Publikationen

Caries and periodontitis, the most wide-spread oral diseases around the world, are caused by bacterial adherence and biofilm formation onto the natural as well as restored tooth surface. One possible way to prevent the pathogenic consequences of intraoral biofilm formation might be the modification of the tooth surface by application of an anti-adhesive coating that interferes with the bacterial attachment and subsequent bacterial accumulation. The objective of this study was to investigate the effect of an experimental, low surface free energy nano-composite coating material on biofilm formation in situ. For this purpose, an organic/inorganic nano-composite coating (NANOMER (R), INM, Saarbrucken, Germany) with a surface free energy of 18-20 mJ/m2 was applied to enamel as well as titanium specimens. The nano-composite coated specimens and un-coated controls were attached to removable intraoral splints and carried by volunteers over 24 h in the oral cavity. After intraoral exposure, specimens were processed for transmission electron microscopic analysis. On non-coated enamel and titanium control samples a multi-layer of adherent bacteria was found. In contrast, on nano-composite coated specimens strongly reduced biofilm formation was observed. In most areas of the surface-coated specimens only a 10-20 nm thick electron dense layer of adsorbed salivary proteins with adherent protein agglomerates of 20-80 nm diameter could be detected. In addition, detachment of the adsorbed biofilm from the nano-composite coated surfaces was evident in electron microscopic micrographs. The present investigation provides ultrastructural evidence that it is possible to cover enamel as well as titanium with a nano-composite coating revealing easy-to-clean surface properties that cause reduced biofilm formation and accelerated removal of adherent biofilms under oral conditions.

Individual SnO2 nanowires were integrated in suspended micromembrane-based bottom-up devices. Electrical contacts between the nanowires and the electrodes were achieved with the help of electron- and ion-beam-assisted direct-write nanolithography processes. The stability of these nanomaterials was evaluated as function of time and applied current, showing that stable and reliable devices were obtained. Furthermore, the possibility of modulating their temperature using the integrated microheater placed in the membrane was also demonstrated, enabling these devices to be used in gas sensing procedures. We present a methodology and general strategy for the fabrication and characterization of portable and reliable nanowire-based devices.

Nanosized BaTiO3 powders with a specific surface area of 60-75 m2/g have been prepared by precipitation of a titanium ester with Ba(OH)2 solution at temperatures less than 100 °C. The effects of the Ba(OH)2 concentration, isopropanol mixing with water as a solvent, the Ba:Ti ratio and surface modifiers on the surface area, the particle size, the crystalline phase, the agglomeration and aggregation degree of the synthesized powders as well as dielectric properties of sintered pellets have been investigated. The properties of the obtained powders have been characterized with XRD, BET, TG-DTA, ICP-AES, HRTEM and dilatometer. A high concentration of Ba(OH)2 can increase the agglomeration and aggregation degree of the particles while the addition of isopropanol in water is beneficial for lowering it. To obtain stoichiometrical barium titanate, the ratio of Ba:Ti should be 1.1. The leaching of barium ions during processing can be limited by washing the powder with ammonia solution at pH 10.2. A BaTiO3 ceramic (95.8% of the theoretic density) has been fabricated by sintering the powders at 1250 °C for 2 h.

Nanocrystalline BaSnO3 with a primary particle size of 40-60 nm was prepared through hydrolysis of a barium tin isopropoxide and following crystallization. The thermal decomposition, the crystallization and the microstructure of the obtained powders were investigated with the help of TG-DTA, IR, XRD, HRSEM and HRTEM. The organic rest groups in the as-prepared powder decompose thermally at 350 °C, which is accompanied by the building of BaCO3 that disappear again at 600 °C. The crystallization of BaSnO3 takes place at 500-600 °C. Single-phase BaSnO3 powders have been obtained at a temperature as low as 600 °C. The amorphous as-prepared powder shows a cluster structure. Nucleation of BaSnO3 beginning at 350 °C was observed under HRTEM, and the spherical nano-particles of BaSnO3 calcined at 760 °C crystallize well and are strongly aggregated. The presented results indicate a heterogeneous nucleation and growth mechanism by the formation of BaSnO3.

