IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS3-TuP

Paper SS3-TuP3
The Evolution of Surface Topography of Alkali Halides Crystals During Ion Stimulated Desorption

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Adsorption/Desorption Poster Session
Presenter: M. Szymonski, Jagiellonian University, Poland
Authors: F. Krok, Jagiellonian University, Poland
J.J. Kolodziej, Jagiellonian University, Poland
B. Such, Jagiellonian University, Poland
P. Czuba, Jagiellonian University, Poland
P. Piatkowski, Jagiellonian University, Poland
M. Szymonski, Jagiellonian University, Poland
Correspondent: Click to Email
Ion-stimulated-desorption (ISD) of alkali halide (RbI, KBr) surfaces under 5 keV He+ bombardment is investigated in UHV by means of non-contact Atomic Force Microscopy (nc-AFM) and Quadrupole Mass Spectroscopy (QMS). Irradiated surface topography and corresponding desorption fluxes are studied. Although, for the energy range of He+ ions used in the present work, desorption of alkali halides occurs predominantly via electronic processes, there are significant differences between ISD and the electron stimulated desorption (ESD). Recently, present authors@footnote 1,2@ have demonstrated that ESD of alkali halides proceeds in a layer-by-layer mode and oscillating desorption fluxes are observed. These ESD oscillations have been explained to be due to creation of Frenkel pairs in the bulk, their diffusion, and their recombination with surface modulated accordingly to changing surface topography. For ISD studied in the present work AFM images show that the surface erosion does not follow the layer-by-layer scheme and no oscillation in desorption fluxes are found. We propose that these (not anticipated) differences between electron- and ion- stimulated desorption are caused by ballistic processes at the surface. While most of the primary ion beam energy is deposit deep in the bulk leading to production of Frenkel pairs some projectiles colliding violently with top-layer ions may introduce additional nucleation centers for vacancies on surface. Moreover the shallow collision cascades, which extend to the top crystal layers are likely to induce mobility in alkali halide top crystal layer. These ballistic processes interfere with electronic processes and destroy the layer-by-layer desorption scheme. @FootnoteText@@footnote 1@B. Such, J. Kolodziej, P. Czuba, P. Piatkowski, P. Struski, F. Krok and M. Szymonski, Phys. Rev. Lett., 85 (2000) 2621. @footnote 2@R. Bennewitz, S. Schar, V. Barwich, O. Pfeiffer, E. Meyer, F. Krok, B. Such, J. Kolodziej, M. Szymonski, Surf. Sci. Lett., 474 (2001) L197.