The Editorial Board of the journal “Bulletin of the Russian Academy of Sciences: Physics” monthly assigns one of the articles of each thematic issue the honorary status of “Editor’s Choice”. We hope that the selected articles will be of interest to a wide range of readers.
Volume 85, issue 9, September 2021
Thematic issue “Phase Transition & New Materials”
Yu. M. Gufan, E. N. Klimova, and R. A. Kutuev, Symmetry of the Non-Atomic Interactions of N-Atomic Energy and the Atomistic Theory of High-Order Elastic Modules // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 9, P. 998-1002.
The ability to calculate simple mechanical characteristics of a crystal is an extremely important property for any theory of the structure of a solid. The presence of such a possibility – provided the consistency of the result obtained – first means some general consistency of the theory: the area of its fundamental applicability in this case can be quite wide, not limited, for example, to the microscopic structure of the crystal, which means that the theory can surpass the status of a highly specialized model. In addition, the ability to calculate the mechanical characteristics of an object can be used to obtain constraints on the values of the parameters appearing in these calculations. The fact is that the mechanical characteristics, although often with rather moderate accuracy, are amenable to direct measurement on samples. If the same characteristics can be expressed – if not analytically, then at least computationally – through the parameters of the theory, then from these expressions ranges of parameter values can be obtained that agree with the measurement results, or at least do not contradict them.
It is shown that the requirement of computability of high-order elastic moduli for an abstract crystal itself leads to rather significant restrictions on how a microscopic theory of its structure, based on modeling the interaction of particles constituting the crystal, can look like. Based on this requirement, the authors construct a criticism of the now widely used approaches to the construction of a theory (the pseudopotential method, calculations from first principles, the electron density functional method, the embedded atom method) and offer a schematic description of how a theory could be constructed based on the model direct accounting for multiparticle interactions. In this paper the restrictions of the theory are obtained on the dependence of the calculated total potential energy of interaction of the particles constituting the crystal on the polynomials determined from symmetric considerations in the radius vectors of the particles constituting bounded and determined by symmetry clusters. Since the result is based only on considerations determined by the symmetry of the crystal structure, the requirements obtained (more precisely, the general scheme for their preparation) can be considered mandatory for the microscopic theory, which claims to be able to describe the mechanical properties of a crystal.
Thematic issue “Electron and probe microscopy, and complementary methods in research of nanostructures and nanomaterials”
V. I. Bondarenko, I. N. Trunkin, I. G. Gorlova, N. B. Bolotina, and A. L. Vasiliev, Investigating the Vacancy Structure of TiS3 Single Crystals // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 8, P. 858-862
Titanium trisulfide (TiS3) – one of the representatives of trichalcogenides, a material with great potential for field-effect transistors, photodetectors, and power generators. Studies of TiS3 single crystals in different scientific groups have shown that their resistivity at room temperature can differ by more than 10 times. It was assumed that an increase in the conductivity of TiS3 crystals can be associated with a violation of the stoichiometry of the composition, in connection with which it can be assumed that the conductivity depends on the density of sulfur vacancies.
The method of high-resolution transmission scanning electron microscopy with registration of electrons scattered at high angles (10-15°, in comparison with Bragg scattering, in which electrons are scattered at angles of 3-5°) using a high-angle ring dark-field detector allows one to obtain contrast from columns of atoms depending on the atomic number Z to the power γ (γ = 1.6-2) and on the number of atoms in a chain parallel to the e-beam. Using such images, it is possible to assume the presence of vacancies, try to estimate their number in the column and to determine the density of vacancies in the sample.
In this work, we simulated the images of TiS3 single crystals with different numbers of sulfur vacancies in chains parallel to the e-beam for different sample thicknesses. An easy and fast method was proposed for estimating the number of vacancies in a chain from the intensity of images of atomic columns. The results showed that the used method differs insignificantly from the known method for estimating the number of atoms by approximation by Gaussians, and the scatter of data can be associated with the position of vacancies in the chain of sulfur atoms parallel to the electron beam. The calculations made it possible to estimate the density of vacancies in low-resistance and high-resistance samples and to confirm the hypothesis about the influence of vacancies of sulfur atoms on the conductivity. In addition, the ordering of vacancies in low-resistance TiS3 samples was found.
