Surface core-level shift photoelectron diffraction from As/Si(111)

We have studied the arsenic-terminated Si(lll)-(1 x 1) surface with low energy photoelectron diffraction. On this ideally terminated surface, the Si 2p core-level consists of a bulk component and a single well separated surface component shifted to 0.75 eV higher binding energy compared to the bulk component, We have measured the intensities of the surface and bulk components of the Si 2p core-level, and the single component As 3d core-level, as functions of azimuthal angle, The recorded azimuthal scans for the Si 2p surface component showed extremely large intensity variations, For a photon energy of 130 eV and emission angle of 45 degrees for example, the intensity of this component was found to vary by 400 percent upon an azimuthal rotation of the sample by 45 degrees, The experimental data were compared to model calculations of the photoelectron diffraction utilizing a fully convergent multiple scattering formalism. The best fit to the data was consistently found in all the azimuthal scans for an outward relaxation of the As atoms from the Si bulk positions by 0.2 Angstrom. This is in good agreement with earlier structural determinations of this surface.