New Publications

Effect of a Substrate on the Magnetoelectric Effect in Rare-Earth-Doped Bismuth Iron Garnet

Aplesnin, S. S.; Masyugin, A. N.; Sitnikov, M. N.; Ishibashi, T. Source: JETP LETTERS, 110 (3):223-230; 10.1134/S0021364019150074 AUG 2019

The mechanism of relaxation of the electric polarization in thin films of rare-earth-doped bismuth iron garnet on glass and gallium gadolinium garnet substrates is determined in magnetic fields of 0 and 12 kOe in the temperature range of 80–380 K. The change in the sign of the residual electric polarization after switching off the electric field and the magnetic-field-induced shift of the hysteresis loop in the applied magnetic field are found. Linear and quadratic magnetoelectric effects with the tensor components depending on the substrate type are observed. The linear magnetoelectric effect is related to the spin–orbit coupling of electrons at the film–substrate interface, whereas the quadratic one is determined by the exchange–striction mechanism.

Experimental and Theoretical In Situ Spectral Magneto-Ellipsometry Study of Layered Ferromagnetic Structures

Maximova, O. A.; Lyaschenko, S. A.; Vysotin, M. A.; Tarasov, I. A.; Yakovlev, I. A.; Shevtsov, D. V.; Fedorov, A. S.; Varnakov, S. N.; Ovchinnikov, S. G. Source: JETP LETTERS, 110 (3):166-172; 10.1134/S0021364019150098 AUG 2019

A method for processing of in situ spectral magneto-ellipsometry data has been developed to analyze planar ferromagnetic nanostructures. A multilayer model containing a ferromagnetic layer with two interfaces, a nonferromagnetic buffer layer, and a nonferromagnetic substrate has been tested within a new approach to the interpretation of magnetic-field-modulated spectral ellipsometric measurements involving the magnetooptical Kerr effect in the transverse configuration. In particular, the effect of the thickness of the ferromagnetic layer on the results of magneto-ellipsometric measurements has been analyzed. The measurements have been performed with polycrystalline Fe films with different thicknesses on a nonferromagnetic SiO2/Si(100) surface. The diagonal and off-diagonal components of the complex dielectric tensor in the spectral range of 1.38–3.45 eV have been determined by processing spectral magneto-ellipsometric data. The results have been compared to the available data obtained by other authors and to the calculation of the dielectric tensor of Fe within the density functional theory.

Structural, Optical, and Thermoelectric Properties of the ZnO:Al Films Synthesized by Atomic Layer Deposition

Tambasov, I. A.; Volochaev, M. N.; Voronin, A. S.; Evsevskaya, N. P.; Masyugin, A. N.; Aleksandrovskii, A. S.; Smolyarova, T. E.; Nemtsev, I., V; Lyashchenko, S. A.; Bondarenko, G. N.; Tambasova, E., V Source: PHYSICS OF THE SOLID STATE, 61 (10):1904-1909; 10.1134/S1063783419100354 OCT 2019

Aluminum-doped zinc oxide thin films have been grown by atomic layer deposition at a temperature of 200°C. Using X-ray diffraction, it has been established that the ZnO:Al thin films exhibits the reflections from the (100), (002), (110), and (201) ZnO hexagonal phase planes. The (101) and (102) planes have also been detected by electron diffraction. The ZnO:Al thin films grow smooth with a root-mean-square roughness of Rq = 0.33 nm and characteristic nanocrystallite sizes of ~70 and ~15 nm without additional aluminum or aluminum oxide phases. The transmission at a wavelength of 550 nm with regard to the substrate has been found to be 96%. The refractive indices and absorption coefficients of the ZnO:Al thin films in the wavelength range of 250–900 nm have been determined. The maximum refractive indices and absorption coefficients have been found to be 2.09 at a wavelength of 335 nm and 0.39 at a wavelength of 295 nm, respectively. The optical band gap is 3.56 eV. The resistivity, Seebeck coefficient, and power factor of the ZnO:Al thin films are ∼1.02 × 10–3 Ω cm, –60 μV/K, and 340 μW m–1 K–2 at room temperature, respectively. The maximum power factor attains 620 μW m–1 K–2 at a temperature of 200°C.

Lead-Free Hybrid Metal Halides with a Green-Emissive [MnBr4] Unit as a Selective Turn-On Fluorescent Sensor for Acetone

Li, Mingze; Zhou, Jun; Molokeev, Maxim S.; Jiang, Xingxing; Lin, Zheshuai; Zhao, Jing; Xia, Zhiguo Source: INORGANIC CHEMISTRY, 58 (19):13464-13470; 10.1021/acs.inorgchem.9b02374 OCT 7 2019

