The MBE-method with plasma activation of nitrogen is used to obtain III-nitride HEMT heterostructures containing an ultrathin AlN barrier. The influence of the nucleation and buffer layer growth modes on the crystalline quality, surface morphology, and electrophysical properties of experimental HS samples is studied. The sheet resistance of the optimized HS is less than 230 Ω/□. Test microwave transistors with Schottky gate are manufactured. The parametric model of the HEMT based on an AlN/GaN HS is proposed.

In the last few years, lead halide nanocrystals with perovskite mineral structures (PNСs) have attracted increasing attention due to their excellent optical and physical properties, which make them promising for liquid crystal displays, light-emitting diodes, solar concentrators and basic elements of quantum computing systems. Initially, the synthesis of PNСs was carried out using oleic acid and oleylamine as organic surface ligands, and the materials obtained in this way did not have sufficient colloidal and photostability for practical applications. This problem was partially overcome by the use of phosphonic acids and other types of molecules as ligands, but in this case, the reaction is often incomplete, resulting in some of the metal precursors remaining in the product, which in turn leads to a gradual degradation of the optical properties of PNСы. Here, we demonstrate the effective application of a method of additional purification of CsPbBr3 PNC solutions obtained by colloidal synthesis using tetradecylphosphonic acid as a ligand by gel permeation chromatography. As a result of this procedure, we were able to remove the excess of unreacted precursors from the synthesized nanocrystals, which allowed us to achieve the preservation of a high value of the quantum yield of PNCs fluorescence within 6 months from the moment of their synthesis. The results open perspectives for creation of more efficient material for application in the fields of quantum technologies and, in particular, for creation of single photon sources.

The spectra of the optically detected magnetic resonance for single NV– centers have been experimentally studied in two solid-state samples in the range of hyperfine interactions between the electron spin and the nitrogen nucleus spin in the same NV– center. This study has been aimed at reaching a maximal microwave frequency resolution in the experimental setup used. For measurements, two low-nitrogen (no higher than 50 ppb) diamond single-crystal samples have been grown. Measured time T_2^* of the spin decoherence in NV– centers was about 2 μs in one sample and 20 μs in the other. For both samples, the spectrum of the optically detected magnetic resonance for the hyperfine splitting of a single NV– center and 14N atom has been taken and investigated. The resolution in these samples has been estimated at a level of 3.5 and 0.18 MHz, respectively. It has been noted that the resolution of the spectrum improves with increasing time T_2^* of the spin decoherence of the single NV– center.

Optically detectable magnetic resonance spectra were measured for ensembles of NV-centers in CVD diamonds with different C-13 contents. The obtained spectra were described using a model based on the spin Hamiltonian. The magnitude of the magnetic field applied to the sample was estimated using the constructed model and experimental data.

В данной работе проводится исследование трехспиновой системы 14NV-13C, которая включает электронный спин NV-центра и ядерные спины атомов 13С и 14N. В этой системе наблюдается двукратное вырождение энергетических уровней в нулевом магнитном поле (вырождение Крамерса) из-за инвариантности спинового гамильтониана к обращению времени. Для исследования влияния магнитного и электрического поля на энергетические уровни системы было проведено моделирование спектров оптически детектируемого магнитного резонанса (ОДМР) этой гибридной квантовой системы в рамках метода спин-гамильтониана при одновременном воздействии на систему магнитного и электрического или внутрикристаллического поля. Построенная модель хорошо согласуется с экспериментальным спектром ОДМР одиночного комплекса 14NV-13C, локализованном в образце сверхчистого алмаза с помощью конфокального микроскопа. По расщеплению спектра ОДМР в нулевом магнитном поле и по данным квантово-химического моделирования было определено, что атом 13С расположен в третьей координационной сфере NV-центра, и соответствующий этому положению тензор сверхтонкого взаимодействия электронного спина NV-центра и ядерного спина изотопа углерода 13С использовался в модели. В результате численные расчеты показали, что вырождение снимается только магнитным полем, независимо от наличия какого-либо электрического (кристаллического) поля, что делает данную квантовую систему перспективным для магнитометрии.

Using the method of molecular beam epitaxy with the plasma activation of nitrogen, experimental AlN/GaN heterostructures (HSs) with an ultrathin AlN barrier are obtained. The layer resistance of the optimized structures is less than 230 Ω/□. The scattering processes that limit the mobility of a two-dimensional electron gas (2DEG) in undoped AlN/GaN HSs with an ultrathin AlN barrier are studied. It is shown that in the range of ns characteristic for AlN/GaN HEMT HSs (ns > 1 × 1013 cm–2), a noticeable contribution to the scattering of charge carriers is made by the roughness of the heterointerface.

Monodisperse silica globules of about 250–300 nm in size have been synthesized by the sol-gel method. These globules form the basis for the synthesis of artificial opals – three-dimensional photonic crystals and disordered opal matrices. Matte coatings on quartz glass consisting of monodisperse silica globules and barium titanate xerogel doped with erbium and ytterbium, demonstrating up-conversion luminescence of erbium, have been synthesized. A change in the photonic band gap caused by heat treatment in the reflectance spectra of synthetic opals containing barium titanate xerogel and residues of ethylene glycol not removed by heat treatment has been shown.

