Materials Literature
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Single-crystal synchrotron-radiation data have been recorded, using an area detector, for a crystal of dimensions 4 x 8 x 125 p,m, composition SiO2, and the structure redetermined. R = 0.116 for 394 reflections with F > 6tr(F). The unit cell, and the framework of SiO4 tetrahedra, sharing corners, with channels paralle…
The microstructure and electrical properties of calcium-modified barium titanate ceramics of compositions (Ba1−xCax)TiO3 have been investigated. From the influence of the CaO content and stoichiometry on the said characteristics of the materials, it is concluded that the cationic ratio, α=(Ba+Ca)/Ti, is the predominan…
Band structures are calculated for perovskite-type compounds KM${\mathrm{F}}_{3}$ (with M=Mn, Fe, Co, Ni, Cu, and Zn) on the basis of the extended H\"uckel tight-binding method and a partial density of states as well as a total density of states is presented for comparison with available experimental data. Our calcula…
Abstract Phase separation of two immiscible polymer blends can be controlled by ionic cross‐interactions of the end‐groups as promoted by proton transfer from acid end‐groups of polymer PA to aliphatic tert ‐amine end‐groups of PB. IR spectroscopy supports the occurrence of proton transfer with formation of ammonium c…
Abstract Poly( L ‐ornithine) having azo aromatic side chain was synthesized by the water‐soluble carbodiimide procedure. The photochemical properties of the azo polypeptide poly[ N δ ‐ p ‐(phenylazo)benzoyl‐ L ‐ornithine] (PPABLO) was investigated by absorption and circular dichroism spectroscopy in hexafluoro‐2‐propa…
Thermoelectric power of annealed β-Ag2Se thin films of different thicknesses has been measured both while heating and cooling by the integral method. It is found that it remains practically constant (in β-Ag2Se phase) during heating while it is a function of temperature while cooling. The thermoelectric power in both…
The surface composition of a series of symmetric diblock copolymers of polystyrene (PS) and polymethylmethacrylate (PMMA) was studied using x-ray photoelectron spectroscopy (XPS). Each copolymer was composed of N segments where N ranged from 270 to 5200. At large N, where the system is highly segregated, the surface i…
Granular alloys of iron with other transition metals have been fabricated in both Al2O3 and SiO2 matrices. Both stable (Fe-Ni, Fe-Co) and metastable (Fe-Cu) alloys have been achieved. Under appropriate deposition conditions, the grains are single-phase alloys ranging in size from 15 to 50 Å. Superparamagnetism and enh…
Angle-resolved photoemission spectra were measured using synchrotron radiation for thin films of the pentatriacontan-18-one molecule [${\mathrm{CH}}_{3}$(${\mathrm{CH}}_{2}$${)}_{16}$CO(${\mathrm{CH}}_{2}$${)}_{16}$${\mathrm{CH}}_{3}$] with their long axes perpendicular to the substrate surface. At the preparation of…
Abstract Polyethylene films were surface grafted with glycidyl methacrylate (GMA) by UV irradiating the film for 5 min together with benzophenone. Poly(ethylene glycol) (PEG) was attached to the grafted surface through reaction with the epoxy groups. This yielded a surface which consisted of 95% PEG as measured with E…
The polar interface interaction between a chiral smectic-A liquid crystal and a solid substrate results in an induced ferroelectric polarization and chiral reorientation of the director in the liquid crystal near the surface.
We employ density functional methods to derive the free energy and grand potential functionals appropriate to homopolymers and blends. The grand potential functionals are minimized by the single-monomer densities of the blends or homopolymers, and the nonideal portions of the free energies possess functional Taylor ex…
In some crystalline and glass ceramic IR upconverting materials, the visible light intensity resulting from the IR excitation can be reduced by a prior x-ray exposure. Such behavior is studied for medical x-ray imaging applications. A model is developed to describe the interactions between the microscopic defects resp…
C 4 H 4 INO 2 cristallise dans P4 1 ou P4 3 avec a=6,339 et c=15,445 A, Z=4; affinement jusqu'a R=0,019. La structure est stabilisee par de fortes interactions intermoleculaires I...O. La polarisation calculee pour un monocristal et les resultats d'un test pyroelectrique de Kundt-Burker conduisent a une attribution de…
(LaS) 1.14 NbS 2 is a misfit layer compound built of alternate double layers of LaS with La in square pyramidal coordination with sulphur and sandwiched with NbS 2 as occurs in 2H-NbS 2 . The electrical transport properties and magnetic properties were determined using single crystals and powder compacts. The compound…
A new type of Monte Carlo algorithm to calculate packing fraction and general particle dispersion characteristics for arbitrary random packs of spherical particles is presented. Given arbitrary quantities of arbitrary sizes with arbitrary mass densities, the algorithms calculate the close random packing fraction. If d…
A gas-phase reaction mechanism is proposed for the chemical vapor deposition (CVD) of amorphous silicon from silane or disilane at atmospheric pressure. The gas stream in the CVD reactor is populated by silanes, silylenes, and disilenes in a variety of sizes. Silylenes form by the decomposition of silanes, and they ra…
In ultrasmall quantum nanostructures the interparticle Coulomb energy is a small perturbation to single-particle confinement and kinetic energies. Third-order perturbation theory has been used to calculate energies of excitons and biexcitons confined in quantum box nanostructures. The confined biexciton is more stable…
Using fully quantal methods, we investigate various manifestations of the geometric phase in bound and free diatom systems. Adiabaticity and degeneracy are not invoked in the discussion.Received 3 May 1989DOI:https://doi.org/10.1103/PhysRevLett.64.256©1990 American Physical Society
Visible luminescence between 2.0–3.5 eV of undoped and boron-doped diamond formed by plasma-assisted chemical vapor deposition has been investigated by cathodoluminescence. Electroluminescence from Schottky diode of boron-doped semiconducting diamond has been observed for the first time and found to be due to the same…