The team of authors includes leading specialists of the Federal Research Center “Crystallography and Photonics of the Russian Academy of Sciences”, National Research Center “Kurchatov Institute”, Kotelnikov Institute of Radio Engineering and Electronics Russian Academy of Sciences working in the field of condensed matter physics and structural methods in materials science. The theory of using a unique method for evaluating the vacancy structure in crystals has been implemented in the laboratory of electron microscopy of the Federal Research Center “Crystallography and Photonics of the Russian Academy of Sciences”.
Thematic issue “Structure and Dynamics of Molecular Systems”
O. A. Raitman, E. V. Raitman, N. L. Zaichenko, G. V. Lyubimova, A. A. Scherbina, and A. V. Lyubimov, Controlling the Aggregation of Amphiphilic Spiropyrans in Langmuir Monolayers // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 8, P. 868-872
The possibility of controlling the physicochemical properties of photosensitive materials using external influences opens broad prospects for their application in various fields of science and technology. Thus, the phenomenon of changes in the optical characteristics of ultrathin films based on photochromic compounds because of aggregation rearrangements can be used in the development of information recording devices and optical signal processing, in holography, medicine, sensorics, etc. It is known that a several spiro compounds exhibit thermally and photoinduced H– and J-aggregation in organic solvents; however, the behavior of Langmuir monolayers from amphiphilic spiropyrans, which are resistant to temperature changes, a high activation barrier of the isomerization reaction, and significant spectral distinguishability of isomers, is practically not studied. This paper devoted to studying the possibility of controlling the aggregation state of Langmuir monolayers of photochromes on liquid substrates by introducing a diluent and varying the surface pressure is of increased interest for scientists working in the field of photochemistry, as well as physical, colloidal, and supramolecular chemistry. It is shown that amphiphilic 1′-hexadecyl-3 ‘, 3′-dimethyl-6-nitro-1′, 3′-dihydrospiro [chromene-2,2’-indole] (SP1) in the spiro form does not form stable monolayers on the aqueous subphase, while the merocyanine form of this compound completely spreads over the surface and forms a true monolayer. It was demonstrated that in the planar state of the studied substance the tendency to aggregation sharply increases, which is confirmed by the appearance and growth of the absorption band in the 620 nm region. The formation of mixed monolayers of SP1 and cetyl alcohol molecules, as well as external mechanical action, makes it possible to control the degree of aggregation of spiropyran in monomolecular films and achieve complete spreading of the compound over the water surface while maintaining the photochromic properties of the substance in the two-dimensional state. The results obtained open broad prospects for the use of compounds of the spiropyran series in molecular electronics and for the creation of nanoscale optically active systems.
The team of authors includes leading specialists from the Mendeleev University of Chemical Technology, Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences and the Semenov Federal Research Center of Chemical Physics of the Russian Academy of Sciences. The employees of the last one work in the field of synthesis of optically active and photosensitive compounds, are engaged in their incorporation into polymer matrices. Scientific group from the Mendeleev Chemical Technical University and Frumkin Institute of Physical Chemistry and Electrochemistry RAS is studying the behavior of chromo-, ion- and luminophores at the interface. The cooperation of these scientific groups makes it possible to carry out unique research aimed at studying the laws governing the course of photochemical reactions in two-dimensional ordered systems.
Thematic issue “Phase Transformations and the Strength of Crystals”
R. V. Sundeev, A. M. Glezer, A. V. Shalimova, A. V. Krivoruchko, A. A. Veligzhanin, O. V. Vakhrushev, EXAFS and EELFS Spectroscopy in Analyzing the Atomic Structure of the Bulk and Surface Ti50Ni25Cu25 Alloy Domains upon Extreme Impacts by Megaplastic Deformations and Quenching from a Melt // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 7, P. 732-739
Under extreme exposure, i.e. large (megaplastic) deformations (MPD), the transformation of the atomic structure in the crystalline state of materials is realized under conditions of nonequilibrium thermodynamics and the specificity of relaxation processes (especially at low temperatures). This leads to the appearance of unusual structural states with special characteristics of chemical and topological inhomogeneity. It is most difficult to obtain the structural features under the influence of MPD in amorphous alloys, where local inhomogeneities of the atomic structure can arise. Under these conditions, the combined application of the EXAFS and EELFS methods is extremely necessary and effective, allowing one to represent the evolution of transformations of the atomic system both in the bulk and on the surface of the alloys as the MPD value varies.
