AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP35
A New @super 3@He Spin-Echo Spectrometer for Ultra-High Resolution Inelastic and Quasi-Elastic Helium Atom Scattering

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: G. Alexandrowicz, University of Cambridge, UK
Authors: A.P. Jardine, University of Cambridge, UK
P. Fouquet, University of Cambridge, UK
S. Dworski, University of Cambridge, UK
G. Alexandrowicz, University of Cambridge, UK
H. Hedgeland, University of Cambridge, UK
J. Ellis, University of Cambridge, UK
A. Allison, University of Cambridge, UK
Correspondent: Click to Email
Quasi-elastic helium atom scattering (QHAS) is a unique tool for studying surface dynamics on atomic length and picosecond time scales@footnote 1@. Conventional QHAS experiments, using time-of-flight methods, have limited resolution due to the velocity spread in the probing helium beam and can only investigate exceptionally fast processes. The recently established technique of @super 3@He spin-echo@footnote 2@@footnote 3@ is not limited by the velocity spread and can be used to study surface diffusion events over much greater time scales. The method is based on manipulating the precession of the nuclear spin in a polarised beam of @super 3@He atoms. Any energy change at the surface is seen as a change in the final polarisation of the beam. The key difficulty in applying the SE techniques to surface studies is in achieving a fully spin-polarised beam at sufficiently high energy (~8 meV) for a sufficient range of momentum transfers to be probed, to allow full k-space mapping of surface processes. We have have recently completed commissioning of a unique @super 3@He Spin-Echo apparatus, which operates at such beam energies. We show that the instrument increases the range of measurable time scales by three orders of magnitude. The main features of the apparatus are described, and we illustrate its the scope of application with recent experimental data, not only for surface diffusion, but also for the measurement of surface vibrations and helium-surface potentials. The results have unprecedented accuracy. @FootnoteText@ @footnote 1@ A. P. Jardine, J. Ellis and W. Allison, J. Phys. Condens. Matter 14, 6173 (2002)@footnote 2@ M. DeKieviet et. al. Phys. Rev. Lett. 75, 1919 (1995)@footnote 3@ M. DeKieviet et al. Surf. Sci. 377-379, 1112 (1997).