The surface adsorption characteristics of trimethylamine-alane, H3AlNMe3, on a SiO2 substrate have been investigated using X-ray photoelectron spectroscopy and static secondary ion mass spectrometry. Molecular adsorption prevails at exposures of ~15 langmuirs with the aluminum centers becoming five-coordinate via binding to surface oxygen centers. High XPS X-ray flux (>240 W) results in migration of NMe3 to silicon centers, ascertained by comparison with the adsorption of NMe3 gas. At exposures greater than ~30 langmuirs an aluminum-rich species is formed, with the ratio of Al:N close to 2:1. Similar results are obtained for dosing of bis- (trimethylamine)-alane, H3Al(NMe3)2. Ab initio molecular orbital calculations (HF/D95*) on H3AlNH3 and H2O, and H3AlOH2, as model systems for the interaction of H3AlNMe3 with surface oxygen centers, gave formation of H3AlNH3(OH2) as energetically favored by 4.53 kcal mol−1 and its fragmentation to H3AlOH2 and NH3 requiring 13.16 kcal mol−1; association of H3AlOH2 and H3AlNH3 to H2(NH3)Al(µ-H)2Al(OH2)H2, as a model for the aluminum-rich species, is also favored by 3.39 and 3.24 kcal mol−1 for two isomers with different orientations of the H atoms on sp3 oxygen.