Том 44, № 11 (2018)
- Жылы: 2018
- Мақалалар: 28
- URL: https://journals.rcsi.science/1063-7850/issue/view/12903
Article
Intracavity Waveguide Spectroscopy of Thin Films
Аннотация
The method of intracavity waveguide spectroscopy for measuring low optical losses in thin films is proposed. The method also allows one to distinguish transverse and longitudinal modes in low-gain lasers without introducing considerable losses into the cavity.
Dielectric Losses in MPCVD Diamonds in the 25–30 and 250–350 GHz Bands Depending on Growth Parameters
Аннотация
A complex systematic study of the effect of various parameters of the CVD diamond growth in a microwave plasma (MPCVD diamonds), such as substrate temperature, the chemical composition of a gas mixture, etc., on dielectric losses in two frequency bands (25–30 and 250–350 GHz) for more than ten samples of various series is carried out. A correlation between the values of the losses in these two frequency bands is identified.
Observation of the Rabi Splitting of Oxygen Atomic Levels in Filament Plasma Formed by a Femtosecond Ti:Sa Laser Pulse
Аннотация
Dynamics of the emission spectrum of a highly focused femtosecond laser pulse under filamentation in air have been investigated. A peak at 735 nm and a drop in the laser-beam intensity at the fundamental wavelength are observed in the spectrum of a laser pulse passed through the filamentation zone. It is shown that the peak is likely due to the Rabi splitting of the O I levels and breaking of the LS coupling for the 3p5P level in a strong laser field.
The Effect of the Fin Shape and Thickness of the Buried Oxide on the DIBL Effect in an SOI FinFET
Аннотация
In this paper, we simulated the dependence of the effect of reducing the drain-induced barrier lowering on the thickness of a buried oxide layer in a finned (vertical) metal-oxide-semiconductor field effect transistor (FinFET) based on silicon-on-insulator technology. Three shapes of the fin with the rectangle, trapezoid, and triangle cross sections were considered. The drain-induced barrier lowering effect significantly depends on both the fin shape and the thickness of the buried oxide layer. The smallest drain-induced barrier lowering effect occurs when the thickness of the buried oxide layer is small for the fin of a triangular shape. This behavior of the drain-induced barrier lowering effect is strongly correlated with the behavior of the parasitic capacitance between a gate and a source.
Emission Regimes of 1.06 μm Spectral Bandwidth Two-Sectional Lasers with Quantum Dot Based Active Layer
Аннотация
We have investigated two-sectional semiconductor lasers with an active region comprising five layers of InGaAs quantum dots, emitting in the spectral range near 1.06 μm. Regimes of passive mode-locking, passive Q-switching, and mode-locking with pulse modulated amplitude are realized. The transition conditions between generation regimes are investigated. The frequency tuning range with current increase in the Q-switched regime exceeds more than 4 times. The duration of the mode-locked pulses was 2 ps at the pulse repetition rate of 44.3 GHz.
Heat Transfer Enhancement in a Heated Liquid Film under the Action of External Artificial Perturbations
Аннотация
Heat transfer in a heated film of distilled water under the action of external artificial perturbations with “the most dangerous wavelength” and variation in the Reynolds number from 300 to 500 has been studied. It has been shown that the action of artificial perturbations with an increase in the heat flux density leads to a change in the rivulet-wave structure of the flow, increase in wave amplitudes, and, finally, heat transfer enhancement.
Clusters of Spikes in CMOS Image Sensors Irradiated by Protons and Neutrons
Аннотация
The distribution of pixels with high-value dark current in CMOS image sensors irradiated by protons with the energy of 1000 MeV and neutrons with a continuous spectrum simulating the energy spectrum of atmospheric neutrons is explored. Data on generation of spike clusters in the irradiated sensors and the exposure time influence on the cluster parameters are obtained.
A Chain Model of a Zigzag Contact of Lateral Graphene-Like Heterostructures
Аннотация
A simple structural model is proposed for the zigzag interface formed by contacting two-dimensional graphene-like compounds AB and CD (both free and formed on a metal). For the graphene–hexagonal boron nitride system, analytical expressions for the electron spectrum, density of states, and atom occupation numbers at the interface are obtained. The results of calculating the densities of states and occupation numbers within two alternative approximations are in good agreement.
