Publikationen

The synthesis of nano-scaled materials using several variations of the single source precursor concept in sol-gel and chemical vapour deposition techniques is demonstrated. Mono- and biphasic ceramics and cermets (metallic phases incorporated in a metal oxide phase) are addressed. The materials prepared are all nanocrystalline in a range from 5 to 50nm. The ceramics belong inter alia to the spinel and perowskite-type. In the biphasic ceramic systems, especially NdAlO3 in Al2O3 is highlighted. In the cermet family Ge, Sn and Pb in either their oxide matrices or in perowskite matrices (M´MO3, M´ = Ca, Sr, Ba; M = Ge, Sn, Pb) and Al and Ga in Al2O3 or Ga2O3 matrices are discussed. Two general concepts are presented in more detail: 1) the arrangement of mutually dependent ligands in the precursor molecule, to facilitate intra-molecular cascade or domino reactions, and 2) the role of metastable phases for physical patterning. The temperature and pressure dependent formation of aluminum/aluminum oxide composites and their structural consequences leading to zero-dimensional ball-shape spheres or to one-dimensional nano-wires is shown as well as the core shell structures of such composites.

Zr(OPri)4∙(PriOH) reacts with N-phenylsalicylideneimine in anhydrous benzene in 1 : 2 molar ratio to afford [Zr{O(C6H4)CH=NPh}2{OPri}2] (1). Further reactions of 1 with various glycols yield heteroleptic complexes of the type [Zr{O(C6H4)CH=NPh}2{O-G-O}] [where-G-= (CH2)2 (2), (CH2CHCH3) (3), (CH3CHCHCH3) (4), (CH2CHC2H5) (5), (CH2)3 (6), (CH2CH2CHCH3) (7), and (CH2)6 (8)]. All new derivatives have been characterized by elemental analyses, FTIR and NMR (1H and 13C{1H}) studies. FAB mass spectra of 1 and 7 revealed the monomeric nature of these complexes. Complete hydrolyses and low temperature transformations of 1 and 7 using sol-gel technique formed tetragonal phase of ZrO2 at 700 °C, whereas transformation of tetragonal to monoclinic phase occurred at 900 ° C. SEM observations of these samples indicate formation of agglomerates of nanocrystalline zirconia (Scherer analysis).

A new combinatorial technique has been developed for the parallel synthesis of multi-component solid-state inorganic materials. As an example to illustrate the utility of this new method, a phase relationship investigation for the ternary system Fe2O3-TiO2-Al2O3, is presented with a much wider composition range in comparison with the previous investigations by conventional means. The combinatorial composition spreading in a ternary system was realized by three combined triangular pyramid-shaped layers produced by the injection moulding technique in the final shape of a triangular prism, followed by a subsequent dividing and mixing process. The consistency of the phase relationship analyzed by XRD with the previous reports proved the reliability of the new combinatorial strategy. The samples were also characterized by SEM and ICP-AES.

A direct gravure printing process for UV-curable indium tin oxide (ITO) nanoparticle patterns on polyethylene terephthalate and polyethylene naphthalate foils is presented for use as transparent electrodes. Both large-area coatings and patterns of ITO with thicknesses from 0.2 to > 1 μm and feature sizes on the order of 100 μm were realized with a sheet resistance down to 400 Ω□ and a transmission > 85% in the visible. In order to reach the lowest sheet resistance, a post-treatment under inert or reducing conditions at temperatures of 130 to 180 °C was used. Special requirements regarding the gravure printing of electronic material from nanoparticles and potential applications are discussed.

Fabrication of multilayer thin films through layer-by-layer (lbl) deposition of charged nanoparticles on tin-doped indium oxide (ITO) coated and uncoated glass substrates are reported. The thin films were constructed by alternately dipping a substrate into a colloidal suspension of chitosan capped zinc sulphide (ZnS) nanoparticles (30 nm) and citrate stabilized colloidal gold (Au) nanoparticles (20 nm) leading to electrostatic interactions between the oppositely charged nanoparticle layers. Thin films consisting of up to 200 deposition cycles by multiple dipping have been studied and surface morphology, changes in the optical absorption characteristics, thickness, uniformity, roughness and electrical characteristics are reported. The multilayered assemblies, attached to the surface by strong ionic bonds, were highly stable and could not be removed by moderate scratching. The current–voltage characteristics in the forward and reverse bias conditions demonstrated rectifying behaviors in the onset of conduction voltage which makes these films attractive for future electronic devices.

We present a set of criteria to optimize photodetectors based on n-type metal oxide nanowires and a comparison methodology capable of overcoming the present lack of systematic studies dealing with such devices. The response of photoconductors is enhanced following different fabrication strategies, such as diminishing the distance between the electrical contacts, increasing the width of the photoactive area, or improving the electrical mobility of the nanomaterials. The validity of the theoretical background is verified by experimental results obtained with devices based on ZnO nanowires. The performances of our devices show that the normalized gain of single ZnO nanowire-based photodetectors exceeds those of thin films.