Electronic structure and chemical properties of Pt overlayers on Nb(110)

Photoemission, low-energy electron diffraction, and Auger-electron spectroscopy have been used to study the growth of Pt overlayers on Nb(110) and to determine the effect of electronic structure and overlayer morphology on surface chemical activity. It is found that Pt forms first a commensurate structure and then an incommensurate monolayer, both of which have a modified electronic structure. The Pt partial density of states is centered -2.7 eV below the Fermi level $E_F$ and has a reduced density of states at $E_F$. At nominal monolayer coverage the intensity of the modified Pt electronic states reached a maximum and no CO chemisorption was observed. Further deposition of Pt, above a couple of monolayers, produced a surface whose electronic structure and surface structure resembles Pt(111) and molecular chemisorption of CO on Pt was observed. Comparison of our results with data reported for Pd on other refractory metals shows that the interaction between the Pt metal overlayer and the Nb substrate produces similar chemical effects.