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Ab initio study of γ-Al<inf>2</inf>O<inf>3</inf> surfaces

Abstract:

Starting from the theoretical pbkp_rediction of the γ-Al 2O3 structure using density-functional theory in the generalized gradient approximation, we have studied the (1 1 1), (0 0 1), (1 1 0), and (1 5 0) surfaces. The surface energies and their corresponding structures are computed and compared with pbkp_redictions for (0 0 0 1) α-Al2O3 and available experimental results for γ-alumina surfaces. (1 1 1) and (0 0 1) surfaces are pbkp_redicted to be equally stable, but to show quite different structure and reactivity. Whereas a low coverage of highly reactive trigonal Al occurs on (1 1 1), (0 0 1) exhibits a more dense plane of both five-coordinate and tetrahedral Al. Microfaceting of a (1 1 0) surface into (1 1 1)-like planes is also observed. The implications for the structure of ultrathin dielectric films and for the surfaces of disordered transition aluminas are discussed.