There is a unique Ti50Ni25Cu25 alloy among functional alloys with shape memory effect which can be obtained in the amorphous state using two different methods of extreme exposure: quenching from the liquid state (QLS) and MPD. We present the results of a detailed structural analysis of this unique material after QLS and MPD. The studies of the local atomic structure of the initial amorphous state obtained by the QLS method and the secondary amorphous state obtained by the MPD were performed using the EXAFS spectroscopy method under synchrotron radiation (shown in the figure) and the EELFS spectroscopy method. Comparison of changes in the local atomic structure of the crystalline Ti50Ni25Cu25 alloy during MPD on the surface of the sample and in the bulk of the sample showed that the volume of the material is gradually amorphous of the crystalline Ti50Ni25Cu25 alloy under study. The local atomic structure of this alloy after MPD (n = 6) reproduces the local atomic structure of the alloy after MPD. In this case, on the surface, the studied alloy after MPD remains, most likely, in a state close to the crystalline state and is noticeably supersaturated with oxygen atoms.
The team of authors includes leading specialists of the Bardin Central Research Institute of Iron and Steel Industry, National Research Center “Kurchatov Institute”, MIREA – Russian Technological University and National Research Technological University “MISiS”, working in the field of physics of large plastic deformations and structural methods for studying amorphous and nanocrystalline materials. The theory and practice of EELFS technique was developed and implemented in the laboratory of surface physics of the Kurdyumov Institute of Metal Science and Physics of Metals, as a part of the Bardin Central Research Institute of Iron and Steel Industry.
Thematic issue “Acoustic Physics”
A. V. Sadovnikov, S. A. Nikitov, Using Mandelstam–Brillouin Spectroscopy to Study Energy-Efficient Devices for Processing Information Signals on the Basis of Magnon Straintronics // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 6, P. 595-598
We show how an approach based on the methods of magnon straintronics can be used to create magnon logic devices with control over the amplitude and phase of spin waves. Spin wave quanta – magnons propagating in magnetic materials, due to their unique properties, can be used in promising systems for processing information signals with low energy consumption at different spatial and time-domain scales. Low power consumption is ensured by the fact that magnons are chargeless quasiparticles and during their propagation in the layers of magnetic dielectrics there is practically no Joule heating.
Recently, there has been increasing interest in research on energy efficient methods for controlling the properties of propagating spin waves. Magnon devices are considered as an alternative to modules that carry out logical operations based on elements of semiconductor microelectronics based on the use of the charge of current carriers (electrons or holes). In this case, the presence of the spin of current carriers and spin-wave excitations makes it possible to create the next generation of electronics devices – dielectric magnons with significantly improved parameters of speed, power consumption, and smaller spatial dimensions of elements. As a demonstration of this physical effect, using the method of Mandelstam-Brillouin spectroscopy, in structured ferrite-piezoelectric bilayers, voltage-controlled spin-wave transport along a lateral structure consisting of two magnon-crystal microwave guides was investigated. The possibility of efficient tuning of the spin-wave characteristics by applying an electric field to the piezoelectric layer is shown. The transformation mechanism of the spectra of spin-wave signals consists in the value of the gradient of the internal magnetic field controlled by elastic deformations in the region near the gap between the lateral structures. The results obtained can be used to create energy-efficient devices for processing information signals, such as demultiplexers with frequency-space selectivity.
The authors are from Saratov State University and the Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, carrying out research in the Laboratory of magnon metamaterials, created in Saratov in 2012. Two unique complexes of Mandelstam-Brillouin spectroscopy of magnetic materials and living systems, the only two in the Russian Federation, have been launched in the laboratory and are in continuous operation.
