AVS 45th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS2-WeM

Paper SS2-WeM5
Energy Dependent Al(111) Oxidation Kinetics

Wednesday, November 4, 1998, 9:40 am, Room 309

Session: Gas-Surface Dynamics
Presenter: I. Zori@aa c@, Chalmers University of Technology, Sweden
Authors: H. Ternow, Chalmers University of Technology, Sweden
I. Zori@aa c@, Chalmers University of Technology, Sweden
M. Zäch, Chalmers University of Technology, Sweden
B. Kasemo, Chalmers University of Technology, Sweden
Correspondent: Click to Email
We have investigated the oxidation kinetics of the Al(111) surface at different O@sub 2@ kinetic energies, using molecular beam technique, Auger electron spectroscopy, AES, and surface plasmon spectroscopy. The central issue we concentrate in this report is how the oxide growth kinetics depends on kinetic energy of the impinging O@sub 2@ molecules. A series of oxygen uptake experiments, a la King and Wells, were performed for two oxygen beam energies yielding low (<0.08) and high (>0.8) initial dissociative sticking probabilities. The total coverage (chemisorbed plus oxidic oxygen) was increased in steps of 0.1 ML until the surface was saturated with oxygen. Between each step the surface was analyzed by AES and surface plasmon measurements. Al(LVV) transitions influenced by oxygen chemisorption and oxide formation were measured as a function of the total amount of oxygen on (in) the sample for different oxygen beam energies. We find the appearance of oxide in a submonolayer regime at a threshold coverage which depends on oxygen beam energy. Furthermore, the growth kinetics of the oxidic phase is also energy dependent. We attribute the latter to energy and coverage dependent dissociation dynamics, resulting in an energy dependent distribution of oxygen atoms among available adsorption sites. Surface plasmon spectroscopy (plasmon energy and lifetime dependence on total oxygen coverage) also reflects the existence of the well defined threshold for oxide appearance as well as heterogeneous distribution of chemisorbed and oxidic phases on the surface. A simple kinetic model which accounts for these observations is presented.