Molecular orientations and adsorption structures of α-sexithienyl thin films grown on Ag(110) and Ag(111) surfaces

Molecular orientations and adsorption structures of alpha-sexithienyl (6T) thin films grown on Ag(110) and Ag(111) surfaces were studied by near edge X-ray absorption fine structure (NEXAFS) and reflection high energy electron diffraction (RHEED). The out-of-plane (perpendicular to the surface) and in-plane (parallel to the surface) orientations of the 6T molecules were determined by analyzing the polarization dependence of S 1s to pi* or sigma* resonance intensity. 6T molecules grew on Ag(110) and Ag(111) with their molecular planes parallel to the substrate surface irrespective of film thickness. On Ag(110), a novel pseudo-one-dimensional structure of 6T molecules oriented toward [001] direction could be observed. The models for adsorption structures of 6T on Ag(110) and Ag(111) are proposed by taking account of the lattice commensurability. (C) 2004 Elsevier B.V. All rights reserved.