Temperature-dependent low-energy electron diffraction from aluminum

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Abstract
The intensity profiles for near normal specular and normal incident nonspecular LEED beams for the three low-index surfaces (100), (110), and (111) of aluminum have been measured as a function of temperature. From the decrease in the intensities the effective Debye temperature has been found as a function of peak energy. The mean square surface normal atomic displacements relative to the bulk are compared with calculations from the Jones et al. model. The experimentally determined ratios at zero energy are 3.6 for the (100), 4.1 for the (111), and 8.0 for the (110) surface. Theoretical calculations of the Debye temperature as a function of energy from these values agree reasonably well with experimental measurements. Electron attenuation for normal penetration into the surface for the three crystallographic planes has been determined in terms of the incident electron energy. The values are α(100) = 0.16 E0.25, α(110) = 0.12 E0.26, and α(111) = 0.20 E0.22, where α is defined as the ratio of the diffraction amplitudes from successive layers in the crystal. The shift of the peaks towards lower energy is linear over a wide temperature range and has been interpreted in terms of an increase in the surface thermal expansion which amounts to several times the bulk value. This is qualitatively supported by interplanar and interrow determinations at different temperatures.

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