NEGATIVE DIRECT RECOIL SPECTROSCOPY STUDY OF THE INITIAL OXIDATION OFAL(111)

The submonolayer oxygen-covered Al(111) surface has been studied by Ne gative Direct Recoil Spectroscopy (DRS) with the aim of detecting or d ismissing the presence of subsurface oxygen atoms. Experiments were pe rformed at room temperature and with a coverage of 75% of saturation a s measured by DRS. Four possible subsurface adsorption sites have been checked selectively and results compared with those from computer sim ulations. No subsurface oxygen was found in any of these sites down to the detection limit of DRS, which has been determined to be as small as 2.5% here. This is much less than that previously found by MEIS. On the basis of our results, the decrease of the work function, while th e surface approaches the monolayer coverage (result reported by severa l groups in the past), cannot be attributed to the penetration of oxyg en atoms below the surface. (C) 1998 Elsevier Science B.V. All rights reserved.