure 0.67 kPa (2 kPa when water was used). The films do not diffract Xray when prepared below 700°C. At 700°C, they start to crystallize as γ-alumina. EDS, EPMA, ERDA, RBS, FTIR and TGA revealed that films prepared in the range 350-415°C, without water in the gas phase, have an overall composition Al2O3-x(OH)2x, with x tending to 0 with increasing temperature. Al2O3 is obtained above 415°C. When water is added in the gas phase, the film composition is Al2O3, even below 415°C. Coatings deposited in these conditions show promising protection properties.