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SUMMARY:A two dimensional approach for measuring surface phonons using hel
 ium spin echo - Pepijn Kole\, SMF Group\, Cavendish Laboratory
DTSTART:20101014T150000Z
DTEND:20101014T153000Z
UID:TALK26522@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:Helium spin echo is a powerful technique for measuring surface
  dynamics on atomic length-scales with high temporal resolution. Besides a
 dsorbate diffusion\, the technique can also be employed for studying inela
 stic processes\, such as surface phonons and adatom vibrational modes. A u
 nique property of Spin Echo is its ability to measure scattered intensity 
 as a function of both incoming and outgoing wavelengths\, known as the two
 -dimensional wavelength intensity matrix\, containing all information abou
 t elastic and inelastic scattering processes. The approach is independent 
 of incident beam energy and therefore attains ultra high energy resolution
 . \n\nHere we present the first measurement of a two-dimensional wavelengt
 h intensity matrix\, performed on the Rayleigh mode of a Cu(111) crystal o
 f which the dispersion relation is well known. The conditions were chosen 
 such that the phonon peak and elastically scattered intensity are very nar
 rowly spaced\, making it extremely difficult for other techniques to separ
 ate and identify the two peaks. In the matrix measured with the Spin Echo 
 technique\, two separate features are clearly visible\, corresponding to t
 he Rayleigh mode and elastically scattered intensity. \n\nThe main advanta
 ge of the 2D intensity matrix over traditional phonon measurements is that
  line shapes and peak positions can be obtained directly as a function of 
 incident energy\, without the need for deconvolving experimental influence
 s. We discuss the benefits and difficulties of the technique and compare t
 hem with results of 1D phonon measurements. \n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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