AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS2+AS+PS-WeM

Paper SS2+AS+PS-WeM3
Oxygen Negative Ion Emission from Al(100) Bombarded by Li@super+@ Ions

Wednesday, October 27, 1999, 9:00 am, Room 607

Session: Ion-Surface Interactions I
Presenter: J.A. Yarmoff, University of California, Riverside
Authors: J.A. Yarmoff, University of California, Riverside
W.K. Wang, University of California, Riverside
B.-L. Young, University of California, Riverside
B.C. Corbitt, University of California, Riverside
Z. Sroubek, Academy of Sciences of Czech Republic
Correspondent: Click to Email
The intensity of oxygen negative ions sputtered from metal surfaces (V, Mo, Cu) by rare gas ions is known to increase by up to 3 orders of magnitude when the surface work function is lowered by alkali metal adsorption. A resonant charge transfer process from the surface bands to the oxygen affinity level is apparently responsible for the negative ion formation, and such a process is strongly dependent on the surface potential. We have measured the intensities and kinetic energy distributions of O@super-@ sputtered from Al(100) via bombardment by 200 eV Li@super+@ ions. In contrast to experiments with rare gas ions, the O@super-@ intensity is found to be relatively independent of the work function changes induced by Cs deposition (@DELTA@@phi@ = - 3 eV). For O@super-@ kinetic energies above 20 eV there is no increase in the yield, and it increases by only a factor of 2-3 at lower O@super-@ kinetic energies. The energy distribution depends exponentially upon the O@super-@ kinetic energy, and has a cutoff at about 120 eV. These results suggest that the yield of oxygen particles sputtered from clean Al(100) by Li@super+@ is already nearly completely ionized due to the local potential perturbation caused by the projectile. Thus, a further lowering of the surface potential by the deposition of alkali adsorbates has little effect. This is clear evidence of the localized nature of the resonant charge exchange process, and the first evidence that such a local effect can be induced by the primary particle.