Low-energy electron diffraction study of multilayer relaxation on a Pb{110} surface

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Abstract
A low-energy electron diffraction (LEED) experiment was carried out on a Pb{110} surface at -140 °C. Intensity data were collected for ten nondegenerate beams at normal incidence and 15 nondegenerate beams at θ=15°, φ=0°. Quantitative intensity analyses of the two sets confirmed the substantial contraction of the first interlayer spacing that was found by other workers with room-temperature ion-shadowing and -blocking measurements. The results of the LEED analyses, averaged over the two experimental data sets, are the following: first-interlayer spacing compressed by 16.3%, second-interlayer spacing expanded by 3.4%, and third-interlayer spacing compressed by 4.0%. The modified point-ion model can be made to predict relaxation values in good agreement with experiment for the first and the third layer, but not for the second, if the restoring force to bulk positions that opposes surface relaxation is made much smaller than in other metals.