Strong anisotropies in the unoccupied electronic structure of Si(111)/Cu interfaces via polarization dependent Cu L2,3XAS

The partial (s-d) density of empty states at the Cu sites of ultrathin Si(111)/Cu interfaces has been investigated by X-ray absorption spectroscopy (XAS) with linear polarized light at the Cu L2,3edges. The absorption spectra are found to strongly depend on whether the polarization vector is oriented parallel to the surface or nearly normal to it: a metallic character is shown in the former case, whereas a quasi-gap appears in the latter. These anisotropies are found to be extraordinaryly more pronounced in the case of the annealing-induced quasi-5 × 5 Si/Cu interface.