Showing papers by "Sergey M. Zharkov published in 2021"
TL;DR: In this article, the magnetic core of all the nanoparticles was shown to be nanocrystalline with the crystal parameters corresponding only to the Fe3O4 phase covered with a homogeneous amorphous silica (SiO2) shell of about 6 nm in thickness.
Abstract: Fe3O4@SiO2 core-shell nanoparticles (NPs) were synthesized with the co-precipitation method and functionalized with NH2 amino-groups. The nanoparticles were characterized by X-ray, FT-IR spectroscopy, transmission electron microscopy, selected area electron diffraction, and vibrating sample magnetometry. The magnetic core of all the nanoparticles was shown to be nanocrystalline with the crystal parameters corresponding only to the Fe3O4 phase covered with a homogeneous amorphous silica (SiO2) shell of about 6 nm in thickness. The FT-IR spectra confirmed the appearance of chemical bonds at amino functionalization. The magnetic measurements revealed unusually high saturation magnetization of the initial Fe3O4 nanoparticles, which was presumably associated with the deviations in the Fe ion distribution between the tetrahedral and octahedral positions in the nanocrystals as compared to the bulk stoichiometric magnetite. The fluorescent spectrum of eosin Y-doped NPs dispersed in water solution was obtained and a red shift and line broadening (in comparison with the dye molecules being free in water) were revealed and explained. Most attention was paid to the adsorption properties of the nanoparticles with respect to three dyes: methylene blue, Congo red, and eosin Y. The kinetic data showed that the adsorption processes were associated with the pseudo-second order mechanism for all three dyes. The equilibrium data were more compatible with the Langmuir isotherm and the maximum adsorption capacity was reached for Congo red.
12 citations
TL;DR: In this paper, the effect of Pd, Au and PdAu nanoparticles on sensor response of cobalt phthalocyanine films to hydrogen was studied, and it was shown that the sensor response increased in the order CoPc (0.2Au 0.8 and PD0.8 A 0.2 ) to hydrogen.
8 citations
TL;DR: In this paper, (Co+Al)-doped ZnO films have been synthesized by the RF magnetron sputtering, and they exhibit ferromagnetic behavior at room temperature with much greater magnetization and magneto-optical activity compared to the Co-doped films.
Abstract: (Co + Al)-doped ZnO films have been synthesized by the RF magnetron sputtering. Films of this composition have first been obtained in mixed atmosphere of Ar + H2. High hydrogen concentration of 20–50% has been used together with high enough substrate temperature of 450 °C. The used technological conditions affected the morphology, chemical composition, optical, electric, and magnetic properties of the films to an even more than in the case of Co-doped ZnO films synthesized under the same conditions and studied earlier. The films exhibit ferromagnetic behavior at room temperature with much greater magnetization and magneto-optical activity compared to the Co-doped films. At the same time, the hydrogenated films show an increase in electric conductivity in comparison with samples synthesized in the atmosphere of Ar + O2. The magnetic nature of the hydrogenated films has been associated with the defect-related mechanism.
7 citations
TL;DR: In this paper, phase formation in a solid state reaction in Al/Cu bilayer and multilayer thin films was studied by the methods of in situ transmission electron microscopy, electron diffraction, simultaneous thermal analysis and x-ray diffraction.
Abstract: Phase formation in a solid state reaction in Al/Cu bilayer and multilayer thin films was studied by the methods of in situ transmission electron microscopy, electron diffraction, simultaneous thermal analysis and x-ray diffraction. It was established that the phase formation sequences in the (Al/Cu)n (n = 2, 15) multilayer thin films (θ-Al2Cu → γ1-Al4Cu9 → η2-AlCu) and Al/Cu bilayer thin films (θ-Al2Cu → η2-AlCu → γ1-Al4Cu9) were different. It was assumed that the phase formation process in the thin films was strongly affected by a number of copper/aluminum interfaces due to the changes of aluminum and copper diffusion current.
4 citations
TL;DR: In this article, it was shown that the induced magnetic anisotropy in high-coercivity films relates to the modification of the Co lattice, which passes from a distorted fcc to an hcp structure during the growth of crystallites in a magnetic field.
3 citations
TL;DR: In this paper, a solid-state reaction process in Ag/Al multilayer thin films has been investigated by the methods of in situ electron diffraction, simultaneous thermal analysis, transmission electron microscopy and X-ray diffraction with the aim of studying the phase formation kinetics of intermetallic compounds.
3 citations
TL;DR: In this article, the authors used oleylamine and 1-hexadecylamine (HDA) surfactants to synthesize greigite nanoparticles with minor inclusions of Fe9S11 phase.
