Structure and morphology of quaterphenyl thin films on Au(1Â 1Â 1)-The influence of surface contamination by carbon

Quaterphenyl thin films were grown on Au(1 1 1) surfaces which were intentionally covered by different amounts of carbon. The films were investigated by X-ray diffraction and atomic force microscopy. An epitaxial character of the quaterphenyl crystallites could be confirmed for films grown on a clean Au(1 1 1) surface, with the (2 1 1) plane of quaterphenyl parallel to the Au(1 1 1) surface. It was found that the in-plane orientation of the quaterphenyl crystallites is determined by aligning the long molecular axes along 〈11¯0〉Au and 〈112¯〉Au, facing the aromatic units of the molecules parallel to Au(1 1 1). Carbon coverages of 15% or 50% of the Au(1 1 1) surface cause a change in the orientation of the crystallites and a loss of the epitaxial orientation of the crystallites. In case of 15% carbon coverage the (2 0 1) plane of quaterphenyl crystallites develops parallel to Au(1 1 1), and 50% carbon coverage causes a (0 0 1) orientation of the crystallites. Both planes are cleavage planes of quaterphenyl. The film morphology consists of aligned needles for quaterphenyl films grown on the clean Au(1 1 1) surface, bent and randomly oriented needles at 15% carbon coverage and of uniformly distributed hillocks at 50% carbon coverage. The corresponding morphologies can be explained by the crystal structure features of quaterphenyl in combination with the orientation of the molecules within the thin films.