Molecular orientations and adsorption structures of α-sexithienyl thin films grown on Ag (1 1 0) and Ag (1 1 1) surfaces

Molecular orientations and adsorption structures of α-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 π* or σ* 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.