Electronic properties of thin Zn layers on Pd(1 1 1) during growth and alloying

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• 作者：Andreas Bayer ; Ken Flechtner ; Reinhard Denecke ; Hans-Peter Steinrü ; ck ; Konstantin M. Neyman and Notker Rö ; sch
• 关键词：Photoelectron emission ; Alloys ; Metallic films ; Palladium ; Zinc ; Growth ; Density functional calculations
• 刊名：Surface Science
• 出版年：2006
• 出版时间：1 January 2006
• 年：2006
• 卷：600
• 期：1
• 页码：78-94
• 全文大小：625 K

文摘

The growth and alloying of thin Zn layers on Pd(1 1 1) was investigated using X-ray and ultraviolet photoelectron spectroscopy as well as low energy electron diffraction and correlated with density functional calculations. At 105 K, the formation of a pseudomorphic Zn monolayer is observed. Upon heating this layer to 550 K or upon deposition of 1 ML at 550 K, an ordered p(2 × 1) PdZn surface alloy with a Pd:Zn ratio of 1:1 is formed, with a characteristic Pd 3d_5/2 peak at a binding energy of 335.6 eV. For deposition of 3 ML Zn at 550 K or by heating 3 ML, deposited at low temperature, to 500 or 600 K, a PdZn alloy with a Pd:Zn ratio of again 1:1 is found in the surface region, with a Pd 3d_5/2 peak at 335.9 eV; the direct preparation at 550 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 2.4 and 3.9 eV closely resembles the spectrum of Cu(1 1 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(1 1 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(1 1 1) is taken as explanation for the similar chemical activity of both systems in methanol steam reforming.