Efficient and surface site-selective ion desorption by positron annihilation

Abstract

We compared positron- and electron-stimulated desorption (e+SD and ESD) of positive ions from a TiO2(110) surface. Although desorption of O+ ions was observed in both experiments, the desorption efficiency caused by positron bombardment was larger by one order of magnitude than that caused by electron bombardment at an incident energy of 500 eV. e+SD of O+ ions remained highly efficient with incident positron energies between 10 eV and 600 eV. The results indicate that e+SD of O+ ions is predominantly caused by pair annihilation of surface-trapped positrons with inner-shell electrons. We also tested e+SD from water chemisorbed on the TiO2 surface and found that the desorption of specific ions was enhanced by positron annihilation, above the ion yield with electron bombardment. This finding corroborates our conclusion that annihilation-site selectivity of positrons results in site-selective ion desorption from a bombarded surface.

Coincident measurement of the energy spectra of Doppler-shifted annihilation gamma quanta and positron-induced secondary electrons

“…The ability to construct electron time-of-flight and gamma spectra in coincidence with each other allows future experiments with the capability to correspond annihilation events with the resulting electron emission processes. Planned experiments include the collection of a gamma-Auger coincidence spectra from the surface of materials known for positron stimulated ion desorption [7]. In addition, by analyzing the Doppler-broadened gamma spectrum in coincidence with a range of electrons in the Auger spectrum that may correspond to a multi-Auger process, it may be possible to determine the particular annihilation event that results in multi-Auger emission [8].…”

Study on Mechanisms of Photon-Induced Material Removal on Silicon at Atomic and Close-to-Atomic Scale

“…Photon-induced desorption refers to the reactions in which atoms/molecules are desorbed as neutrals or ions due to electronic excitation stimulated by photons. Several models have been proposed to describe the mechanisms of photon-induced desorption; these models include the Knotek–Feibelman (KF) [ 37 , 38 ], Menzel–Gomer–Redhead (MGR) [ 39 , 40 ], and Antoniewicz model [ 41 , 42 ]. The KF model is based on the ionization of a core level, followed by an Auger decay.…”

Positron Annihilation-Induced Auger Electron Spectroscopy Measurements of a TiO2(110) Surface

“…PAES studies of TiO 2 (110) can also provide important insights relevant to the understanding of positron-stimulated desorption of O + from TiO 2 (110). In particular, experimental demonstration of the positron surface state on the TiO 2 (110) surface, measurement of the relative annihilation probabilities for the oxygen and titanium core levels and the experimental observation of multi-electron emission are all important for the current understanding of positron-stimulated desorption of O + [8].…”