Organic‐organic heteroepitaxy: facts, concepts and perspectives

Abstract

Organic-organic heteroepitaxy can represent the winning technique for growing crystalline and oriented heterostructures of organic semiconductors. However, a sound physical interpretation of mechanisms that control epitaxy is still missing for these low symmetry molecular systems, generally not obeying the usual lattice matching rules for inorganic systems. We discuss here a couple of paradigmatic examples of organicorganic heteroepitaxy suggesting a possible physical rationale for the formation of the heterostructure interfaces as it arises from experimental characterization and computer modeling with atom-atom potential simulations.

Substrate Selection for Full Exploitation of Organic Semiconductor Films: Epitaxial Rubrene on β‐Alanine Single Crystals

“…Following established arguments of organic epitaxy, the azimuthal ordering of RUB films on β‐ala(010) can be rationalized. We have already pointed out that the orientation mechanism for building organic heterointerfaces is dictated by molecular scale corrugations of the involved crystalline surfaces.…”

“…The investigation of the energy landscape with properly selected intermolecular potentials can provide a more robust rationalization of observed epitaxial relations . Moreover, symmetry arguments determine the number of equivalent isoenergetic orientations to be found on a substrate .…”

“…For example, the weak epitaxy growth introduced by Yan and co‐workers and the epitaxy on van der Waals surfaces allow for the deposition of RUB films directly on dielectric substrates, but by exploiting only organic epitaxy the best outcomes in terms of crystalline quality have been achieved, as already demonstrated for other small molecules . Different aspects have to be considered for a suitable substrate selection, including the symmetry of the involved surfaces, the adhesion energy at the interface, and local corrugations . An appropriate substrate choice stimulates the epitaxial growth of RUB thin films with a unique orientation, even if successful integration into the devices may be hardly achieved.…”

Epitaxy of oligothiophenes on alkali metal hydrogen phthalates: Simulations and experiments

“…The size of overlayer and substrate models was selected on the basis of previous successful results on several different heteroepitaxial systems. [9][10][11][12][13][14] One molecule thick overlayers with the same molecular arrangement of the bulk crystal were built based on 25 molecules for the 4T(001) and 6T(100) islands (a × b = 4 × 3 and b × c = 2 × 3 unit cells, respectively) and on 14 molecules for the 4T(010) and 6T(010) islands (a × c = 6 × 1 unit cells). Potential energy maps were calculated with 351 3 grid points spaced by 0.22 Å. Simulations of the heteroepitaxial interfaces were performed by 1024 docking runs for each overlayer/substrate pair to explore the azimuthal configuration space.…”

“…In fact, previous studies of various organic-organic epitaxial systems have demonstrated that the mechanism which selects the textural order of heteroepitaxial interfaces is predominantly dictated by the surface corrugations at both substrate and overlayer contact planes, 7,8 determining the possible azimuthal orientations at the interface. [9][10][11][12][13][14] Therefore, epitaxial relations can be established even in incommensurate systems, i.e., with high lattice misfit. Surface corrugation can be described in terms of furrows, arising from molecular crystal packing in the substrate, where the overlayer molecules can lie.…”