Structural studies of 2,2′-bipyridine on Au(100)

Abstract

The adsorption of 2,2′-bipyridine (2,2′-BP) on Au(100) in acidic solution was investigated by electrochemical methods and in-situ scanning tunneling microscopy (STM). The organic molecules form an ordered monolayer on Au(100)-(1×1) at positive charge densities. The film was imaged with molecular resolution. The structure of the adlayer is determined by substrate-adsorbate coordination and lateral π-stacking. The misfit between potential molecular and substrate coordination sites gives rise to highly ordered ‘kinked’ stacking rows. The intermolecular distance within one chain amounts to (3.7±0.2) Å. Molecules are tilted from the normal to the chain axis by an angle α=18°. The distance between two adjacent rows, which are rotated by 45° with respect to the 01̄1-direction of the (100)-lattice, is (10.2±0.4) Å. Furthermore, the potential (charge)-induced formation and dissolution of the ordered 2,2′-BP monolayer were studied in detail. Due to the uneven distribution of ‘local charge density’ on reconstructed (hex) and unreconstructed (1×1) patches of a partially reconstructed Au(100) surface a highly selective decoration of the squared regions with molecular stacks could be achieved.