Search

Плівки арсеніду кадмію на підкладках окисленого кремнію отримані ВЧ-магнетронним розпиленням. Досліджено структуру та морфологію поверхні методами АСМ та раманівської спектроскопії. На спектрі КРС присутні характерні для плівок Cd3As2 піки при 194, 249 і 303 см – 1. Рухливість носіїв в зразках склала 0,15-1,7·103 см2В – 1с – 1 при концентрації 0,7-4,4·1019 см – 3. Встановлено, що для зразка №1 в інтервалі температур T = 10 ÷ 15 K реалізується механізм електропровідності за законом Мотта. Це можна пояснити тим, що мікроскопічне розупорядкування стає важливим для локалізації електронів в цьому температурному регіоні. Цьому сприяє зниження температури або зростання ступеня безладу. В цьому випадку стрибок стає можливим тільки всередині енергетичної смуги Мотта поблизу рівня Фермі. Перенесення заряду в зразку №2 при T = 220 ÷ 300 K здійснюється шляхом стрибкової провідності електронів зі змінною довжиною стрибка по локалізованим станам, що лежать у вузькій смузі енергій поблизу рівня Фермі. Ці стани можуть створюватися міжзеренними межами і дислокаціями. Співвідношення між значеннями кулонівської щілини Δ і шириною зони локалізованих станів W узгоджуються з відповідним механізмом провідності. Cadmium arsenide films on oxidized silicon substrates were obtained by RF magnetron sputtering. The structure and morphology of the surface were studied by atomic force microscopy (AFM) and Raman spectroscopy (RS). The Raman spectrum contains peaks characteristic for Cd3As2 films at 194, 249, and 303 cm − 1. The carrier mobility in the samples was 0.15-1.7·103 cm2V − 1s − 1 at concentrations of 0.7- 4.4·1019 cm − 3. It has been established that for the sample No 1 in the temperature range T = 10-15 K, the variable-range hopping (VRH) conductivity mechanism according to the Mott law is implemented. This can be explained by the fact that a microscopic disorder becomes important for electron localization in this temperature region. This is due to a decrease in temperature or an increase in the degree of disorder. In this case, the jump becomes possible only inside the Mott energy band near the Fermi level. The charge transfer in sample No 2 at T = 220-300 K is carried out by the VRH conductivity of the jump over localized states lying in a narrow energy band near the Fermi level. These states can be created by grain boundaries and dislocations. The relations between the values of the Coulomb gap Δ and the zone width of localized states W are consistent with the corresponding conduction mechanism.

The cycle of citric acid production with the formation of gypsum-containing waste was considered and options for processing and utilization of citrogypsum were proposed. The methods obtained include: the use of citrogypsum in the production of building materials, the extraction of rare earth metals, as well as the creation of a high-quality organic-mineral fertilizer, during the creation of which it is possible to reduce the negative effect not only from the accumulation of citrogypsum, but also from manure stored in the filtration fields. In the future, the resulting fertilizer can be used for reclamation of technologically disturbed territories.

Experimental data on the mechanism of the grazing interaction of fast electron beams with planar dielectric surfaces of various materials are analyzed. New experimental results regarding the grazing interaction between electrons with an energy of 10 keV and metalized structured surfaces are reported. The difference between the processes of the interaction of fast electron beams with planar and structured surfaces is demonstrated.

Investigations of materials of the quasi-binary system Zn3As2–Mn3As2 have been performed. We present band structure calculations of crystal structures of Zn3As2, Mn3As2 and ZnMn2As2 within the framework of the density functional theory (DFT) and DFT + U method. The calculations based on first-principles were made using plane waves normalized on pseudopotential with the Quantum Espresso software package. Was obtained, that fundamental gap for Mn3As2 and Zn3As2 is equal to the optical band gap, while the band gaps for ZnMn2As2 was closer. The calculation for Mn3As2 and ZnMn2As2 by method DFT + U were performed; in these cases, the fundamental band gaps are closer to the optical band gaps, respectively. Considering the series Zn3As2 → ZnMn2As2 → Mn3As2, an increase in the Fermi energy was observed: Ef = 7.5 → 8.98 → 12.04 eV. It was established that the band gap of ZnMn2As2 (Eg = 0.6 eV) is a direct band gap corresponding to the transition between points Γ→Γ of the Brillouin zone. The Eg value obtained by us is closely known from experiments on optical absorption and the study of the temperature dependence of resistivity with Eg values equal to 0.8 eV and 0.76 eV, respectively. For Mn3As2 and ZnMn2As2, splitting is observed in density of states (DOS) between spin up and spin down electrons.

The magnetic properties of the new semimagnetic semiconductor (Zn1-xFex)3As2 with x < 0.04 have been investigated over a wide temperature range. Single crystals of ZFA were grown using the modified Bridgeman technique. The results of X-ray analyses and the magnetometry data show that the border of solid solutions in this system lay near x = 0.015. Further increasing of x leads to the growing of the second phase, which was identified as Fe2As. A notable feature of our magnetometry results is the spin-glass-type freezing of magnetic moments in the temperature range of 10 - 50 K. The value of the freezing temperature decreases when the magnetic field increases and in 2 kOe magnetic field the effect is no longer observable. It is likely that the observed freezing phenomena are due to the cluster nature of magnetic properties of ZFA. The thermoremanent magnetization measurements give evidence for two types of clusters in the magnetic system of ZFA.

