Microscopic investigations of the indium nitride crystals with flower-like morphology grown by means of halide chemical vapour deposition under atmospheric pressure

Indium nitride prepared under atmospheric pressure using a halide chemical vapour deposition method has been examined by means of a variety of analytical techniques. From the scanning electron microscopic observations of the crystals deposited onto a Si(100) substrate, it was found that they have flower-like morphology. Based on the electron diffraction and X-ray photoelectron spectroscopic analyses, it was deduced that the flower-like InN crystals have a stoichiometry close to In:N=1:1. Transmission electron diffraction and selected area electron diffraction images showed that each petal and a style constituting the flower are of single crystals form with staggered hexagonal bipyramidal structure.     

X-ray structure refinement of single crystals of CeB6 and Ce0.75La0.25B6 solid solution grown by the solution method

Single crystals of CeB₆ and Ce_0.75La_0.25B₆, prepared by crystallization from solutions in molten aluminium, were investigated using X-ray diffractometry. Experimental data were corrected for thermal diffuse scattering and extinction effects. Structural parameters were refined and the residual electron density was calculated. The results were compared with previous studies. Vacancies at the boron position were established for both compounds.     

Design of lactide copolymers as biomaterials

A very important goal of researchers today is providing poly(L -lactide) (PLA)-based polymers with controllable degradation profiles, various (soft or elastic) mechanical properties, reactivity for chemical modification, and other functionalities while keeping the favorable characteristics of PLA. This article concerns the synthetic methods and properties of the following novel lactide copolymers: (1) random and block copolymers of depsipeptide and L -lactide with reactive (ionic) side-chain groups, (2) comb-type PLA and branched PLA, and (3) PLA-grafted polysaccharide and PLA with terminal saccharide residues. Poly(depsipeptide-random-L -lactide)s and polydepsipeptide-block-poly(L -lactide)s with reactive (ionic) side-chain groups should be useful for the preparation of matrices and microspheres with reactive surfaces because of their amphiphilic structures. Comb-type PLA and branched PLA show lower crystallinities than linear PLA. PLA-grafted polysaccharide should be useful for the preparation of matrices with various microstructures and mechanical and degradation properties through the introduction of hydrophilic segments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 453–462, 2004     

Investigation of nonsolvated electron reactions by means of the positron annihilation method

The validity of a model developed by us in which the positronium precursor is mainly the nonsolvated electron makes it possible to study the reactivity of nonsolvated electrons using data on positronium formation probabilities in solutions of electron acceptors. The rate constants thus obtained agree in most cases with those determined with picosecond pulse radiolysis techniques.     

Large-area graphene single crystals grown by low-pressure chemical vapor deposition of methane on copper

Graphene single crystals with dimensions of up to 0.5 mm on a side were grown by low-pressure chemical vapor deposition in copper-foil enclosures using methane as a precursor. Low-energy electron microscopy analysis showed that the large graphene domains had a single crystallographic orientation, with an occasional domain having two orientations. Raman spectroscopy revealed the graphene single crystals to be uniform monolayers with a low D-band intensity. The electron mobility of graphene films extracted from field-effect transistor measurements was found to be higher than 4000 cm(2) V(-1) s(-1) at room temperature.     

Proton transfer reactions in aqueous solution of 2-vinylquinoline copolymers

Fluorescence spectra of atactic and isolaclic poly-2-vinylquinoline and copolymers of 2-vinylquinoline and four non fluorescent comonomers have been measured as a function of pH. The homopolymers and the copolymers with pyrrolidone show two band fluorescence spectra; their intensity ratio changes with pH, polymer concentration and excitation wavelength. For the other copolymers the emission of the protonated heterocycle is only a shoulder of the emission of the neutral form. A kinetic scheme has been proposed to explain these results.     

Investigation of gas-solid reactions by means of thermal analysis/mass spectrometry

During the production of powder-metallurgical and ceramic materials the evolution of gaseous reaction products can result in large structural imperfections. Reaction sintering of titanium aluminides from mixtures of elemental powders can be accompanied by swelling effects combined with considerable volume swelling of the sintered parts [1]. The firing of thick-film pastes containing ruthenium oxide on substrates of AlN ceramics entails the formation of bubbles impairing the function of thick film resistors [2]. These investigations contribute to the clarification of the causes of both phenomena.     

