Peer-reviewed Publications |
Borisov, A. G., Sidis, V., Roncin, P., Momeni, A., Khemliche, H., Mertens, A., & Winter, H. (2003). F- formation via simultaneous two-electron capture during grazing scattering of F+ ions from a LiF(001) surface. PHYSICAL REVIEW B, 67(11), 115403.
Résumé: For slow F+ ions (v<0.05 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence, large fractions of negative F- ions have recently been observed in the reflected beam, while for neutral F-0 projectiles no negative F- ions are produced in the same velocity range [P. Roncin , Phys. Rev. Lett. 89, 043201 (2002)]. From detailed studies on projectile energy loss and charge fractions, the conclusion was drawn that the F- ions are formed from F+ via a simultaneous capture of two electrons from adjacent F- sites at the surface. We present a theoretical description of the double-electron-capture process leading to F- formation from F+ projectiles grazingly scattered from the LiF(001) surface. We use quantum chemistry calculations to determine the relevant Hamiltonian matrix and close-coupling solution of the time-dependent Schrodinger equation. The theoretical results are in good agreement with experimental observations.
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Khemliche, H., Borisov, A. G., Momeni, A., & Roncin, P. (2002). Exciton and trion formation during neutralization of Ne+ at a LiF(001) surface. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 191, 221–225.
Résumé: The grazing angle interaction of 2 keV Ne+ projectiles with a LiF(0 0 1) surface is studied with the combination, in coincidence, of projectile and electron time-of-flight spectroscopy. The measurements reveal that besides the standard Auger neutralization process that leads to electron ejection, there is another neutralization mechanism that does not result in electron emission. The latter process has been identified as the formation of an electron-bihole complex termed trion. We report here the detailed study of the scattering angle dependence of these two neutralization channels, with comparison with the process leading to population of surface excitons. (C) 2002 Published by Elsevier Science B.V.
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Khemliche, H., Villette, J., Borisov, A. G., Momeni, A., & Roncin, P. (2001). Electron bihole complex formation in neutralization of Ne+ on LiF(001). PHYSICAL REVIEW LETTERS, 86(25), 5699–5702.
Résumé: Neutralization of low keV Ne+ ions at a LiF(001) surface is studied in a grazing incidence geometry. The combination of energy loss and electron spectroscopy in coincidence reveals two neutralization channels of comparable importance. Besides the Anger process, the Nef neutralization can proceed via peculiar target excitation, corresponding to the formation of an electron bihole complex termed trion.
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Roncin, P., Borisov, A. G., Khemliche, H., Momeni, A., Mertens, A., & Winter, H. (2002). Evidence for F- formation by simultaneous double-electron capture during scattering of F+ from a LiF(001) surface. PHYSICAL REVIEW LETTERS, 89(4), 043201.
Résumé: Slow F+ ions (v<0.1 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence exhibit a high probability for forming F- ions in the reflected beam, whereas no negative ions are found for neutral F-0 projectiles. From detailed studies of projectile energy loss and charge transfer, we find evidence for a correlated double-electron capture process in the formation of the F- ions.
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Rousseau, P., Khemliche, H., Borisov, A. G., & Roncin, P. (2007). Quantum scattering of fast atoms and molecules on surfaces. PHYSICAL REVIEW LETTERS, 98(1), 016104.
Résumé: We present evidence for the diffraction of light keV atoms and molecules grazingly scattered on LiF(001) and NaCl(001) surfaces. At such energies, the de Broglie wavelength is 2 orders of magnitude smaller that the mean thermal atomic displacement in the crystal. Thus, no coherent scattering was expected and interaction of keV atoms with surfaces is routinely treated with classical mechanics. We show here that well-defined diffraction patterns can be observed indicating that, for grazing scattering, the pertinent wavelength is that associated with the slow motion perpendicular to the surface. The experimental data are well reproduced by an ab initio calculation.
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Villette, J., Borisov, A. G., Khemliche, H., Momeni, A., & Roncin, P. (2000). Subsurface-channeling-like energy loss structure of the skipping motion on an ionic crystal. PHYSICAL REVIEW LETTERS, 85(15), 3137–3140.
Résumé: The skipping motion of Ne+ ions in grazing scattering from the LiF(001) surface is studied for velocity below 0.1 a.u. with a time-of-flight technique. It is demonstrated that suppression of electronic excitation and dominance of optical phonon excitation in the projectile stopping results in an odd 1,3, 5,... progression of the energy loss peaks, a feature usually ascribed to subsurface channeling. The experimental findings are well reproduced by parameter-free model calculations where thermal vibrations are the dominant cause for the ion trapping and detrapping.
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Actes de Conférences |
Roncin, P., Khemliche, H., Momeni, A., & Borisov, A. G. (2001). Translational spectroscopy in grazing collisions on insulators. The importance of the transient negative ion and of target excitations. In PHOTONIC (pp. 571–579).
Résumé: Energy loss spectroscopy is applied to grazing collisions of keV ions on insulator surfaces. For W projectiles, analyzing in coincidence the energy loss, the final charge state and the secondary electrons, the role of the intermediate negative ions formed on the surface is outlined. The study is extended to other projectiles to probe the influence of the projectile affinity level.
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