Formation of a Nanophase Wetting Layer and Metal Growth on a Semiconductor
Аннотация
Based on the data on the atomic density of a film and degree of its homogeneity during the formation of the interface between 3d transition metals (Cr, Co, Fe, or Cu) and silicon, a new concept of forming a contact between a reactive metal and a semiconductor has been justified. According to this concept, the low-temperature vapor-phase deposition of a metal onto a semiconductor is accompanied by the formation of a two-dimensional nanophase wetting layer of a metal or its mixture with silicon with a thickness of several monolayers, which significantly affects the interface formation and structure. This concept changes a perspective of forming a contact between a metal and a semiconductor substrate: it is necessary to take into account not only the formation of surface phases and clusters and/or the mixing process, but also the effect of elastic wetting of a substrate by the forming phases.
Amorphous Films of Ternary Zinc and Tin Oxides for Transparent Electronics
Аннотация
Amorphous films of two varieties of zinc stannate (ZnSnO3 and Zn2SnO4) have been considered that were fabricated by radio-frequency sputtering of ceramic compound targets containing ZnO and SnO2 in 1: 1 and 2: 1 ratios. The elemental and phase compositions of the films and their optical and electrical parameters were determined. The transparency of the films in the visible spectral range is on average 87%. Zinc stannate amorphous films have a high electrical conductivity in contrast to amorphous ZnO and SnO2. This phenomenon, which makes it possible to use zinc stannate amorphous films in transparent and flexible electronics, is explained.
An Experimental Cell for a Radio Light Receiver
Аннотация
The problem of creating a receiver for incoherent microwave radiation from sources realized on the basis of ultra-wideband oscillators of chaotic oscillations and objects and surfaces “illuminated” by these sources has been considered. The structure of the device is proposed, the experimental sample is described, and its ability to register sources of incoherent microwave radiation with an integrated output power of ~2 mW at a distance of more than 100 m is shown.
Strain Concentration Effect in Cu–Al–Ni Single Crystals under a Longitudinal Bending Force
Аннотация
The behavior of a superelastic Cu−14.2% Al−4%Ni single crystal in the case of high reversible strains under a longitudinal bending force was investigated. The effect of strain confinement along the crystal length was revealed and studied. The highest reversible strains (up to 10%) were shown to be confined within the central part of the bent crystal.
Impact of Plastic Straining in the Martensitic State on the Development of the Superelasticity and Shape Memory Effects in Titanium-Nickelide-Based Alloys
Аннотация
The superelasticity and shape memory effects upon torsional straining of samples of the binary titanium nickelide based alloy with the B19' martensitic phase structure have been investigated. It has been found that, in samples plastically strained during their loading up to a specified torsional strain of ~39%, the superelasticity value can attain 6.3%, which is comparable with the classical superelasticity effect. The superelasticity manifestation in the martensitic state upon torsion straining of the samples has been compared with the results of similar studies on tensile straining of the titanium nickelide-based alloy samples.
Thermal Characteristics of High-Efficiency Photovoltaic Converters of High-Power Laser Light
Аннотация
The influence exerted by the heat removal conditions on the extent of overheating of photovoltaic converters of high-power (>103 W/cm2) laser light has been studied. The temperature of the p–n junction of photovoltaic cells was measured by recording the instantaneous values of the open-circuit voltage generated by laser light. The effect of cooling in high-efficiency photovoltaic cells (efficiency = 55%) via removal of a substantial part of absorbed optical power by the photocurrent into the external load was demonstrated. It was shown that, at laser radiation power of 2.5 W, the overheating of a photocell with an area of 1.7 × 10–3 cm2 relative to the copper heatsink temperature is 48°C in the no-load conditions and 30°C in operation with the optimal load.
An in situ Study of the Kinetics of a Solid-Phase Reaction Activated by the Energy of Elastic Stresses Arisen upon the Formation of the Cu/As2Se3 Nanosized Film Structure
Аннотация
For the first time, the kinetics of a solid-phase chemical reaction activated by the energy of elastic stresses generated upon the formation of the Cu/As2Se3 nanosized film structure is investigated in situ. It is shown that the time at which a solid-phase chemical reaction starts, as well as the voltage of the Cu/As2Se3 heterolayer, significantly depends on the thickness of the As2Se3 film. At a critical thickness of the As2Se3 film, which is equal to 110 nm, a threshold value of the energy of elastic stresses is achieved. Relaxation of this energy over new defects (micropores and microcracks) generated in the film system leads to the activation of a solid-phase chemical reaction and an increase in its rate. A mechanism of the operation of a positive feedback between the chemical reaction in a solid phase and elastic stresses is proposed.