Domain structure of amorphous block copolymers cast from solution

Three types of domain structures, namely spherical, rodlike, and lamellar, of A-B and A-B-A (or B-A-B) block copolymers cast from solutions are discussed on the basis of a criterion that the structures originate at a critical micelle concentration as a result of microphase separation of the block segments and the micelles formed maintain their structures into the solid state without reorganization. It is concluded that the micelles shrink mostly in the direction perpendicular to the interface between the two phases within the micelles because of the appreciable orientation of the block segments in this direction. In other words, the spherical micelle shrinks isotropically to form a spherical domain having a diameter proportional to the 2/3 power of the degree of polymerization (molecular weight) of the corresponding block segment. Rodlike and lamellar micelles, on the other hand, shrink anisotropically to form rodlike and lamellar domains such that the diameter and the thickness of the respective domains are roughly proportional to the 1/2 power of the degree of polymerization of the corresponding block segment.     

Elucidation of the structure of alkane chains in solution by means of 1H NMR

Solvent shifts of a series of alkanes have been studied in perfluorohexane, carbon tetrachloride and diiodomethane. The methylene proton resonances for longer alkyl chains are shifted downfield in perfluorohexane, but upfield in diiodomethane. It is suggested that n-alkanes have a tendency to adopt folded structures in solution, the degree of folding for n-alkane chains in perfluorohexane being larger than that in diiodomethane.     

Electroenzymatic reactions. Investigation of a reductive dehalogenase by means of electrogenerated redox cosubstrates

As an illustration of how cyclic voltammetry can be used to unravel the mechanisms and kinetics of redox enzymes, the reductive dechlorination of trichloroethylene and tetrachloroethylene by a typical reductive dehalogenase, the tetrachloroethene reductive dehalogenase of Sulfurospirillum multivorans (formerly called Dehalospirillum multivorans), was investigated by means of several electrochemically generated cosubstrates. They comprised the monocation and the neutral form of methylviologen, the neutral form of benzylviologen, and cobaltocene. Cyclic voltammetry is used to produce the active form of the cosubstrate under controlled potential conditions. It shows large plateau-shaped catalytic responses, which are used to measure the kinetics of the enzymatic reaction as a function of the substrate and cosubstrate concentrations. The variation of the rate constant for the cosubstrate reaction with its standard potential shows the transition between two asymptotic behaviors, one in which the reaction is under diffusion control and the other in which it is under counter-diffusion control. Simple fitting of this plot allows an estimation of the standard potential of the electron acceptor center in the enzyme (E degrees = -0.57 V vs NHE).     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.     

Lamellar single crystals of nylon‐10,10 grown from a dimethylformamide solution

A new solvent, dimethylformamide (DMF), and the traditional solvent, 1,4‐butanediol, were used to prepare single crystals of nylon‐10,10 from a dilute solution. The lamellae grown from DMF inhabited a more perfect structure and regular shape than those crystals crystallized from traditional solvents such as 1,4‐butanediol and glycerin. These thin and perfect lamellar crystals demonstrated patterns of variation in spacing different from those of melt‐crystallized spherulites on heating. Specifically, the two main spacings slightly separated rather than continuously approaching each other when the temperature was greater than 180 °C. This is a novel phenomenon observed in nylons. Nevertheless, the usual pattern of change in spacing was observed during the cooling process. These lamellar crystals showed more compact spacing of the (002) and (010/100) planes than spherulites at room temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 729–735, 2001     

The influence of the acoustic resonance frequency on chemical reactions in solution

The special features of the influence of low-frequency infrasonic and sonic range vibrations on various physicochemical processes were analyzed. Systems containing both low- and high-molecular-weight components of heterogeneous, microheterogeneous, and homogeneous interactions were studied.     

Investigation of molecular structure of KNO3 by means of gas-phase electron diffraction

Ivanovo Chemical Technology Institute. Ivanovo State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 4, pp. 51–55, July–August, 1991.