Photoemission Study of the Pb/Ni(111) Surface Phases

Abstract. Pb/Ni(111) surface phases were investigated by synchrotron radiation photoemission, low-energy electron diffraction (LEED) and angular resolved ultraviolet photoelectron spectroscopy (ARUPS). For room temperature evaporation, two surface ordered layers, (3x3) and (4x4), were observed. The Pb 5d and Pb 4f core levels as well as valence band spectra indicated a weak chemical interaction between Pb and Ni, and the formation of a close packed overlayer with Pb atoms in two different adsorption sites. Annealing of the Pb/Ni(111) surface led to the formation of the (√3x√3)R30° reconstruction characterized by a topmost layer consisting of a substitutional alloy. The transformation to the (√3x√3)R30° structure was accompanied by the appearance of a strong photoelectron diffraction effect confirming embedding of Pb atoms in the Ni(111) first surface layer. CO adsorption results showed that lead atoms simply blocked the CO adsorption sites for the unannealed Pb/Ni(111) surface whilst the surface alloy exhibited a chemical effect of weakening of the CO – Ni bond. The Pb 5d core level shift indicated charge transfer from Pb to the surface, particularly for (4x4) and (√3x√3)R30° structures. ARUPS results proved electronic structure dependence on surface structure. The ARUPS plots for the (√3x√3)R30° structure were substantially different compared to two other structures whilst the CO adsorption affects only intensities of main spots.