Photoelectron diffraction effects in core-level photoemission from Na and Te atoms adsorbed on Ni(001)

Abstract

The diffraction of photoelectrons emitted from the $\mathrm{Na} 2p$ and $\mathrm{Te} 4d$ core levels has been investigated both experimentally and theoretically for these atoms adsorbed in various configurations on an Ni(001) surface. The experiments were performed in the photon energy range $\hslash \omega =70\mathrm{}-115$ eV and the various modes of observing the photoelectron diffraction effects are described. Emphasis is on the azimuthal diffraction patterns which are shown to be sensitive to photoelectron kinetic energy, polar angle of emission, and adsorbate species. It is found that these patterns can be matched quite well by theoretical calculations using a multiple-scattering formalism and parameters taken from previous low-energy electron diffraction studies. In the case of Na, no adjustment is required to these parameters. In the case of Te, a match is obtained only after a rigid shift of the energy scale by 8 eV. The sensitivity of the calculated diffractions patterns to the input parameters is reported, and it is suggested that the measurements could form the basis of a surface structural technique with a $d_{\perp }$ spacing sensitivity of ∼0.1 Å.