Search

In this work we studied transport properties of eutectic InSb-MnSb crystals with oriented MnSb needle-like inclusions under a hydrostatic pressure up to P = 8 GPa and after its application. We show that the pressure-induced variation of the samples resistivity and transport parameters at room temperature can be interpreted in the terms of crystal phase transition of the InSb matrix. We argue that the irreversibility of this transition, deduced from transport measurements, may stem from the composite nature of the crystals studied. The resistivity of the samples subjected to high pressures increases upon cooling, which can be a consequence of the increased disorder accompanying the irreversible transition. Magnetotransport data for these samples suggest that charge carriers interact with a low-temperature magnetic phase. The latter can be formed by isolated Mn atoms in the InSb matrix.

We study the conductivity and magnetoresistance of the α‴ phase solid solution of (Cd1−xZnx)3As2 (x = 0.45). Single crystals of (Cd1−xZnx)3As2 are obtained by the modified Bridgman method. The space group and tetragonal lattice parameters of single crystals are found to be I41/amd and a = b = 8.56(5) Å, c = 24.16(6) Å. The temperature dependence of the conductivity and magnetoresistance is studied in the temperature range of 1.6–320 K and in the presence of a transverse magnetic field from 0 to 10 T. Mixed conductivity is analyzed using Hall resistivity data and standard quantitative mobility spectrum analysis. The concentration and mobility of holes are determined at different temperatures. The presence of two types of holes with different mobilities is demonstrated in the temperature range of 1.6–19 K, while with increasing temperature, just one type of charge carrier is observed in the mobility spectrum.

Background/Objectives: The issue of effective wound healing remains highly relevant. The objective of the study is to develop an optimal method for the synthesis of nanosized cerium oxide powder obtained via the thermal decomposition of cerium carbonate precipitated from aqueous nitrate solution for the technical creation of new drugs in production conditions; the select modification of synthesis under different conditions based on the evaluation of the physicochemical characteristics of the obtained material and its biological activity, and an evaluation of the broad-spectrum effect on cells involved in the regeneration of skin structure as well as antimicrobial properties. Methods: Several modes of the industrial synthesis of cerium dioxide nanoparticles (NPs) were carried out. The synthesis stages and the chemical and physical parameters of the obtained NPs were described using transmission electron microscopy (TEM), X-ray diffraction, Raman spectroscopy, and mass spectrometry. The cell cultures of human fibroblasts and keratinocytes were cultured with different concentrations of different nanoceria variations, and the cytotoxicity and the metabolic and proliferative activity were investigated. An MTT test and cell counting were performed. The antimicrobial activity of CeO2 variations at a concentration of 0.1–0.0001 M against Pseudomonas aeruginosa was studied. Results: The purity of the synthesized nanoceria powders in all the batches was >99.99%. According to TEM data, the size of the NPs varied from 1 nm to 70 nm under different conditions and methodologies. The most optimal technology for the synthesis of the nanoceria with the maximum biological effect was selected. A method for obtaining the most bioactive NPs of optimal size (up to 10 nm) was proposed. The repeatability of the results of the proposed method of nanoceria synthesis in terms of particle size was confirmed. It was proven that the more structural defects on the surface of the CeO2 crystal lattice, the higher the efficiency of the NPs due to oxygen vacancies. The strain provided the best redox activity and antioxidant properties of the nanoceria, which was demonstrated by better regenerative potential on various cell lines. The beneficial effect of synthesized nanoceria on the proliferative and metabolic activity of the cell lines involved in skin regeneration (human fibroblasts, human keratinocytes) was demonstrated. The antimicrobial effect of synthesized nanoceria on the culture of the most-resistant-to-modern-antibiotics microorganism Pseudomonas aeruginosa was confirmed. The optimal concentrations of the nanoceria to achieve the maximum biological effect were determined (10−3 M). Conclusions: It was possible to develop a method for the industrial synthesis of nanoceria, which can be used to produce drugs and medical devices containing CeO2 NPs.

We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition using the eutectic compound (GaSb)0.59(MnSb)0.41 as target for sputtering. For the studied films we have observed ferromagnetism and an anomalous Hall effect above room temperature, confirming the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggest that the films under study have a homogenous columnar structure in the bulk while MnSb inclusions accumulate near the surface. This is in good agreement with the high mobility values of charge carriers. Based on our data we conclude that the magnetic and magnetotransport properties of the films at room temperature are defined by the MnSb inclusions.

We demonstrate that measurements of the photo-electromagnetic effect using terahertz laser radiation provide an argument for the existence of highly conductive surface electron states with a spin texture in Dirac semimetals (Cd1−xZnx)3As2. We performed a study on a range of (Cd1−xZnx)3As2 mixed crystals undergoing a transition from the Dirac semimetal phase with an inverse electron energy spectrum to trivial a semiconductor with a direct spectrum in the crystal bulk by varying the composition x. We show that for the Dirac semimetal phase, the photo-electromagnetic effect amplitude is defined by the number of incident radiation quanta, whereas for the trivial semiconductor phase, it depends on the laser pulse power, irrespective of wavelength. We assume that such behavior is attributed to a strong damping of the interelectron interaction in the Dirac semimetal phase compared to the trivial semiconductor, which may be due to the formation of surface electron states with a spin texture in Dirac semimetals.

Charge carriers parameters on a 2D-layer surface for (Cd _1−x−y Zn _x Mn _y ) _3 As _2 ( y = 0.08) (the concentration ${n}_{2D}$ = 1.9 × 10 ^12 cm ^–2 , the effective value of the 2D-layer ${d}_{2D}={n}_{2D}/{n}_{3D}$ = 14.5 nm, the wave vector ${k}_{F}$ = 0.1 nm ^–1 , the charge carriers relaxation time due to dispersion ${\tau }_{D}$ = 1.8 × 10 ^–13 s, the velocity of charge carriers on Fermi surface ${v}_{F}=\hslash {k}_{F}/{m}_{c}$ = 2.6 ^5 × 10 ^5 m s ^−1 , the mean free path ${l}_{F}={v}_{F}{\tau }_{D}$ = 47.7 nm) were determined. It was found that the dependence of the cyclotron m ass m _с (0)/m _0 on Fermi wave vector k _F for (Cd _1−x−y Zn _x Mn _y ) _3 As _2 ( y = 0.08) is in compliance with a theoretical linear dependence, that describes mass-less Dirac fermions.

Specific features and regularities of self-assembly and self-organization of multi-walled carbon nanotubes (MWCNT) have been studied for diffusion-limited conditions (method of drops) in water-based (deionized water) colloidalal solutions with aerosil exposed to DC electric fields with magnitudes of 15 to 25 V. Studies of hierarchical structure formation during drop evaporation in uniform electric fields have revealed the formation of 40–120 nm sized linear piecewise formations, 25–45 nm sized fractal structures and 250 nm sized diffuse structures from MWCNT – COOH + aerosil + H2Odw. The structures have been studied using confocal microscopy, X-ray diffraction, Raman scattering, atomic force microscopy, IR spectroscopy and scanning electron microscopy. The sizes of the observed micro- and nanostructures decrease following the hyperbolic law d = 1/U in the approximation d → 2R, their growth rate increasing as U2. We show that intense ultrasonication of functionalized MWCNT – COOH + aerosil + H2Odw in colloidal solutions causes the formation of the so-called “breathing" modes in axis centered single-walled carbon nanotubes. This is confirmed by short-wave Raman scattering excitation and enables the existence of both combined sp2-hybridization types with π- and σ- carbon bonds and the metallic and semiconductor conductivity types in the material thus showing good promise of these structures for nanoelectronics.