Nonequilibrium theory of scanning tunneling spectroscopy via adsorbate   resonances: nonmagnetic and Kondo impurities
  We report on a fully nonequilibrium theory of the scanning tunneling microscopy (STM) through resonances induced by impurity atoms adsorbed on metal surfaces. The theory takes into account the effect of the tunneling current and finite bias on the system and is valid for arbitrary intra-adsorbate electron correlation strength. It is thus applicable to the recent STM experiments on Kondo impurities. 
M. Plihal and J. W. Gadzuk