AN EXPERIMENTAL CHARACTERIZATION OF SI(111) SURFACES BY SI 2P X-RAY PHOTOELECTRON DIFFRACTION

X-ray photoelectron diffraction (XPD), which is a by-product of the usual XPS process combined with available angle-resolved electron detection, is used to characterize crystallographically clean Si(1 1 1) surfaces. The anisotropic core level electron emission angular dependence, due to the clastic scattering mainly in the direction of internuclear axes, is given by polar and azimuthal scans of the Si 2p core level intensities I(Si)(theta) and I(Si)(phi) in some particular high symmetry space directions. For each 30-degrees azimuthal rotation, one of the three particular polar scan signatures could always be recovered and recognized, in agreement with the azimuthal symmetry of the (1 1 1) face. The experimental angles of the core level signal enhancements are compared with the theoretical atomic bulk row-directions which are expected to give XPD features in the frame of the forward focusing theory. This simple approach is sufficient to explain a main part of the XPD patterns suggesting the preponderance of bulk contributions in the emergence of the XPD contrast. Nevertheless the comprehension of the complete fine structure is subjected to the examination of the 7 x 7 reconstruction contribution and of interference features only reached by single scattering or, if needed, multiple scattering calculations.