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14th International Workshop Inelastic Ion-Surface Collisions, Ameland, 2002-09-08 to 2002-09-13
Abstract:
Low energy ion scattering is very surface sensitive if scattered ions are analyzed. By time-of-flight
(TOF) techniques, also neutral and charge integrated spectra (ions plus neutrals) can be obtained,
which yield information about deeper layers. In the literature, the observation of a more or less
pronounced surface peak was reported for charge integrated spectra, the intensity of the surface
peak being higher at low energies and for heavy projectiles.
Aiming at a more profound physical understanding of this surface peak, we performed
TOF-experiments and computer simulations for He projectiles and a copper target. Experiments
were done in the range 1–9 keV for a scattering angle of 129°. The simulation was performed using
the MARLOWE code for the given experimental parameters and a polycrystalline target. At low
energies, a pronounced surface peak was observed, which fades away at higher energies. This peak
is quantitatively reproduced by the simulation, and corresponds to scattering from ~2 atomic layers.
Analyzing the contributions of the individual outermost atomic layers, one finds that the surface peak
is due to binary collisions of projectiles with atoms in the first and second layer, while the
contribution from deeper layers is dominated by multiple scattering.