The possibility of using NV-defects in diamond at room temperature on nanometer spatial scales to measure magnetic fields was studied. For these purposes, samples with high concentrations of NV-centers are usually used, which increases the signal level but prevents the measurement of inhomogeneous fields on the scale of molecules or nanostructures. The parameters of a weak magnetic field were measured taking into account Earth's field by measuring the hyperfine structure of the optically detected magnetic resonance spectrum to calibrate and determine the resolution of a magnetic field sensor on a single NV-defect.

The possibility of initiation of nuclear chemical processes in the Pb cathode during a glow discharge in a low-temperature deuterium-containing nonequilibrium plasma leading to a significant (at times) decrease in the isotope content of some impurity elements (specifically, Zn) and increasing others (specifically, W, Fe, Mn, and Al). Such processes can be understood by introducing the existence in nuclear matter of metastable non-nucleon excitations of internal shaking (isu-states) formed by initiating actions on the nuclei of electrons with high (on chemical scales) kinetic energy Ee ~ 3–5 eV.

A method for estimating the isotopic composition and concentration of NV-centers in diamond using Raman scattering and photoluminescence spectra is presented. The proposed laboratory technique was used to study the spatial distribution of the 13C isotope and NV-centers in samples of CVD-diamond with isotopically modified layers.

n Erratum to this paper has been published: https://doi.org/10.1134/S1063739723900043

This paper studies the design of a nonlinear model of AlGaAs/InGaAs/GaAs рHEMT microwave-frequency range transistors with a gate length of 0.15 µm using parametric analysis methods. In the calculations, not only nonlinear current sources but also the dependences of the nonlinear gate-source and gate-drain capacitances on voltages are studied. It is shown that the proposed model makes it possible to describe the IV characteristics of the studied device adequately in the range of drain currents from 0 to 100 mA and the frequency range from 5 to 45 GHz. The error of the model does not exceed 3%.

A method of vector magnetometry, implemented using a single NV–13C spin system in a diamond, is proposed. The method is based on a priori knowledge of the hyperfine interaction characteristics and on the presence of experimentally measured line positions in the optically detectable magnetic resonance spectrum of such a system. The method was experimentally tested on the NV–13C system, in which the 13С atom is located in the third coordination sphere of the NV center.

Individual electron–nuclear spin systems in solids are promising platforms for implementation of second-generation quantum technologies. The recognized leader among such systems is the negatively charged nitrogen–vacancy color center (NV center) in diamond with hyperfine coupling to nuclear spins of carbon-13 (13C), which are widely used as a quantum memory in emerging quantum technologies because of their weak interaction with the environment. Recently, pairs of 13C–13C nuclei (dimers) in diamond with NV centers have been proposed and actively studied for this purpose because they have extremely long coherence times (minutes at room temperature) in the singlet state. The eigenstates of the spin Hamiltonian of the NV–13C–13C system were found and used to calculate the probabilities of EPR transitions between nuclear-spin sublevels of NV-center states with electron spin projections mS = 0 and mS = –1. The obtained expressions form the basis for choosing the optimal parameters of microwave and radiofrequency pulses transforming a particular dimer into the singlet state. An example of such a prediction for a specific NV–13C–13C spin system using data for the spatial positions of the 13C spins and the internal spin–spin couplings obtained earlier by quantum chemistry methods is presented.

A highly accurate method for modeling InAlAs/InGaAs MHEMT transistors of the UHF frequency range with a gate length of 0.15 μm is considered. This method takes into account the nonlinear dependences of the internal parameters on the applied voltages. It is established that the maximal error of modeling is not larger than 1.5

В этой статье представлено описание методологии проектирования усилителя мощности 40 Вт Ku-диапазона 14,25-14,75 ГГц для спутниковой связи, использующего силовые транзисторные ячейки GaN-транзистора с высокой подвижностью электронов (HEMT) (CGHV1J025D) от Wolfspeed. Усилитель реализован по технологии гибридных СВЧ интегральных схем на подложке из оксида алюминия. УМ показывает измеренные характеристики выходной мощности более 40 Вт для непрерывного сигнала с PAE более 40 %.

It is shown that artificial radioactivity can be initiated under conditions of a glow-discharge plasma. When analyzing the isotopic and elemental composition in the near-surface region of Pd and Ni cathodes, initial and those treated for 40 hours under conditions of deuterium- or protium-containing plasma, changes were detected, respectively, in the isotopic ratios of Pt and Pb impurity isotopes in the Pd cathode and of Fe, Cu, and Zn in the Ni cathode, as well as a significant reduction in the amount of these impurity elements in the cathodes and the formation of W isotopes in the Pd cathode. Possible nuclear processes that cause the established artificial radioactivity are considered.

It is shown for the first time that multilayer periodic BaTiO 3 /SiO 2 structures formed by the sol–gel method are tunable photonic crystals with dependence of the photonic band gap from the temperature of the sample. The shift of the minimum in the reflection spectrum in the photonic band gap is observed from 616 to 610 nm in the sample-temperature range from +184 to +24°C, respectively, and is reproduced for several samples synthesized at a temperature of 450°C.