Disproportionation of dimethylalane on aluminum surfaces. Part II. Quantumchemistry studies

A proposed surface disproportionation growth mechanism of dimethylaluminum hydride (DMAH) on aluminum surfaces has been investigated with quantum chem istry methods and found to be thermodynamically consistent. Planewave pseud opotential calculations of optimized adsorbate structures, heats of reactio n, and activation barriers have been employed to construct a quantitative g rowth model. Results support a mechanism involving the decomposition of DMA H to dimethylaluminum, monomethylaluminum, and methyl fragments in the grow th process. Rate simulations of the growth mechanism agree well with experi ments and are able to reproduce the low apparent activation energies observ ed experimentally, while still including elementary reactions with activati on barriers as high as 20 kcal/mol. Additionally, simulations provide insig ht into experimental observations via the prediction of a dominant surface methyl coverage under growth conditions. Where experiment and calculations overlap, a general accuracy of approximately 5 kcal/mol is observed. (C) 20 01 Elsevier Science B.V. All rights reserved.