Organic–inorganic hybrid metal halides with zero-dimensional (0D) structure has emerged as a new class of light-emitting materials. Herein, a new lead-free compound (C9NH20)2MnBr4 has been discovered and a temperature-dependent phase transition has been identified for two phases (space group P21/c and C2/c) in which individual [MnBr4]2– anions connect with organic cations, (C9NH20+) (1-buty-1-methylpyrrolidinium+), forming periodic structure with 0D blocks. A green emission band, peaking at 528 nm with a high photoluminescence quantum efficiency (PLQE) of 81.08%, has been observed at room temperature, which is originated from the 4T1(G) to 6A1 transition of tetrahedrally coordinated Mn2+ ions, as also elaborated by density functional theory calculation. Accordingly, a fast, switchable, and highly selective fluorescent sensor platform for different organic solvents based on the luminescence of (C9NH20)2MnBr4 has been developed. We believe that the hybrid metal halides with high PLQE and the exploration of these as a fluorescence sensor will expand the applications scope of bulk 0D materials for future development.

Magnetism in spin crossover systems: Short-range order and effects beyond the Heisenberg model

Kuz'min, V., I; Orlov, Yu S.; Zarubin, A. E.; Ovchinnikova, T. M.; Ovchinnikov, S. G. Source: PHYSICAL REVIEW B, 100 (14):10.1103/PhysRevB.100.144429 OCT 21 2019

To study non-Heisenberg effects in the vicinity of spin crossover in strongly correlated electron systems we derive an effective low-energy Hamiltonian for the two-band Kanamori model. It contains a Heisenberg high-spin term proportional to exchange constant as well as a low-spin term proportional to spin gap parameter ɛs. Using cluster mean field theory we obtain several non-Heisenberg effects. Near the critical value of spin gap ɛcs there is a magnetic phase transition of first order. In the vicinity of ɛcs in the paramagnetic phase we observe nontrivial behavior of the Curie constant in the paramagnetic susceptibility in the wide range of temperature. Reentrant temperature behavior of nearest-neighbor spin-spin correlations is observed at ɛs>ɛcs. Finally, the pressure-temperature magnetic phase diagram for ferroperriclase is obtained using the effective Hamiltonian.

Ion reduction in iron oxide and oxyhydroxide nanoparticles during ultrasonic treatment

Stolyar, S. V.; Bayukov, O. A.; Yaroslavtsev, R. N.; Knyazev, Yu. V.; Ladygina, V. P.; Gerasimova, Yu. V.; Iskhakov, R. S. Source: ADVANCED POWDER TECHNOLOGY, 30 (11):2620-2625; 10.1016/j.apt.2019.08.009 NOV 2019

The effect of ultrasonic treatment of iron oxide and iron oxyhydroxide nanoparticles (ferrihydrite nanoparticles synthesized by Klebsiella oxytoca microorganisms, ferrihydrite nanoparticles synthesized by a chemical method and hematite nanoparticles) is studied. Samples of nanoparticles were investigated using transmission electron microscopy, Mössbauer spectroscopy and X-ray diffraction methods. The formation of the α-Fe metal phase from nanoparticles of iron oxides and iron oxyhydroxides was detected. The metal phase is formed as a result of the reduction of iron ions during cavitation treatment. According to the experimental results, the presence of a protein or a polysaccharide component is necessary for the course of this reaction.

Electrophysical properties of hydroxylated endohedral metallofullerene with gadolinium

Dudnik, Alexander, I; Vnukova, Natalia G.; Drokin, Nikolay A.; Bondarev, Vitaliy S.; Shestakov, Nikolay P.; Tomashevich, Yevgeniy, V; Churilov, Grigory N. Source: JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 135 10.1016/j.jpcs.2019.109094 DEC 2019

The paper presents the results of experimental measurements of constitutive and electrophysical properties in hydroxylated endohedral metallofullerene with gadolinium sample. We extracted endohedral metallofullerene from carbon condensate, synthesized in high-frequency arc discharge plasma. Later hydroxyl groups were added. Via methods of infrared and x-ray photoelectronic spectroscopy, it was established that the molecules of hydroxylated endohedral metallofullerene have the Gd@C82Ox(OH)y, x + y=(40–42) composition. The method of measuring the electrical impedance in the frequency range from 100 Hz to 100 MHz shows that the resulting hydroxylated fullerene is an ion conductor. The measured frequency dependences of the dielectric permittivity and conductivity of hydroxylated fullerene are explained based on the assumption of an inhomogeneous distribution of electric charges in the material volume. Dielectric-hysteresis loops in the frequency range of 25 Hz–1 MHz and temperature range of 80–300 K, and volt-ampere characteristics were measured. The obtained results imply the appearance of residual polarization induced by the electric field in hydroxylated fullerene. However, the constant dipole moment is absent.

