Molecular architecture through substrate patterning: bithiophene on clean and sulphur patterned Ni(110)

Here bithiophene monolayers formed on clean Ni(110) and the Ni(110) c(2x2)S and p(4x1)S sulphur reconstructions are contrasted. Investigations with a variety of techniques are presented with particular emphasis on angle-resolved ultra-violet photoemission spectroscopy and its ability to give information on the nature of the chemical bond and, through application of symmetry selection rules, the molecular orientation. On the clean Ni substrate the bithiophene is strongly bound through the re orbitals, flat lying and disordered. S modification passivates the substrates and turns off the pi interaction. On the c(2 x 2)S substrate no strong preference for the molecular orientation is indicated. In contrast the p(4 x 1)S substrate's corrugated structure acts as a template that forces the assembly of the molecular monolayer. This monolayer is ordered with the molecular axis parallel to the substrate ridges ([001] azimuth). The molecules adopt a syn-conformation, and it is suggested that the sulphur atoms of both rings are involved in bonding to the Ni atoms exposed on the sides of the ridges of the reconstruction. (C) 1999 Elsevier Science B.V. All rights reserved.