Incommensurate structures and epitaxial growth of Li on Ru(0001): A quantitative low-energy electron-diffraction study.

Abstract

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 ${\mathrm{\ensuremath{\Theta}}}_{\mathrm{Li}}$=0.61 and ${\mathrm{\ensuremath{\Theta}}}_{\mathrm{LI}}$=0.78, incommensurate structures oriented along high-symmetry directions of the substrate were observed. Fully dynamical LEED calculations of a (5\ifmmode\times\else\texttimes\fi{}5) structure modeling the Li overlayer at ${\mathrm{\ensuremath{\Theta}}}_{\mathrm{Li}}$=0.64 revealed a Li-Ru interlayer spacing of 2.17\ifmmode\pm\else\textpm\fi{}0.10 \AA{}. The computational effort for solving this structure could be significantly reduced by using a (5\ifmmode\times\else\texttimes\fi{}1) unit mesh instead of the (5\ifmmode\times\else\texttimes\fi{}5) 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 ${\mathit{D}}_{\mathrm{Li}\mathrm{\ensuremath{-}}\mathrm{Li}}$=2.35\ifmmode\pm\else\textpm\fi{}0.10 \AA{} and ${\mathit{D}}_{\mathrm{Li}\mathrm{\ensuremath{-}}\mathrm{Ru}}$=2.35\ifmmode\pm\else\textpm\fi{}0.10 \AA{}; the Li hard-sphere radius turns out to be 1.52\ifmmode\pm\else\textpm\fi{}0.05 \AA{}, close to the metallic Pauling radius.