c(2×2)S/Cr(001) surface and near-surface structure determined using angle-resolved photoemission extended fine structure

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Abstract
We report the surface and near-surface structure of c(2×2)S/Cr(001) determined from angle-resolved photoemission extended fine structure (ARPEFS). The sulfur 1s photoemission partial cross section was measured in the [001] and [011] emission directions, yielding fine-structure amplitudes up to 50–70 %. Qualitative results were obtained from Fourier transforms of the ARPEFS, revealing geometrical information beyond 10-Å path-length difference from the photoemitter. Structural parameters were determined with greater precision by comparing the Fourier-filtered data to multiple-scattering spherical-wave calculations. The high directional sensitivity of ARPEFS was apparent in the analysis of normal [001] and off-normal [011] emission-direction data. Sulfur adsorbs in the fourfold hollow site 1.17 Å above the first chromium layer, and the first- to second-layer chromium distance contracts to 1.31 Å, 8% less than the 1.44-Å bulk value. Analysis of the near-surface contribution to ARPEFS showed that deeper layers essentially retain the bulk separation.