Structural determination of a palladium single crystal using photoelectron and Auger-electron angular distributions.

Abstract

The angular distributions of Pd 3${\mathit{d}}_{5/2}$ (${\mathit{E}}_{\mathit{k}}$=1151.5 eV), Pd 3${\mathit{d}}_{3/2}$ (${\mathit{E}}_{\mathit{k}}$=1146.3 eV), and Pd 3${\mathit{p}}_{3/2}$ (${\mathit{E}}_{\mathit{k}}$=954.5 eV) photoelectrons and Pd ${\mathit{M}}_{5}$VV Auger electrons (${\mathit{E}}_{\mathit{k}}$=327.5 eV) were investigated for a single-crystal Pd(100) surface. We have observed pronounced anisotropies in both photoelectron and Auger-electron intensities as a function of the polar emission angle \ensuremath{\theta} along the principal azimuthal directions 〈001〉 and 〈011〉. We find that the observed angular distributions can be explained by the forward scattering of the outgoing electron waves (regardless of whether they are photoelectrons or Auger electrons) by the atoms overlying the emitter. Direct structural information was obtained by using the kinetic-energy dependence of the angular distributions of photoelectrons and Auger electrons in that zeroth-order forward-focused peaks are independent of energy, whereas the first-order interference intensities shift with energy. Forward-scattering spectroscopy is a very powerful technique in determining the relaxation of surface atoms despite a lack of translational symmetry normal to the surface. We have shown that the Pd(100) surface does not relax within 1.0\ifmmode^\circ\else\textdegree\fi{}. The experimentally observed angular distributions are consistent with a single-scattering model in which forward focusing dominates the photoelectron and Auger-electron angular distributions.