Determination of the Surface Geometry for the Aluminum (110) and (111) Surfaces by Comparison of Low-Energy-Electron-Diffraction Calculations with Experiment

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Abstract
Low-energy-electron-diffraction calculations have been extended to the (110) and (111) surfaces of aluminum in order to determine the spacing between the surface and bulk layers of the crystal. The A1(110) surface is found to be contracted by 10% to 15% from the bulk interlayer spacing, and the A1(111) surface is found to deviate from the bulk spacing by less than 5%. This amounts to a determination of the surface-layer position to within 0.1 Å. Results of calculations on all experimentally measured beams for these surfaces are compared with the experimental results for several assumed interlayer spacings. These comparisons are made with respect to qualitative peak shapes, peak positions, and relative peak amplitudes of the specular and all measured nonspecular beams from each surface. In order to achieve this agreement, it has been necessary to include the four outermost crystal layers and to describe the ion-core potential with five phase shifts in the 40-150-eV energy range.