EVOLUTION OF LATERAL ORDER AND MOLECULAR REORIENTATION IN THE BENZOATE/Cu(110) SYSTEM

Abstract

Coverage-dependent adsorption studies of benzoic acid on a Cu(110) single crystal surface resulted in a sequence of novel, large periodicity structures containing differently oriented benzoate species, as shown by LEED, STM and FTIR. At low coverage, only flat-lying benzoate species are present and faceting of step edges is observed. The favorable mobility of flat-lying species results in formation of large, single domain islands with a [Formula: see text] periodicity containing four molecules per unit cell. Additional adsorption produces island growth, with single domains typically covering entire terraces and, simultaneously, addition of a fifth benzoate species per unit cell oriented perpendicular to the surface. This structure, denoted as the “α phase,” corresponds to a local coverage of θ=0.21 ML. Then, the periodicity changes to a [Formula: see text] structure with single and paired rows of upright species, retaining the dominant <4, 3> direction and large single domain sizes, in addition to six flat-lying species. The second structure, referred to as the “β phase,” corresponds to a local coverage of θ= 0.23 ML. The saturation coverage, c(8×2) structure, at θ=0.25 ML, grows in from step edges and contains only upright benzoate species. The results are interpreted in terms of the interplay between molecular orientation, site-specificity, diffusion and the intermolecular interactions favoring long range, two-dimensional order.