Growing HgTe/Cd<Subscript>0.735</Subscript>Hg<Subscript>0.265</Subscript>Te quantum wells by molecular beam epitaxy

HgTe/Cd_0.735Hg_0.265Te nanostructures with HgTe quantum wells 16.2 and 21.0 nm thick are grown without additional doping on (013)CdTe/ZnTe/GaAs substrates by the method of molecular beam epitaxy. The compositions and thicknesses of the wide-gap layer and quantum well in the course of growth are performed by means of ellipsometry. The accuracy is Δx ? ±0.002 mole fractions of cadmium telluride in determining the composition and Δd ? 0.5 nm in determining the thickness of the wide-gap layer and quantum well. The central fragments of the wide-gap layers ≈ 10 nm thick are additionally doped by indium for a ～ 10¹⁵ cm^?3 volume concentration of charge carriers to be reached. Galvanomagnetic research in a wide range of magnetic field intensities at liquid helium temperatures reveals dimensional quantization levels and the presence of a two-dimensional electron gas in grown nanostructures. High mobility of the two-dimensional electron gas μ _e is obtained: 2 · 10⁵ and 5 · 10⁵ cm²/V · s for electron densities N _s equal to 1.5 · 10¹¹ and 3.5 · 10¹¹ cm^?2, respectively.     

Modeling the formation of silicon nanoclusters during annealing SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layers

The mechanism of formation of silicon nanoclusters in layers of nonstoichiometric composition is studied by Monte Carlo simulation. Interest in silicon nanoclusters (Si-nc) coated with an oxide layer is due to their applications in modern optoelectronics and nanoelectronics. A lattice Monte Carlo model is proposed to study atomic processes in the Si-SiO₂ system. The formation of silicon nanoclusters during annealing of single SiO layers and SiO₂-SiO-SiO₂ layered structures is studied. Along with the diffusive motion of particles, the model takes into account the formation and collapse of mobile molecules of silicon monoxide. It is shown that accounting for transport of silicon under high-temperature annealing due to the motion of SiO accelerates the formation of Si-nc. Dependences of the size of nanoclusters on temperature, annealing time, and the composition of the SiO _x layer are obtained. It is found that annealing of silica films containing layers of nonstoichiometric composition can lead to the formation of silicon nanoclusters or cavities.     

An indirectly heated metal oxide hot cathode with a 100-cm<Superscript>2</Superscript> area

Results of designing of a sectioned metal oxide hot cathode with indirect heating and a total emission coating area of 100 cm² are described. The design of the hot cathode enables control of the working surface temperature and allows one to change emission surface without replacing the whole hot cathode. The thermal test results are presented. The possibility is shown of applying the hot cathode in the uncharacteristic mode of gas discharge formation in medium vacuum conditions.     

Features of the <Superscript>85</Superscript>Rb Spectrum in a Cell with an Antirelaxation Coating

Distortion of the spectrum of the D₁-line of ⁸⁵Rb in optical cells with an antirelaxation coating on the inner walls of the cell is studied. The spectrum shape is found to be significantly dependent on the velocity and direction of changes in the laser frequency. A physical explanation is provided for these features, which are confirmed by numerical simulations. The effect of the magnetic field on the spectrum shape is discussed.     

Voltage-current characteristics of diodes on MBE-grown Hg<Subscript>0.78</Subscript>Cd<Subscript>0.22</Subscript>Te layers

Results of measuring the voltage-current characteristics (VCCs) of diodes for IR detectors with the cutoff wavelength λ _c = 11μm are presented. The diodes are based on variband Hg_0.78Cd_0.22Te layers grown by molecular beam epitaxy on semi-insulating GaAs substrates. It is found that diffusion current and generation current in the depletion layer of the p-n junction are the main mechanisms of carrier generation at the reverse bias voltage V ₁ < −0.2 V. It is shown that good agreement between calculated and experimental VCCs is achieved if the decrease of the effective depth of recombination levels in the depletion layer as a result of the Poole — Frenkel effect is taken into account, as well as the longitudinal charge spreading in the reverse current diffusion component.     

Use of <Superscript>44</Superscript>Ti in the time-differential γγ perturbed-angular- correlation method for studying condensed matter

The principal aspects of ⁴⁴Ti application in time-differential γγ perturbed-angular-correlation method (TDPAC) for studying condensed matter are discussed. In the presented spectrometer modification, the efficiency of ⁴⁴Ti application can be considerably increased by using thin NaI scintillator crystals. Promising techniques for ⁴⁴Ti production and a method for synthesizing samples are described. Examples of TDPAC studies of titanium (rutile TiO₂) and scandium (Sc₂O₃) oxide samples are shown.     

