Recent progress in coincidence studies on ion desorption induced by core excitation

Abstract

This paper reports on recent studies of photostimulated ion desorption (PSID) usingelectron ion coincidence (EICO) spectroscopy combined with synchrotron radiation.H+ desorption fromH2O dissociatively adsorbedon Si(111) and SiO2/Si(111) surfaces (H2O/Si(111) and H2O/SiO2/Si(111)) was studied for Si L-edge excitation. The Si2p–H+ photoelectron photoion coincidence (PEPICO) and Si 2p photoelectron spectra ofH2O/Si(111) andH2O/SiO2/Si(111) showthat H+ desorption probability increases as the number of positive charges at the Si site increases. TheH+ desorption probability per Si 2p ionization for theSi4+ site was estimated andfound to be 5–7 × 10−5. Weproposed a mechanism that H+ desorption is induced by Si 2p photoionization accompanied by a Si LVVV double-Augertransition. This article also reviews recent EICO work on site-specific ion desorption of1,1,1-trifluoro-2-propanol-d1 (CF3CD(OH)CH3)adsorbed on Si(100) surfaces, and on the mechanisms of PSID of poly(tetrafluoroethylene) (PTFE)and TiO2(110). Clear site-specific ion desorption was observed for the C 1s core excitation of aCF3CD(OH)CH3 sub-monolayer on Si(100). A spectator-Auger-stimulated ion-desorption mechanism was proposedfor F+ desorption induced by a transition from F 1s toσ(C–F)* of PTFE.O+ desorption inducedby O 1s excitation of TiO2(110) was attributed mainly to three-hole final states resulting from multi-electron excitation/decay. ForO+ desorption induced byTi core excitation of TiO2(110), on the other hand, charge transfer from an O 2p orbital to a Ti 3d orbital, instead of theinteratomic Auger transition, was proposed to be responsible for the desorption. Theseinvestigations demonstrate that EICO spectroscopy combined with synchrotron radiation isa useful tool for studying PSID.