Crystal structure of p-hexaphenyl thin films

Wide angle x-ray diffraction on vapor deposited thin films of p-hexaphenyl on GaAs substrates reveals that the preferred growth of the crystallites on the substrate is strongly dependent on the sample preparation conditions. At low substrate temperatures and high deposition rates we detect two directions of preferred growth with the (11-1) and/or (20-3) planes of hexaphenyl parallel to the surface of the substrates; at both these orientations the molecular chains are parallel to the surface. At high substrate temperatures and low deposition rates the (001) plane is parallel to the substrate; for this type the molecular chains are standing on the substrate. Some minor influence to the preferred growth is given also by the purity of the hexaphenyl; the thickness of the thin films has no effect.