Electron stimulated desorption from PF3 adsorbed on Pt. II. Negative ions

Abstract

We have studied electron stimulated desorption (ESD) of negative ions from PF3 molecules adsorbed on a Pt substrate over a wide electron energy range (0–175 eV). ESD from adsorbed PF3 gives rise to several negative ion fragments: F− (predominantly), F−2, P−, and PF−. The F− yield produced in the electron energy range 0–15 eV proceeds via dissociative electron attachment (DEA); the F− yield exhibits a peak around 11.5 eV with an onset around 7.5 eV. At electron energies above ∼15 eV, F− ions are produced via dipolar dissociation (DD). We have found that the F− ions produced from a 1 ML PF3/Pt surface via a DEA process with 11.5 eV electron impact desorb with a peak kinetic energy of ∼0.7 eV, while the F− ions generated via DD by 175 eV electron impact desorb with a peak kinetic energy of ∼1.2 eV. The F−2 yield curve also shows a peak at ∼11.5 eV; the onset of the F−2 yield from adsorbed PF3 is ∼9 eV. The F−2 yield in the electron range 9–15 eV is initiated via DEA. The P− signal from PF3 adsorbed on Pt has an onset at ∼16 eV. We have identified some possible DEA and DD processes leading to desorption of negative ions from adsorbed PF3. We suggest that Rydberg core-excited (1-hole, 2-electron) transient anion states of PF3, formed by capture of low energy electrons, dissociate to produce the F− and F−2 ions for E(e)<15 eV.