"Step-up" Versus "Step-down" Scattering Asymmetry in the Neutralization of H- on Vicinal Surfaces
Boyan Obreshkov, Uwe Thumm
James R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS, USA
We present numerical results based on a wave-packet propagation study of charge transfer between H- ions and free-electron stepped (vicinal) metal surfaces . We derive an effective potential for the motion of the active electron within a Thomas-Fermi-von Weizsaecker model and extend this model to include imagecharge effects. We first calculate the H- affinity level shift and width in fixed-ion approximation and then solve a rate equation for the negative-ion-survival probability for projectiles that are incident with a kinetic energy of 50 eV. We find an enhancement of electron loss near the steps of the surface due to the Smoluchowski effect. As a consequence, ion survival is more likely if the projectiles approach steps from above than from below .
This work was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, and by the National Science Foundation.References:
 B. Obreshkov and U. Thumm, Phys. Rev. A 74, 012901 (2006).
 B. Obreshkov and U. Thumm, Surf. Sci. 601, 622 (2007).
Presented at ISIAC, August 2007 in Crete, Greece.
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