LI+ NEUTRALIZATION IN BACKSCATTERING FROM ALKALI AL(100) SURFACES - COMPARISON BETWEEN THE VARIOUS ALKALIS/

The Li+ ion neutralisation by back-scattering from an Al(100) surface partially covered by alkali adsorbates is theoretically studied, using a previously developed model representation of the Li+ ion-alkali ads orbate-Al substrate system [A.G. Borisov, G.E. Makhmetov, D. Teillet-B illy, J.P. Gauyacq, Surf. Sci. 350 (1996) L205], Three alkali adsorbat es are studied: Na, K and Cs and the differences between their effects are discussed. In the back-scattering geometry, the neutralisation pr obability is found to be quite different for lithium bouncing from the alkali adsorbate or from the Al substrate; it is also different for t he various alkali adsorbates. The present results are found to be in q uantitative agreement with the recent experimental data of Weare and Y armoff [C.B. Weare, J.A, Yarmoff: Surf. Sci. 345 (1996) 359]. These re sults confirm the importance of the local variation of the charge tran sfer process on the surface, as well as the capability of the charge t ransfer process to probe the local electronic potentials. A large prob ability for Li(2p) excited atom formation by collision on the adsorbat e sites is also found in the present study, even in the limit of very low alkali coverages. (C) 1998 Elsevier Science B.V. All rights reserv ed.