AVS 51st International Symposium
    Surface Science Friday Sessions
       Session SS1-FrM

Paper SS1-FrM11
H@sub 2@O-Induced Instabilities at Alumina Surfaces Under Non-UHV Conditions

Friday, November 19, 2004, 11:40 am, Room 210B

Session: Hydrated Surface Phenomena
Presenter: J.A. Kelber, University of North Texas
Authors: F. Qin, University of North Texas
N.P. Magtoto, University of North Texas
J.A. Kelber, University of North Texas
D.R. Jennison, Sandia National Labs
Correspondent: Click to Email
We report that ordered, transitional phase Al@sub 2@O@sub 3@ films grown on Ni@sub 3@Al single crystal substrates undergo dramatic reorganization and morphological changes upon exposure to H@sub 2@O under non-UHV conditions at room temperature. Notably, the reconstruction does not involve the formation of an UHV-stable hydroxide. STM, AES, LEED and XPS have been used to probe the reactivities of 7 Å - 20 Å thick, ordered Al@sub 2@O@sub 3@ films grown on Ni@sub 3@Al(110) and on Ni@sub 3@Al(111) substrates for 10@super-8@ Torr < P@sub H2O@ < 1 Torr at 300 K. STM near-atomic resolution image of the surface of an as-grown Al@sub 2@O@sub 3@/Ni@sub 3@Al(110) oxide film (estimated thickness, ~ 7 Å ) indicates a 10 Å repeat distance between rows, in excellent agreement with the results of a first-principles DFT calculation of an ultrathin kappa-phase film. LEED pattern of this film with a 2 x 1 unit cell confirms this structure. Both films are inert toward H@sub 2@O under UHV conditions. We demonstrate that (a) both films undergo severe surface reorganization to a rough, irregular morphology upon exposure to H@sub 2@O at pressures above 10@super-5@ Torr, 300 K, although Al(OH)@sub 3@ formation is only observed above 1 Torr, as predicted by thermodynamics and observed on sapphire(0001); (b) the film grown on the (110) substrate (Al@sub2@O@sub 3@/Ni@sub 3@Al(110)) is significantly more sensitive to H@sub 2@O vapor than the Al@sub 2@O@sub 3@/Ni@sub 3@Al(111) film, and this may be due to the incommensurate nature of the oxide/Ni@sub 3@Al(110) interface; (c) the degree of reconstruction increases with time at constant P@sub H2O@; (d) bias-dependent STM indicates that this reaction is initiated at surface terrace sites, rather than at defect sites or by diffusion to the interface; and (e) the reaction is pressure-dependent, rather than exposure-dependent, indicating that this reaction is cooperative in nature.