Real-Space Surface Crystallography from Ion Scattering

Abstract

Ion beams in the kiloelectronvolt energy range impinging on crystal surfaces are atomic-size probes of the nanoscale magnifying and focusing "lenses" formed by the periodic structures. These lenses disperse the scattered and recoiled atom trajectories into macroscopic projections according to their velocities as a function of projectile/target atom masses and deflection angles. The resulting patterns reflect the near-surface interatomic vectors. The spatially and temporally resolved images of these patterns can now be acquired by means of new developments in ion scattering spectrometry, providing direct, element-specific, real-space projections of surface structure. The resulting scattering and recoiling imaging spectrometry (SARIS) provides unique capabilities for analyzing surface composition and structure and for investigating the interactions of ions with surfaces. A classical ion trajectory program called scattering and recoiling imaging code (SARIC) that simulates the spatial and time intensity distributions of the SARIS images has been developed. A quantitative comparison of experimental and simulated images is achieved by means of a two-dimensional reliability (R) factor. Examples of applications include experimental stereographic projections of the Ni(110) and Pt(111) surfaces, the termination layer of the CdS(0001) surface, the chemisorption of Cl 2 on Ni(110) and H 2 on Pt(111), and the atomic lenses in the Pt(111) surface.

Surface structure analysis of atomically smoothBaBiO3Films

“…This is done by combining the power of atomic layer-by-layer molecular beam epitaxy (ALL-MBE) 2 , enabling production of films with perfect surfaces, with the extreme surface sensitivity of the low energy Time-of-Flight Scattering and Recoil Spectroscopy (TOF-SARS) 3,4 and the Mass Spectroscopy of Recoiled Ions (MSRI) 5 techniques. Angle-Resolved (AR) TOF-SARS could determine in principle inter-atomic spacings with a resolution approaching 0.01Å, comparable to lateral values obtained in surface X-ray crystallography and even better in the direction perpendicular to the surface.…”

“…Angle-Resolved (AR) TOF-SARS could determine in principle inter-atomic spacings with a resolution approaching 0.01Å, comparable to lateral values obtained in surface X-ray crystallography and even better in the direction perpendicular to the surface. 4 This comparison is to be judged also from the perspective of having a table-top experimental setup as opposed to the requirement of very intense synchrotron light. However, in order to reach such accuracy one needs samples with very smooth surfaces.…”

Peer Reviewed: Imaging Spectrometry from Nature’s Own Atomic Lenses

“…SARIS, on the other hand, probes the positions of atomic cores. C Cl l 2 2 c ch he em mi is so or rp pt ti io on n SARIS images of 4-keV Ar + scattering from clean Ni(110) and the same surface exposed to Cl 2 gas have been used to probe the chemisorption site of chlorine atoms (19). The images clearly revealed regions of altered intensities due to the chlorine.…”

Note: A large open ratio, time, and position sensitive detector for time of flight measurements in UHV

“…Micro channel plate (MCP) based position sensitive detectors are now widely used in atomic and molecular physics as well as in surface science. Such detectors can be place in the focal plane of an electrostatic analyzer 1,2 to allow ion energy measurements or simply placed in view of the interaction zone to record neutral and charged scattered particles scattered 3,4 or emitted from the surface 3,5 . Depending on the respective geometry of the target and primary beam, such detectors are well suited for a variety of surface science techniques such as direct recoil spectroscopy (DRS) low energy ion scattering (LEIS) 1 , grazing incidence ion scattering 4 as well as grazing incidence atom diffraction 6 .…”