S.Yu. Turishchev, A. Schleusener, O.A. Chuvenkova, E.V. Parinova, P. Liu, M.D. Manyakin, S.I. Kurganskii, V. Sivakov

Abstract

The composition and atomic and electronic structure of a silicon nanowire (SiNW) array coated with tin oxide are studied at the spectromicroscopic level. SiNWs are covered from top to down with a wide bandgap tin oxide layer using a metal–organic chemical vapor deposition technique. Results obtained via scanning electron microscopy and X-ray diffraction showed that tin-oxide nanocrystals, 20 nm in size, form a continuous and highly developed surface with a complex phase composition responsible for the observed electronic structure transformation. The "one spot" combination, containing a chemically sensitive morphology and spectroscopic data, is examined via photoemission electron microscopy in the X-ray absorption near-edge structure spectroscopy (XANES) mode. The observed spectromicroscopy results showed that the entire SiNW surface is covered with a tin(IV) oxide layer and traces of tin(II) oxide and metallic tin phases. The deviation from stoichiometric SnO2 leads to the formation of the density of states sub-band in the atop tin oxide layer bandgap close to the bottom of the SnO2 conduction band. These observations open up the possibility of the precise surface electronic structures estimation using photo-electron microscopy in XANES mode.

Опубликовано: 17 января 2023
https://doi.org/10.1002/smll.202206322

E.V. Parinovaa, S.S. Antipov, V. Sivakov, E.A. Belikov, I.S. Kakuliia, S.Yu.Trebunskikh, S.Yu.Turishchev

Abstract

Successful integration of the ferritin Dps protein of native origin with the developed surface of a silicon nanowires array has been demonstrated. The possibility of protein localization has been realized for different types of silicon nanostructures in terms of conductivity, different volumes of wires arrays pores available for this localization, and different wire array morphology. The observed results show the possibility of effective removal of buffer solution salts from the cultural medium, in which ferritin Dps remains on the 3D-developed porous surface of silicon nanowires. The findings demonstrate the effectiveness of a simple and affordable method to functionalize the engineered and technologically advanced silicon nanowire surface with a nanoscale ferritin Dps bioculture.

Опубликовано: 17 февраля 2022
https://doi.org/10.1016/j.rinp.2022.105348

Ya.A. Peshkov, Yu.A. Yurakov, K.A. Barkov, V.A. Terekhov, G.P. Potudanskii, S.I. Kurganskii, S.A. Ivkov, Y.G. Semov, A.I. Bazlov, E.P. Domashevskaya

Abstract

We present a combined investigation of the electronic structure of bulk arc-melted full-Heusler Co2-xFe1+xSi (x = 0, 0.5, 1) and CoFeSi alloys using density functional theory and ultrasoft X-ray emission spectroscopy. We perform first-principles calculations of the spin-polarized total and partial density of states for the Co and Fe 3d (s, p) as well as for the Si 3s (p, d) orbitals. It is demonstrated that only Co2FeSi alloy exhibits a half-metallic behavior. However, the inverse CoFe2Si alloy shows pseudogap and high spin polarization at the Fermi level. We carry out ultrasoft X-ray emission Si L2,3 measurements, which provide the information about the local partial density of states of Si 3s and 3d orbitals in the valence band localized on Si atoms. We compare the measured spectra with our theoretical calculations and discuss them in terms of the contribution of s and d-electrons to the bonding. The Si and transition-metals sd and dd bonding formation is shown in the Co2−xFe1+xSi and CoFeSi alloys. The high spin polarization values, along with the extremely high Curie temperature, make these compounds potential candidates for spintronic applications.

Опубликовано: 5 марта 2022
https://doi.org/10.1140/epjb/s10051-022-00303-2

Н.А. Борщ, Н.С. Переславцева, С.И. Курганский

Аннотация

Представлены результаты расчетов пространственной структуры и электронных спектров различных изомеров анионных ванадий-германиевых кластеров VGe−n (n = 5−19). Расчеты проводились с использованием трех функционалов — B3LYP, B3PW91 и PBE в комбинации с базисом 6-311 + g(d). Интерпретация результатов расчетов пространственной структуры кластеров с помощью данных по их фотоэлектронной спектроскопии позволила решить сразу две задачи — во-первых, выполнить верификацию правила Уэйда−Мингоса для данного ряда кластеров, а во-вторых, на основе исследования зависимости результатов оптимизационных расчетов пространственной структуры кластеров от используемого функционала максимально исключить ошибки при анализе результатов и с наибольшей достоверностью установить пространственную структуру кластеров.

