Search

Protein-based bottom-up synthesis of functional nanomaterials and devices is one of the most promising areas in bio-nanotechnology. Here, we demonstrate that organic assemblies can serve as biologically controllable scaffolds for the deposition of inorganic nanoparticles. In this work, wild-type M13 phages were employed for controlled mineralization of zinc oxide particles. Our aim was to construct layered structures of organic and inorganic materials which contain alternating layers on a smooth substrate. The structure, elemental composition, and also the integrity of the organic and the biologically-templated inorganic layers were studied. A uniform nano-hybrid structure without significant thickness fluctuations was fabricated by using a high concentration of M13 phages and a carbon-coated substrate. The current study gives insight into the combination of organic–inorganic materials to form a multilayered structure, which in turn sets the stage for the fabrication of electronic devices, e. g. actuators or capacitors.

The influence of five different proteins on the crystallization of ZnO was investigated. The aim was to create bio-inspired artificially-synthesized materials by applying the knowledge acquired about naturally occurring inorganic/bio-organic composites. We found that the lower the isoelectric point of a protein, the more efficient is the adsorption of this protein at ZnO. Thus, electrostatic interaction is the main force responsible for the adsorption between proteins and ZnO. The isoelectric point of the protein does not play any role in the morphology of the ZnO crystallites. Morphology and crystallographic orientation of ZnO crystallites remain practically unaltered when globular proteins are employed during the synthesis. On the other hand, the use of an elongated protein causes a significant increase in the size of the ZnO crystallite. The synthesis under investigation provides a base for the generation of innovative composites with combined properties of ZnO and biological functions of native proteins.

Nanocomposites made of polymer-derived Si–C–N ceramic reinforced by single-wall carbon nanotubes (SWCNTs) were prepared for the first time. The synthesis procedure involved ultrasonic dispersion of the nanotubes into a liquid polysilazane precursor polymer, followed by cross-linking and thermolysis. With the aid of nanoindentation testing, dependence of the mechanical properties of the composites on the concentration and agglomeration state of SWCNTs, was studied. The nanotube-filled composites showed improved mechanical performance, as reflected by an increase in Young's modulus which was found to be correlated with the microstructure of the composites, in particular the degree of dispersion of the nanotubes inside the matrix, whereas the hardness is hardly affected.

Crystalline In(OH)3 and UV-emitting In2O3 thin films with a unique columnar morphology have been successfully prepared for the first time via a simple aqueous solution deposition method. In the present study, sulfonate-terminated self-assembled monolayers on single-crystal Si wafers were used as substrates for the film deposition. Uniform In(OH)3 thin films formed on self-assembled monolayers in aqueous solutions of InCl3.4H2O at 60°C. These films, containing columnar In(OH)3 crystals, showed preferential growth orientation along the [100] direction. The current understanding of the film formation mechanism was discussed. After annealing in air at 400°C, these films were converted to nanocrystalline In2O3 films without modification of the morphology. Photoluminescence emission from In2O3 films was reported at approximately 3.4eV, which was ascribed to the near-band-edge emission.

Chemical bath deposition has been introduced as a means to produce films of inorganic substances with low engineering expenditure and close to ambient temperature. Organic additives have been used to control the growth of zinc oxide particles in solution and prevent the formation of the typical rod-like morphology. In the present work an attempt is made to combine these two approaches in order to produce thin films of zinc oxide. In the presence of β-cyclodextrin, spherical nano-crystalline deposits were obtained from solution; polyethylene glycol induced the formation of nano-structured thin films. With polyvinylpyrrolidone as an additive, uniform films were deposited. The structure of these films was analyzed by X-ray diffraction and transmission electron microscopy, which revealed the presence of domains of locally oriented nanocrystals. A mechanism of oriented attachment is proposed to explain the formation of domained ZnO films.

Besides conventional high-temperature sintering processes for the preparation of ceramics, synthesis routes like chemical and physical vapor phase deposition or molecular beam epitaxy as well as sol-gel and polymer thermolysis carried out at decreased temperatures gain in significance. Such a trend is especially pronounced in the case of the deposition of oxide-based solids from aqueous solutions induced by organic templates. This approach is inspired by biomineralization that in general involves the formation of well-structured and complex-shaped organic/inorganic composites by the deposition of an inorganic solid on an organic matrix that consists of biomolecules like proteins. It occurs at ambient conditions with respect to temperature, pressure and atmosphere. The imitation of these processes by technical means is the deposition of thin oxide films from aqueous solutions in the presence of organic self-assembled monolayers. Besides general features of this technique like low synthesis temperatures, processing costs and equipment expenditure as well as the line-of-sight deposition suitable for coating complex shaped and/or temperature-sensitive substrates the characteristics of the films and their mechanisms of formation are discussed by way of the oxide systems TiO 2 , ZrO 2 and ZnO.

Amorphous Si37C32N31 and Si37C29N34 ceramics were produced by pyrolysis of a polyhy-dromethylsilazane precursor. Their structure was investigated by X-ray and neutron diffraction. Wide angle diffraction showed that the Si-atoms are preferentially bonded to nitrogen atoms, but also bonding to carbon atoms was found. This suggests that the excess carbon atoms form an amorphous graphite-like phase. Small angle scattering revealed that the ceramics are inhomogeneous. The evolution of the phase separation during annealing was investigated and it was concluded that amorphous Si3N4 precipitates grow in the Si-C-N materials. The results are compared with previous results for amorphous Si24C43N33 produced from a polysilylcarbodiimide precursor [1 - 3].

In recent years, the pyrolysis of preceramic organometallic compounds became of increased interest for the synthesis of new inorganic materials. The main objective of this process route is to build up novel materials from molecular units in order to design the material on an atomic scale. According to this process, preceramic polymers are synthesized from monomer units. After cross-linking of such precursors, the obtained preceramic networks will be transformed by pyrolysis into amorphous materials. Further increase of the temperature yields thermodynamically metastable and/or stable crystalline phases. Because of the fraction of covalent bonding providing high thermally, chemically and mechanically stable materials, materials based on the Si-B-C-N system are of special interest. Bulk materials, coatings, and fibers of such materials reveal quite interesting high temperatus properties.

This paper reviews recent results on the synthesis of novel materials at the Pulvermetallurgisches Laboratorium (PML). The preparation of nano-sized ceramic powders as well as new powder technological approaches in the field of colloidal processing are discussed. Additionally, liquid-phase sintering of beta aluminas and of silicon carbide is described. Complementary to these investigations the synthesis of covalent materials by powder-free methods by using preceramic compounds (precursors) is a topic of current activity. Research in this field focus mainly on the precursor synthesis, the processing of precursors to ceramic thin films, coatings and bulk materials as well as on the investigation of the materials properties.

An amorphous covalent silicon-, carbon- and nitrogen-containing solid is prepared by the thermolysis of a polyvinylsilazane. Crystallization of the metastable material is induced by subsequent heat treatment at 1600°C. For that purpose, microwave and conventional heating are applied and compared. The resulting materials are investigated by conventional and analytical transmission electron microscopy and X-ray diffraction. In the case of the conventionally heated material, thermal degradation occurs accompanied by a strong reduction of the nitrogen content. In contrast, kinetic stabilization of the Si–C–N solid by microwave heating is observed. Based on thermodynamic considerations, a model for the high-temperature behavior of the material is presented.