Thematic issue “Nuclear Physics and Elementary Particle Physics. Nuclear Physics Technologies”
M. V. Chushnyakova, I. I. Gontchar, N. A. Khmyrova, A. А. Klimochkina, Relativistic Mean-Field Effective Nucleon–Nucleon Forces in the Dynamic Modeling of Heavy Ion Fusion // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 5, P. 490-495
The work is devoted to one of the most interesting problems of modern nuclear physics – dynamic modeling of the fusion of atomic nuclei. Experiments on the collision of complex nuclei have been carried out in many laboratories in different countries since the 1960s. As a result of these experiments, a new class of nuclear reactions was discovered – deeply inelastic transfer reactions, and nuclei of new chemical elements with atomic numbers from 104 to 118 were synthesized. Computer simulation of collisions leading to nuclear fusion helps to understand the features of the process and reduce the cost of experiments.
One of the important components in our calculations is the interaction energy of two nuclei, which we obtain by convolving the nucleon-nucleon interaction (“NN forces”) with the densities of interacting nuclei. In recent years, the forces obtained in the framework of the theory of the relativistic mean field (TRMF forces) are considered as the most progressive NN forces. We have systematically applied these forces to simulate nuclear fusion in this paper and also in [1. M.V. Chushnyakova et al. // Journal of Physics G. 48 (2021) 015101]. In total, 6 sets of parameters of TRMF forces that were found in the literature were analyzed. Unexpectedly, it turned out that many of these parameters lead to an unrealistic energy of the nucleus-nucleus interaction: it lacks a region where the strong nuclear interaction exceeds the Coulomb repulsion. Accordingly, fusion of nuclei becomes impossible. Only two sets of parameters (HS and NL2) provide a realistic view of the potential energy with a Coulomb barrier.
In this work, as well as in , using 13 reactions as an example, it is shown that TRMF forces with HS and NL2 parameters make it possible to describe high-precision experimental data on nuclear fusion cross sections with a typical error of 3-5%. The figure illustrates this result for five reactions.
Thematic issue “Physics of Cosmic Rays”
A. N. Turundaevskiy, O. A. Vasiliev, D. E. Karmanov, I. M. Kovalev, I. A. Kudryashov, A. A. Kurganov, A. D. Panov & D. M. Podorozhny, Main Results from the NUCLEON Experiment // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 4, P. 353–356.
One of the most urgent problems of cosmic ray (CR) physics now is the determination of the chemical composition of abundant CRs with the highest energy. During the beginning of the work on the NUCLEON observatory, there was a consensus regarding the behavior of the spectra of the main abundant (produced mainly in sources) nuclei up to energies no higher than several TeV. In 2014-2017 the NUCLEON space experiment was carried out. The NUCLEON is a modern high-tech spectrometer that has incorporated the advanced technologies of physical experiment. A characteristic feature of the equipment is the very insignificant consumed flight resources, such as weight, power consumption, dimensions. This is explained by the fact that a new technique for recording the energy of CR particles has been used for the first time in the spectrometer. The authors called this method KLEM (Kinematic Light – Weight Energy Meter) to emphasize its main advantage – a low-mass energy meter, which gives a gain of almost an order of magnitude in the “aperture/mass” parameter in comparison with traditional methods.
Despite the small amount of consumed resources, over 2.5 years of the orbital experiment, a data bank was obtained, including about 20 million events. This number exceeds the total statistics of all direct experiments with similar goals over the past 50 years, which made it possible to obtain spectra of abundant cosmic ray nuclei up to energies of several hundred TeV. For the first time, the integration of ground-based and orbital measurements of the CR energy spectrum took place, which made it possible to directly calibrate the data obtained in ground-based experiments. The difference of the spectrum from the power-law form at 2 – 500 TeV was statistically proved. In the energy range up to 5·1014 eV, the chemical composition of cosmic rays was determined with element-by-element resolution, and a number of features were found in the energy spectra of CR elements. The result obtained is the factual material necessary for constructing and refining models of the Galaxy and its energy balance.
The team of the authors of the article consists of the staff of the Institute of Nuclear Physics of the Moscow State University, who for many years worked on the preparation and conduct of the NUKLON experiment, and then on the processing of the results obtained. The team is one of the leading research groups in the field of cosmic ray astrophysics.
Thematic issue “Physics of Auroral Phenomena”
A. S. Nikitenko, O. M. Lebed, Yu. V. Fedorenko, J. Manninen, N. G. Kleimenova, L. I. Gromova, Localization of the Scattering Area of the Auroral Hiss by Ground-based Multipoint Measurements at High Latitudes // Bulletin of the Russian Academy of Sciences: Physics, 2021, Volume 85, Issue 3, P. 287–291.