Tribological behavior of intermetallic Fe<Subscript>3</Subscript>Al alloy treated by intensive beams of nitrogen ions

The structure, phase composition, and tribological behavior of intermetallic Fe₃Al alloy subjected to ion-beam nitriding at 670–870 have been studied. The ion-beam treatment of the alloy proved to result in nitrogen-modified layers of up to 15–18 nm thick and microhardness up to 13200 MPa. The formation of nitride AlN phases with cubic and hexagonal lattices was registered in the nitrided layers. The formation of aluminum nitrides with the cubic lattice of NaCl structural type is shown to increase the wear resistance of Fe₃Al alloy 25–28 times, and with the hexagonal one it increases 5–8 times.     

Investigation of Annealing Temperature on Structural and Morphological Properties of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles for Humidity Sensor Application

Cr₂O₃ nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temperatures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr₂O₃ varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr₂O₃ nanoparticles at 400 nm. The humidity sensor of the Cr₂O₃ nanoparticles was studied by two temperature method. 1000 °C annealed Cr₂O₃ nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr₂O₃ nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased.     

Oscillatory behaviors in initial film boiling: Implications on the triggerability of single droplet vapor explosions

A transient one-dimensional film boiling model was developed to study the film boiling dynamics that would occur when a hot spherical droplet is immersed in cold liquid. The focus of this study was to investigate the effects of noncondensible gas, liquid temperature, droplet temperature, and ambient pressure on film boiling during the initial growth phase. The results indicate that the film generally stablizes with more noncondensible gas present, higher liquid and lower droplet temperature. Small ambient pressurizations cause violent fluctuations of the film pressure while higher ambient pressure suppresses these oscillations. These qualitative behavior of film boiling around hot spherical droplet suggests that the spontaneous triggering of small-scale single droplet vapor explosions is led by the oscillatory characteristics of vapor film in its initial growth phase.     

Plasma erosion opening switch for fast discharges with current growth rate about 10<Superscript>12</Superscript> A/s<Superscript>1</Superscript>

The article presents the construction of a plasma erosion opening switch, capable of creating the discharge with electrical current of several tens kiloamperes and a growth rate up to 10¹² A/s in the circuit with the inductive load up to 100 nH. The results of test experiments with imitator of load are presented. The discharge circuit under consideration will be used for the experiments for creation of shock waves in plasma.     

Determination of the <Superscript>14</Superscript>C Concentration in a Liquid Scintillator for a Neutrino Detector

A setup has been developed for studying ultralow ¹⁴C concentrations in liquid scintillator samples for a large neutrino detector. The setup is located at the low-background underground laboratory of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) at a depth of 4900 m of water equivalent. The ¹⁴C concentrations in a liquid scintillator based on linear alkyl benzene, the background counting rates, and the spectra of particle energies deposited in the technological scintillator sample have been measured. The ratio ¹⁴C/¹²C = (1.41 ± 0.12) × 10^–16 has been obtained. A model of the γ-ray background has been developed, with which it is possible to extract the energy spectrum of 14C and reduce the systematic uncertainty of measurements.     

Dependence of the sizes of damaged regions around indium contacts to p-type CdHgTe on GaAs substrates on the annealing temperature and time

It is found that damaged regions are formed around indium contacts to p-type CdHgTe {310} heteroepitaxail layers (HELs) on GaAs substrates and the sizes of these regions depend on the temperature and time of annealing in air. It is shown experimentally that at an annealing temperature of 90 °C, the rate of expansion of the damaged regions is about 4 µm/h, and at temperatures of 120 °C, it is more than 25 µm/h. After 488 hours of annealing of plates of CdHgTe HELs at 60 °C in air, the formation of damaged regions around the indium contacts to the p regions was not observed. The studies were performed on plates of p-type CdHgTe HELs on GaAs substrates whose surface was covered with SiO₂ and Si₃N₄ dielectrics (with a total thickness of about 0.15 µm), with windows where p-n junctions were generated by ion implantation of boron.     

