IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS2-ThP

Paper SS2-ThP2
Low-Energy Ion Scattering Study of Ag-Al Surface Composition@footnote 1@

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Beam Interactions with Surfaces Poster Session
Presenter: R. Bastasz, Sandia National Laboratories
Authors: R. Bastasz, Sandia National Laboratories
J.A. Whaley, Sandia National Laboratories
W.P. Ellis, Los Alamos National Laboratory
Correspondent: Click to Email
Diffusion and segregation effects have been examined for the Ag-Al system using the surface-specific technique of low-energy ion scattering (LEIS), which probes the outer atomic layer of materials.@footnote 2,3@ Thin (25 µm) foils of high-purity Ag and Al were placed in contact with each other and mounted on a heater assembly in a UHV chamber with the Al surface exposed. Initially LEIS signals from O and Al atoms were observed on the native oxide surface, but after cleaning by 1 keV He@super +@ bombardment only He@super +@ scattering from surface Al atoms was detected. The surface composition was then measured as a function of temperature up to 575 °C. No Ag was observed on the outer Al surface of Ag-Al foil samples heated to <500 °C. At 500 °C, prolonged heating resulted in the appearance of a LEIS signal from Ag at the Al surface. When the temperature of a fresh sample assembly was increased to near the eutectic (about 555 °C), the solids reacted rapidly to form a two-phase system@footnote 4@ and a LEIS signal from surface Ag immediately appeared. LEIS measurements of the surface composition of the clean binary system in the range 25-550 °C showed the Ag surface coverage to increase with temperature. Above the eutectic temperature, the Ag coverage decreased. Such LEIS measurements make it possible to determine the diffusivity of Ag in Al as well as the segregation enthalpy for Ag on Al surfaces. @FootnoteText@ @footnote 1@ This work was supported by the US Department of Energy under contract DE-AC04-94AL85000. @footnote 2@ E. Taglauer, in: "Surface Analysis- The Principal Techniques", J. C. Vickerman, Ed. (Wiley, 1997) Chap. 6. @footnote 3@ R. Bastasz, J. A. Whaley, and W. P. Ellis, Surf. Rev. Lett. 6 (1999) 605. @footnote 4@ A. J. McAllister and J. J. Murray, Bull. Alloy Phase Diagr. 1 (1983) 36.