H Van Hove

Pt10Ni90(111) single crystal alloy: Determination of the surface composition by AES, XPS and ISS

Abstract The surface composition of the Pt 10 Ni 90 (111) single crystal alloy has been determined from AES, XPS and ISS experiments. The clean surface is largely enriched with platinum: 30–40% in the top layer instead of 10% in the bulk. This enrichment concerns mainly the ultimate surface layer and appears to be only slightly dependent on the sample temperature.

Experimental determination of equilibrium surface segregation in Pt-Ni single crystal alloys

Abstract The very surfaces of Pt-Ni alloys after equilibration at 725 K were investigated by ion scattering spectroscopy and shown to be strongly enriched in Pt: 37, 96 and 99 at% for Ni 90 Pt 10 , Ni 50 Pt 50 and Ni 22 Pt 78 bulk compositions respectively. The composition dependent sputtering yield ratios together with the values for the segregation enthalpy both point to a matrix effect as the dominant parameter for the segregation process.

The segregation in single crystal Ni−Pt alloys: A model for multilayer segregation

Equilibrated (111) surfaces of Ni−Pt single crystal alloys terminate with a Pt-enriched layer. A multilayer segregation model including a Pt−Pt bond strengthening accounts well for the observed results.

Low energy ion scattering study of Be and Sn segregation in their alloys with Cu

Abstract A quantitative study of the segregation of Be and Sn in their respective alloys with Cu has been carried out using low energy ion scattering spectroscopy (LEIS) as an experimental tool for surface analysis. Both Be and Sn show a somewhat unexpected behaviour which cannot be accounted for within the framework of classical segregation theories [1]. The Be segregation is completely driven by its surface oxidation: at the very surface of Cu-Be samples (with a bulk concentration of 12.5 mole% Be) and after equilibrium conditions have been reached, only oxygen can be detected. As far as Sn segregation in Cu-Sn alloys is concerned, one observes an unusually pronounced increase in the surface concentration of Sn with increasing temperature: in a sample (with a bulk concentration of 4.0 mole% Sn) the Sn surface concentration increases from about 17 mole% at room temperature till 85 mole% at 350°C. Moreover, the appearance of a Sn-Sn double collision peak in the low energy ion spectra indicates a certain ordering of the segregated species.

Low Energy Ion Scattering Studies of Sodium Segregation in ZnO

The segregation of Na and K, native sub ppm bulk impurities in ZnO is studied on its polar surfaces using photoemission and low energy ion scattering techniques. On the (000\(\overline 1 \))-face, the resulting lowering of the electrostatic surface energy acts as a strong additional segregation force. The angular dependence of the ion intensities, backscattered from the segregated Na, shows that the Na atoms are slightly protruding out of the (000\(\overline 1 \)) surface.