Scanning tunneling spectroscopy of transition-metal impurities at the surface of gold

The magnetic properties of an impurity atom vary greatly depending on the nature of the impurity d level. We have used scanning tunneling spectroscopy to systematically probe the local electronic structure of individual transition-metal impurities having different d-level configurations. Atoms from the $3d$ row of the periodic table were adsorbed onto a Au(111) substrate and spectroscopically probed with an ultrahigh vacuum scanning tunneling microscope at a temperature of 6 K. Elements near the center of the $3d$ row (V, Cr, Mn, and Fe) displayed featureless electronic structure over the energy range studied, while elements near the ends of the row (Ti, Co, and Ni) showed narrow resonances near the Fermi energy. These spectroscopic features are interpreted as a combination of the Kondo resonance and bare d resonance, and are consistent with trends observed in the Kondo temperature of bulk impurities.