Influence of preparation conditions on the monolayer structure: Bi- and terthiophenes in solution and UHV

In this work we report on STM and LEED investigations of donor-acceptor-sub stituted bi- and terthiophene monolayers on weakly interacting substrates p repared under two different conditions: by evaporation in UHV and by adsorp tion at the liquid/solid interface. A detailed comparison of the results sh ows that the ordering is mainly given by the intermolecular interactions, b ut the observed molecular structures can also depend on the specific prepar ation conditions. In all cases the orientation with respect to the substrat e is strongly influenced by the environment. At the liquid/solid interface the molecule-substrate interaction seems to be reduced by the solvent, lead ing to close-packed structures with no phase relation with respect to the s ubstrate, whereas for UHV-prepared monolayers well-defined azimuthal orient ations were found.