ANGULAR-DEPENDENCE OF THE EXFAS (EXTENDED FINE AUGER STRUCTURE) IN MGO(100) SURFACES - SHORT-RANGE ORDER VERSUS DIFFRACTION EFFECTS

We report the complete analysis of the angular dependence of the featu res observed in the MgO(100) surface measured at kinetic energies high er than the Auger L2,3VV line. The angular detection of the extended f ine structure presents strong variations in both intensity and periodi city, showing a preferential emission along the low-index direction. O n the contrary, in angular-integrated detection, the EXFAS features sh ow remarkable similarities as a function of the azimuthal collection a ngle. In angular detection, the EXFAS signal consists of two overlappi ng electronic contributions. One has an EXAFS-like origin (as evidence d in polycrystalline samples) and the other, as pointed out in the pre sent work, has a diffractive nature due to the forward-scattering effe ct experienced by the valence band electron escaping the crystalline s urface.