Metal oxides such as titanium dioxide and zink oxide are well-known semiconductors. They are used in various a wide
variety of functional devices. The size and morphology of the material has a substantial effect on device performance.
Here, we propose to manufacture a hierarchic assembly of nanomaterials on the micrometer scale to arrive at new
functionalities for photonic devices. The construction of the materials follows a bottom-up assembly that mimics
processes that occur in nature.
Mesoscopic structures are important for photonics applications. Here we describe the preparation of (sub)micrometer
droplet or line patterns of organic semiconductors by a simple casting process. Dewetting during the solvent evaporation
leads to the formation of regular structures that are caused by the so-called dissipative structures that develop during nonequilibrium
conditions. Controlling the casting conditions (concentration, speed, etc) we were able to tailor the resulting
patterns. Examples for the patterns are luminescent or conducting aggregates that can be used as organic transistors.
Coating the self-organized structures with metals is an easy process to produce patterend metal surfaces, which can be
sued in plasmonics.
Mesoscopic structures are important for photonics applications. Here we describe the preparation of honeycomb films
with pore diameters of 3 to 7 μm from a crosslinkable polymer by the breath-figure technique, which involves the
evaporation of a solution of the solute at high humidity. The honeycomb films then were used as templates for less-thendense
packing of microspheres or for the adsorption of nanocrystalline inorganic oxides. Application of the strongly light
scattering and highly porous honeycomb films are in the field of photocatalysis.
A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or "domes", of organic compounds, both polymeric and low-molar-mass, on various substrates such as silicon, mica, glass, and indiumtin-oxide. The produced patterns are characterized by a regular 2-dimensional array of similar-sized domes. Here we report on the reversible shape change of polymeric domes (between lens and sphere) and the irreversible shape
change of domes made of low-molar-mass compounds, e.g. due to crystallization. Control of crystallization leads to the formation of single crystallites of a non-linear-optically active p-nitro phenol salt.
When an organic solution of a polymer is dropped on a hydrophilic surface, e. g. a glass substrate, polymer film is dewetted on the
surface during evaporation of solvent, leaving several polymer patterns such as stripes, dots (domes) and polygon networks. Dewetting phenomena are not only observed in polymer films but also in low mass molecular films. A cyanine-dye complex was prepared from a cationic cyanine dye and an anionic amphiphile. When a chloroform solution of the cyanine complex was spread on a glass substrate by a roller, micro-domes of the cyanine-dye complex formed in dewetted films. The roller draws the three-phase line (the air-solid-liquid boundary of the droplet of the chloroform solution) with a constant rate, which leads to a two-dimensional ordered array of micro-domes. Typically, the size of micro-domes obtained were several or several ten micrometers in width and one micrometer in height. The diameter and height of micro-domes depended on the roller speed. Fluorescence microscopy shows that the cyanine-dye complex is condensed in each micro-dome. The micro-domes consist of polycrystals and gave fluorescence emission that was difference from a chloroform solution of the cyanine-dye complex.
A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the solute on substrates such as silicon, mica, glass, and indium-tin-oxide. The dome size can be controlled by the casting conditions. Higher concentration and slower evaporation of the solvent leads to larger domes. Upon annealing, the dyes may crystallize and form polycrystalline or single crystalline domes or crystalline fibers. Photophysical properties of the domes were investigated and it was found that the absorption and fluorescence spectra depend on the aggregate kind (polycrystalline or single crystalline) and the dome size.
A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the low molar mass solute on substrates such as silicon, mica, glass, and indium-tin-oxide. Using dewetting, the organic hole transporting material of organic light emitting diodes was patterened into micrometer-sized domes on an indium-tin-oxide electrode. Annealing led to a structural change of the domes, which was investigated by optical and electron microscopies. The dewetted dome samples were then coated with electron transport material and top electrode to give functioning organic light emitting diodes. Microscope imaging reveals a strong luminescence from the micrometer-sized domes.