Dislocation arrangements in pentacene thin films

We have studied the growth of pentacene films (2--8 monolayers) on modified Si-wafer surfaces by means of synchrotron x-ray diffraction. The diffraction data reveal a nonthermal damping of the (coherent) Bragg reflection intensities according to an exponential dependence on the $3∕2$ power of the momentum transfer. The simultaneous presence of strong diffuse scattering centered around the Bragg positions indicates the presence of local defects. A quantitative analysis of the Bragg and diffuse scattering allows us to identify screw and edge dislocations as the main defects on the molecular scale. We quantify dislocation densities as a function of substrate termination.