Miniaturized Suspended-Substrate Two-Conductors Resonator and a Filter on Its Base

Leksikov, Aleksandr A.; Serzhantov, Alexey M.; Govorun, Ilya, V; Afonin, Aleksey O.; Ugryumov, Andrey, V; Leksikov, Andrey A. Source: PROGRESS IN ELECTROMAGNETICS RESEARCH M, 84 127-135; 10.2528/PIERM19060604 2019

The paper is devoted to an investigation of two-conductor suspended-substrate resonators. For the purpose of miniaturization conductors of a resonator are folded. Four types of the resonator differing in conductors' configurations were considered. Their Q0-factors and resonant frequencies were studied. Based on results of the study two types of the resonator appeared unsuitable for an application in compact filters. Two other types were investigated in concern of their interaction: dependencies of coupling coefficients versus space between resonators and ver-sus distance from substrate's surfaces, and package's covers were obtained. Based on the depen-dences a type of the resonator suitable for designing compact BPF was chosen. A four-pole BPF was simulated and fabricated. Good agreement between simulated and experimental results is observed. The main filter's characteristics are the next: substrate has ε = 80, thickness 0.5 mm, lateral sizes 0.13λg × 0.09λg (18.7 mm × 13.2 mm). The central frequency is 305 MHz; bandwidth is 39 MHz; passband minimum insertion loss is 2.0 dB; passband return loss is less -14.6 dB; -40 dB stop-band width is 480 MHz.

Novel Derivatives of Adamantyl-substituted Quinolin-6-amines and Synthesis of Imidazo[4,5-f]quinolines Therefrom

Abramov, A. A.; Kulagina, M., V; Gavrilova, N. A.; Semichenko, E. S.; Kondrasenko, A. A.; Suboch, G. A. Source: RUSSIAN JOURNAL OF ORGANIC CHEMISTRY, 55 (8):1234-1237; 10.1134/S1070428019080256 AUG 2019

N-(Adamantan-1-yl)alkyl-substituted 5-nitrosoquinolin-6-amines were synthesized for the first time by the amination of 5-nitrosoquinolin-6-ol with primary N-[(adamantan-1-yl)alkyl]amines. The resulting nitrosoquinolinamines were reduced with hydrazine hydrate over Pd/C to N6-[(adamantan-1-yl)alkyl]quinoline-5,6-diamines. The latter were heated in formic acid to obtain previously unknown 3-[(adamantan-1-yl)alkyl]-3H-imidazo[4,5-f]quinolines.

Structure and Thermal Decomposition of Nd(III), Gd(III) and Tb(III) 2-Thiobarbiturates

Golovnev, N. N.; Molokeev, M. S.; Sterkhova, I., V Source: RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 64 (9):1146-1151; 10.1134/S0036023619090134 SEP 2019

Complexes [Ln2(H2O)62-Htba−O,O')4(Htba−O)2]n (Ln = Tb (I), Gd (II), Nd (III); and H2tba is thiobarbituric acid) have been synthesized. According to single-crystal X-ray diffraction, monoclinic crystals of I–III are isostructural. They contain three independent Htba ions (one terminal and two bridging) and two independent Ln3+ ions. Six Htba ligands (two terminal and four O,O'-bridging) and two water molecules are coordinated to one Ln3+ ion, and four O,O'-bridging Htba ions and four water molecules are coordinated to the other Ln3+ ion to form square antiprisms. The antiprisms are bound by Htba bridging ions into layers. Numerous hydrogen bonds and π–π interactions stabilize the structures of the compounds. Thermal decomposition of complexes I and II performed in air results in mixtures of oxides and oxysulfates, whereas complex III forms Nd2O2SO4.

Transparent conductive oxides for the epsilon-near-zero Tamm plasmon polaritons

Bikbaev, Rashid G.; Vetrov, Stepan Ya; Timofeev, Ivan, V Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 36 (10):2817-2823; 10.1364/JOSAB.36.002817 OCT 1 2019

We demonstrate the possibility of using transparent conducting oxides [aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), indium tin oxide (ITO)] to form Tamm plasmon polaritons in the near-infrared spectral range where the permittivity of oxides is near zero. The spectral properties of the structures are investigated in the framework of the temporal coupled-mode theory and confirmed by the transfer matrix method. It is found that in the critical coupling conditions, the maximal 𝑄-factor of a Tamm plasmon polariton is achieved when a photonic crystal is conjugated with the AZO film, while at the conjugation with the ITO films, the broadest spectral line is obtained. The sensitivity of the wavelength and spectral width of the Tamm plasmon polariton to changes in the oxide film thickness, bulk concentration of a dopant, and angle of incidence is demonstrated.

Morphology stability of polymethylmethacrylate nanospheres formed in water-acetone dispersion medium

Nemtsev, Ivan, V; Shabanova, Olga, V; Shestakov, Nikolay P.; Cherepakhin, Alexander, V; Zyryanov, Victor Ya Source: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 125 (10):10.1007/s00339-019-3036-4 OCT 2019

The aim of this study is to develop a manufacturing technique of polymethylmethacrylate (PMMA) nanospheres to produce a more stable opal template. Water–acetone mixture was used as a dispersion medium to synthesize a PMMA opal structure. Morphology features, IR vibrational spectra and glass transition temperatures of the PMMA nanospheres formed in the water–acetone dispersion medium (nanospheres A) have been studied comparing with the same prepared in distilled water solution without acetone (nanospheres B). A dependence of a shrinkage degree of the nanoparticles on the acetone volume has been investigated. It has been revealed that under an electron beam action the shrinkage degree of the nanospheres A is in the range of 7–16% while the shrinkage of the nanospheres B is 18–25% at the same conditions. The nanospheres A are less flexible and soft as compared to the nanospheres B. Additionally, an ability of the PMMA nanoparticles fabricated in the water–acetone dispersion medium to form the ordered opal structures is demonstrated to be the similar to the nanospheres B.

