Real-space surface crystallography: Experimental stereographic projections from ion scattering

Scattering and recoiling imaging spectrometry (SARIS) in the blocking configuration is used to obtain experimental two-dimensional stereographic projections of the Ni(110) and Pt(111) surfaces. The development of this technique as an element-specific real-space surface crystallography that is sensitive to interatomic spacings in the surface and subsurface layers of a crystal is described. This projection imaging method is based on the blocking of atomic trajectories scattered from subsurface layers by atoms in layers nearer to the surface. The resulting magnification of the blocking cones, as captured by a gated position-sensitive microchannel plate detector, is ∼ 10. The images of the blocking patterns provide direct information on interatomic spacings and surface symmetry and structure. Classical ion trajectory simulations using the three-dimensional scattering and recoiling imaging code (SARIC) are used to simulate the stereographic projections and blocking patterns and to provide quantitative interpretations. The method is sensitive to interatomic spacings in the surface and subsurface layers. The physical properties of the blocking process are derived from analysis of the data and a simplified, approximate, two-atom model of the scattering/blocking process is developed.