Barth S.,Institute of Materials Chemistry |
Jimenez-Diaz R.,University of Barcelona |
Sama J.,University of Barcelona |
Daniel Prades J.,University of Barcelona |
And 4 more authors.
Chemical Communications | Year: 2012
Simultaneous localized growth and device integration of inorganic nanostructures on heated micromembranes is demonstrated for single crystalline germanium and tin oxide nanowires. Fully operating CO gas sensors prove the potential of the presented approach. With this simple CMOS compatible technique, issues of assembly, transfer and contact formation are addressed. © 2012 The Royal Society of Chemistry.
Seibel C.,University of Wurzburg |
Nuber A.,University of Wurzburg |
Bentmann H.,University of Wurzburg |
Mulazzi M.,University of Wurzburg |
And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014
We report on the spectroscopic observation of a quantized electronic fine structure near the Fermi energy in thin Fe films grown on W(110). The quantum well states are detected down to binding energies of ∼10 meV by angle-resolved photoelectron spectroscopy. The band dispersion of these states is found to feature a pronounced anisotropy within the surface plane: It is free-electron-like along the ΓH̄ direction while it becomes heavy along ΓN̄. Density functional theory calculations identify the observed states to have both majority and minority spin character and indicate that the large anisotropy can be dependent on the number of Fe layers and coupling to the substrate. © 2014 American Physical Society.
Blaha P.,Institute of Materials Chemistry
Journal of Physics: Conference Series | Year: 2010
A short introduction to periodic bandstructure methods suitable for the calculation of Mössbauer parameters is presented. These methods are based on density functional theory (because we want to treat big and complicated systems) and must be accurate not only in the bonding region (like pseudopotential approaches), but also near the atomic nuclei since Mössbauer parameters depend crucially on the wave functions at/near the nucleus. A numerical basis set as in augmented plane wave (APW) based methods is very well suited for this purpose and the APW method is briefly sketched. The results for Y BaFe2O5 are discussed in more detail and compared with experiment. © 2010 IOP Publishing Ltd.
Polyimides withstand extreme heat and chemically aggressive solvents, while being considerably less dense than metals. That is why they are very popular in industry, for example as an insulation layer on PCBs or in aerospace applications. However, it is precisely their high stability, which makes polyimides very difficult to process. Neither melting nor etching can be used to bring them into the correct shape. At TU Wien, a new synthesis method has now been developed which opens up completely new possibilities for this material class: it has been possible to produce angular polyimide particles for the first time using a technical trick. "Small plastic particles are usually obtained as spherical objects," says Miriam Unterlass from the Institute of Materials Chemistry at TU Wien. However, roundish particles are poorly suited for many applications. "Particle-containing liquids are extensively used as paints and protective coatings," says Unterlass. "The geometric shape of the particles then determines how the particles are arranged and move within the liquid." Many such dispersions do not dry uniformly, because an unfavourable current is produced during evaporation which transports the particles in a particular direction. Clearly, one would prefer paints to dry homogeneously. There have been repeated attempts to give polyimide particles or similar materials an angular shape, but until now there has been little success. Miriam Unterlass' team at TU Wien has now tried a completely new approach. At first, two different molecules, which usually combine in a rather disorganised manner, are used to produce an angular salt crystal. The salt crystal is formed by conducting the reaction in a gel. The viscous gel slows down the speed of the molecules, which decelerates the reaction, producing well-ordered, high-quality crystals with a diameter of hundreds of micrometres – these are visible to the naked eye. Then comes the crucial step: the crystals are heated, thus producing a further chemical reaction. The salt crystal is converted into polyimide in the solid-state. The salt crystals do not dissolve nor do they melt – it is just the heat that does the trick. Aside, water is created as harmless byproduct. The angular shape of the original salt crystal is retained and an angular polyimide particle lacking any curvature is created. The material for special uses The material withstands almost any solvent and remains stable up to 700 degrees. There are many uses for resistant particles of this kind. They could be combined with other materials to produce protective coatings, or special materials for space travel. This research success was made possible due to an unusual combination of very different areas of chemistry: "Gel crystallisation, high-performance materials, solid-state synthesis and crystallography are areas that are rarely combined," says Miriam Unterlass. "It was not easy to bring such different approaches together, but it was definitely worth it in the end." It should be possible to use the same method (production of a salt in gel, which is then heated to convert it into polymer particles which take on the crystal shape) to synthesise other high-performance materials. Further experiments are already under way. Explore further: Designer materials: Entropy can lead to order, paving the route to nanostructures More information: Konstantin Kriechbaum et al. Shape-Anisotropic Polyimide Particles by Solid-State Polycondensation of Monomer Salt Single Crystals, Macromolecules (2015). DOI: 10.1021/acs.macromol.5b01545
Huang M.-R.,Institute of Materials Chemistry |
Gu G.-L.,Institute of Materials Chemistry |
Ding Y.-B.,Institute of Materials Chemistry |
Fu X.-T.,Institute of Materials Chemistry
Fenxi Huaxue/ Chinese Journal of Analytical Chemistry | Year: 2012
Advanced solid-contact ion selective electrodes (ISEs) constructed from electrically conducting polymers are systematically summarized based on the latest literatures and our latest work. Due to the unique conjugation structure and dual functions of electronic and ionic conductivity, conjugated conductive polymers can act as ion-to-electron transducers to realize the sensitive detection of ions. The solid-contact ISEs with conducting polymers, such as polyaniline, polypyrrole and polythiophene, as intermediate layers have been successfully used to detect ions at nanomolar level concentrations. Such ISEs are expected to play an important role in various areas such as environmental monitoring, drug manufacturing, medical treatment and food safety. Copyright © 2012, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences.