Publications

Application of multi-angle scattering maps to stepped surfaces

Kolasinski, Robert K.; Whaley, Josh A.; Ward, Donald K.

This study examines channeling, multiple scattering, and neutralization/re-ionization of ions scattered along the stepped Al(332) plane. Our experimental approach involves probing the surface with 1–2 keV He+ and Ne+ beams, and then systematically mapping the scattered ion fluxes over a large solid angle. This provides comprehensive ion channeling information over all directions, rather than along a few low-index azimuths, as is common practice in ion scattering spectroscopy. We first probe the surface with 2 keV He+ at near-normal incidence, and then map the backscattered particle flux (both ions and neutrals) via time of flight (TOF) spectrometry. The features contained in these maps can be correlated with axial and inter-planar channeling effects, and are reproduced well via binary collision simulations. Sensitivity to the stepped surface topography is heightened considerably for oblique ion incidence in the forward-scattering direction. In this geometry, we used 2 keV Ne+ to probe the surface and mapped the corresponding scattered fluxes of both single and multiply-charged ions. In both cases, the scattering intensity depends strongly on the precise trajectory taken along the surface, and is particularly sensitive to how extensively the incident ions interact with the step edges. We interpret the information contained in these maps by considering several mechanisms for charge transfer and double ion production. The formation of Ne++ appears to be correlated with a previously observed inelastic mechanism that occurs when the collision apsis, Rmin, is less than 0.65 Å. This contributes to an energy loss of 48 ± 8 eV for Ne+ undergoing single scattering; the Rmin threshold for this inelastic step coincides with the emergence of a distinct Ne++ peak. Using the information gained from the maps, we propose methods for extending this approach to chemisorbed layers.