Structural and electronic properties of a surface alloy of Pd and Cu on Cu{001}

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Abstract
The c(2×2) surface phase obtained from deposition of submonolayer amounts of Pd onto a clean Cu{001} surface is proven to have a top layer consisting of an ordered 50%-50% mixture of Pd and Cu atoms, and no ordered content in deeper layers, analogous to the structure found for Cu{001}c(2×2)-Au. The structure of the top layer is almost planar, with the Pd atoms located 0.02±0.03 Å outwards from the Cu atoms, and an interlayer distance from the Cu atoms to second (100% Cu) layer equal to the Cu{001} bulk interlayer spacing (1.807 Å). Angle-resolved photoemission spectra show that the valence band of the surface alloy is characterized by a well-defined Cu 3d–derived band and by the appearance of features due to Pd. The narrower width of the observed photoemission peaks compared with the valence band of Cu-rich Cu-Pd alloys studied by others confirms the ordered-alloy nature of the Cu{001}c(2×2)-Pd surface phase.