THE REACTION PATHWAY FOR THE GROWTH OF ALUMINA ON HIGH SURFACE-AREA ALUMINA AND IN ULTRAHIGH-VACUUM BY A REACTION BETWEEN TRIMETHYL ALUMINUM AND WATER

It is demonstrated that it is possible to grow thin alumina films on an alumina substrate by the sequential adsorption of water and trimethyl aluminum (TMA) both on high-surface-area alumina and in ultrahigh vacuum (UHV) at room temperature. The presence of the resulting layer is demonstrated on high surface-area substrates using infrared spectroscopy and in UHV using electron energy-loss spectroscopy (EELS). The correspondence between the reaction on high surface-area alumina and in UHV allow the surface species to be identified using infrared spectroscopy on the high surface-area sample, and the kinetics to be measured in UHV. A film formation reaction mechanism is proposed that is consistent with the experimental results. It is suggested that TMA can react with hydroxylated alumina to form an adsorbed dimethyl aluminum species and evolve methane. This can further react with water to evolve further methane and leave adsorbed methyl groups. These react rather slowly with water resulting finally in the formation of a hydroxylated alumina surface.