Molecular architecture via substrate templating: a submolecular resolution STM study of bithiophene on Ni(1 1 0) 4×1-S

Bithiophene, used as a model for the technologically important longer oligothiophenes, was adsorbed on the highly corrugated (4×1)S reconstructed Ni(1 1 0) surface. These studies have been performed to test the ability of controlling the electronic and geometric structure of the organic/inorganic interface by substrate patterning. Low temperature STM clearly confirms the ability of the above template to align the molecules along the raised ridges of the substrate. At high coverages strings of molecules are evident. The periodicity within the strings is generally forced by the substrate and the molecules are closely packed. Occasionally less dense one-dimensional rows are observed with a periodicity resulting from molecular self assembly. At low coverages the molecules are well resolved under bias conditions where tunnelling via the frontier orbitals (highest occupied molecular orbital or lowest unoccupied molecular orbital) should dominate. However, the molecular STM images are not a simple reproduction of the frontier orbitals.