BaSnO3 powders have been prepared from the tin oxide hydrate gel and the Ba(OH)2 solution via hydrothermal synthesis route. The influence of the process parameters on the characteristics of BaSnO3 has been studied. A powder with the single-phase of BaSnO3 can be obtained only when the concentration of Ba(OH)2 solution is no less than 0.2 M and the ratio of Ba:Sn lies between 1.0 and 1.2. At a hydrothermal temperature of 330°C or higher, uniform BaSnO3 powders can be directly prepared through hydrothermal reaction. When the hydrothermal temperature is lower than 250°C, the as-prepared powder consists of BaSn(OH)6 that transforms through an amorphous phase into BaSnO3 by calcination at 260°C. In the hydrothermal temperature range of 130-250°C, a higher temperature can promote the crystallization of BaSnO3, increases its specific surface area and decreases the average particle size. The duration of the hydrothermal reaction affects the morphology of the powder particles. The effects of the nonaqueous solvents on the properties of powders have also been investigated.

Single-step synthesis of one-dimensional Ge/SiCxNy core-shell nanocables was achieved by chemical vapor deposition of the molecular precursor [Ge{N(SiMe3)2}2]. Single crystalline Ge nanowires (diameter ~ 60 nm) embedded in uniform SiCxNy shells were obtained in high yields, whereby the growth process was not influenced by the nature of substrates. The shell material exhibited high oxidation and chemical resistance at elevated temperatures (up to 250 °C) resulting in the preservation of size-dependent semiconductor properties of germanium nanowires, such as intact transport of charge carriers and reduction of energy consumption, when compared to pure Ge nanowires.

Ligand L (4,5-bis[(2′-hydroxyethyl)thio]1,3-dithiole-2thione) which crystallizes in the monoclinic system (P21/n) displays a 1-D network generated by a succession of intra-molecular and inter-molecular hydrogen bonds. Weak π-π and S⋯S interactions are also observed in the supramolecular structure. Reaction of L with one equivalent of mercury(II) iodide affords the adduct [HgI2L] (la). The crystal structure of this complex shows that coordination occurs exclusively via the sulfur atom of the thione function (C=S). The ligation on HgI2 induces a change of the hydrogen bond pattern generated by the hydroxyl substituents: only intermolecular hydrogen bonds are present, organizing the adduct 1a in form of centrosymmetrical dimers in the solid state. The propensity of HgI2 to build-up chains via μ2-iodo ligand may be at the origin of the modification of the hydrogen bond network.

Nonstabilized and silica-stabilized zirconia (ZrO2) crystallites with sizes between 3 and 4 nm were synthesized by a novel combined sol-gel and solvothermal process. After adding zirconium n-propoxide to a solution of isobutanol, propionic acid, and water, a transparent nanoparticulate sol was synthesized by a sol-gel process. The average hydrodynamic diameter of the amorphous ZrO2 nanoparticles was approximately 5 nm. A following solvothermal process led to a crystalline fraction of the powder consisting of 31 wt% tetragonal (t) phase ZrO2. This fraction was doubled to 61 wt% by adding 10 mol% 3-methacryloxypropyl trimethoxysilane (MPTS) and increased to 96 wt% by a subsequent calcination at 800 °C. The crystallite sizes were also confirmed by means of Brunauer-Emmett-Teller and high-resolution transmission electron microscopy.

A novel sol-gel synthesis route for the preparation of a transparent organic-inorganic nanocomposite was developed by combining methacrylic acid (MA) stabilized, amorphous ZrO2 nanoparticles, which were synthesized by the sol-gel process, with an organic-inorganic dodecandioldimethacrylate (DDDMA)/3-methacryloxypropyl trimethoxysilane (MPTS) hybrid matrix. The average hydrodynamic particle size was determined to be approximately 6 nm by photon correlation spectroscopy. HR-TEM micrographs present irregular shaped zirconia particles with diameters up to 3 nm. Nearly solvent-free nanocomposites with zirconium (Zr) contents up to 15.2 mol% were synthesized and photochemically cured to transparent crack-free bulks. The surface charged nanoparticles in 1-propanol had an electrophoretic mobility of 0.017 (μm cm)/(V s), measured by Laser Doppler Anemometry (LDA) and a refractive index ne of 1.648 ± 0.007 determined by spectroscopic ellipsometry. After filling the nanocomposite into a linear electrophoresis cell (1 × 1.6 × 0.8 cm3), positively charged high refractive nanoparticles migrated through the low refractive hybrid matrix toward the cathode by the application of an electric potential difference of 2 kV/cm for 96 h. A 67% increase in Zr over a distance of 8 mm between the cathode and anode was observed by high-resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDXS).