Landolt-Börnstein - Group III Condensed Matter Inelastic helium atom scattering


This chapter talks about experimental methods for determining inelastic helium atom scattering. Enormous strides have been made in the experimental determination of surface phonon dispersion curves. It is not, however, the inelastic scattering of neutrons so much used for bulk phonon dispersion curve studies that has led the way, but the inelastic scattering of low-energy helium atoms and electrons. Neutrons have too low a scattering cross section to be useful for surface studies, except for fine powders or high surface/volume ratio materials such as grafoil. A number of investigators, have succeeded in producing low energy (~ 20 meV) helium atom beams with energy resolution sufficiently good to permit the determination of surface phonon dispersion curves. Recent advances have improved the resolution obtainable to ~ 0.2 meV. The technique employed is to expand helium gas through a nozzle cooled to liquid nitrogen temperature and to chop the beam to select out helium atoms with energies in a very small range. The atoms scattered by the target are detected with a mass spectrometer. By measuring the time of flight of the scattered atoms and using conservation of energy and momentum, the surface phonon frequency and wave vector can be obtained.

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Title Inelastic helium atom scattering
Book Title
Electronic and Vibrational Properties
In Experimental methods
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Chapter DOI
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Landolt-Börnstein - Group III Condensed Matter
  • G. Chiarotti
  • Authors
  • R. F. Wallis
  • S. Y. Tong
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