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 Δ₁ gap of the vanadium substrate (approximately ±{}2 eV around EF). 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 kF (1.19 A^-1) and the energies of critical points, X₁ (7.60 ±{} 0.15 eV) and X_4^' (2.5 ±{} 0.3 eV) in the E(k) dispersion of the Δ₁ band in the {Γ}-{Δ}-X direction. The bottom of the Δ₁ band, i.e., Γ₁ 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 Δ₁ 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 k_∥ of the discrete s-p quantum-well states is described by a significantly enhanced electron effective mass (m*>2mₑ). 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.