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.

Negative ion formation in electron-stimulated desorption of CF2Cl2 coadsorbed with polar NH3 on Ru(0001)

“…F 2 Ϫ ions as well as large intensities of F Ϫ ions have been reported in ESD of metal/fluorine systems. 20,21 The deposition of NH 3 onto a CF 2 Cl 2 layer preadsorbed on Ru͑0001͒ ͓Fig. 5͑b͔͒ results in the observation of a large enhancement of F Ϫ and Cl Ϫ ion yields, in agreement with previous results.…”

Electron-driven chemistry of halogenated compounds in condensed phases: Effects of solvent matrices on reaction dynamics and kinetics

“…The observed decrease in F À and Cl À with high H 2 O coverage is expected because of elastic and inelastic scattering as the desorbed ions pass through the overlayer [21]. To summarize, the data indicate a substantial enhancement of relative anionic ESD yield for fractional monolayers of CF 2 Cl 2 on a metal surface upon coadsorption with H 2 O (results for co-adsorption with NH 3 and CH 3 OH can be found elsewhere [14,30,89]). …”

Effects of electron irradiation on structure and bonding of SF6 on Ru(0001)

“…Time-of-flight (TOF) mass separation of desorbing species is accomplished by pulsing the primary electron beam and gating a retarding grid with a repetition rate of 10 kHz and duration of 200 ns. Unless otherwise specified, angular distributions of desorbing F + have been measured for incident electron kinetic energies of 350 eV (250 eV electron gun energy [15][16][17]. All ESDIAD measurements reported in this paper are made with the sample cooled to~25 K. Thermally induced changes in ESDIAD patterns were «frozen» after annealing by cooling to~25 K, before measurements were made.…”