Controlled Formation of β-Si3N4 on Native Oxidized Silicon Wafers in Ammonia Flow

Crystallography Reports - The formation of β-Si3N4 for subsequent growth of AlGaN and GaN heterostructures of silicon wafers has been studied. It is established that the native oxide layer...     

Kinetics of the gas-phase chlorination of activated carbon with carbon tetrachloride

The chlorination of activated charcoals KAU and SCN with CCl₄ vapor in the temperature range 300–600 °C and also the thermal stability of the added chlorine has been studied. It is shown that chlorination with CCl₄ vapor led to the addition of up to 22 mass % (6.2 mmol/g) of chlorine to the surface layer of the carbon. The added chlorine is desorbed from the surface with formation of HCl, while at temperatures above 500 °C desorption of chlorine goes practically to completion. The effective rate constants and the energies of activation of the processes of chlorination and desorption have been found.     

Synthesis and thermochemical characteristics of Na2O · Al2O3 · 2.5H2O

A pure phase of monosodium aluminate hydrate Na₂O · Al₂O₃ · 2.5H₂O (MAH) is synthesized and characterized by means of XRD, IR, SEM, TGA, and DSC. The heat capacity of the compound is measured in the temperature range of ?100 to 100°C, and the thermal contributions to enthalpy and entropy are calculated. The standard entropy, enthalpy, and Gibbs energy of formation of MAH at 298 K are estimated.     

Nanosized Pd(0)-arabinogalactan composites as catalysts in the Sonogashira reaction

Zero-valent palladium nanoparticles stabilized by arabinogalactan polysaccharide matrix were successfully used for the first time as phosphine-free catalyst in the cross-coupling of terminal alkynes with aryl and hetaryl halides.     

Characterization of single-crystal sapphire substrates by X-ray methods and atomic force microscopy

The possibility of characterizing a number of practically important parameters of sapphire substrates by X-ray methods is substantiated. These parameters include wafer bending, traces of an incompletely removed damaged layer that formed as a result of mechanical treatment (scratches and marks), surface roughness, damaged layer thickness, and the specific features of the substrate real structure. The features of the real structure of single-crystal sapphire substrates were investigated by nondestructive methods of double-crystal X-ray diffraction and plane-wave X-ray topography. The surface relief of the substrates was investigated by atomic force microscopy and X-ray scattering. The use of supplementing analytical methods yields the most complete information about the structural inhomogeneities and state of crystal surface, which is extremely important for optimizing the technology of substrate preparation for epitaxy.     

Optical properties and orientational order of deoxyribonucleic acid molecules at interfaces

A high degree of planar orientational order of DNA molecules in thin films has been discovered by the oblique-polarized-beam method. The coefficients of surface birefringence of films with different thicknesses are measured. The thickness of optically anisotropic surface layers, which are characterized by macroscopic values higher than the diameter of DNA molecules by three orders of magnitude in terms of thickness, is determined. A difference in the main polarizabilities of the monomer unit of DNA, which is estimated for the films, is compared with the corresponding value for the solution measured by flow birefringence. The effect of temperature on the coefficient of birefringence of the films is examined. A comparison of the data on the native and denatured DNA shows that the degree of orientational order for the single-helix structure is smaller than that for the double helix.     

Particular artifacts of topographic images of dielectrics in atomic-force microscopy

Particular artifacts of atomic-force microscopy (AFM) images of dielectrics, which are related to the presence of a static charge on the surface, are described. Artificial climate control with the use of a TRACKPORE ROOM-02 climatic box during measurements makes it possible to remove the static charge, owing to which the quality of AFM images and reliability of measured metric surface characteristics increase. Comparative analysis of the surface roughness measured under conventional conditions of microscope operation (static charge is present on a dielectric surface) and under the conditions of controlled artificial climate (static charge is completely removed) is performed. It is established that, in the presence of a static charge on the surface, roughness measurements may yield both overestimated and underestimated values; the largest increase in error is observed in measurements of micro-and nanosized surface areas.     

Synthesis,Molecular, and Crystal Structure of a Complex of Pentacoordinated Zinc with Chloride Ions and Pyridine-2-Carbaldehyde Hemiacetal

The reaction between pyridine-2-carbaldehyde and zinc chloride in wet MeCN yielded a zinc chelate complex with hemiacetal formed in situ from the hydrated pyridine-2-carbaldehyde and the second molecule of pyridine-2-carbaldehyde. According to X-ray diffraction data, the pentacoordinated environment of the zinc ion is formed by two chlorine atoms and the N,N',O-tridentate ligand. In the crystal, molecules are combined into a 3D supramolecular framework due to the intermolecular hydrogen bonds O–H···Cl, C–H···Cl, and π–π stacking interactions between pyridine rings.