Materials Literature
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The electronic and optical properties of (Zn,Mg)(S,Se) wide-gap solid solutions are studied using ab initio techniques and starting from the previously determined atomistic structure of the alloy. Compositional disorder is shown to close substantially the gap with respect to the predictions of the virtual-crystal appr…
Solutions containing KAu(CN) 2 (∼5 × 10 - 4 M), methanol (0.3 M), and nitrous oxide (2.5 × 10 - 2 M) are γ-irradiated in the presence of colloidal gold (∼6 × 10 - 5 M; mean particle size, 15 nm). The hydroxymethyl radicals, • CH 2 OH, which are generated in these solutions, reduce Au(I) in Au(CN) 2 -, and the reduced…
Strong and sustained electron emission at low electric fields was observed in undoped, nanostructured diamond. Electron emission of 10 milliamperes per square centimeter was observed at applied fields of 3 to 5 volts per micrometer. These are the lowest fields ever reported for any field-emitting material at technolog…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelf-Assembly of [2]Catenanes Containing Metals in Their BackbonesMakoto FujitaView Author Information Coordination Chemistry Laboratories, Institute for Molecular Science, Myodaiji, Okazaki 444, Japan Cite this: Acc. Chem. Res. 1999, 32, 1, 53–61Publication Date (Web):Novem…
The layered and hexagonal yttrium-based surfactant mesophases templated by anionic surfactant (C(n)()H(2)(n)()(+1)OSO(3)(-) and C(n)()H(2)(n)()(+1)SO(3)(-)) assemblies were synthesized by the homogeneous precipitation method using urea. The layered mesophase is formed of a layered but curving or bending microstructure…
The unsymmetrical porphyrazine (tetraazaporphyrin) bearing a single peripheral bis(dimethylamino) functionality, Mg[pz(NMe(2))(2)(Pr)(6)], was prepared by base-catalyzed cross condensation of dipropyl maleonitrile (in excess) with dimethylamino maleonitrile. The freebase (2H[pz(NMe(2))(2)(Pr)(6)]) and centrally metala…
Cannabis plants have been cultivated in Europe, Asia, Africa and the Americas for hundreds, perhaps even thousands of years as a source of three main products-hemp fibre, cannabis seeds and medicinal or narcotic preparations (Fairbairn, 1976). Hemp fibre is obtained from cannabis stems, and has been used over the cent…
The temperature dependence of the 7 Li NMR shift was measured for LiMn 2 O 4, LiMn 2 - y Ni y O 4 ( y = 0.1, 0.25, 0.33), LiMn 2 - y Co y O 4 ( y = 0.25, 0.5, 1.0), Li[Mn 2 - y Li y ]O 4 ( y = 0.1, 0.33), and λ-MnO 2 spinel oxides. The 7 Li NMR shift can be separated into temperature-independent and -dependent compone…
In the search for boron nanotubes, the geometrical duals of carbon nanotubes, we employ the Euler−Poincare formula for a cylinder, P − C + F = 0. As may be seen in the attached figure, boron nanotubes may be imagined as arising from a correspondence between a boron atom and the center of each of the faces in a carbon…
Au colloids in the 2-3-nm size regime were prepared by in situ reduction of HAuCl(4) in the presence of poly(amidoamine) dendrimers. The dendrimers encapsulate the colloids, imparting stability to the aqueous colloidal solutions. The nanocomposite materials can be isolated by precipitation. The dendrimer generation us…
A quantitative analysis of gallium species (GaO 4 tetrahedra and GaO 6 octahedra) by means of X-ray absorption spectroscopy (XANES and EXAFS) at the Ga K-edge was performed on a series of gallium oxides with various phases and SiO 2 -supported ones. XANES spectra of gallium oxides showed two distinguishable peaks that…
On the basis of a new ab initio, all-electron response scheme, formulated within time-dependent density-functional theory, we solve the puzzle posed by the anomalous dispersion of the plasmon linewidth in K. The key damping mechanism is shown to be decay into particle-hole pairs involving empty states of d-symmetry. W…
ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTNanometer Gold Clusters Protected by Surface-Bound Monolayers of Thiolated Poly(ethylene glycol) Polymer ElectrolyteW. Peter Wuelfing, Stephen M. Gross, Deon T. Miles, and Royce W. MurrayView Author Information Kenan Laboratories of Chemistry University of North Caroli…
Various iron porphyrin systems were found to catalyze the dehydration of aldoximes, such as heptanaldoxime or phenylacetaldoxime, into the corresponding nitriles under mild conditions ( t = 20 °C, neutral or slightly acidic pH). In all these systems, the presence of both the iron porphyrin catalyst and a reducing agen…
Local density calculations of the electronic structure of FeSi, FeSi_{1-x}Al_x and Fe_{1-x}Ir_xSi systems in the B20 structure are presented. Pure FeSi has a semi-conducting gap of 6 mRy at 0 K. Effects of temperature (T) in terms of electronic and vibrational excitations are included. Various measurable properties, s…
In Al-free PrBa_2Cu_3O_{7-y} single crystals the kink in the temperature dependence of magnetic susceptibility chi_{ab}(T), connected with Pr antiferromagnetic ordering, disappears after field cooling (FC) in a field H || ab-plane. The kink in chi_c(T) remains unchanged after FC in H || c-axis. As a possible explanati…
Recently, Zou et al. (Phys. Rev. Lett. 80, 1074, 1998) reported the observation of bulk superconductivity (SC) for a PrBa_2Cu_3O_x (Pr123) single crystal grown by the traveling-solvent floating zone (TSFZ) method. The aim of this Comment is to show the inconsistency of the value of effective magnetic moment μ_{eff} re…
We use a hybrid Monte Carlo algorithm in which a single-cluster update is combined with the over-relaxation and Metropolis spin re-orientation algorithm. Periodic boundary conditions were applied in all directions. We have calculated the fourth-order cumulant in finite size lattices using the single-histogram re-weigh…
The Hall resistivity rho_{xy} of LuNi_2B_2C is negative in the normal as well as in the mixed state and has no sign reversal typical for high-T_c superconductors. A distinct nonlinearity in the rho_{xy} dependence on field H was found in the normal state for T < 40K, accompanied by a large magnetoresistance reaching +…
Mesoporous titania with a large surface area has been prepared by calcination of hybrid composites. The composites were obtained by the incorporation of the biopolymer chitosan in titania networks produced from titanium isopropoxide by a sol−gel process. The resultant titania is of the pure anatase form. The effect of…