Reverse current in <Emphasis Type="Italic">p-n</Emphasis> junctions with a field electrode on heteroepitaxial CdHgTe/GaAs structures

Results of measuring the current-voltage characteristics of diodes with a control electrode are presented. The diodes are based on graded energy-gap Cd_0.22Hg_0.78Te (MCT) layers grown by molecular beam epitaxy (MBE) on a semi-insulating GaAs substrate. The diodes are designed for the IR radiation photodetectors with the cutoff wavelength λ_c = 10 μm. It is shown that the surface currents contribute substantially to the reverse currents of MBE MCT photodiodes during enrichment and depletion. A critical built-in charge density value for which the surface leakage level is under 20% of bulk current is obtained.     

Temporal characteristics of light collection in the liquid scintillation counter with a volume of 1.5 m<Superscript>3</Superscript> and quasi-mirror reflection

The temporal behavior of light collection in the 1.5-m³-volume mirror-reflecting counter filled with a highly transmitting liquid scintillator has been investigated. Using the Monte Carlo method and assuming that the luminescence decay time of the liquid scintillator is zero (τ_LS = 0), it has been ascertained that, in the case of a short flash in a counter, the exponential phase of light collection is characterized by time τ_col = 15.0 ± 1.7 ns, which is does not depend on scattering of light in the medium. The measured exponent index τ_act = 37 ± 3 ns of an actual pulse due to a muon is determined both by light collection time τ_col ≈ 15 ns and luminescence decay time τ_LS ≈ 20 ns of the scintillator in the large-volume counter.     

Wear Behaviour of In Situ Al/TiB<Subscript>2</Subscript> Composite: Influence of the Microstructural Instability

In this present work, the in situ Al (A380)/5 wt%TiB₂ composites were fabricated through salt–melt reaction using halide salts such as potassium hexafluorotitanate (K₂TiF₆) and potassium tetra fluoroborate (KBF₄) salts as precursors. The composites were produced at four different melt temperatures (700, 750, 800, 850 °C). The formation of particle was confirmed from XRD results. The wear behaviour of Al/5 wt% TiB₂ composite was investigated by varying the wear test parameters such as sliding temperature (25, 100, 150, 200 °C), applied load (10, 20, 30, 40 N), sliding velocity (0.4, 0.7, 1, 1.3 m/s). The microstructure of Al/5 wt% TiB₂ composite was correlated with the wear characteristics of the composites. The wear resistance of Al/5 wt% TiB₂ composite was significantly improved due to the presence of TiB₂ particle in Al matrix material. The composite produced at melt temperature 800 °C showed a higher wear resistance at applied load: 10 N, sliding temperature: 25 °C and sliding velocity: 0.7 m/s. The wear mechanism for each of the tested condition was identified from the worn surfaces using scanning electron microscopy (SEM). ANOVA test was carried out to find out significant factor for the wear resistance of composite. The checking of adequacy of experimental value for the wear behaviour of composite for different testing condition was analysed by residual plots using statistical software.     

Numerical simulation of droplet formation in a micro-channel using the lattice Boltzmann method

This study investigates droplet formation in a micro-channel using the lattice Boltzmann (LB) method. A cross-junction micro-channel and two immiscible, water and oil phase fluids, were used to form the micro-droplets. Droplets are formed by the hydrodynamic instability on the interface between two immiscible fluids when two immiscible fluids are imported simultaneously in a cross-junction micro-channel. The Shan & Chen model, which is a lattice Boltzmann model of two-phase flows, is used to treat the interaction between immiscible fluids. The detailed process of the droplet formation in the cross-junction micro-channel was illustrated. The results of the droplet formation by the LBM predicted well the experimental data by PIV (particle image velocimetry). The effect of the surface tension and the flow rate of water phase fluid on the droplet length and the interval between droplets was also investigated. As the surface tension increased, the droplet length and the interval between droplets were increased. On the other hand, when we increased the flow rate of the water phase fluid under the condition of the fixed oil-phase fluid flow rate, the droplet size was increased while the interval between droplets was decreased.     

