Nj. Sack et al., INELASTIC AND ELASTIC PROCESSES IN THE TRANSMISSION OF F-, AND F-2(-)FROM PF3(, F)RU(0001) THROUGH THIN RARE-GAS FILMS/, Physical review. B, Condensed matter, 54(7), 1996, pp. 5130-5144
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.