Crystal-face specificity in surface segregation of CuNi alloys

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Abstract
Cu segregation to the (210) and (111) surfaces of a Cu5Ni95 alloy has been measured. Measurements by low-angle X-ray photoemission show greater levels of Cu segregation to the atomically rougher (210) surface (56% Cu) than to the low-index (111) surface (45% Cu). High-resolution photoemission measurements of the Cu 2p3/2 core level show surface-shifted features at a reduced binding energy 0.31-0.35 eV below the bulk binding energy. Apparent anomalies in previous evidence for crystal-face specificity of segregation are discussed in relation to charge transfer at the surface, and directionally enhanced forward scattering of electrons by metal overlayers.