The work is devoted to the study of the features of the exit to the Earth’s surface of natural magnetospheric electromagnetic radiation of the auroral hiss type according to ground-based observations of electromagnetic fields in the very low frequency range (VLF, from hundreds of hertz to tens of kilohertz). Auroral hiss is one example of noise emissions whose field parameters change randomly over time. Research team from the Polar Geophysical Institute has developed a method for analyzing data from ground-based observations of this kind of radiation. This method uses the representation of the field parameters as their distribution densities, while other methods use the averaged values of the field parameters. To interpret the results of ground-based observations, a numerical model of the propagation of auroral hiss radiation from the generation region to the ground-based observer is developed. The model includes the following modules: 1) generation of electrostatic waves at altitudes of 10,000 – 20,000 km; 2) propagation of electrostatic waves to the region in the ionosphere occupied by small-scale inhomogeneities of electron concentration; 3) scattering into the exit cone of electrostatic waves on small-scale inhomogeneities; 4) propagation of scattered waves in the lower ionosphere and the Earth – ionosphere waveguide.
The paper presents the results of ground-based observations of the VLF auroral hiss at three spatially separated points, Barentsburg (Svalbard Archipelago), Lovozero (Kola Peninsula, Russia) and Kannuslehto (Finland). There were cases when auroral hiss was registered only in the observatory of Barentsburg and when bursts were recorded by all three stations simultaneously. Only the collaborative use of the developed data analysis methods and the propagation model of auroral hiss allowed them to show that the burst recorded in the observatory of Barentsburg is caused by the existence of a scattering area of small-scale inhomogeneities of electron concentration which is located to the southwest of the observatory. The registration of auroral hiss bursts at all three points is caused by the simultaneous existence of two scattering areas in the ionosphere located at different latitudes.
Thematic issue “New Materials and Technologies for Security Systems”
A.M. Zarezin, P.A. Gusikhin, V.M. Muravev, S.I. Gubarev, I.V. Kukushkin, A New Family of Plasma Excitations in a Partially Gated Two-Dimensional Electron System // Bulletin of the Russian Academy of Sciences: Physics, Volume 85, Issue 2, pages 113–117 (2021)
Collective fluctuations of charge density – plasmons, have been studied in two-dimensional electronic systems (2DES) for more than 50 years. Many theoretical and experimental works have considered these excitations in 2DES of various configurations, including those with strong shielding by a closely spaced metal shutter. However, it turned out that in 2DES, only partially covered by a gate, new plasma modes are excited that differ from those previously considered and investigated. Despite its prevalence in actually studied structures, this case has been ignored for a long time. In order to study this issue, experimental work was carried out on 2DES in GaAs/AlGaAs heterostructures, partially shielded by a metal gate. This manuscript concludes a series of papers considering different geometries of the hybrid configuration of a 2DES with a gate and a contact.
Two different geometries were investigated – a 2DES disk with a central gate in the form of a disk of a smaller diameter and a perimetric contact (Corbino geometry) and a rectangular 2DES with a gate in the form of a narrow strip and side contacts. The measurements were carried out using the experimental equipment of the Laboratory of Nonequilibrium Electronic Processes of the Institute of Solid State Physics of the Russian Academy of Sciences in a cryostat with a temperature of 4.2 K and down to 1.5 K under helium vapor pumping. To detect plasma resonances, a unique optical non-invasive technique was used based on the high sensitivity of the luminescence spectrum of two-dimensional electrons to the heating of the 2DES caused by the absorption of the microwave signal.
The paper presents the results of the observation of plasma excitations in the indicated systems, obtained curves of absorption of microwave radiation depending on the frequency and applied magnetic field, and plotted the corresponding dispersion and magnetodispersive dependences. It turned out that in a 2DES with partial shielding, a family of plasma oscillations is observed that is physically different from both ordinary unshielded plasmons and plasmons in fully shielded 2DES. In addition, when the gate and contact were electrically connected, a special low-frequency mode was observed, the properties of which depend on the connected external circuit. Thus, the studies carried out have identified plasmons in partially shielded 2DES into a special family associated directly with charge oscillations in the gate and near gate regions, also containing a “tricky” hybrid mode, frequency, magnetic field behavior and Q factor of which can be changed by connecting various external electrical circuits.
