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Etude expérimentale de l'interaction rasante d'atomes et d'ions sur des surfaces isolantes

Abstract : Grazing collisions (<3 deg.) of keV ions and atoms: H^+, Ne^+, Ne^0 , Na^+ on LiF (001) single crystal, an ionic insulator, are investigated by a time of flight technique. The incident beam is chopped and the scattered particles are collected on a position sensitive detector providing differential cross section while the time of flight gives the energy loss. Deflection plates allow the charge state analysis. Secondary electrons are detected in coincidence allowing direct measurements of electron emission yield, angular and energetic distribution through time of flight measurements. The target electronic structure characterized by a large band gap, governs the collisional processes: charge exchange, electronic excitations and electron emission. In particular, these studies show that the population of local target excitations "surface excitons" is the major contribution to the kinetic energy transfer (stopping power). Auger neutralization of Ne^+ and He^+ ions reveals the population of quasi-molecular excitons, an exciton bound on two holes. Referenced in the literature as "trion". A direct energy balance determines the binding energy associated with these excited states of the surface. Besides these electronic energy loss processes, two nuclear energy loss mechanisms are characterized. These processes imply momentum transfer to individual target atoms during close binary collisions or, if the projectile is charged, to collective mode of optical phonons induced by the projectile coulomb field. The effect of the temperature on the scattering profile, the contribution of topological surface defects to the energy loss profile and to skipping motion on the surface are analyzed in view of classical trajectory simulations.
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Submitted on : Monday, October 16, 2006 - 2:06:42 PM
Last modification on : Wednesday, October 14, 2020 - 3:56:58 AM
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  • HAL Id : tel-00106816, version 1



Jérôme Villette. Etude expérimentale de l'interaction rasante d'atomes et d'ions sur des surfaces isolantes. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2000. Français. ⟨tel-00106816⟩



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