Compositional analysis of mixed–cation-anion III–V semiconductor interfaces using phase retrieval high-resolution transmission electron microscopy

Employing exit‐plane wave function (EPWF) reconstruction in high‐resolution transmission electron microscopy (HRTEM), we have developed an approach to atomic scale compositional analysis of III‐V semiconductor interfaces, especially suitable for analyzing quaternary heterostructures with intermixing in both cation and anion sub‐lattices. Specifically, we use the focal‐series reconstruction technique, which retrieves the complex‐valued EPWF from a thru‐focus series of HRTEM images. A study of interfaces in Al_0.4Ga_0.6As–GaAs and In_0.25Ga_0.75Sb–InAs heterostructures using focal‐series reconstruction shows that change in chemical composition along individual atomic columns across an interface is discernible in the phase image of the reconstructed EPWF. To extract the interface composition profiles along the cation and anion sub‐lattices, quantitative analysis of the phase image is performed using factorial analysis of correspondence. This enabled independent quantification of changes in the In–Ga and As–Sb contents across ultra‐thin interfacial regions (approximately 0.6 nm wide) with true atomic resolution, in the In_0.25Ga_0.75Sb–InAs heterostructure. The validity of the method is demonstrated by analyzing simulated HRTEM images of an InAs–GaSb–InAs model structure with abrupt and graded interfaces. Our approach is general, permitting atomic‐level compositional analysis of heterostructures with two species per sub‐lattice, hitherto unfeasible with existing HRTEM methods.     

Heteroepitaxy of AIIIBV films on vicinal Si(001) substrates

GaAs films on Si substrates miscut from the (001) plane by 6° in the [110] direction are grown by molecular beam epitaxy (MBE). GaAs films are grown both on the Si surface terminated by arsenic atoms and on thin pseudomorphic GaP/Si layers. The condition of formation of the As sublayer and the first monolayer of GaP on the Si surface is defined as the GaAs film orientation (001) or \((00\bar 1)\) . The processes of Si surface preparation and formation of the As sublayer and GaAs and GaP epitaxial layers are monitored by means of high-energy electron diffraction reflection (RHEED). The grown structures are investigated by methods of X-ray diffraction, atomic force microscopy (ATM), high-resolution transmission electron microscopy (HRTEM), and low-temperature luminescences. It is shown that the epitaxial film orientation affects both the surface morphology and its crystalline properties. Intense photoluminescence is obtained from the In_0.17Ga_0.83As quantum well structure grown on the GaAs/Si buffer layer.     

Effect of Atmosphere and Temperature on the Tribological Behavior of the Ti Containing MoS<Subscript>2</Subscript> Coatings Against Aluminum

MoS₂ coatings exhibit low coefficient of friction (COF) when sliding against aluminum; however, the magnitudes of their COF show high sensitivity to environmental conditions. Ti could reduce the sensitivity of the frictional behavior of MoS₂ coatings to moisture. This study examines the tribological properties of Ti containing MoS₂ coating (Ti–MoS₂) tested against an aluminum alloy (Al-6.5% Si) in ambient air (58% relative humidity, RH), dry oxygen, dry air and dry N₂ (< 4% RH) atmospheres. The Ti–MoS₂ coating exhibited similar COF values under an ambient (0.14), dry oxygen (0.15) and dry air (0.16) atmospheres. It was found that oxidation of MoS₂ to MoO₃ was responsible for high COF under these testing conditions as revealed by Energy-dispersive X-ray Spectroscopy (EDS) and micro-Raman spectroscopy. However, a low and stable COF of 0.07 was observed under a dry N₂ condition. This work further showed that the tests performed at elevated temperatures, up to 400 °C in a dry N₂ atmosphere sustained the low and stable COF of the Ti–MoS₂ coatings. The sliding tests performed under a dry N₂ atmosphere prevented the formation of MoO₃ and as a result, the Ti–MoS₂ coatings maintained low COF values. Low COF values were also attributed to the formation of MoS₂ transfer layers.     

Superthin Solar Cells Based on A<Superscript>III</Superscript>B<Superscript>V</Superscript>/Ge Heterostructures

A comparative analysis of the prospects of creating superthin, light-weight, and highly efficient solar cells based on A^IIIB^V/InGaAs and A^IIIB^V/Ge heterostructures is performed. Technological problems and prospects of each variant are discussed. A method of thinning of A^IIIB^V/Ge heterostructures with the use of an effective temporary carrier is proposed. The method allows the process to be performed almost with no risk of heterostructure fracture, thinning of the Ge junction down to several tens of micrometers (or even several micrometers), significant enhancement of the yield of good structures, and also convenient and reliable transfer of thinned solar cells to an arbitrary light and flexible substrate. Such a technology offers a possibility of creating high-efficiency thin and light solar cells for space vehicles on the basis of mass-produced A^IIIB^V/Ge heterostructures.