INELASTIC AND ELASTIC PROCESSES IN THE TRANSMISSION OF F-, AND F-2(-)FROM PF3(, F)RU(0001) THROUGH THIN RARE-GAS FILMS/

We have studied the transmission of low-energy (<10 eV) F+, F-, and F- 2(-) ions through ultrathin Kr and Xe films. The ions are produced by electron-stimulated desorption from a PF3-covered Ru(0001) surface at 25 K, and their yields and angular distributions are measured with a d igital, angle-resolving ion detector. The rare-gas films are condensed onto the PF3 layer, acid the yield and angular distribution of the io ns are measured as a function of the rare-gas film thickness. We find that F+ ions are attenuated nearly completely by similar to 1 ML of Kr or Xe, and attribute this to both one-electron charge transfer and el astic scattering. Surprisingly, we find an increase in F- yield for th e first rare-gas layer with respect to the clean surface value, which is accompanied by a dramatic change in the ion angular distribution. T he F- yield decreases to zero around 2.5 ML Kr or Xe; we explain the F - attenuation and the change in the F- angular distributions in an ela stic-scattering model. The increase in yield is attributed to a reduct ion in the neutralization probability of F- with the surface in the pr esence of the rare-gas layer.