Thematic issue “Wave Phenomena in Inhomogeneous Media”
The paper is devoted to the dynamics of electromagnetic waves at the interfaces between two media, in particular, metals and dielectrics, due to the broad prospects of using composite materials in micro- and nanodevices of photonic and plasmonic technology. A high-frequency electromagnetic field causes oscillations of both free and bound charges in dielectric, semiconducting media, and metals. In this case, as a result of charge oscillations, secondary electromagnetic waves are emitted, which hybridize with polarization waves of bound and free charges in the medium and propagate in the volume of the medium, as well as along the interface between the media in the form of plasmon-polariton waves.
An external electromagnetic field of weak intensity causes a linear response of the dielectric constant of the metal. With an increase in the amplitude of the external field, anharmonic oscillations of electrons and ions, interband transitions appear, which lead to the manifestation of nonlinear polarization mechanisms. An intense electromagnetic wave or a powerful electromagnetic pulse generates nonlinear plasmon-polariton waves – cnoidal waves, kinks and solitons in the volume of the conducting medium and at the interface between the conducting and dielectric media. The properties and dynamics of cnoidal waves and solitons depend on the parameters of the exciting electromagnetic waves and pulses, as well as on the geometry of the system and the properties of the media in which plasmon polaritons are excited.
The paper presents the results of a theoretical study of linear and nonlinear processes during the propagation of plasmon-polaritons at a plane interface between a metal and a dielectric medium, depending on the boundary conditions and the energy density of the exciting electromagnetic wave. The analysis of the dynamics of plasmon-polariton waves was carried out by solving nonlinear equations obtained on the basis of a quantum hydrodynamic model for the Schrödinger equation, which allows one to consistently describe the physical mechanisms causing the nonlinear response of free electrons in a metal to the effect of an external electromagnetic field. It is shown that the profiles of the envelopes of the plasmon-polariton cnoidal waves and their periods are transformed when the source power and/or the conditions for the excitation of plasmon-polaritons at the interface between the media change. In particular, at a certain ratio of parameters, a shock wave in the form of a kink/antikink arises. Thus, by changing the power of the source of the external electromagnetic field, it is possible to control the period and shape of a nonlinear plasmon-polariton wave propagating in plasmonic nanodevices.
Thematic issue “Nano-optics, Photonics and Coherent Spectroscopy”
S.N. Bagayev, S.M. Arakelian, A.O. Kucherik, D.N. Bukharov, O. Ya. Butkovsky, Nano-Optics of Thin-Film Laser-Induced Topological Structures on a Solid Surface: Fundamental Phenomena and Their Applications // Bulletin of the Russian Academy of Sciences: Physics, Volume 84, Issue 12, pages 1427–1438 (2020)
Artificial materials with functional properties depending on the topology are now widely used in various fundamental and applied fields of physics. Such materials demonstrate the dependence of electrical (topological insulators) or optical (photonic crystals) characteristics on the realized sample topology. In most cases, we are talking about the study of spatially periodic structures, e.g. quasicrystals and superlattices. At the same time, fractal systems that demonstrate the properties of scale invariance – self-reproduction/self-similarity of their structure in a certain range of scales – are of great interest. For structures of this type, problems arise that make it possible, on the basis of new physical principles, to develop elements and devices of photonics and optoelectronics with the implementation of quantum-size effects in macroscopic phenomena, e.g. due to the possibility of the formation of correlated states in nanoclusters. Within the framework of this work, the possibilities of laser formation of cluster systems on the surface of various materials are demonstrated, the processes of their formation are investigated, growth models are proposed, and surface states are studied.
The study makes it possible to control the electrophysical properties of thin-film structures, and to find the optimal values of their parameters depending on the topological features and the selected elemental composition. The proposed methods and models can be useful and promising for the development of thin-film elements and systems of nanophotonics and nanoelectronics based on new physical principles, for use in high-tech industrial sectors of industry.
