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 possibilit y of using substrate emission XPD for the elucidation of adsorbate-sub strate registry in these cases of strongly scattering adsorbate atoms and anticipated atop adsorption sites. Although scattering effects wit hin the substrate, for sub-surface emitters, clearly complicate the in terpretation of the data, simple symmetry arguments do give substantia l support to the identification of atop adsorption sites in both syste ms.