Blocking map of He+ scattered from a Si(0 0 1)-(2 × 1) surface

Scattering and recoiling imaging spectrometry (SARIS) in the “blocking configuration” for the system of 5 keV He+ scattering from a Si(0 0 1)-(2 × 1) surface has been used to measure a two-dimensional blocking map. The map demonstrates that this real-space surface crystallographic technique is sensitive to interatomic spacings in the surface and subsurface layers of a crystal. Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) and “two-atom” molecular dynamics (MD) simulations are used to interpret the blocking patterns and to provide quantitative interpretations of the experimental data. The “blocking configuration”, in which atomic trajectories scattered from subsurface layers are blocked by atoms in layers nearer to the surface, is demonstrated to be a viable method for simultaneous acquisition of data from the surface and individual surface layers. It is found that the blocking map is representative of the crystal geometry. The results show that the major blocking cones for 5 keV He+ on Si(0 0 1)-(2 × 1) originate from fourth to seventh-atomic layer scattering, while cones of lesser intensity are observed from as deep as the 12th-atomic layer.