A. Yu. Yurenya, A. A. Nikitin, R. R. Gabbasov, M. A. Polikarpov, V. M. Cherepanov, M. A. Chuev, M. A. Abakumov & V. Ya. Panchenko, Studying the Effect of Brownian Motion on the Mössbauer Spectra of Nanoparticles in a Medium Simulating Cell Cytoplasm // Bulletin of the Russian Academy of Sciences: Physics, Volume 84, Issue 11, pages 1399–1402 (2020)
Understanding the principles of Brownian motion of particles in solutions of macromolecules is the most important task for a number of scientific fields. In cell biophysics, one of these areas is related to the study of intracellular transport processes. Various macromolecular biopolymers, such as proteins, polysaccharides, and nucleic acids, occupy from 5 to 40 % of the volume of liquid biological media (in literature, this effect is often called macromolecular crowding), which has a significant impact on all biological processes occurring in the cell. Studying the parameters of the motion of particles and macromolecules in such conditions is extremely difficult since the details of this motion are hidden on the nanoscale. Modern experimental approaches are based on optical measurements, the research capabilities of which in relation to nanoscale objects have a number of significant limitations. Earlier, we proposed a new approach to studying the dynamics of Brownian particles. The approach is based on Mössbauer spectroscopy of nanoparticles dispersed in the studied medium and made on the basis of the 57Fe isotope. Due to the Doppler effect, the Brownian motion of nanoparticles leads to a uniform broadening of their mössbauer spectra. The diffusion coefficient of nanoparticles is directly related to the value of this broadening, which makes it possible to determine it experimentally. The time resolution of the proposed approach is determined by the lifetime of the 57Fe core excited state which is less than 10-7 s, which largely determines the uniqueness of the data obtained.
In this work, for the first time, the nanoscale motion under conditions of macromolecular crowding has been studied using the method of Mössbauer spectroscopy. In this task, we studied the motion parameters of nanoparticles with a diameter of 9 nm that are part of solutions with different contents of large-molecular BSA protein. It was shown that the availability of macromolecules in solutions with identical macroscopic viscosity slows down the average velocity of Brownian motion of nanoparticles in the nanosecond measurement range. This effect increases with the increasing concentration of macromolecules in the solution.
The Brownian motion of particles leads to a broadening of the lines of their mössbauer spectrum. The value of this broadening is directly related to the particle diffusion coefficient in the studied system, which allows us to determine its value by calculations (on the left). In accordance with the Stokes-Einstein equation, the values of the nano-viscosity were calculated from the set values of the diffusion coefficient. Even though the macroscopic viscosity of solutions with different BSA contents is identical, the actual viscosity experienced by nanoparticles depends on the concentration of BSA macromolecules (on the right).
Thematic issue “Fundamental Problems of Nuclear Physics, Nuclei at the Boundaries of Nucleon Stability, High Technologies”
L. N. Generalov & S. M. Selyankina, R-Matrix Analysis of Reactions with Excitation of the 10B Compound Nucleus at Energies of 6.5–19.5 MeV // Bulletin of the Russian Academy of Sciences: Physics, Volume 84, Issue 10, pages 1224–1233 (2020)
Interest in R-matrix studies of reactions is attracted by the possibility of searching for new ones, refining the characteristics of known shells, and evaluating the cross sections of nuclear reactions from limited sets of experimental data. This work was initiated by the appearance of new experimental data on differential cross sections of the threshold reaction 9Be(p,α2)6Li*.
An R-matrix analysis is performed for experimental data on 9Be(p,p0)9Be, 9Be(p,p1)9Be* (1.670 МэВ), 9Be(p,p2)9Be* (2.430 MeV), 9Be(p,n0)9B, 9Be(p,d0)8Be, 9Be(p,α0)6Li, 9Be(p,α2)6Li* (3.5618 MeV), 7Li(3He,p0)9Be reactions at 6.5–19.5 MeV excitation energies of 10B compound nucleus. Experimental data on differential and integral cross sections of the 9Be(p,α2)6Li* (3.5618 MeV, Eπ=0+) reaction at proton energy Ep = 2.3–4.5 MeV are included in the analysis, along with data on differential cross sections of the 9Be(p,n0)9B reaction at angle 0° in the Ep = 2.2–3.5 MeV energy range.
New 10B levels are determined and characteristics of states detected earlier are improved to supplement the EXFOR database.