Emission Properties of Metal Porous Cathodes Modified by Nanocarbon
Аннотация
The results of studying the emissive ability, structure, and elemental composition of the surface of an impregnated cathode with a fine-grained tungsten matrix with addition of polyhedral multilayer carbon nanostructures of the fulleroid type (0.2−0.7 wt %), impregnated with barium-calcium aluminate with addition of sulfoadduct of carbon nanoclusters (0.1−0.2 wt %), are presented. The tests in diode prototypes showed that these cathodes provide a current density of 20 A/cm2.
Optical Characterization of the Structural Imperfection of Two-Dimensional MoS2 Crystallites
Аннотация
Two-dimensional molybdenum disulfide crystallites grown by mechanical exfoliation and chemical vapor deposition have been studied. It is shown that both methods can be used to obtain individual crystallites with a monoatomic thickness and similar optical properties. It is found that crystallites grown by chemical vapor deposition have a higher defect concentration than those grown by mechanical exfoliation.
Study and Development of Photovoltaic Structures Based on Quantum Dot Solids of PbS with Various Ligands
Аннотация
The photoconductivity of condensates of lead-sulfide quantum dots (QDs)—QD solids—with various organic ligands is studied. It is demonstrated that the QD solid photoconductivity increases exponentially with a reduction in length of ligand molecules and does not depend on their chemical structures, since it is governed by hopping transport of charge carriers. In contrast, the photocurrent in photovoltaic ITO/PEDOT: PSS/PbS/ZnO/Al elements depends on the ligand structure, since this structure sets the positions of QD energy levels and thus affects the efficiency of charge carrier transfer to electrodes. The difference between mechanisms of generation of photoconductivity and photovoltaic currents is discussed.
The Effect of Charge Transport Mechanisms on the Efficiency of AlxGa1 – xAs/GaAs Photodiodes
Аннотация
Photovoltaic characteristics of heterostructure AlxGa1 – xAs/GaAs p–i–n photodiodes fabricated by molecular-beam epitaxy have been studied. Efficiencies of 50% were reached in conversion of monochromatic light in the photovoltaic mode at power density of up to 200 W/cm2 at a wavelength λ = 830 nm. A relationship was demonstrated between the “saturation currents” for the diffusion-related charge-transport mechanism (Shockley) in p–i–n photodiodes, calculated from dark current–voltage characteristics, and the experimental values of efficiency. As the “saturation current” of the diffusion-related charge-transport mechanism increases by an order of magnitude, a relative decrease in the efficiency from the maximum value by more than 10% is observed under excitation by constant or pulsed monochromatic light.
Synthesis of Carbon Fibers in the Decomposition of Acetylene and Propane–Butane Mixture in a Plasma Jet
Аннотация
Carbon fibers are prepared during the conversion of acetylene and propane–butane mixture in a jet of the helium and argon plasma without using catalysts. The synthesis is carried out in a plasma jet reactor. The synthesis products are studied by electron microscopy, synchronous thermal analysis and energy dispersive X-ray spectroscopy. The effect of the synthesis parameters on the structure and properties of the carbon fibers prepared in the volume is established. When the propane–butane mixture is decomposed in an inert medium, conditions are found for the synthesis of cylindrical carbon nanofibers of a tortuous shape with a diameter of up to 20 nm and a length-to-diameter ratio of up to 1000. The decomposition of acetylene at 350 Torr produces nanofibers formed by a chain of straight cylinders with a diameter of up to 20 nm, and cylindrical fibers are synthesized in the form of spirals of up to 200 nm in diameter at 150 Torr.
The Spectrum of Ion Cyclotron Emission from Neutral Beam Injection Heated Plasma on the TUMAN-3M Tokamak
Аннотация
Radiation at the ion cyclotron resonance frequencies in both the ohmic mode and the injection heating mode—ion cyclotron emission (ICE)—is observed on the TUMAN-3M tokamak (minor radius a = 0.25 m, major radius R0 = 0.5 m, toroidal field BT = 1 T, plasma current Ip ≤ 180 kA, and average plasma electron density ne ≤ 5 × 1019 m–3). Usually, the ICE is associated with the presence of high-energy ions in the plasma. Such ions may be products of a thermonuclear reaction or arise as a result of additional plasma heating, e.g., by means of electromagnetic waves or by injection of beams of high-energy atoms (neutral beam injection, NBI). The properties of the ICE in the TUMAN-3M tokamak in the NBI-heating mode and their possible connection with the features of fast ion trajectories and their energy spectrum are considered.
