Materials Literature
按标题、摘要、年份、主题和来源检索公开元数据。结果保留作者、摘要、分类与原始来源链接。
The average dimensions and the anisotropy of the main chain of a side-chain liquid crystalline polymer are determined in the different mesophases on a series of five different molecular weights. From the comparison of the main-chain dimensions, one deduces that the main chains adopt nearly a self-avoided walk in the i…
At high magnetic fields and low temperatures, numerous extreme type-II superconductors exhibit Landau quantization of electronic motion. We present an analytic construction of the quasiparticle spectrum in this regime, based on the high-field expansion. The spectrum is gapless and is separated from the familiar low-fi…
Using a simple mean-field theory and MC simulations we demonstrate the existence of a vapour-liquid transition in a fluid with purely repulsive Yukawa pair interactions and a density-dependent screening parameter. This transition does not fit into the classical Van der Waals picture, as the mechanism of liquid condens…
The lattice parameter of a single-crystal boron-doped synthetic diamond has been measured in the range 4.2-300 K by x-ray diffraction (Bond method), with precision . Over the whole range the results are consistent with A, where T is the absolute temperature. The dilation due to doping indicates a boron concentration o…
Abstract The crystal and magnetic structures of the perovskite YBaCuFeO 5+δ have been studied in the temperature range T = 4.2-300 K by powder neutron diffraction. In addition to the antiferromagnetic ordering transition at T N = 442 K, a commensurate–incommensurate magnetic transition is detected at T N ′ = 190 K. Be…
The cations [Pd2Cl2L]2+ and [KL2′+ (L = [18]aneN2S4, L′ =[15]aneO5) have been used as templates for the synthesis of unique three-dimensional polyiodide networks. The metal cations in [Pd2Cl2L]1.5I5(I3)2 are linked into infinite chains by pairwise hydrogen bonding; the resulting cationic polymers run through channels…
Not threading rings on chains, but chains through rings results in a new class of main-chain polyrotaxanes. The cations of bipyridinium salts thread through the crown ether units of a poly(ester crown ether) chain (shown below). The threading efficiency m/n of the polyrotaxane is controlled by stoichiometry and temper…
The heterogenization of a titanium(IV) silsesquioxane complex in an MCM-41 molecular sieve, by tailoring the polarity of MCM-41, results in self-assembled materials (see the space-filling model on the right) that are active, truly heterogeneous, and recyclable catalysts for liquid-phase alkene epoxidation.
Two new molecular magnets, the dodecanuclear manganese complexes of the type [Mn12O12(O2CR)16(H2O)4] (known for R = CH3, new for R = o-ClC6H4, o-BrC6H4) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization…
We have identified the surface polar structure of wurtzite-type ZnO films by coaxial impact-collision ion scattering spectroscopy. High-quality ZnO epitaxial films were prepared on sapphire (α-Al2O3) (0001) substrates by laser molecular beam epitaxy using a ZnO ceramic target. The (0001̄) crystallographic plane (the O…
The ground-state energy of excitons confined in microspherical crystallites with a finite-height potential wall is studied variationally as a function of the particle radius in the so-called strong-confinement regime. Exciton energies for dot radii in the range 5-40 Å are calculated and compared with experimental and…
We report a systematic study of the electronic transport properties of the metallic perovskite oxide as a function of the oxygen stoichiometry . The electrical resistivity, magnetoresistance, susceptibility, Hall effect and thermopower have been studied. All of the transport coefficients are dependent on the value of…
Intense chiroptical properties and efficient reversibility of the chemical redox cycle support the adaptability of the CuI/CuII complex system 1/2 for the development of a binary molecular device. Reduction proceeds with ascorbic acid, and oxidation with ammonium persulfate.
Small molecules of the indene and pseudoazulene type like 1 and 2 form columnar mesophases! These compounds do not possess peripheral flexible chains like conventional columnar liquid crystals. Instead, polarizable chlorine and sulfur atoms, as well as the polar cyano group, function as unusual soft regions between th…
Frequency upconversion of cw infrared radiation at 1.06 μm into the visible in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glass samples is presented. Intense green and red emission bands around 530, 555, and 670 nm, respectively, are observed in addition to near-infrared 830 and 925 nm less intense signals. Energy tra…
We study the dynamics of a system composed of interacting units each with a complex internal structure comprising many subunits and treat the case in which each subunit grows in a multiplicative manner. We propose a model for such systems in which the interaction among the units is treated in a mean field approximatio…
A mechanical switch in a [2]catenane, made up of a cyclobis(paraquat-p-phenylene) tetracation interlocked with a macrocyclic polyether containing a redox-active tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene ring system, can be thrown either chemically or electrochemically. The neutral TTF unit resides “insi…
We have measured the energy-momentum density of amorphous silicon dioxide using an $(e,2e)$ spectrometer with 20.8 keV incident, 19.6 keV scattered, and 1.2-keV ejected electron energies. The amorphous ${\mathrm{SiO}}_{2}$ sample was prepared by oxidizing a thin silicon membrane. The experimental data show a valence e…
The results of a combined study of the temperature variation of photoluminescence (PL) and dc conductivity from high optical-quality free-standing porous silicon films are presented. PL spectra of the samples have been studied in the range 10–300 K. Dc conductivity (σ) on these samples have been studied from 90 to 300…
Molecular dynamics (MD) simulation of the diffusion of water in both atactic polypropylene (aPP) and amorphous isotactic polypropylene (iPP) models has been performed. Constant particle number, constant pressure, and constant temperature (NPT) MD was employed for both systems consisting of three polypropylene chains o…