IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Friday Sessions
       Session SS2-FrM

Paper SS2-FrM2
Chemisorption of O@sub2@ on Al(111): Non-Adiabatic Pathway to Abstraction, and Simulation of STM Data

Friday, November 2, 2001, 8:40 am, Room 121

Session: Gas-Solid Dynamics: Theory and Experiment
Presenter: J.Z. Sexton, University of California, San Diego
Authors: J.Z. Sexton, University of California, San Diego
A.J. Komrowski, University of California, San Diego
A.C. Kummel, University of California, San Diego
M. Binetti, Universitat Essen, Germany
O. Weisse, Universitat Essen, Germany
E. Hasselbrink, Universitat Essen, Germany
Correspondent: Click to Email
There exists controversy in the literature surrounding the initial oxidation of the Al(111) surface. (1) DFT calculations show the activated reaction of O@sub2@ with Al(111) cannot be modeled using a single potential energy surface and consistency with the observed reaction barrier requires a non-adiabatic charge transfer process.@footnote 1@ The calculations show that the initial charge transfer is most favorable for end-on collisions with Al(111) which is consistent with an abstraction mechanism.@footnote 1@ (2) Abstractive chemisorption in the oxidation of aluminum is a process in which an oxygen molecule reacts with the surface producing one atom bound to the surface and one atom ejected into the gas phase. We have experimentally verified this mechanism using supersonic molecular beams to dose the clean Al(111) surface with variable incident energy O@sub2@. The evidence is as follows: (a) STM images show a transition between exclusively single O-adatom reaction products to more pairs of O-adatom reaction products as the O@sub2@ translational energy is raised from 0.025 eV (thermal) to 0.8 eV. (b) The ejected O-atoms have been detected in the gas phase with REMPI laser spectroscopy. This is consistent with an end-on, non-adiabatic reaction. (3) Interpretation of O-Al(111) reacted sites in STM images can be interpreted in terms of long range dissociation, abstraction, or diffusion.@footnote 2@ The main issue of the controversy is the assignment of single O-Al(111) reacted sites on the room temperature surface. We are performing cluster and slab calculations to simulate the appearance of O - Al(111) features in STM images. The existence of nearly degenerate adsorption sites for oxygen adatoms and local relaxation of the Al surface complicates the interpretation of the STM images. @FootnoteText@ @footnote 1@Y. Yourdshahyan, et al, Sol. St. Comm. 117, 531 (2001). @footnote 2@M. Schmid and P. Varga, in AVS Symposium Abstracts, SS-TuP4, Seattle, WA, (1999) p. 109.