Electron stimulated desorption from PF3 adsorbed on Pt .1. Positive ions

We have studied electron stimulated desorption (ESD) of positive ions from PF, molecules adsorbed on a Pt substrate over a wide electron energy range (0-175 eV). Electron bombardment of 1 ML PF3 adsorbed on the Pt surface gives rise mainly to an F+ signal, whereas ESD from 6 ML thick PF3 film (thick PF3 layer) leads to P+, PF+, and PF2+ signals, in addition to F+. We find that the onset for F+ desorption from the 1-ML PF3/Pt is at similar to 26.5 eV, while the F+ threshold from the thick PF3 layer is similar to 28.5 eV. The P+ appearance potential from the thick PF3 layer is similar to 23 eV. The ESD F+ ion energy distribution has a peak energy of similar to 4 eV for all electron impact energies and a full. width at half maximum (FWHM) of similar to 3 eV. The P+ ions desorb with a peak energy of similar to 2 eV under 55 eV electron impact; the FWHM of the P+ energy distribution is similar to 2 eV. We suggest that the near threshold P+ formation from PF3 corresponds to the excitations of the 6a(1) level, while the F+ threshold for adsorbed PF3 on the Pt surface is due to the excitation of the F 2s level. Our results suggest that beyond near threshold (>32 eV), the excitation of the F 2s level also contributes significantly to the formation of P+ and PF+ ions from adsorbed PF3. (C) 1996 American Institute of Physics.