Self-assembly of 1-nitronaphthalene on Au(111)

We report low-temperature scanning tunneling microscopy and near-edge X-ray absorption fine structure investigations of the organic molecule 1-nitrona phthalene adsorbed on the reconstructed Au(111) surface. Depending on the c overage, molecular structures of distinct dimensionality are observed. Afte r saturation of the step edges with molecules, clusters form on the substra te terraces at coverages up to 0.15 monolayers (ML). The smallest clusters consist of three molecules and are stable at specific surface reconstructio n sites only. In contrast, pinwheel-shaped clusters comprised of ten molecu les are observed on various inequivalent sites of the reconstructed Au surf ace. For coverages larger than 0.2 ML one-dimensional molecular double chai ns prevail. The structure of the decamers and the chains is determined by i ntermolecular electrostatic forces, whereas their position and orientation are affected by the surface reconstruction. At saturation coverage a period ic two-dimensional close-packed arrangement of molecules that is independen t of the surface reconstruction occurs simultaneously with one-dimensional structures along the uniaxial reconstruction domains. The structural featur es are discussed in terms of competing effects of intermolecular forces and the interaction with the substrate. (C) 2000 Elsevier Science B.V. All rig hts reserved.