Crystal size versus paddle wheel deformability: selective gated adsorption transitions of the switchable metal-organic frameworks DUT-8(Co) and DUT-8(Ni)

Ehrling, Sebastian; Senkovska, Irena; Bon, Volodymyr; Evans, Jack D.; Petkov, Petko; Krupskaya, Yulia; Kataev, Vladislav; Wulf, Toshiki; Krylov, Alexander; Vtyurin, Alexander; Krylova, Svetlana; Adichtchev, Sergey; Slyusareva, Evgenia; Weiss, Manfred S.; Buechner, Bernd; Heine, Thomas; Kaskel, Stefan Source: JOURNAL OF MATERIALS CHEMISTRY A, 7 (37):21459-21475; 10.1039/c9ta06781g OCT 7 2019

Switchable pillared layer metal–organic frameworks M2(2,6-ndc)2(dabco) (DUT-8(M), M = Ni, Co, 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]octane, DUT – Dresden University of Technology) were synthesised in two different crystallite size regimes to produce particles up to 300 μm and smaller particles around 0.1 μm, respectively. The textural properties and adsorption-induced switchability of the materials, obtained from both syntheses, were studied by physisorption of N2 at 77 K, CO2 at 195 K and n-butane at 273 K, revealing pronounced differences in adsorption behavior for Ni and Co analogues. While the smaller nano-sized particles (50–200 nm) are rigid and show no gating transitions confirming the importance of crystallite size, the large particles show pronounced switchability with characteristic differences for the two metals resulting in distinct recognition effects for various gases and vapours. Adsorption of various vapours demonstrates consistently a higher energetic barrier for the “gate opening” of DUT-8(Co) in contrast to DUT-8(Ni), as the “gate opening” pressure for Co based material is shifted to a higher value for adsorption of dichloromethane at 298 K. Evaluation of crystallographic data, obtained from single crystal and powder X-ray diffraction analysis, showed distinct geometric differences in the paddle wheel units of the respective MOFs. These differences are further disclosed by solid-state UV-vis, FT-IR and Raman spectroscopy. Magnetic properties of DUT-8(Co) and DUT-8(Ni) were investigated, indicating a high-spin state for both materials at room temperature. Density functional theory (DFT) simulations confirmed distinct energetic differences for Ni and Co analogues with a higher energetic penalty for the structural “gate opening” transformation for DUT-8(Co) compared to DUT-8(Ni) explaining the different flexibility behaviour of these isomorphous MOFs.

Evolution of the resonances of two parallel dielectric cylinders with distance between them

Bulgakov, E. N.; Pichugin, K. N.; Sadreev, A. F. Source: PHYSICAL REVIEW A, 100 (4):10.1103/PhysRevA.100.043806 OCT 8 2019

We study evolution of resonant modes by traversing over the distance between two parallel dielectric cylinders. The processes of mutual scattering of Mie resonant modes by cylinders result in an interaction between the cylinders which lifts a degeneracy of resonances of the isolated cylinders. There are two basic scenarios of evolution. For strong interaction of cylinders resonances bypass the Mie resonances with increase of the distance. That scenario is typical for low-lying resonances (monopole and dipole). For weak interaction of cylinders the resonances are bound around the Mie resonances of isolated cylinders that form the second scenario. Both scenarios demonstrate a significant enhancement of the Q factor compared to the case of an isolated cylinder

Understanding perceived color through gradual spectroscopic variations in electrochromism

Mishra, Suryakant; Yogi, Priyanka; Chaudhary, Anjali; Pathak, Devesh K.; Saxena, Shailendra K.; Krylov, Alexander S.; Sagdeo, P. R.; Kumar, Rajesh Source: INDIAN JOURNAL OF PHYSICS, 93 (7):927-933; 10.1007/s12648-018-1353-7 JUL 2019

A bias-dependent in situ Raman scattering and UV–Vis absorption spectroscopic change has been correlated with the corresponding color change of an electrochromic device in an attempt to explain how to understand the relationship between actual perceived color and its absorption/transmittance spectra. For this, the bias across an electrochromic device was increased gradually, rather than abruptly turning ON and OFF, to see subtle variations in Raman and absorption spectra due to bias. Raman scattering establishes that viologen changes its oxidation state reversibly between two redox species (EV2+ to EV+•) as a result of bias-induced dynamic redox process. A gradual variation in Raman and absorption spectra, which shows maximum absorption corresponding to the yellow light, accompanies similar variation in color change of the device as visible by naked eye. These spectroscopic results are correlated with the perceived blue color, in the reflected light, by the eye to understand the actual reason behind this. Maximum absorption of yellow light by the device resulting in blue appearance has been explained using the concept of additive and subtractive primary colors.

