Ab initio investigation of surface chemistry of alumina ALD on hydroxylated γ-alumina surface

Atomic layer deposition (ALD) of alumina using trimethyl aluminum (TMA) and water on amorphous alumina is analyzed using periodic-dispersion corrected DFT calculations. The energetics of the investigated reactions suggest that monomethyl aluminum (MMA) is the most abundant reaction intermediate at ALD operating conditions. The dominant reaction path toward the methylation of the surface is found to be adsorption of TMA on bridge oxygen via Lewis acid-base complex formation followed by ligand exchange reactions (LERs) with hydroxyls and surface water in its vicinity. Further adsorption and LERs of TMA leads to a saturated methylated surface (similar to 6.4 CH3 nm(-2)) which is in agreement with experimental observations and infrared spectra. The surface restructuring that is observed in almost all the reactions investigated seems to play an important role in the formation of conformal alumina films