INFRARED STUDY OF THE SURFACE SPECIES FORMED BY SEQUENTIAL CHEMICAL-VAPOR-DEPOSITION OF TRIMETHYLALUMINUM AND METHANOL ON A HYDROXYLATED ALUMINA SURFACE

Infrared spectroscopy is used to follow the chemical changes, as a fun ction of temperature, after sequentially adsorbing trimethylaluminum ( TMA) and methanol on hydroxylated alumina. Deuterium-labeled methanol is used to distinguish between the chemistry of methyl and methoxy spe cies. To differentiate between methanol adsorbed on TMA-derived sites and on alumina, the adsorption of methanol is studied on alumina alone . The coverage of methanol on alumina alone is only 34 +/- 2% of that which adsorbs on a TMA-covered surface. Initial adsorption of methanol on Al(CH3)(2)(ads) formed by TMA adsorption, rapidly replaces a methy l by a methoxy species. Further reaction of methanol at similar to 400 K replaces the second methyl species leading to Al(CH3O)(2)(ads). Thi s thermally decomposes on heating to yield primarily dimethyl ether an d surface formate species. It is also very reactive with water and rap idly forms adsorbed hydroxylated alumina and methanol.