Metal–organic interfaces based on copper-phthalocyanine monolayers are studied in dependence of the metal substrate (Au versus Cu), of its symmetry [hexagonal (111) surfaces versus fourfold (100) surfaces], as well as of the donor or acceptor semiconducting character associated with the nonfluorinated or perfluorinated molecules, respectively. Comparison of the properties of these systematically varied metal–organic interfaces provides new insight into the effect of each of the previously mentioned parameters on the molecule–substrate interactions.

We have determined the full molecular 3D packing of thin organic films of the archetypical organic n-type semiconductor N, N'-dioctyl-3,4:9,10-perylene tetracarboxylic diimide (PTCDI-C 8) by surface X-ray crystallography. We show that PTCDI-C 8 forms smooth layered films on Al 2O 3 (11-20) with an outstanding degree of molecular order. The thin-film structure is found to consist of a triclinic unit cell with the plane of the aromatic core tilted by 67 +/- 2 degrees with respect to the surface plane, which differs significantly from the bulk structure. The 3D crystallites extend with vertical coherent order across the entire film thickness.

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 ∼280 Å. 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.

By a combined AFM/X-ray study, we unveil a reconstruction at the organic interface accompanying the Stranski-Kranstanov growth of di-indenoperylene (DIP) deposited on fluorinated cobalt-phthalocyanines (F 16 CoPc). This reconstruction involves an abrupt change in the F 16 CoPc packing in those areas covered by DIP. After the total completion of the first DIP monolayer, the entire F 16 CoPc interfacial layer is reconstructed and eventually becomes buried under the growing DIP film. We demonstrate that the morphological transition from smooth to highly textured heterostructures occurring at a threshold temperature of 70 °C is intimately related to the thermal activation of the reconstruction of the underlying F 16 CoPc layers. This study provides further understanding of the molecular-scale processes that ultimately determine the controlled growth of organic heterojunctions.