Geometrical implications of lateral interactions in chain systems: Li(1 x 2) and Li(1 x 4) on molybdenum (211)

The local geometries of Li adsorbed on the furrowed (211) surface of Mo hav e been investigated by a LEED-IV analysis using an energy of 30-180 eV. Ads orbate-induced lateral interactions mediated mainly through the substrate t urn out to be mainly responsible for the formation of the low-coverage and Li(1 x 4) and Li(1 x 2) chain systems, which have been investigated quantit atively. While the adsorbate-induced vertical relaxations in the substrate have been found to remain small, the lateral relaxations reach values up to 0.15 Angstrom. Especially for the Li(1 x 4) structure, these relaxations a re correlated, forming wave-like regions of lateral compression and dilatat ion. They seem to be the consequence of adsorbate-induced Friedel oscillati ons of the electron density of the substrate, which screen the charge of th e adatoms along the [(1) over bar 11]-channel direction of Mo(211). Further more, as concluded from the bond lengths determined by IV-LEED, the Li-meta l bond is much less ionic than that predicted by the Langmuir-Gurney model of chemisorption. (C) 2000 Elsevier Science B.V. All rights reserved.