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

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 ${\mathrm{\Delta }}_1$ gap of the vanadium substrate (approximately ±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${\mathrm{̊}}^{\mathrm{-}1}$) and the energies of critical points, ${\mathit{X}}_1$ (7.60 ± 0.15 eV) and ${\mathit{X}}_{4^{\prime }}$ (2.5 ± 0.3 eV) in the E(k) dispersion of the ${\mathrm{\Delta }}_1$ band in the Γ-Δ-X direction. The bottom of the ${\mathrm{\Delta }}_1$ band, i.e., ${\mathrm{\Gamma }}_1$ point, was estimated to be -6.4±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 ${\mathrm{\Delta }}_1$ 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 ${\mathit{k}}_{\mathrm{\parallel }}$ 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. © 1996 The American Physical Society.