AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA2
Effects of CH@sub 3@OH, H@sub 2@O and O@sub 2@ on Ultrathin Ordered Alumina Films under Non-UHV conditions: Hydrogen Bonding and Pressure Gaps

Monday, October 31, 2005, 2:20 pm, Room 203

Session: Oxide Surfaces Structure and Reactivity
Presenter: J. Kelber, University of North Texas
Authors: M. Jain, University of North Texas
F. Qin, University of North Texas
M. Magtoto, University of North Texas
J. Kelber, University of North Texas
Correspondent: Click to Email
STM, AES and LEED have been used to probe the reactivities of ~ 7.5 Å thick, ordered Al@sub 2@O@sub 3@ films grown on Ni@sub 3@Al(110) and Ni@sub 3@Al(111) substrates for CH@sub 3@OH, H@sub 2@O and O@sub 2@ at intermediate pressures (10@super -8@ Torr - 10@super -1@ Torr ) at room temperature. Results for H@sub 2@O show that at pressures above 10@super -4@ Torr, 300 K a surface reconstruction is initiated at defect sites which gradually leads to complete loss of long range order without formation of a UHV-stable hydroxide.@footnote 1@ The effect is pressure, rather than exposure-dependent, indicating a cooperative effect. Similar exposures to CH@sub 3@OH at > 10@super -4@ Torr, 300 K also induce a reorganization of the oxide film, though less severe than is observed for equivalent exposures of H@sub 2@O. STM constant current imaging at 2.0 V tip/sample bias of an Al2O3/Ni3Al(111) film after a total CH3OH exposure of 5.4 x 105 L at 10@super -4@ Torr, 300 K, reveals disordering of the oxide surface. Imaging at 0.1 V, and LEED however, reveals that the oxide/substrate interface still retains long-range order. C coverage remains < 0.05 monolayers at all exposures. Exposures of Al@sub 2@O@sub 3@/Ni@sub 3@Al(111) and Al@sub 2@O@sub 3@/Ni@sub 3@Al(110) to pure O@sub 2@ at pressures > 10@super -4@ Torr, 300 K result in no change to the film observable by AES, LEED or STM. No effect is observed for any of these gases at pressures < 10@super -7@ Torr, even for exposure times > 6 hours. These data indicate that intermolecular hydrogen bonding is important for inducing cooperative reactions at oxide surfaces and intermediate pressures.The data will be discussed with regards to issues of oxide stability and metal particle sintering during catalytic reactions. @FootnoteText@@footnote 1@F. Qin, N.P. Magtoto, J.A. Kelber, Surf. Sci. 565 (2004) L277. This work was supported by the Robert Welch Foundation under grant B-1356.