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-ThP4
New Approaches to Diffusion and Electronic Properties of Surfaces: Spin-Echo Quasielastic Helium Scattering (SE-QHAS) and Metastable Helium Atom Scattering (MHAS)

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

Session: Beam Interactions with Surfaces Poster Session
Presenter: P. Fouquet, Cavendish Laboratory, UK and MPI für Strömungsforschung, Germany
Authors: P. Fouquet, Cavendish Laboratory, UK and MPI für Strömungsforschung, Germany
A.P. Jardine, Cavendish Laboratory, UK
J. Ellis, Cavendish Laboratory, UK
W. Allison, Cavendish Laboratory, UK
G. Witte, Ruhr-Universität, Germany
Correspondent: Click to Email
We present current progress of two major new developments in atomic beam surface scattering: QHAS is a uniquely powerful technique for studying diffusion on atomic length and time-scales. Since helium atoms scatter from the diffusing species as they move, QHAS gives a detailed reciprocal space map of the paths the atoms take as they traverse the surface. We demonstrate the way that QHAS data can be used to study potential energy surfaces of diffusing atoms and adatom-adatom potential energies, as illustrated by analyses of experimental data on the CO/Cu(001) and Na/Cu(001) systems.@footnote 1@ Till now, QHAS has been limited to systems showing very high mobilities (D > 5 x 10@super -6@ cm@super 2@ s@super -1@), we show how measurements can be made over a much wider range of mobilities by using spin echo techniques and give details of a new ultra high resolution scattering machine that is being developed in the Cavendish. In contrast to that, metastable, excited He-atoms are highly sensitive to the surface electron density. We have shown experimentally that MHAS is capable of measuring the valence state occupation of alkali metals during growth on Cu(001).@footnote 2@ Our data interpretation has since found support by theoretical work which proved that, for the investigated systems, MHAS exclusively probes the electronic density of states projected onto the He 1s state.@footnote 3@ We have extended our measurements to alkaline earth metals (Ba), semiconductor surfaces (GaAs(100)) and oxygen coadsorption. The data supply novel information about the metallisation transition of ultrathin metal films as well as the catalytic oxidation of semiconductors. @FootnoteText@ @footnote 1@ J. Ellis, A.P. Graham, F. Hofmann, J. P. Toennies, Phys. Rev. B 63, 195408 (2001). @footnote 2@ P. Fouquet, G. Witte, Phys. Rev. Lett. 83, 360 (1999). @footnote 3@ L.N. Kantorovich et al., Surf. Sci. 444, 31 (2000).