Publikationen

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).

The paper reports first on the electrochemical behavior in liquid Li+ electrolytes of 200 nm thick single sol-gel (CeO2)0.81-TiO2 electrochromic (EC) layers deposited by the dip-coating process. The electrolytes were solutions of 1 M LiCO4 dissolved in dry propylene carbonate (PC) (containing 0.03wt% of water) and wet PC containing up to 10wt% of water, respectively. Then an electrochemical quartz crystal microbalance was used as a sensitive detector to analyze the mass changes occurring during the Li+ ion exchange processes. These electrochemical processes were studied for 370 nm thick double layers, deposited on gold-coated quartz crystal electrodes and sintered at 450 °C in air. The electrolytes were the same solutions with water content varying from 0.03 up to 3wt% of water. The processes have been studied in the potential range from -2.0 to + 1.0 V vs. Ag/AgClO4 during 100 voltammetry cycles. The composition of the (CeO2)0.81-TiO2 layers was found to change during the early cycles, mainly because of an irreversible Li+ intercalation. It was found, however, that the mass change observed during cycling is not due only to a pure Li+ ion exchange process but also involves the adsorption/desorption or exchange of other cations and anions contained in the electrolyte. These ions are Li+ and ClO4- in dry electrolyte and Li+, hydrated Li(H2O)n+ and ClO4- in wet electrolyte. The improvement of the reversibility of the intercalation and deintercalation processes as well as the faster kinetics observed in wet electrolytes are finally discussed in terms of a model in which the formation of hydrated Li+ ions takes an important role.

The reaction of the oligoalumosiloxane [Ph2SiO]8[AlO(OH)]4 (1) with hexamethyldisilazane leads to the triple ionic [Ph2SiO]8[AlO2]2[AlO(O-SiMe3)]2[NH4-THF]2∙2 THF (2) and in the presence of pyridine to [Ph2SiO]8[AlO1.5]4∙2py∙1.5 C7H8 (3). Apart from the usual characterization techniques (NMR and IR spectroscopy) the molecular structures of 2 and 3 have been determined by single-X-ray diffraction analyses. Both alumosiloxanes 2 and 3 present new types of molecular structures with a central four membered Al2O2-ring, on which the further aluminium atoms are attached via oxygen atoms. This leads to an Al4-lozenge, which is centered in subtriangles by oxygen atoms.

Treatment of polymethyl methacrylate with dodecylamine and diethylenetriamine produces a chemornechanical polymer, which undergoes large macroscopic motions as a result of selective recognition of substrates (effectors) in the surrounding aqueous solution. The kinetics of these fully reversible expansions and contractions are compared to those of effector absorption and desorption. The expansion correlates with a polymer particle weight increase, which is in turn found to be largely a function of the uptake of water necessary for solvation of the effector molecules. The selectivity of the motions depends on the nature and placement of the effector ionic sites, and also on the size and nature of the organic residues. Ion pairing between the protonated amine functions and inorganic anions or anionic groups of organic effectors plays a decisive role. The large effects seen with aromatic effectors such as nucleotides, in contrast with saturated analogues, point to cation-pi and C-H-pi interactions as essential elements for the distinction between different effectors, including isomeric compounds. The material exhibits symmetric expansion/pH profiles, which depend distinctly on the ionic strength of the solution. The strong dependence of the motions not only on the applied pH, but also on the concentrations of two simultaneously active effectors, such as AMP and phosphate, present chemically induced logical gate functions; this is tentatively explained by a two-site binding model. In contrast, the large expansions produced by simultaneous action of, for example, copper or zinc and amino acids or peptides are due to co-complexation between the metal ions and known organic chelators. With such ternary complexes, volume expansions by factors of up to 15 are possible with effector concentrations as low as 0.25 mm. The sensitivity can be further increased by miniaturization of the polymer particles; the velocity of the response can be optimized by increasing the surface-to-volume ratio. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)