Scattering of low energy Ne + ions on Ni(001) and Ni(001)Au (segregated) surfaces

Abstract

Low energy (2.4–9.5 keV) ion scattering of Ne from Ni(001)Au (segregated) surfaces on a Ni-1% Au single crystal has been studied using a time-of-flight (TOF) system which collects both neutrals and ions thereby revealing, at certain crystal orientations, the scattered yield from second layer as well as first layer atoms. Good agreement was found between experimental and computer simulated spectra for both the clean Ni and Au-segregated surfaces. In the latter case the overlayer containing ∼90% Au and 10% Ni was assumed to have the same FCC(001) structure as the clean Ni. LEED patterns from the segregated surface, however, show extra spots indexed approximately as (2 × 6). Azimuthal scans of the Ni scattering yield coming predominantly from the second layer in the segregated case show similar symmetry, i.e. the FCC(001) (1 × 1) symmetry, for both clean Ni and Au-segregated surfaces. However, the gold overlayer is evidently not strictly substitutional, in view of the LEED patterns. No evidence was found of Au in the second layer.