Occurrence of Topologically Nontrivial Phases, Cascade of Quantum Transitions, and Identification of Majorana Modes in Chiral Superconductors and Nanowires (Scientific Summary)

Val'kov, V. V.; Mitskan, V. A.; Zlotnikov, A. O.; Shustin, M. S.; Aksenov, S. V. Source: JETP LETTERS, 110 (2):140-153; 10.1134/S002136401914011X JUL 2019

The problems of occurrence and experimental identification of topologically nontrivial phases in condensed matter have been reviewed. The results of the study of the effect of strong intra- and interatomic Coulomb interaction on a quantum phase transition with change in the topological index in an ensemble of Hubbard fermions on a triangular lattice have been reported. Nontrivial topology of the phase of coexistence of d + id chiral superconductivity and 120° spin ordering in a system with the triangular lattice has been discussed and the formation of Majorana modes in such a phase has been demonstrated. A cascade of quantum transitions that occurs at the variation of the magnetic field or the electrochemical potential has been analyzed for an open nanowire with the Rashba spin-orbit coupling and the induced superconducting pairing potential. It has been shown that anomalies of magneto- and electrocaloric effects are manifested near such quantum transitions and can be used to experimentally test materials on the existence of topologically nontrivial phases in them. The switching of the spin-polarized current in the topological superconducting phase has been predicted for a semimetal/superconducting wire/semimetal structure in the weak nonequilibrium regime.

Manifestation of Spin Correlations in Monocrystalline ErAl3(BO3)(4)

Bedarev, V. A.; Merenkov, D. N.; Kobets, M., I; Zvyagin, A. A.; Poperezhai, S. N.; Gnatchenko, S. L.; Zajarniuk, T.; Vasevych, T.; Gutowska, M. U.; Szewczyk, A.; Gudim, I. A. Source: LOW TEMPERATURE PHYSICS, 45 (9):1041-1045; 10.1063/1.5121279 SEP 2019

A substantial magnetic contribution into specific heat capacity is found in monocrystalline ErAl3(BO3)4 at temperatures below 5 K. The results of measured ESR spectra at 4,2 K confirm manifestation of short-range magnetic order as well. The obtained data is discussed invoking the model accounting for spin-spin interaction between rare-earth ions in paired clusters.

Magnetic and structural correlations in the warwickite Mn2OBO3

Gnezdilov, V; Pashkevich, Yu; Kurnosov, V; Zhuravlev, O., V; Wulferding, D.; Lemmens, P.; Kazak, N., V; Knyazev, Yu, V; Ovchinnikov, S. G. Source: LOW TEMPERATURE PHYSICS, 45 (9):1046-1052; 10.1063/1.5121280 SEP 2019

We report a Raman scattering study of single-crystalline homometallic oxyborate Mn2OBO3, a compound realizing a one-dimensional ribbon-structure. Phonon excitations as a function of temperature and light polarization are compared to lattice dynamical calculations, giving evidence for a strong coupling between lattice and magnetic degrees of freedom. Furthermore, a broader feature with a distinct structure emerges at low temperatures. Based on our theoretical analysis, we assign this signal to specific two-magnon scattering processes related to high energy flat-band magnon branches.

Experimental study of the magnetic characteristics of nanocrystalline thin films: the role of edge effects

Belyaev, B. A.; Izotov, A., V; Skomorokhov, G., V; Solovev, P. N. Source: MATERIALS RESEARCH EXPRESS, 6 (11):10.1088/2053-1591/ab4456 SEP 2019

Magnetic characteristics and their spatial distribution of magnetron sputtered nanocrystalline NiFe thin films of various compositions were investigated by ferromagnetic resonance (FMR) and magneto-optical Kerr effect microscopy. A sharp increase in the FMR linewidth and a strong deviation of the uniaxial magnetic anisotropy field were observed near the film edges. It was shown that the observed magnetic anisotropy behavior can be explained by assuming that besides the field-induced uniaxial magnetic anisotropy an additional source of the uniaxial anisotropy near the film edges exists, with the easy axis parallel to the edges. The possible origins of this additional contribution were discussed.

