Investigating Measurement Errors in Dual-Frequency Probing Technique by Mathematical Modeling

We present mathematical modeling of the process of determining the time coordinate of the moment of arrival of a pulse echo in the dual-frequency probing technique, as well as graphs of the involved measurement error versus the comparator’s discrimination threshold for different ratios of frequencies and distances and ratio of the frequencies of emitted pulses. Mathematical modeling has revealed limiting cases in which the measurement error increases and can reach 3–4%. Analysis of results has made it possible to identify additional requirements for the mathematical processing of received signals to keep the error within 1%.

     

Reverse recovery of Si/Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> heterodiodes fabricated by direct bonding

We have studied the process of reverse recovery of Si/Si_{1 − x} Ge _x heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si_{1 − x} Ge _x wafers of the same orientation containing 4–8 at. % Ge. An increase in the germanium concentration N _Ge in p-Si_{1 − x} Ge _x layer is accompanied by a decrease in the reverse recovery time of heterodiodes. The presence of a sharp drop in the reverse current on the diode recovery characteristic can be explained by the existence of a narrow region with decreased minority carrier lifetime at the bonding interface (compared to carrier lifetime in the bulk), which is caused by the accumulation of misfit dislocations (generated by bonding (in this region). The results demonstrate the principal possibility of creating fast-recovery diodes based on the Si/Si_{1 − x} Ge _x heterosystem for high-power semiconductor devices manufactured using the direct bonding technology.     

A comparative study of switching possibilities of silicon diodes with different axial distribution shapes of recombination centers

Three groups of silicon p ⁺-n-n ⁺ diodes with a small turn-off time ensured by charged particle irradiation were studied in the high-power (3 kA) and short (50 μs) current pulse switching modes. The diodes of the first group were irradiated by electrons with a 550-keV energy, those of the second group were irradiated by protons with a 2.5-MeV energy and then by electrons with a 6-MeV energy, and those of the third group were irradiated by electrons with a 6-MeV energy. The studied diodes have a 16-mm semiconductor element diameter and 3-kV maximum permissible disabled voltage. The radiation doses were selected in such a way as to obtain an approximately equal current carrier lifetime near the p ⁺-n junction (4 μs), measured by the Lacks method, when the forward current density is 1 A/cm². It was determined that, when diodes of the first group change to the OFF position, the peak power of energy losses is two and more times smaller than that of diodes of the second and third groups, when they are switched off. The diodes of the first group also feature a substantially smaller voltage, when the forward current is at maximum (by two times as compared with diodes of the second group and by seven times as compared with diodes of the third group) and significantly smaller (by several times) voltage spike at a sharp forward current increase instant.     

PIM-1/MIL-101 hybrid composite membrane material: Transport properties and free volume

A hybrid composite membrane material based on the PIM-1 polymer of intrinsic microporosity and MIL-101 nanoparticles of mesoporous chromium terephthalate has been prepared and tested. Fourier-transform IR spectroscopy has revealed the presence of interaction between the polymer matrix and the nanoparticles introduced into it. The addition of MIL-101 nanoparticles leads to an increase in the permeability and diffusion coefficients for gases (He, O₂, N₂, CO₂) compared to the original polymer. Using positron annihilation lifetime spectroscopy (PALS), it has been shown that these changes result from an increase in the free volume in the polymer composite material.     

Microstructure and Physicomechanical Properties of a Cu-8 at % Pd Alloy

The evolution of the structure, microhardness, and electrical resistivity has been studied during prolonged low-temperature annealings of the Cu-8 at % Pd alloy. An increase in the microhardness and electrical resistivity after annealings at temperatures of 250 and 300°C has been revealed; the preliminary deformation significantly accelerates and enhances this effect; and the X-ray diffraction patterns remain unchanged and correspond to an fcc solid solution. Using transmission electron microscopy, the state of an atomic short-range order has been detected in the quenched alloy; prolonged annealings of the deformed alloy lead to the formation of microregions of the ordered L1₂ phase.     

Current-voltage characteristics of isotype SiC-SiC junctions fabricated by direct wafer bonding

Results obtained in a study of current-voltage characteristics of isotype SiC-SiC structures fabricated by direct bonding of single-crystal n-type 6H-SiC wafers with a donor concentration of ～10¹⁶ cm^?3 are presented. The initial wafer bonding was done in deionized water. To enhance the adhesion, the structure was thermally annealed at 1250°C. All the features of the current-voltage characteristics measured are consistently explained in terms of the hypothesis that the SiC-SiC interface is a variable-thickness channel filled with a native SiO_x oxide of thickness 10–100 nm. The minimum experimentally measured differential resistance of the structure (6 Θ cm²) is limited by the current transport in the oxide layer, which occurs by the mechanism of space-charge-limited currents.     

Weldability of corrosion-resistant high-nitrogen austenitic Kh22AG16N8M-type steels

The influence of thermal treatment on the structures and mechanical properties of welds of corrosion-resistant high-nitrogen austenitic 05Kh22AG16N8M-type steels is studied. In these steels, austenite is found to be highly resistant to discontinuous precipitation and the formation of σ phase and δ ferrite upon cooling regardless of the temperature of heating for quenching (from 900 to 1250°C) and the cooling conditions (water, air, furnace). Welding of these steels can produce high-strength welds with an enhanced impact toughness.