SURFACE STUDIES BY SLOW ELECTRON DIFFRACTION.
WISCONSIN UNIV MADISON
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The low energy electron diffraction from the surface of silver and its temperature dependence have been measured. From measurement of the Debye-Waller factor, it has been determined that the mean square thermal displacement normal to the surface of the surface atoms is 2.0 plus or minus 0.2 times that for the bulk atoms and that this excess amplitude falls to the bulk value approximately as e-n where n indexes the atomic plane. These results agree with the model calculations. However, these experiments indicate the excess thermal amplitude is nearly isotropic in disagreement with simple arguments and model calculations. This discrepancy may be due to non-ideal experimental surfaces. The diffuse scattering in the vicinity of the diffraction maxima has been identified as the thermal diffuse scattering. The expected thermal diffuse scattering for low energy electrons is calculated for a simple model. Experiments show the angular dependence, temperature dependence, dependence on the diffraction vector and the integrated intensity are those expected. The temperature measurements lead to independent determinations of the penetration of the electrons into the crystal. The penetration may be described by a linear absorption coefficient which is approximately proportional to the electron energy to the minus one-half power for energies between 50 and 300 e.v. The measurement of the diffuse scattering leads to the possibility of measuring the angular dependence of the atomic structure factor. Author
- Physical Chemistry