X-ray/Atomic Force Microscopy Study of the Temperature-Dependent Multilayer Structure of PTCDI-C8 Films on SiO2

Combining atomic force microscopy, X-ray specular reflection, and grazing incidence X-ray diffraction experiments provides a thorough characterization of the structural properties of PTCDI-C-8 films on native silicon dioxide as a function of both growth and post-annealing temperatures. We disclose that monomolecular islands and terraces are polycrystalline with lateral sizes of only similar to 280 angstrom. While the lateral size of the crystallites remains unaffected by an increase of the growth temperature, the ordering along the surface normal is greatly enhanced, thereby reducing the density of topographical grain boundaries. Similarly, optimal post-annealing temperatures cause a better vertical ordering of the multilayer. From a detailed analysis of the X-ray reflectivity as obtained for the best ordered film, we provide accurate information on the vertical structure in the thin film and determine the tilt of the perylene cores.