Electronic structure of silver and copper ultrathin films on V(100): Quantum-well states

Abstract

Angular-resolved photoemission and inverse-photoemission spectroscopies have been used to investigate the valence-electron states in ultrathin films of silver and copper deposited on a V(100) surface. For both noble metals, discrete s-p derived states are observed within the ${\mathrm{\ensuremath{\Delta}}}_{1}$ gap of the vanadium substrate (approximately \ifmmode\pm\else\textpm\fi{}2 eV around ${\mathit{E}}_{\mathit{F}}$). These states are analyzed using a simple quantum-well picture. For a pseudomorphically grown (centered tetragonal) silver film in the bulklike limit we have determined ${\mathit{k}}_{\mathit{F}}$ (1.19 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$) and the energies of critical points, ${\mathit{X}}_{1}$ (7.60 \ifmmode\pm\else\textpm\fi{} 0.15 eV) and ${\mathit{X}}_{{4}^{\ensuremath{'}}}$ (2.5 \ifmmode\pm\else\textpm\fi{} 0.3 eV) in the E(k) dispersion of the ${\mathrm{\ensuremath{\Delta}}}_{1}$ band in the \ensuremath{\Gamma}-\ensuremath{\Delta}-X direction. The bottom of the ${\mathrm{\ensuremath{\Delta}}}_{1}$ band, i.e., ${\mathrm{\ensuremath{\Gamma}}}_{1}$ point, was estimated to be -6.4\ifmmode\pm\else\textpm\fi{}0.3 eV by fitting the experimentally determined points with a free-electron parabola. In the case of copper overlayers, it was not possible to determine the dispersion of the bulklike ${\mathrm{\ensuremath{\Delta}}}_{1}$ band because Cu films thicker than two monolayers showed poor order. At low coverages (1--2 ML) of both silver and copper, we find that dispersion in ${\mathit{k}}_{\mathrm{\ensuremath{\parallel}}}$ of the discrete s-p quantum-well states is described by a significantly enhanced electron effective mass (${\mathit{m}}^{\mathrm{*}}$>2${\mathit{m}}_{\mathit{e}}$). This is interpreted as due to strong hybridization of these states with the d derived states of the vanadium substrate. \textcopyright{} 1996 The American Physical Society.