Materials Literature
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In Konzentrationen bis hinab zu 0.3 Gew.-% bildet eine neuartige Familie von Bisharnstoffdicarbonsäuren ein Hydrogel (siehe Bild). Der Aggregationszustand (Vesikel, Gel oder Faser) hängt ab vom pH-Wert, von der Ionenstärke und vom Molekulargewicht des Gelbildners. Somit lassen sich die Eigenschaften des Gels durch Des…
An investigation was carried out on thin permanent phase polarization gratings recorded in Langmuir–Blodgett films using two orthogonal circularly polarized Ar-ion laser beams. The films are composed of amphiphilic azo-dye molecules and manifest an extremely large value of photoinduced optical anisotropy, Δn≈0.36. The…
Diffusion barrier characteristics and electrical properties of self-aligned MgO layers obtained from a Cu(Mg) alloy film have been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing a Cu(Mg) film in an oxygen ambient and prevented interdiffusion of Cu in SiO2 up to 700 °C. The the…
Two tetradentate bispinene-bipyridine type ligands, each with six stereogenic carbon centers, were synthesized from (-)-alpha-pinene. Their ability to predetermine chiral configurations at metal centers was studied. The two diastereoisomers, L1 and L2, differ in their absolute configuration at the bridgehead position.…
A crossover as a function of temperature is found in the zero-field aging properties of the relaxor ferroelectric Pb(Mg(1/3)Nb(2/3))O3. Below a temperature near which nonlinear susceptibility has indicated a suspected phase transition, the time-frequency dependence shows simple scale-independent behavior resembling th…
Tetradentate Janus heads L−: Staples for the construction of square tetranuclear clusters of the type [M4L8] 1 (M=Ni, Zn; see picture). The [2×2] grids 1 are generated in a one-pot reaction by self-assembly. The magnetic susceptibility of the nickel complex [Ni4L8] Ni-1 exhibits an increase of χT at low temperature du…
Hochverzweigte und maßgeschneiderte Carbosilane wie 1 dienen als Trägermaterial für Diaminoaryl-PdII-Katalysatoren. Die hochverzweigten Katalysatoren weisen ein ähnliches katalytisches Verhalten auf wie die einkernigen Stammverbindungen und bieten eine echte Alternative zu den aufwändig herzustellenden Dendrimer-Katal…
The dependence of sonoluminescence on ambient pressure and temperature is measured. As water is cooled, there occurs a 100-fold increase in light emission which can be accompanied by only slight changes in the ambient radius of the pulsating bubble. This suggests that water vapor trapped in the collapsing bubble is a…
Hyperbranched carbosilane compounds such as 1 are conveniently prepared, soluble supports for diaminoaryl PdII catalysts. The hyperbranched catalyst shows similar activity behavior to its parent mononuclear catalyst and provides a competitive alternative to the corresponding but more tediously produced dendrimer catal…
Transparent TeO2-based glass ceramics consisting of nanocrystalline particles such as 15K2O.15Nb2O5.70TeO2 have been prepared, and the effect of surface layers on the second harmonic (SH) intensity has been examined using the Maker fringe method. An enhanced second harmonic generation (SHG) with fine fringe patterns h…
Die Entstehung komplexer Morphologien in lebenden und nicht belebten Systemen ist für Wissenschaftler, die den Ursprung und die Entwicklung von Form und Struktur erforschen, ein großes Rätsel. Während der vergangenen Jahre machten Biologen einerseits und Physiker andererseits bahnbrechende Fortschritte bei der Erkläru…
Nanosized metal-oxide-based composites—novel supramolecular entities—have been assembled and even cross-linked under one-pot conditions. The supramolecular entity (see picture) consists of a paramagnetic icosahedral capsule of the type {MoFe} as a host which encloses a potential electron-reservoir noncovalently bonded…
Photo- and radioluminescence, decay kinetics, and thermoluminescence are reported for a set of Ce3+-doped phosphate glasses. The presence of Gd3+ ions in the glass host matrix at concentrations above 20% enhances the energy transfer towards the Ce3+ emission centers, which results in a remarkable enhancement of the ra…
We report on the observation of stimulated emission in ZnO/MgxZn1−xO superlattices well above room temperature. Two kinds of superlattices grown by laser molecular-beam epitaxy showed clear systematics on the quantum subband levels in absorption and spontaneous emission spectra. Stimulated emission with excitonic orig…
A red phosphor, Li-doped Gd2O3:Eu3+ with high cathodoluminescent brightness was developed. In contrast to Gd2O3:Eu3+ which showed an irregular shape of agglomerated fine particles (the mean particle size <0.5 μm), the morphology of Li doped Gd2O3:Eu3+ crystals was quite regular and pseudospherical (the mean par…
Multiphoton photoelectron spectroscopy reveals the multiple excitation of the surface plasmon in silver nanoparticles on graphite. Resonant excitation of the surface plasmon with 400 nm femtosecond radiation allows one to distinguish between photoemission from the nanoparticles and the substrate. Two different previou…
Recently, an electromagnetic metamaterial was fabricated and demonstrated to exhibit a “left-handed” (LH) propagation band at microwave frequencies. A LH metamaterial is one characterized by material constants—the permeability and permittivity—which are simultaneously negative, a situation never observed in naturally…
At concentrations as low as 0.3 wt % a novel family of bis-urea dicarboxylic acids gel water (see picture). The aggregation state (vesicles, gel, or fibers) depends on the pH, the ionic strength, and the molecular weight of the gelator. In this way, the gelation properties of an aqueous system are controlled by the mo…
The emergence of complex form in living and nonliving systems remains a deep question for scientists attempting to understand the origins and development of shape and structure. In recent years, biologists and physicists have made significant advances in explaining fundamental problems in fields such as morphogenesis…
The real part of the refractive index n(omega) of a nearly transparent and passive medium is usually taken to have only positive values. Through an analysis of a current source radiating into a 1D "left-handed" material (LHM)-where the permittivity and permeability are simultaneously less than zero-we determine the an…