Materials Literature
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Push−pull organic molecules that combine a polyfunctionalized electron-donating carbazole moiety with a new acceptor group, 4-methylene-4 H- oxazol-5-ones, were synthesized and characterized as nonlinear optical chromophores with promising μβ values. First-order hyperpolarizability and dipole moments were calculated b…
Fast, electrically switchable reflectors based on cholesteric gels are described. The gels can be patterned locally to reflect different colors (see Figure) and it is shown that the threshold of (reversible) switching is determined by the pitch. This means that areas that reflect different colors can be switched seque…
Ultrasonic attenuation spectroscopy was successfully applied for in-situ determination of particle size during the crystallization of a molecular crystal in two different polymorphic forms. The crystallization of l -glutamic acid was carried out under different cooling conditions by which the α- or β-polymorphic form…
We present an exact asymptotic solution for electron transition amplitudes in an infinite linear chain driven by an external time-dependent electric field. This solution extends the Landau-Zener theory for the case of an infinite number of states in the discrete spectrum. In addition to the transition amplitudes we ca…
Gratings inscribed on stretched azobenzene elastomer (AE) films show reversible changes in the diffraction of light upon extension or retraction of the film. Polarized optical micrographs of two gratings on an AE film with their fringes parallel (left) and perpendicular (right) to the strain direction after relaxation…
Photovoltage signals were observed at ultrathin metal oxide $({\mathrm{TiO}}_{2},{\mathrm{Cu}}_{2}\mathrm{O},\mathrm{}\mathrm{ZnO})/$ metal structures by transient and spectral photovoltage (PV) techniques. The sign, the spectral behavior and the time-dependent relaxation of the PV are determined by the nature of the…
The dependence of block copolymer interdomain spacing d on polymer volume fraction φ P in solution, d ∼ P, is examined through a series of styrene−isoprene diblock copolymers in four solvents, three of them strongly selective (nonsolvents for polystyrene). The exponent β is found to depend on solvent selectivity (both…
Side-chain fluorinated copolymers present very specific wetting and tacking properties that are strongly related to their organization. We have studied the structure of these systems by X-ray scattering in the liquid crystalline regime, as a function of the ratio of fluorinated groups on one hand and of the copolymeri…
The creation of a second-order nonlinear susceptibility ${\ensuremath{\chi}}^{(2)}$ in thermally poled silica glasses is known to be related to positive charge migration. As opposed to currently used models, we herein propose a model that takes into account charge dissociation and charge recombination occurring during…
Gold nanoparticles act as seeds for the growth of mesoporous silica shells according to the method described here for the synthesis of silica/gold nanocomposites. It is shown that the silica matrix is highly crystalline with mesopores that extend throughout the structure. The Figure depicts the procedure used and the…
The dielectric response of layered perovskite-related insulating ${\mathrm{SrNbO}}_{3.5}$ and conducting ${\mathrm{SrNbO}}_{3.41},$ ${\mathrm{SrNbO}}_{3.45},$ and ${\mathrm{La}}_{0.2}{\mathrm{Sr}}_{0.8}{\mathrm{NbO}}_{3.5}$ single crystals is investigated. The measurements are performed along the c axis, i.e., perpend…
We investigate numerically the structure of topological defects close to a spherical particle immersed in a uniformly aligned nematic liquid crystal. To this end we have implemented an adaptive mesh refinement scheme in an axi-symmetric three-dimensional system, which makes it feasible to take into account properly th…
We present three-dimensional simulations of field emission from single-wall and multi-wall carbon nanotubes. The structures considered are the metallic ideally open (5,5), (10,10), (15,15) and (5,5)@(10,10)@(15,15) nanotubes. For the multi-wall structure, flat and convex terminations are considered. The scattering cal…
Thermal conductivity, resistivity, Seebeck coefficient, and Hall measurements on polycrystalline Sn-clathrate compounds with the type-I hydrate crystal structure are reported. Interstitial alkali-metal atoms in these compounds reside inside polyhedral cavities formed by the tetrahedrally bonded Sn network atoms. Local…
An improved and efficient synthetic route to four functionalized bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) derivatives 2-5 is reported. Tetrathiolate 1 was readily prepared from 2,2'-bis(1,3,4,6-tetrathiapentalen-5-one) under carefully controlled conditions. Subsequent reaction of 1 with selected primary alkyl…
Surface plasmon resonance of periodic narrow-grooved metallic thin films were studied with finite-difference time-domain simulations. Two distinguishable modes, surface plasmon polaritons and localized surface plasmons, are associated with different periods. The surface plasmon polaritons have widely extended near-fie…
We report first-principles total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled BN nanotubes, $(n,0)$@(15,0) and $(m,0)$@(20,0). We find that the most favorable double-walled nanotubes studied here are (7,0)@(15,0) and (12,0)@(20,0) in which the interwall di…
Aligned calcite crystals have been grown in an hexagonal arrangement (see Figure) using highly oriented Au (111) films on monocrystalline mica substrates. This alignment is observed over distances larger than the dimensions of monocrystalline Au(111) domains. A change in nucleation face with pH during growth—reflectin…
A spine- or herringbone-like array of molecules characterizes the crystal structure of the organic semiconductor 2,5-bis(4-biphenylyl)thiophene (BP1T). Its bent molecular shape enforces an upright disposition of the molecular long axes against the ab-plane that parallels the crystal faces of the flake-like crystals (s…
Using results of first-principles band structure calculations and a model tight-binding approach, we investigate the local stability of the half-metallic ferrimagnetic (FiM) states in double perovskites ${\mathrm{Sr}}_{2}\mathrm{Fe}M{\mathrm{O}}_{6}$ $(M=\mathrm{Mo},$ Re, and W). In ordered compounds, a generalized do…