Charge exchange for medium energy He and Ne ions in a large-angle collision at solid surfaces.pdf

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Charge exchange for medium energy He and Ne ions in a large-angle collision at solid surfaces.pdf

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Charge exchange for medium energy He and Ne ions in a large-angle collision at solid surfaces

Charge exchange for medium energy He and Ne ions in a large-angle collision at solid surfaces q Yoshiaki Kido *, Syohei Semba, Yasushi Hoshino Faculty of Science and Engineering, Department of Physics, Ritsumeiklan University, Kusatsu-shi, Shiga-ken 525-8577, Japan Received 30 September 2002; accepted 8 November 2002 Abstract Charge exchange in a large-angle single collision was studied for medium energy Het impact on NiSi2(1 1 1), MgO(0 0 1), KI(0 0 1) and Si(1 1 1)- ffiffiffi 3 p ffiffiffi3p -Sb and for Net impact on NiSi2(1 1 1) using a toroidal electrostatic analyzer with an excellent energy resolution eDE=ET of 9 104. We measured charge state distributions (CSDs) for He ions backscattered from the top-layer atoms of single crystals under channeling and blocking geometries. It was found that the CSDs were not equilibrated for He ions scattered from low Z atoms and the lower the target Z number, the larger the average charge. The path-length to attain a charge state equilibrium is very short, in a few mono-layer range and thus it yields surface peaks in backscattering spectra even from amorphous solids which were measured with an electrostatic or magnetic spectrometer. In the case of Net impact on Ni atoms of NiSi2(1 1 1), the CSDs are also not equilibrated and the average charge is gradually decreased with increase in Ne velocity in the velocity range from 0.4 to 0:8 108 cm/s. The CSDs are strongly dependent on exit angle with respect to surface plane. We propose a simple model to explain qualitatively the charge exchange process in a large-angle collision at solid surfaces. 2002 Elsevier Science B.V. All rights reserved. PACS: 34.50.Fa; 34.70.te; 61.80.Mk Keywords: Charge exchange; Medium energy ion scattering; Large-angle collision 1. Introduction High-resolution medium energy ion scattering (MEIS) provides a powerful tool to determine the structure and dynamics of solid surfaces [1–5]. For precise analysis, it is essential to have the knowledge of the