3 citations
10 Mar 2021
TL;DR: In this article, the properties of valleriite were examined using X-ray absorption near-edge structures (XANES) spectra, with a higher electron density at Cu+ centers and essentially differ from those of bornite Cu5FeS4; the Fe K-edge was less informative because of accompanying oxidized Fe-containing phases.
Abstract: Valleriite is of interest as a mineral source of basic and precious metals and as an unusual material composed of two-dimensional (2D) Fe-Cu sulfide and magnesium hydroxide layers, whose characteristics are still very poorly understood. Here, the mineral samples of two types with about 50% of valleriites from Noril'sk ore provenance, Russia, were examined using Cu K- and Fe K-edge X-ray absorption fine structure (XAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), 57Fe Mossbauer spectroscopy, and magnetic measurements. The Cu K X-ray absorption near-edge structures (XANES) spectra resemble those of chalcopyrite, however, with a higher electron density at Cu+ centers and essentially differ from those of bornite Cu5FeS4; the Fe K-edge was less informative because of accompanying oxidized Fe-containing phases. The post-edge XANES and extended XAFS (EXAFS) analysis reveal differences in the bond lengths, e.g., additional metal-metal distances in valleriites as compared with chalcopyrite. The XPS spectra confirmed the Cu+ and Fe3+ state in the sulfide sheets and suggest that they are in electron equilibrium with (Mg, Al) hydroxide layers. Mossbauer spectra measured at room temperature comprise central doublets of paramagnetic Fe3+, which decreased at 78 K and almost disappeared at 4.2 K, producing a series of hyperfine Zeeman sextets due to internal magnetic fields arising in valleriites. Magnetic measurements do not reveal antiferromagnetic transitions known for bornite. The specific structure and properties of valleriite are discussed in particular as a platform for composites of the 2D transition metal sulfide and hydroxide (mono)layers stacked by the electrical charges, promising for a variety of applications.
3 citations
TL;DR: In this article, the authors proposed a layered material valleriite composed of altering atomic sheets of Cu-Fe sulfide and Mg-based hydroxide synthesized via a simple hydrothermal pathway as particles of 50-200 nm in the lateral size and 10-20 nm thick.
Abstract: Two-dimensional phenomena are attracting enormous interest at present and the search for novel 2D materials is very challenging. We propose here the layered material valleriite composed of altering atomic sheets of Cu-Fe sulfide and Mg-based hydroxide synthesized via a simple hydrothermal pathway as particles of 50-200 nm in the lateral size and 10-20 nm thick. The solid products and aqueous colloids prepared with various precursor ratios were examined using XRD, TEM, EDS, X-ray photoelectron spectroscopy (XPS), reflection electron energy loss spectroscopy (REELS), Raman, Mossbauer, UV-vis-NIR spectroscopies, magnetic, dynamic light scattering, zeta potential measurements. The material properties are largely determined by the narrow-gap (less than 0.5 eV) sulfide layers containing Cu+ and Fe3+ cations, monosulfide and minor polysulfide anions but are strongly affected by the hydroxide counterparts. Particularly, Fe distribution between sulfide (55-90%) and magnesium hydroxide layers is controlled through insertion of Al into the hydroxide part and by Cr and Co dopants entering both layers. Room-temperature Mossbauer signals of paramagnetic Fe3+ transformed to several Zeeman sextets with hyperfine magnetic fields up to 500 kOe in the sulfide layers at 4 K. Paramagnetic or more complicated characters were observed for valleriites with higher and lower Fe concentrations in hydroxide sheets, respectively. Valleriite colloids showed negative zeta potentials, suggesting negative electric charging of the hydroxide sheets, and optical absorption maxima between 500 nm and 700 nm, also depended on the Fe distribution. The last features observed also in the REELS spectra may be due to localized surface plasmon or, more likely, quasi-static dielectric resonance. The tunable composition, electronic, magnetic, optic and surface properties highlight valleriites as a rich platform for novel 2D composites promising for numerous applications.
2 citations
TL;DR: In this article, a method for forming HTS ceramics of non-superconducting coating consisting of self-organizing CuO crystals, whose sizes are less than the coherence length, has been developed.
Abstract: A method making it possible to form HTS ceramics of non-superconducting coating consisting of self-organizing CuO crystals, whose sizes are less than the coherence length, i.e., within several tens of nanometers, has been developed. It has been shown that the combination of self-organizing structures in the form of whiskers and nanoparticles which arise as a result of combined sintering of YBa2Cu3O(7–x) powders and electric arc CuO nanopowders results in a significant increase in the current density and appearance of peak effect at high magnetic fields. Very high current density arises from the complex vortex pinning, where whisker defects provide high pinning energy and nanoparticles suppress flux creep. The morphology of such structures can be controlled by a simple change in the concentration of nanodisperse additives. It has been shown that 20 wt % of CuO additive is optimal.