Engineering of K3YSi2O7 To Tune Photoluminescence with Selected Activators and Site Occupancy

Qiao, Jianwei; Amachraa, Mahdi; Molokeev, Maxim; Chuang, Yu-Chun; Ong, Shyue Ping; Zhang, Qinyuan; Xia, Zhiguo Source: CHEMISTRY OF MATERIALS, 31 (18):7770-7778; 10.1021/acs.chemmater.9b02990 SEP 24 2019

The luminescence of rare earth ions (Eu2+, Ce3+, and Eu3+)-doped inorganic solids is attractive for the screening of phosphors applied in solid-state lighting and displays and significant to probe the occupied crystallographic sites in the lattice also offering new routes to photoluminescence tuning. Here, we report on the discovery of the Eu- and Ce-activated K3YSi2O7 phosphors. K3YSi2O7:Eu is effectively excited by 450 nm InGaN blue light-emitting diodes (LEDs) and displays an orange-red emission originated from characteristic transitions of both Eu2+ and Eu3+, while K3YSi2O7:Ce3+ shows green emission upon 394 nm near-ultraviolet (NUV) light excitation. Rietveld refinement verifies the successful doping of the activators, and density functional theory (DFT) calculations further support that Eu2+ occupies both K1 and Y2 crystallographic sites, while Ce3+ and Eu3+ only occupy the Y2 site; hence, the broad-band red emission of Eu2+ are attributed to a small DFT band gap (3.69 eV) of K3YSi2O7 host and a selective occupancy of Eu2+ in a highly distorted K1 site and a high crystal field splitting around Y2 sites. The white LEDs device utilizing orange-red-emitting K3YSi2O7:Eu and green-emitting K3YSi2O7:Ce3+ exhibits an excellent CRI of 90.1 at a correlated color temperature of 4523 K. Our work aims at bridging multivalent Eu2+/Eu3+ and Ce3+ site occupancy in the same host to realize photoluminescence tuning and especially exposes new ways to explore new phosphors with multicolor emission pumped by blue and NUV light for white LEDs.

High-temperature oxidation of europium (II) sulfide

Denisenko, Yuriy G.; Molokeev, Maxim S.; Krylov, Alexander S.; Aleksandrovsky, Aleksandr S.; Oreshonkov, Aleksandr S.; Atuchin, Victor V.; Azarapin, Nikita O.; Plyusnin, Pavel E.; Sal'nikova, Elena I.; Andreev, Oleg V. Source: JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY, 79 62-70; 10.1016/j.jiec.2019.05.006 NOV 25 2019

The process of high-temperature oxidation of EuS in the air was explored in the temperature range of 500–1000 °C. The oxidation reaction enthalpy was determined (ΔH0exp = −1718.5 kJ/mol). The study of oxidation products allowed to establish the mechanism of EuS oxidation with oxygen. At 500–600 °C, EuS is oxidized to a mixture of Eu3+-containing compounds (Eu3S4, Eu2O2S). In the range of 700–1000 °C, only europium oxysulfate Eu2O2SO4 is formed. The structure refinement for Eu2O2SO4 was performed by the Rietveld method. The luminescence intensity of europium oxysulfate Eu2O2SO4 with characteristic 4f-4f transitions from the 5D0 state was investigated as a function of oxidation temperature.

Impedance Spectroscopy Study of a Polymer Composite with Carbon Nanotubes in Contact with an Electrolyte

Markevich, I. A.; Drokin, N. A.; Selyutin, G. E. Source: TECHNICAL PHYSICS, 64 (9):1324-1329; 10.1134/S1063784219090093 SEP 2019

The measured frequency dependence of the electric impedance of a composite based on ultra-high molecular weight polyethylene reinforced with carbon nanotubes in contact with an electrolyte is presented. The behavior of the active and reactive impedance components, permittivity, and conductivity in the frequency range from 0.1 Hz to 120 MHz is analyzed. An equivalent electric circuit simulating the dispersion of the impedance of the polymer composite making contact with the electrolyte is proposed. The formation of a double electric layer at the interface between the polymer composite and electrolyte layer is demonstrated and the electrical characteristics of this layer are determined.

Q-factor optimization in dielectric oligomers

Bulgakov, Evgeny N.; Maksimov, Dmitrii N. Source: PHYSICAL REVIEW A, 100 (3):10.1103/PhysRevA.100.033830 SEP 24 2019

In this paper we propose an optimization procedure for quality-factor (Q-factor) enhancement in dielectric oligomers. The oligomers are introduced as linear periodic chains of dielectric elements the individual Q factors of which are optimized via multipolar conversion in an avoided crossing of two resonant eigenfrequencies. It is demonstrated that when such dielectric elements are assembled into an infinite periodic array the coupling between individual resonances gives rise to an in-Γ optical bound state in the continuum (BIC) unprotected by symmetry. By setting up the oligomers of finite numbers of dielectric elements we observe high quality resonances which occur as traces of the infinite array band structure. The resulting high quality resonances exhibit light localization spots of a few squared wavelengths with Q factors Q>104. The localization is provided by similarity of the field pattern to that of the BIC with the losses at the edges of the array suppressed due to an almost flat BIC host band. The scaling law of the Q factor against the dielectric permittivity is derived.

