Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces -: art. no. 195410

Ag(111) films were deposited at room temperature onto H-passivated Si(111)-(1x1) substrates, and subsequently annealed at 300 degreesC. An abrupt nonreactive Ag/Si interface is formed, and very uniform nonstrained Ag(111) films of 6-12 ML have been grown. Angle-resolved photoemission spectroscopy was used to study the valence band electronic properties of these films. Well-defined Ag sp quantum-well states (QWS's) have been observed at discrete energies between 0.5-2 eV below the Fermi level, and their dispersions have been measured along the (ΓK) over bar, <(ΓM(M'))over bar>, and GammaL symmetry directions. QWS's show a parabolic bidimensional dispersion, with in-plane effective mass of (0.38-0.50)m(o), along the (ΓK) over bar and <(ΓM(M'))over bar> directions, whereas no dispersion has been found along the GammaL direction, indicating the low-dimensional electronic character of these states. The binding energy dependence of the QWS as a function of the Ag film thickness has been analyzed in the framework of the phase accumulation model. A good agreement between experimental data and the above-mentioned model is obtained for the Ag/H/Si(111)-(1x1) system. Hydrogen at the interface not only enhances the Ag film uniformity, but also acts as a barrier modifying the phase change of the Ag-sp electron wave upon reflection at the Ag/Si interface.