OBSERVATION OF VALENCE-BAND STRUCTURE IN THE LVV-AUGER SPECTRA OF THIN EPITAXIAL SODIUM LAYERS

Electron-impact-induced Auger spectra at energies below 30 eV were mea sured from epitaxial sodium films on Cu(001) from a submonolayer up to several layers and assigned to sodium LVV transitions. According to w ell established deconvolution and background-correction techniques, th e line shape of the Na L(2/3) VV transition could be used to determine the sodium valence-band density of states. In agreement with photoemi ssion investigations of the Na density of states, our results also sug gest a strong narrowing of the valence band with respect to the calcul ated density of states for a nearly-free-electron metal. Since CVV Aug er transitions cannot occur in isolated alkali-metal atoms due to the lack of a second valence s-shell electron, the onset of the Na LVV sig nal during the growth of the first monolayer unambiguously marks the f irst stage of an alkali s-level-derived valence-band-like state. Thus, the present model study of Na/Cu(001) demonstrates that CVV Auger spe ctroscopy can be used as a powerful method to investigate the intrigui ng electronic behavior during alkali-metal adsorption.