Mn2+-Based narrow-band green-emitting Cs3MnBr5 phosphor and the performance optimization by Zn2+ alloying

Su, Binbin; Molokeev, Maxim S.; Xia, Zhiguo Source: JOURNAL OF MATERIALS CHEMISTRY C, 7 (36):11220-11226; 10.1039/c9tc04127c SEP 28 2019

To discover new narrow-band green-emitting phosphors is a challenge for backlighting light-emitting diodes (LEDs) used in liquid crystal displays (LCDs). The synthesis and optical properties of Cs3MnBr5 are demonstrated herein. The intrinsic Mn2+ luminescence without concentration quenching leads to intense green emission at 520 nm with narrow full width at half maximum of 42 nm and high photoluminescence quantum yield (PLQY) of 49% under the excitation at 460 nm. When a small amount of Zn2+ is introduced into Cs3MnBr5, the luminescence intensity decreases slightly. However, the thermal stability of Cs3MnBr5 is improved from 82% to 87% with the intensity values at 423 K compared to that at 298 K. The white LED device fabricated using Cs3Mn0.96Zn0.04Br5 (green) and K2SiF6:Mn4+ (red) phosphors with a blue LED chip exhibit a high luminous efficiency (107.76 lm W−1) and wide color gamut (101% National Television System Committee standard (NTSC) in Commission Internationale de L’Eclairage (CIE) 1931 color space), demonstrating its potential application in wide color gamut LCD backlights.

Flux pinning mechanisms and a vortex phase diagram of tin-based inverse opals

Bykov, A. A.; Gokhfeld, D. M.; Savitskaya, N. E.; Terentjev, K. Yu; Popkov, S., I; Mistonov, A. A.; Grigoryeva, N. A.; Zakhidov, A.; Grigoriev, S., V Source: SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 32 (11):10.1088/1361-6668/ab3db7 NOV 2019

Three-dimensional periodic tin structures were synthesized by filling pores in silicon opals with a sphere diameter of 194 nm (Sn190) and 310 nm (Sn300). The samples were examined by the ultra-small-angle x-ray diffraction method, energy dispersive x-ray microanalysis and scanning electron microscopy. It was found that the inverse opal structure consists of tin nanoparticles inscribed in octahedral and tetrahedral pores with diameters of 128 nm and 70 nm for the sample Sn300, and 80 nm and 42 nm for the sample Sn190. The study of the magnetic properties of the samples by SQUID magnetometry showed that magnetization reversal curves exhibit hysteretic behavior. The mechanisms of magnetic flux pinning in the samples depend on the size of the tin nanoparticles. Tin nanoparticles in Sn300 behave like a classical type-I superconductor. The hysteretic behavior of the magnetization reversal curves at low magnetic fields is due to the formation of a network of superconducting contours in Sn300. These superconducting contours effectively trap the magnetic flux. The octahedral tin nanoparticles in Sn190 remain type-I superconductors, but smaller tetrahedral particles behave like type-II superconductors. Type-I and II superconducting particles in Sn190 lead to the coexistence of different mechanisms of flux pinning. These are flux trapping by superconducting contours at low magnetic fields and flux pinning by tetrahedral particles due to the surface barrier at high magnetic fields.

Study of Co(x)Pt(1-x )nanoalloy formation mechanism via single-source precursors

Filatov, E. Yu.; Zadesenets, A. V.; Komogortsev, S. V.; Plyusnin, P. E.; Chepurov, A. A.; Korenev, S. V. Source: POWDER DIFFRACTION, 34 S27-S31; 1 10.1017/S0885715619000162 SEP 2019

This paper is devoted to the study of formation mechanism of metal solid solutions during the thermolysis of single-source precursors in Co–Pt systems with a wide range of superstructural ordering. It is shown that the thermal decomposition of [Pt(NH3)4][Co(C2O4)2(H2O)2]·2H2O salt in helium is critically different from that under hydrogen atmospheres. Thermal degradation under the helium atmosphere is followed by a gradual reduction of platinum and cobalt, and at each thermolysis temperature only one phase is present. At 380 °C an equiatomic Co0.50Pt0.50 solid solution is formed (a = 3.749 (4) Å, Fm−3m space group, V/Z = 13.17 Å3, crystallite size: 5–7 nm). When the precursor is decomposed under a hydrogen atmosphere, the process proceeds mainly through the simultaneous reduction of the platinum and cobalt atoms, and at each temperature section two metal phases are present. The formation of the close to equiatomic Co0.50Pt0.50 solid solution (a = 3.782 (4) Å, Fm−3m space group, V/Z = 13.52 Å3, crystallite size: 7–9 nm) occurs at 450 °C. The calculations of crystallite sizes are confirmed by transmission electron microscopy data.

