Low energy ion backscattering angular distributions of 6Li + from Cu(001)

Abstract

Low energy ion backscattering angular distributions (LEIBAD) from a single crystal may be used to image the atomic structure of the near-surface region. For an incident ion beam oriented randomly with respect to the crystal axes, the ions can penetrate more than 100 Å into the crystal, and the angular distributions of backscattered ions are dominated by the bulk atomic structure. Thus, a bulk stereogram of the crystal may be obtained. For incidence along a low-Miller-index axis of the crystal, shadowing effects limit the penetration depth of the elastically backscattered ions to a region near the surface of the crystal. However, neutralized Li atoms, which are not filtered out of the backscattered yield by the retarding field analyzer used in this study, provide a background characteristic of the bulk of the sample that adds to the signal from the surface plane. These effects are demonstrated by comparing experimentally determined backscattered-ion angular distributions with Monte Carlo simulations for 20 keV 6Li + scattering from a Cu(001) surface. Modifications necessary to improve the surface sensitivity of the technique are discussed.