Scanning tunneling spectroscopy of quantum well and surface states of thin Ag films grown on GaAs(110)

[摘要] We investigate the electronic states of thin Ag films grown on GaAs(110) surfaces at low temperatures by scanning tunneling spectroscopy with single-layer thickness resolution. We identify the quantum-well states arising from the z confinement of the two-dimensional Ag films, and find an unoccupied Shockley-type surface state 180 +/- 30 mev above the Fermi energy. The s-p electronic band dispersion along the Gamma -L direction is found to be shifted upward by 190 +/- 20 meV compared to pure ag(111) surfaces. This shift, and the fact that the Shockley-type surface state is unoccupied and thus also shifted upward compared to pure Ag(111) surfaces are connected to the lattice strain of the quasiperiodically modulated Ag film. Implications of the results for other Ag thin films are discussed.

[关键词] TEMPERATURE-DEPENDENCE;ENERGY BANDS;SILVER FILMS;PHOTOEMISSION;MICROSCOPY;AG(111);OVERLAYERS;CU