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-resol ved ultra-violet photoemission spectroscopy and its ability to give informa tion on the nature of the chemical bond and, through application of symmetr y selection rules, the molecular orientation. On the clean Ni substrate the bithiophene is strongly bound through the re orbitals, flat lying and diso rdered. S modification passivates the substrates and turns off the pi inter action. On the c(2 x 2)S substrate no strong preference for the molecular o rientation is indicated. In contrast the p(4 x 1)S substrate's corrugated s tructure acts as a template that forces the assembly of the molecular monol ayer. This monolayer is ordered with the molecular axis parallel to the sub strate ridges ([001] azimuth). The molecules adopt a syn-conformation, and it is suggested that the sulphur atoms of both rings are involved in bondin g to the Ni atoms exposed on the sides of the ridges of the reconstruction. (C) 1999 Elsevier Science B.V. All rights reserved.