Transformation of the Vavilov–Cherenkov radiation cone under grazing interaction of a relativistic electron with a layer of substance is theoretically studied. It is shown that this effect can occur when the electron enters the substance layer.

The structure of the transition zone of the wedge twin formed inside the grains of polycrystalline titanium was experimentally investigated. The accumulation of low-angle grain boundaries formed during the deformation by twin growing was discovered. Mathematical modeling of the stress state close to the twin zone was described in context of the macroscopic dislocation model. The model allows describing physical processes responsible for the formation of low-angle grain boundaries in a form of dislocation walls close to the transition zone of the wedge twin.

Single crystals of the diluted magnetic semiconductor (Zn1-x Fe x )3As2 (x = 0.005) were obtained by modified Bridgman method. According to the results of the X-ray powder diffractometry, the material was single-phased and isomorphic and corresponded to the pure Zn3As2 (x = 0.0). The research of the electroconductivity and the magnetoresistance was carried out at the temperature range from 10 to 300 K. It was found out that the electroconductivity in the temperature range 11 ÷ 19 K corresponded to the mechanism of the Mott type variable-range hopping conductivity. The microparameters, characterizing electroconductivity (Zn1-x Fe x )3As2 (x = 0.005) at the temperature range of 11 ÷ 19 K, were defined.

Investigations of transverse magnetoresistance have been performed on single crystals of diluted magnetic sem iconductor (Cd0.7Zn0.28Mn0.02)3As2 (CZMA). Based on analysis of the Shubnikov-de Haas (SdH) oscillations, observed in the temperature range T = 4.2 ÷ 30 K and at transverse magnetic field B = 0 ÷ 11 T, the phase shift, β, indicating the presence of the Berry phase was determined.

Charge carriers parameters on a 2D-layer surface for (Cd1−x−yZnxMny)3As2 (y = 0.08) (the concentration n 2 D = 1.9 × 1012 cm–2, the effective value of the 2D-layer d 2 D = n 2 D / n 3 D = 14.5 nm, the wave vector k F = 0.1 nm–1, the charge carriers relaxation time due to dispersion τ D = 1.8 × 10–13 s, the velocity of charge carriers on Fermi surface v F = ℏ k F / m c = 2.65 × 105 m s−1, the mean free path l F = v F τ D = 47.7 nm) were determined. It was found that the dependence of the cyclotron mass m с (0)/m0 on Fermi wave vector k F for (Cd1−x−yZnxMny)3As2 (y = 0.08) is in compliance with a theoretical linear dependence, that describes mass-less Dirac fermions.

Shubnikov-de Haas (SdH) effect and magnetoresistance measurements of single crystals of diluted II-V magnetic semiconductors (Cd

The characteristics of a double-jet electric arc are calculated taking the temperature and ionization argon plasma into account based on magnetogasdynamics equations in the plane-parallel approximation. The results of the calculations were compared with the analogous calculation in the equilibrium plasma approximation and the experimental data.

Characteristics of a double-jet electric arc have been determined by numerical simulation of magnetogasdynamics with allowance for a nonequilibrium character of the ionization-recombination processes and temperature in argon plasma. It is established that the anode and cathode jets play the roles of plasma electrodes, along which the character of arc discharge changes from self-sustained to non-self-sustained.

The interaction of plasma jets in a two-jet electric arc was analyzed based on the results of the numerical solution of magnetogasdynamic equations in a plane parallel approximation of an equilibrium plasma. The role of the mass, heat, and charge transfer processes in the formation of the calculated two-jet arc structure has been established which qualitatively agrees with the experimentally observed properties.

In the work we have presented the results of experimental studies and mathematical modeling for the processes of the structure formation in a transition zone of wedge-type twins system in commercially pure titanium. The process of interaction of structure defects with twinning dislocations during the formation of a wedge-type twin was taken into consideration. It is shown that the interaction alters the stress maximum in vicinity of boundaries in the system two wedge-type twins.

Shubnikov-de Haas (SdH) effect and magnetoresistance measurements of single crystals of diluted II-V magnetic semiconductors (Cd1-x-y Zn x Mn y )3As2 (x + y = 0.4, y = 0.04 and 0.08) are investigated in the temperature range T = 4.2 ÷ 300 K and in transverse magnetic field B = 0 ÷ 25 T. The values of the cyclotron mass m c, the effective g-factor g*, and the Dingle temperature T D are defined. In one of the samples (y = 0.04) a strong dependence of the cyclotron mass on the magnetic field m c(B) = m c(0) + αB is observed. The value of a phase shift close to β = 0.5 indicates the presence of Berry phase and 3D Dirac fermions in a single crystals of (Cd1-x-y Zn x Mn y )3As2 in one of the samples (y = 0.08).