Cu{001}c(2×2)-Pd: An ordered surface alloy

Abstract

A quantitative low-energy electron diffraction (LEED) intensity analysis shows that the room-temperature reaction of Pd atoms with a Cu{001} surface produces a surface alloy, Cu{100}c(2×2)-Pd, analogous to Cu{001}c(2×2)-Au. The structure of Cu{001}c(2×2)-Pd is almost planar, with the Pd atoms located 0.02±0.03 AÌ 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 AÌ). Although there are no ordered Pd atoms beyond the surface mixed layer, there is some evidence for disordered Pd either above or below the alloy layer. 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 dispersion and the photon-energy dependence of these features suggest their probable origins and are consistent with the alloy character of Cu{001}c(2×2)-Pd. © 1988 The American Physical Society.