Role of Surface States in Scanning Tunneling Spectroscopy of (111) Metal Surfaces with Kondo Adsorbates

A nearly free-electron model to describe scanning tunneling spectroscopy of (111) metal surfaces with Kondo impurities is presented. Surface states are found to play an important role giving a larger contribution to the conductance of Cu(111) and Au(111) than Ag(111) surfaces. The different line shapes observed when Co is adsorbed on the different substrates are mainly determined by the position of the surface band onset relative to the Fermi energy and the decay length of the surface state into the substrate. The lateral dependence of the line shape amplitude is found to be bulklike for R|| < or approximately 3-5 A and surfacelike at larger distances, in agreement with experimental data.