X-RAY PHOTOELECTRON DIFFRACTION INVESTIGATION OF THE (2 X-2) OVERLAYERS OF CS AND K ON CU (111)

X-ray photoelectron diffraction measurements have been made for the Cu(111)(2 X 2)-Cs and Cu(111)(2 X 2)-K systems to explore the possibility of using substrate emission XPD for the elucidation of adsorbate-substrate registry in these cases of strongly scattering adsorbate atoms and anticipated atop adsorption sites. Although scattering effects within the substrate, for sub-surface emitters, clearly complicate the interpretation of the data, simple symmetry arguments do give substantial support to the identification of atop adsorption sites in both systems.