AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA1
Structural and Pt Adsorption Properties of Ultrathin Al@sub 2@O@sub 3@(001) Films on Al(111), Mo(110), and Ru(001)@footnote 1@

Thursday, November 5, 1998, 2:00 pm, Room 309

Session: Oxide Growth and Structure
Presenter: D.R. Jennison, Sandia National Laboratories
Authors: D.R. Jennison, Sandia National Laboratories
C. Verdozzi*, Sandia National Laboratories
P.A. Schultz, Sandia National Laboratories
M.P. Sears, Sandia National Laboratories
Correspondent: Click to Email
Using first-principles LDA calculations, we explore Al@sub 2@O@sub 3@ ultrathin films on a variety of metallic substrates. A general principle of interface structure is proposed, which then affects the film-surface termination (i.e., Al or O) and the degree of surface polarity. Several film thicknesses are compared. In the thinnest films, we find a favored phase not observed in bulk crystals, having only four-fold coordinated Al-ions. For all studied substrate materials, this indicates that a structural transformation could occur during film growth, as the film bulk and interfacial energies compete. Large differences, ~50%, are found in the adhesion of a metallic overlayer (Pt) with two vs. three O-layer thicknesses. This is due to greater surface polarity in the latter, which in turn is related to decreased stability of the thinnest film phase. Diffusion barriers are presented for isolated Pt adatoms and predictions made of hop length and symmetry. Huge coverage dependences (five-fold) in the adsorption energy of Pt occur between 1/3 and 1 ML, the binding being ionic when the Pt atoms are isolated (Pt@super +1@ or greater), but image-polarization driven at 2/3 ML and higher coverages. Our results agree with experimental ISS and HREELS data on the thinnest films.@footnote 2@ @FootnoteText@*Current address: Univ. of Edinburgh, Edinburgh EH9 3JX, UK. @footnote1@Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. DOE under Contract DE-AC04-94AL85000. @footnote 2@J. Libuda, et al., Surf. Sci. 318 (1994) 61.