Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5426660 | Surface Science | 2006 | 17 Pages |
The growth and alloying of thin Zn layers on Pd(1Â 1Â 1) was investigated using X-ray and ultraviolet photoelectron spectroscopy as well as low energy electron diffraction and correlated with density functional calculations. At 105Â K, the formation of a pseudomorphic Zn monolayer is observed. Upon heating this layer to 550Â K or upon deposition of 1Â ML at 550Â K, an ordered p(2Â ÃÂ 1) PdZn surface alloy with a Pd:Zn ratio of â¼1:1 is formed, with a characteristic Pd 3d5/2 peak at a binding energy of â¼335.6Â eV. For deposition of 3Â ML Zn at 550Â K or by heating 3Â ML, deposited at low temperature, to 500 or 600Â K, a PdZn alloy with a Pd:Zn ratio of again â¼1:1 is found in the surface region, with a Pd 3d5/2 peak at â¼335.9Â eV; the direct preparation at 550Â K leads to a more homogeneous and better ordered alloy. The valence band spectrum of this alloy with a low density of states at the Fermi level and pronounced maxima due to the “Pd 4d” band at â¼2.4 and 3.9Â eV closely resembles the spectrum of Cu(1Â 1Â 1), in good agreement with the calculated density of states for a PdZn alloy of 1:1 stoichiometry. The shift of the “Pd 4d” band to higher binding energies as compared to Pd(1Â 1Â 1) indicates a charge transfer from Zn to the Pd 4d levels. Overall, the similarity between the ultraviolet photoelectron spectra for the PdZn alloy and for Cu(1Â 1Â 1) is taken as explanation for the similar chemical activity of both systems in methanol steam reforming.