Size effects in the formation of an uncompensated ferromagnetic moment in NiO nanoparticles

Popkov, S., I; Krasikov, A. A.; Dubrovskiy, A. A.; Volochaev, M. N.; Kirillov, V. L.; Martyanov, O. N.; Balaev, D. A. Source: JOURNAL OF APPLIED PHYSICS, 126 (10):10.1063/1.5109054 SEP 14 2019

The magnetic properties of samples of NiO nanoparticles with average sizes of 23, 8.5, and 4.5 nm were investigated. Using the magnetization curves measured in strong (up to 250 kOe) pulsed magnetic fields, the contributions of the free spin and ferromagnetic subsystems were extracted. It has been found that the ferromagnetic contribution increases with a decrease in the nanoparticle size and is proportional to the fraction of uncompensated exchange-coupled spins. It is demonstrated that the uncompensated spins form in the antiferromagnetic NiO oxide due to an increase in the fraction of surface atoms in the nanoparticles with decreasing particle size and defects in the bulk of particles

Four steps for revealing and adjusting the 3D structure of aptamers in solution by small-angle X-ray scattering and computer simulation

Tomilin, Felix N.; Moryachkov, Roman; Shchugoreva, Irina; Zabluda, Vladimir N.; Peters, Georgy; Platunov, Mikhail; Spiridonova, Vera; Melnichuk, Anastasia; Atrokhova, Anastasia; Zamay, Sergey S.; Ovchinnikov, Sergey G.; Zamay, Galina S.; Sokolov, Alexey; Zamay, Tatiana N.; Berezovski, Maxim, V; Kichkailo, Anna S. Source: ANALYTICAL AND BIOANALYTICAL CHEMISTRY, 411 (25):6723-6732; SI 10.1007/s00216-019-02045-0 OCT 2019

Nucleic acid (NA) aptamers bind to their targets with high affinity and selectivity. The three-dimensional (3D) structures of aptamers play a major role in these non-covalent interactions. Here, we use a four-step approach to determine a true 3D structure of aptamers in solution using small-angle X-ray scattering (SAXS) and molecular structure restoration (MSR). The approach consists of (i) acquiring SAXS experimental data of an aptamer in solution, (ii) building a spatial distribution of the molecule’s electron density using SAXS results, (iii) constructing a 3D model of the aptamer from its nucleotide primary sequence and secondary structure, and (iv) comparing and refining the modeled 3D structures with the experimental SAXS model. In the proof-of-principle we analyzed the 3D structure of RE31 aptamer to thrombin in a native free state at different temperatures and validated it by circular dichroism (CD). The resulting 3D structure of RE31 has the most energetically favorable conformation and the same elements such as a B-form duplex, non-complementary region, and two G-quartets which were previously reported by X-ray diffraction (XRD) from a single crystal. More broadly, this study demonstrates the complementary approach for constructing and adjusting the 3D structures of aptamers, DNAzymes, and ribozymes in solution, and could supply new opportunities for developing functional nucleic acids.

Magnetic and magneto-optical properties of Fe3O4 nanoparticles modified with Ag

Petrov, D. A.; Ivantsov, R. D.; Zharkova, S. M.; Velikanova, D. A.; Molokeev, M. S.; Lin, C. -R.; Tso, C. -T.; Hsuc, H. -S.; Tseng, Y. -T.; Lin, E. -S.; Edelman, I. S. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 493 10.1016/j.jmmm.2019.165692 JAN 1 2020

Effect of Ag inclusions on magnetic properties and magnetic circular dichroism (MCD) of Fe3O4 nanoparticles (NPs) in the mixed system of Fe3O4 and Ag NPs in dependence on the relative concentration of the components is presented. The samples were synthesized by the thermal decomposition of the mixture of constant concentration of Fe(NO3)3·9H2O and varied concentration of AgNO3. The synthesized powdered samples consisted of Fe3O4 and Ag NPs located very close with each other, and in the most cases the Fe3O4 NPs were bordered with the Ag nanocrystals. The Ag introducing in the samples does not effect, practically, in the Fe3O4 NPs morphology and size distribution. At the same time, Ag NPs in the powdered samples cause a decrease in the Fe3O4 NPs magnetization and shift of the blocking temperature to lower temperatures, both approximately proportional to the Ag concentration. Most significant changes are revealed in the MCD spectra in the energy region of 1.2–2.2 eV. We have discussed the influence of the Ag NPs on the MCD spectra features in terms of the charge-transfer electron transitions.

Factor analysis of inelastic electron scattering cross section spectra of FeSi2

Igumenov, A. Yu; Parshin, A. S.; Kanzychakova, V. O.; Demin, A. M.; Andryushchenko, T. A.; Mikhlin, Yu L.; Pehelyakov, O. P.; Zhigalov, V. S. Book Group Author(s): IOP Source: 21ST INTERNATIONAL SCIENTIFIC CONFERENCE RESHETNEV READINGS-2017, 467 10.1088/1757-899X/467/1/012010 2019

Iron disilicide is widely used in creation of such nanotechnology devices as photoelectric converters. The investigation of iron silicide FeSi2 with the method of inelastic electron scattering cross-section spectroscopy was carried out. The decomposition of inelastic electron scattering cross-section spectra of FeSi2 to bulk and surface energy loss components using factor analysis was carried out. The amplitude of energy loss components can be used for identification of their origin.

Document Actions