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...     

High-Quality AlN Layers Grown on Si(111) Substrates by Metalorganic Chemical Vapor Deposition

Crystallography Reports - The effect of trimethylaluminum preflow time on the crystalline quality of AlN films grown by metalorganic chemical vapor deposition on Si(111) substrates has been...     

Development of Ni–Mo Sorption-Catalytic Materials for Removing Arsenic Compounds from Middle Distillates

Possibility of using mesoporous materials for obtaining Ni–Mo sorption-catalytic materials for purification of medium-distillate fractions to remove arsenic-containing compounds was examined. It was shown that, in the course of hydropurification, the acidity of the mesoporous material does not directly affect the extent to which the amount of arsenic in hydrocarbons is diminished. It was found that mesoporous supports of the SBA-15, TUD, and MCF types reduce the content of arsenic to less than 0.5 ppm at 360°C and 50 atm of H₂.     

Effect of sodium chloride on the solubility and hydrolysis of epichlorohydrin in water

The mutual solubility of the components in the epichlorhydrin–water–sodium chloride system was studied in the temperature range of 20–90 °С. It was found that epichlorohydrin is salted out as the concentration of NaCl increases. The Sechenov coefficient was determined to be equal to 0.29. It was found that epichlorohydrin reacts with an aqueous solution of sodium chloride to form glycerol dichlorohydrins. Alkali formed during this reaction catalyzes the hydrolysis of epichlorohydrin to glycerol monochlorohydrin, acts as a reagent in the glycidol formation and accelerates its subsequent conversion to glycerol.     

Specific features of solketal synthesis on KU-2-8 cation-exchange resin

Technological specific features of the solketal synthesis on a KU-2-8 cation-exchange resin were improved. Data are presented on the mutual solubility of the components in the glycerol–acetone–water and glycerol–acetone–water–ethanol systems. It is shown that use of ethanol for homogenization of the starting reagents is more than twice more efficient than performing the process with delivery of an emulsion of the reagents or reaching a full solubility of glycerol in acetone due to the 20-fold excess of the latter at 35°C. It is shown that the delivery of a glycerol emulsion in acetone to an immobile bed of a heterogeneous catalyst working in the falling-film mode leads to flooding of the reactor at spraying densities exceeding 0.15 m³ m^–2 h^–1.     

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.     

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.     

Electron microscopy study of the microstructure of Ni–W substrate surface

The surface microstructure of Ni–W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni₉₅W₅ tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO₄ precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950°С is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing in a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.     

Influence of a low-temperature GaN cap layer on the electron concentration in AlGaN/GaN heterostructure

Technical Physics - The influence of low-temperature passivating GaN cap layers on the electrophysical parameters of a 2D electron gas (2DEG) in heterostructure high-electron mobility transistors...     

Technical Storage Ring Complex “Zelenograd” As a Base for an Engineering Center of Advanced Materials,Microelectronics, and Biomedical Technologies

Crystallography Reports - The town of Zelenograd was created as the main research and production center of the Soviet microelectronics industry. The Zelenograd Microelectronics Centre provided a...