DETERMINATION OF SOIL TROPHICITY BY ELECTROPHYSICAL METHOD. MESSAGE 1. DEVICE AND LABORATORY TECHNIQUE

The purpose of this work was to develop a device and technique for determining the soil trophiсity using the electrophysical method based on the measurement of the soil specific resistivity (SR). In the proposed device the F. Wenner installation is used as a sensor. The device has a modular design and includes a voltage boosting module, a PWM generator of rectangular pulses, a rectangular signal inverter and an H-bridge that switches the polarity of the power supply in order to prevent polarization of the electrodes. The metrological characteristics of the specific resistivity measurement as well as the influence of the electrodes immersion depth in the substrate studied are determined. Its significant influence and nonlinear character which was well approximated by the power function were established. The simplest equations for bringing the measured values of the RS to a certain depth of the electrodes in the object studied are proposed.

Properties of CrSi2 Layers Obtained by Rapid Heat Treatment of Cr Film on Silicon

The changes in the morphology and the electrophysical properties of the Cr/n-Si (111) structure depending on the rapid thermal treatment were considered in this study. The chromium films of about 30 nm thickness were deposited via magnetron sputtering. The rapid thermal treatment was performed by the irradiation of the substrate’s back side with the incoherent light flux of the quartz halogen lamps in nitrogen medium up to 200–550 °C. The surface morphology was investigated, including the grain size, the roughness parameters and the specific surface energy using atomic force microscopy. The resistivity value of the chromium films on silicon was determined by means of the four-probe method. It was established that at the temperatures of the rapid thermal treatment up to 350 °С one can observe re-crystallization of the chromium films with preservation of the fine grain morphology of the surface, accompanied by a reduction in the grain sizes, specific surface energy and the value of specific resistivity. At the temperatures of the rapid thermal treatment from 400 to 550 °С there originates the diffusion synthesis of the chromium disilicide CrSi2 with the wave-like surface morphology, followed by an increase in the grain sizes, roughness parameters, the specific surface energy and the specific resistivity value.

Nickel silicide formation with rapid thermal treatment in the heat balance mode

The formation of nickel silicide layers on (111)-Si substrates during rapid thermal annealing in the heat balance mode was studied by the Rutherford backscattering method, X-ray diffraction, transmission electron microscopy, and electrophysical measurements. Nickel films of about 70 nm thickness were deposited by magnetron sputtering at room temperature. The rapid thermal treatment was carried out in a heat balance mode by irradiating the substrates backside with a non-coherent light flux of quartz halogen lamps in the nitrogen medium for 7 seconds up to the temperature range of 200 to 550 °C. The redistribution of nickel and silicon atoms to monosilicide NiSi composition starts already at a temperature of 300 °С and almost ends at a temperature of 400 °С. In the same temperature range, the orthorhombic NiSi phase with an average grain size of about 0.05–0.1 μm is formed. At a rapid thermal treatment temperature of 300 °C, two phases of silicides (Ni2 Si and NiSi) are formed, while a thin layer of unreacted Ni is retained on the surface. This fact can be explained by the high heating rate at the initial annealing stage, at which the temperature conditions of the NiSi phase formation occur earlier than the entire Ni layer manages to turn into the Ni2 Si phase. The layers with a simultaneous presence of three phases are characterized by a high roughness of the silicide-silicon interface. The dependence of the specific resistivity of nickel silicide layers shows an increase to the values of 26–30 μOhm · cm in the range of rapid thermal treatment temperatures of 200–250 °C and a subsequent decrease to the values of about 15 μOhm · cm at a rapid thermal treatment temperature of 400 °C. This value of specific resistivity is characteristic of the high conductivity of the NiSi phase and correlates well with the results of structure studies.

Properties of Alumina Coatings Deposited by Detonation Spraying

Coatings deposited by detonation spraying equipment CCDS2000 using alumina powder are studied. CCDS2000 is characterized by a computer control system, robot compatible spraying unit (gun barrel), a portable chiller, two powder feeders, and other peculiar properties. This installation allows to deposit coatings on complex shape surfaces and thin-walled parts under optimal conditions. Studies of the coating properties included measurements of coating microstructure, porosity, microhardness, adhesion, cohesion, abrasive and erosive wear, and dielectric properties (specific resistivity and dielectric strength). The detonation sprayed coatings have an adhesion of 60-70 MPa, cohesion of 100 MPa, microhardness of 1500 HV100, porosity of about 1% (measured on microsections of coatings using OLYMPUS Stream Image Analysis software). Impregnation of coatings with silicone oil showed that the real open porosity of coatings is up to 6%. Dielectric strength of the ceramic layer with the thickness of 200 μm exceeds 30 kV/mm. Specific resistivity depends on atmospheric humidity and when the relative humidity is less than 60%, the specific resistivity is greater than 1013 Ω·cm.

