CVD-Fabricated aluminum oxide coatings from aluminum tri-iso-propoxide:: Correlation between processing conditions and composition

This paper presents results on aluminum oxide thin films processed using metal-organic (MO) CVD from aluminum tri-isopropoxide (ATI) without any additional oxygen source, in the temperature range 623-973 K. The films do not diffract X-rays, except when grown at 973 K or annealed at 1073 K. Their composition was investigated using several techniques; electron probe micro analysis (EPMA), energy dispersive X-ray spectroscopy (EDX), elastic recoil detection analysis (ERDA), and Rutherford back-scattering spectroscopy (RBS). It corresponds to the formula AlO(OH) for those grown at 623 K. The composition of films prepared above 688 K corresponds to the formula Al2O3. Between 623 K and 688 K, partly hydroxylated films are obtained. This is confirmed by Fourier transform infrared (FTIR) transmission spectroscopy (no OH absorption band in the 3500 cm(-1) region for films prepared above 688 K), and by thermogravimetric analysis (TGA, DTG) (no significant mass loss for films prepared above 688 K). Observations using the transmission electron microscopy (TEM) showed that films prepared at 623 K are amorphous, while those prepared at 973 K are nanocrystalline. In both cases, gamma-Al2O3 crystals are formed and progressively grow on exposure to the TEM electron beam. Knowing the correlation between processing conditions and the composition of such films should help optimize the process with regards to any aimed property of use.