INCOMMENSURATE STRUCTURES AND EPITAXIAL-GROWTH OF LI ON RU(0001) - A QUANTITATIVE LOW-ENERGY ELECTRON-DIFFRACTION STUDY

The structural properties of Li films on a Ru(0001) surface during initial growth were determined employing the technique of low-energy electron diffraction (LEED). For submonolayer coverages between theta(Li)=0.61 and theta(Li)=0.78, incommensurate structures oriented along high-symmetry directions of the substrate were observed. Fully dynamical LEED calculations of a (5X5) structure modeling the Li overlayer at theta(Li)=0.64 revealed a Li-Ru interlayer spacing of 2.17+/-0.10 Angstrom. The computational effort for solving this structure could be significantly reduced by using a (5X1) unit mesh instead of the (5X5) unit cell without losing structural information. The first Li layer is completed at a coverage of 0.78. In the multilayer regime, the Ru(0001)-Li system exhibits also long-range order as indicated by adsorbate-induced hexagonal LEED patterns. LEED structure analyses of Li films with thicknesses of two and three layers revealed that the Li film is grown fcc(111)-like on Ru(0001). The interlayer spacings are D-Li-Li=2.35+/-0.10 Angstrom and D-Li-Ru=2.35+/-0.10 Angstrom; the Li hard-sphere radius turns out to be 1.52+/-0.05 Angstrom, close to the metallic Pauling radius.