Reconstruction of Ensembles of Oscillators with Nonlinear Time-Delay Feedbacks
Аннотация
A method is presented for reconstructing ensembles of nonlinear oscillators coupled with each other by nonlinear time-delay feedbacks. The method allows one, using time series, to reconstruct nonlinear functions of all elements of the ensemble, as well as the architecture of couplings between oscillators and the parameters of all sigmoid coupling functions, including the time delay.
Spatio-Temporal Structure of Alfvén Waves in the TUMAN-3M Tokamak
Аннотация
Spatial and temporal structure of Alfvén waves was studied with array of magnetic probes in compact tokamak TUMAN-3M. Poloidal mode numbers have been determined for Alfven instabilities bursts of the two types: short and long ones. Absence of poloidal rotation of magnetic field perturbations was found for both types of bursts. Also, in both cases, no pronounced asymmetry of magnetic field perturbation in the direction of the major radius was detected.
IR Luminescence of α-Al2O3 – δ at 4–300 K
Аннотация
It is established that simple color centers of the F+ and F type (anion vacancies with one or two electrons, respectively) in anion-deficient corundum (α-Al2O3–δ) crystals can be transformed into complex centers (including divacancy centers of the F2 type) using a special thermo-optical treatment. A fine structure of the photoluminescence bands of complex centers of both the known and unknown natures was recorded in these crystals at helium temperatures in the near-IR range. A comparison with the photoluminescence bands in neutron-irradiated α-Al2O3 samples with the initial stoichiometric composition reveals their complete similarity, which indicates the possibility of nonradiative formation of complex centers in α-Al2O3.
Stabilizing the Metallic State in a Quasi-Two-Dimensional (ET)8Hg4Br12(C6H5Cl)2 Organic Metal under a Pressure of 6 kbar
Аннотация
A quasi-two-dimensional (ET)8Hg4Br12(C6H5Cl)2 organic metal undergoes the metal–dielectric transition at T ~ 90 K upon cooling. An external pressure of P ~ 6 kbar completely recovers the metallic state and makes it possible to observe the Shubnikov–de Hass oscillations with a frequency of F ≈ 215 T and a cyclotron mass of m* ≈ 0.95m0. The behavior of the oscillations is consistent with the Fermi surface representation in the form of electron and hole orbits covering the same areas of the first Brillouin zone.
Generation of Directed Microparticle Flows by Burning Gaseous Fuel in a Nonstationary Mode
Аннотация
In this paper, we have proposed to use accelerated flame propagation in the channel to generate directed flows of microparticles for effectively spraying them onto the substrate surface in the pulsed regime. Using mathematical modeling, we showed the basic possibility of practical using this approach and quantitatively estimated the effectiveness of the proposed procedure when gaseous mixtures based on hydrogen are used.
An Antireflection Coating of a Germanium Subcell in GaInP/GaAs/Ge Solar Cells
Аннотация
Spectral characteristics of the Ge subcell of triple-junction GaInP/GaAs/Ge solar cells have been simulated. It was shown that using a GaInP nucleation layer that creates a shallow diffusion p–n junction in Ge can raise the photogeneration current of the Ge subcell by ~4.5 mA/cm2 as compared with the value in the case of a GaAs nucleation layer. The optimal thickness of the GaInP layer (170–180 nm) makes it possible to additionally raise the photocurrent by ~1.5 mA/cm2. It was experimentally demonstrated that the photogenerated current of the Ge subcell of GaInP/GaAs/Ge solar cells increases by 3.9 mA/cm2 on replacing the GaAs nucleation layer with GaInP and there is an additional gain by 0.9 mA/cm2 on using the optimal thickness of the GaInP nucleation layer.
A New Method of Selective Laser Cladding
Аннотация
A new approach to selective laser cladding using conical laser beams has been elaborated. The initial round laser beam is divided into two or more circular beams with regulated distribution of the laser power between them. The circular beams are converted into conical beams that are focused separately on the surface and on different areas of the deposited material for their efficient heating. The delivery of laser energy into the powder stream is very effective because it provides a complete uniform absorption of laser energy in a dense powder stream (104–106 cm–3). Under wire deposition, substrate heating reduces residual stresses due to temperature gradients and compensates for heat loss from the deposition zone by thermal conduction. The required power density for melt contact formation is significantly reduced.