Quantitative determination of Cu(117) multilayer surface relaxations by LEED

The relaxation of the first seven atomic layers of Cu(117) was determined by quantitative low-energy electron diffraction (LEED). Intensity versus energy spectra, I(E), were measured for the primary beam at near-normal incidence to the (001) terraces. The data collected cover a cumulative energy range of 3200 eV. Computation of I(E) spectra was performed in the angular momentum representation by considering the surface as a single atomic slab. For the variation of parameters, tensor LEED was applied. The experimental spectra are well reproduced over the entire energy range even for regions of low intensity. The first four layer spacings relax in a way to smooth the surface corrugation, whereby the relative changes Δd/d0 amount (from top) to -13%, -2.0%, -10%, and +7%. This leads to a reduction of the vertical distance between step and corner atoms by 0.13 A. Comparison with experimental results for Cu(115) shows that this modification of the step shape is rather independent of the terrace width. Comparison to theoretical results exhibits, however, some discrepancies with respect to both the expansion/contraction sequence and the amplitudes of the layer relaxations