Morphologies, Young’s Modulus and Resistivity of High Aspect Ratio Tungsten Nanowires

High aspect ratio tungsten nanowires have been prepared by selective dissolution of Nickel-aluminum-tungsten (NiAl−W) alloys which were directionally solidified at growth rates varying from 2 to 25 μm/s with a temperature gradient of 300 K·cm−1. Young’s modulus and electrical resistivity of tungsten nanowires were measured by metallic mask template method. The results show that the tungsten nanowires with uniform diameter and high aspect ratio are well aligned. The length of tungsten nanowires increases with prolongation of etching time, and their length reaches 300 μm at 14 h. Young’s modulus of tungsten nanowires is estimated by Hertz and Sneddon models. The Sneddon model is proper for estimating the Young’s modulus, and the value of calculating Young’s modulus are 260–460 GPa which approach the value of bulk tungsten. The resistivity of tungsten nanowires is measured and fitted with Fuchs−Sondheimer (FS) + Mayadas−Shatzkes (MS) model. The fitting results show that the specific resistivity of W nanowires is a litter bigger than the bulk W, and its value decreases with decreasing diameter.

Influence of Substrate Properties on the Defectivity and Minority Carrier Lifetime in 4H-SiC Homoepitaxial Layers

Two fully loaded epitaxial growth runs with 16 wafers in total were conducted in the AIXTRON G5 WW reactor in order to keep epigrowth conditions constant. The wafers were selected with a large spread of specific resistivity and dislocation densities. The resulting epilayers showed very good intra-wafer homogeneities as well as excellent wafer-to-wafer and run-to-run reproducibility with regard to epilayer thickness and doping concentration, point defect concentrations of Z1/2 and EH6/7 and the resulting Shockley-Read-Hall carrier lifetime. We found that the dislocation densities of the underlying substrates are influencing the stacking fault densities of the epilayers, which then vary between 0.1 and 10 cm-2. A substrate effect on the effective minority carrier lifetime was found.

Novel Method for NTC Thermistor Production by Aerosol Co-Deposition and Combined Sintering

A novel three-stage process to produce NTCR sensors is presented. In this process, an uncalcined powder mixture of NiO and Mn2O3 was deposited onto an alumina substrate via aerosol co-deposition (AcD). Then, an electrode structure was screen-printed onto the surface and the composite film was sintered in a multifunctional temperature treatment. Thereby, the sintering of the electrode, the formation of the NiMn2O4 spinel and the removal of film strains took place simultaneously. This enabled a significant reduction in energy demand and workload. The manufactured sensors, both as first prototypes, as well as miniaturized chip components, were characterized by a single-phase cubic NiMn2O4 spinel structure, mechanical stability and electrical properties that were similar to those of classical NiMn2O4 bulk ceramics or tempered aerosol deposited (AD) NiMn2O4 films. Particularly noteworthy was the high reproducibility and low variation of the NTCR parameters, such as the specific resistivity at 25 °C ρ25, the electrical resistance at 25 °C R25 and the thermistor constant B. The NTCR parameters were as aging-stable as for NiMn2O4 bulk ceramics or tempered NiMn2O4 AD-films and could even be further improved by thermal post-treatment.

Microwave Analysis of Scattered and Absorbed Powers of Semiconductor and Metamaterial Cylinder Structures

Here is presented our numerical investigations based on the rigorous solution of the Maxwell’s equations for analyses of absorbed and scattered powers of a semiconductor-metamaterial array with a window defect. The array structure consists of a finite set of infinite parallel, circular cylinders that can be made of the different lossy and/or lossless isotropic materials. We used our developed computer code, which allowed us to consider an array consisting of an arbitrary number of cylinders. According to our code, cylinders can be located at different distances and have differing diameters. There is a limitation: Cylinders should not cross each other. We numerically examined two cylindrical arrays with electromagnetic (EM) band-gap (EBG) defects. The absorbed and scattered powers were analyzed there for parallel and perpendicular polarizations of the incident microwave. We investigated dependencies on the operating frequency and the radius (R) of an arc of the arranged thirteen n-Si cylinders with the low semiconductor specific resistivity of 0.5, 2, and 10 Ω∙m. We have discovered that the arrays may have features of a waveguide or a microwave reflector.