Surface Segregation And Surface Electronic Interactions In Ptcu

Photoemission and Auger electron spectroscopy on Pt0.98Cu0.02 show that the (110) face has over twice as much Cu surface segregation as the (111) face. The Cu 3d-derived surface "density of states" differ strikingly in peak shape and in width (by 0.5 eV). The centroids, compared with bulk Cu d states, are shifted by more than 0.3 eV towards the Fermi level. This is the first experimental correlation between surface segregation and surface bonding. © 1982.1151L86L91Williams, Nason, (1974) Surface Sci., 45, p. 377Donnelly, King, (1978) Surface Sci., 74, p. 89Kerker, Moran-Lopez, Bennemann, (1977) Phys. Rev., 15 B, p. 638Shek, Stefan, Weissman-Wenocur, Pate, Lindau, Spicer, (1981) Journal of Vacuum Science and Technology, 18, p. 533Lindau, Spicer, Miller, Ling, Pianetta, Chye, Garner, (1977) Physica Scripta, 16, p. 388The Pt emission is relatively flat and is spread over a larger width in energy. That the Pt emission does not contribute to the structure assigned as Cu 3d states in the hv=150 eV data, can be seen from the photon energy dependence of the valence band spectra. We have taken data (unpublished) at hv=80, 110 and 130 eV as well. The strengths of the Cu-derived features increase with respect to the rest of the valence band, in accordance with the photon energy dependence of the Pt 5d and Cu 3d photoionization cross-sectionsStohr, Feely, Apai, Wehner, Shirley, (1976) Physical Review B, 14 B, p. 4431By “binding energy” we mean the energy difference between the Fermi level EF and the average energy of the d band as seen in photoemissionThe depth which is sampled is the electron escape depth multiplied by cos 42°The relative strengths of Cu 3d and Pt 5d emissions are estimated as follows. For the (111) alloy sample, the peak area under the difference spectrum PtCu(111)-Pt(111) [i.e. fig. lb] is divided by the area under the pure Pt(111) valence band spectrum (with the inelastic background subtrated). For the (110) alloy sample, the Pt contribution is assumed to be similar to the Pt(111) valence emission. The use of Pt(110) as reference for the PtCu(110) sample would be unlikely to lead to significantly different results at hv = 150eV. Moreover, the emissions integrated over the Pt bandwidths (about 7 eV) should be rather insensitive to the shape of the Pt valence electronic density of statesBrongersma, Sparnaay, Buck, (1978) Surface Sci., 71, p. 657Kelly, Swatzfager, Sundaram, (1979) Journal of Vacuum Science and Technology, 16, p. 664Ng, McLane, Jr., Tsong, (1980) Journal of Vacuum Science and Technology, 17, p. 154Brundle, Wandelt, (1981) Journal of Vacuum Science and Technology, 18, p. 537Kleiman, Sundaram, Barreto, Rogers, (1979) Solid State Commun., 32, p. 919. , Unfortunately, it is beyond the scope of this letter to compare and contrast the present results with these authors' X-ray photoemission results on polycrystalline PtCu foilsMiedema, (1978) Z. Metallk., 69, p. 45