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For the adsorption and self-assembly of organic semiconductors we developed a novel concept that we term "Organic Solid-Solid Wetting Deposition (OSWD). The concept is based on a subtle interplay of binding energies of molecules in reference to the surfaces of nanocrystals and substrates.
The OSWD process enables to grow monolayers and nanostructures of insoluble organic semiconductors and pigments under ambient conditions. The basic idea behind this approach can be described as follows:
Regard the case of a liquid droplet in contact to a solid surface: it will spread on the solid and wet its surface if the adhesion energy between the surface molecules of the droplet and the surface atoms of the substrate exceeds the cohesion energy between the molecules of the droplet. Now, regard some properties of crystals of organic semiconductors and pigments: the organic molecules are assembled into solid crystals via noncovalent bonds such as van-der-Waals interactions and hydrogen bonds. Such bonds are weak compared to e.g. covalent or metallic bonds of inorganic crystals. Thus, it is possible for some organic compounds that, if a direct contact between the surface of organic nanocrystals and the surface of inorganic substrates is established, the binding energy of surface molecules in the nanocrystal is exceeded by the binding energy of the molecules to the substrate (adsorption energy). In this case, molecules detach from the nanocrystal, adsorb on the substrate surface and form monolayers via diffusion, if the molecule-substrate interaction is not too strong. This effect can be discussed as being analogue to the above mentioned classical case of wetting - the spreading of a liquid on a solid. Thus, we refer to this wetting-like process at the interface between two solids as “Organic Solid/Solid Wetting Deposition”.
We developed various approaches to
influence the outcome of OSWD induced
self-assembly.