Growth of thin aluminium oxide films on stainless steel by MOCVD at ambient pressure and by using a hot-wall CVD-setup

The MOCVD-growth of thin aluminium oxide films on stainless steel substrates was studied by infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Film deposition was performed in a hot-wall CVD-reactor (HWR) at atmospheric pressure. Aluminium acetylacetonate (Al(acac)3) and synthetic air were used as precursors. This approach avoids the usage of an expensive vacuum system and expensive precursors, so low-cost films can be achieved. It turned out that a deposition temperature around 600 K is necessary for film growth, but it can not be increased above 770 K due to the depletion of the precursor. Films deposited at 770 K are multicoloured, well adherent, amorphous, and stable up to 1070 K. They consist mainly of Al and O, although the existence of aluminium hydroxides can not be excluded. Annealing at higher temperatures leads to crystallisation and phase transformations: at 1070 K γ-Al2O3 films resulted and at 1380 K α-Al2O3 was formed. These films are spalling.