Опубликовано: 13 июля 2022
DOI: 10.21883/FTT.2022.10.53106.372

Н.А. Борщ, Н.С. Переславцева, С.И. Курганский

Аннотация

В работе представлены результаты компьютерного эксперимента в рамках теории функционала плотности по расчетам атомной структуры и электронного спектра кластеров HfSn-n (n = 15–17). На основе правил Уэйда–Мингоса установлены закономерности формирования моноанионных гафний-допированных кластеров олова, позволяющие оптимизировать прогностические исследования по поиску новых наноструктурированных материалов. Сравниваются результаты расчетов с использованием функционалов B3LYP, B3PW91 и PBE в комбинации с базисом SDD. Проведен анализ влияния функционала на результаты оптимизационных расчетов атомной структуры. Предложена оптимальная стратегия компьютерного эксперимента по моделированию пространственной структуры кластеров на основе олова, подтвержденная сопоставлением с известными экспериментальными данными.

Опубликовано: 21 сентября 2022
DOI: 10.31857/S0002337X22120053

M.Yu. Bocharnikova, M.M. Murtazin, S.N. Grushevskaya, O.A. Kozaderov, A.V. Vvedensky

Abstract

Anodic oxidation of silver–zinc alloys with a concentration of zinc of up to 30 at.% (alpha phase) in a deaerated aqueous solution of 0.1 M KOH was studied by voltammetry and chronoamperometry with synchronous registration of the photocurrent. A preliminary modification of the alloy surface due to the selective zinc dissolution, with monitoring of the potential and charge, was carried out in a deaerated aqueous solution of 0.01 M HNO3 + 0.09 M KNO3. As a result of the modification, the surface layer of the alloy was enriched with an electropositive component and vacancies, whose concentration exceeded the equilibrium concentration. The anodically formed Ag(I) oxide was characterized by an n-type conductivity and the predominance of donor defects in the crystal lattice. Their concentration increased and the width of the space charge region of the semiconductor oxide decreased with an increase in the concentration of non-equilibrium vacancies in the surface layer of the alloy.

Опубликовано: 6 июня 2022
https://doi.org/10.1007/s10008-022-05204-z

S.N. Grushevskaya, I.A. Belyanskaya, O.A. Kozaderov

Abstract

The constant increase in the amount of energy consumed and environmental problems associated with the use of fossil fuels determine the relevance of the search for alternative and renewable energy sources. One of these is hydrogen gas, which can be produced by sunlight-driven photocatalytic water splitting. The decisive role in the efficiency of the process is played by the properties of the photocatalyst. Oxide materials are widely used as photocatalysts due to their appropriate band structure, high-enough photochemical stability and corrosion resistance. However, the bandgap, crystallinity and the surface morphology of oxide materials are subject to improvement. Apart from the properties of the photocatalyst, the parameters of the process influence the hydrogen-production efficiency. This paper outlines the key ways to improve the characteristics of oxide-semiconductor photocatalysts with the optimum parameters of photocatalytic water splitting.

Опубликовано: 14 июля 2022
https://doi.org/10.3390/ma15144915

I.G. Grevtseva, O.V. Ovchinnikov, M.S. Smirnov, A.S. Perepelitsa, T.A. Chevychelova, V.N. Derepko, A.V. Osadchenko, A.S. Selyukov

Abstract

A technique of obtaining plexitonic structures based on Ag2S quantum dots passivated with L-cysteine (Ag2S/L-Cys QDs) in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs) with controlled luminescence properties has been developed. The structural and luminescence properties of Ag2S/L-Cys QDs with Au/CTAB NRs are studied. The effect of plasmonic Au/CTAB NRs on IR trap state luminescence (750 nm) is considered. It has been found that the direct interaction between the components of the plexcitonic nanostructure leads to a significant luminescence quenching of Ag2S/L-Cys QDs, with the luminescence lifetime being constant. This is the evidence for photoinduced charge transfer. The spatial separation of the components of plexcitonic nanostructures due to the introduction of a polymer – poly(diallyldimethylammonium chloride) (polyDADMAC) provides a means to change their mutual arrangement and achieve an increase in the IR trap state luminescence intensity and a decrease in the luminescence lifetime from 7.2 ns to 4.5 ns. With weak plexcitonic coupling in the nanostructures [Ag2S QD/L-Cys]/[polyDADMAC]/[Au/CTAB NRs], the possibility of increasing the quantum yield of trap state luminescence for Ag2S QDs due to the Purcell effect has been demonstrated. In the case of formation [Ag2S QD/L-Cys]/[polyDADMAC]/[Au/CTAB NRs] a transformation of shallow trap state structure was established using the thermostimulated luminescence method.

Опубликовано: 24 февраля 2022
https://doi.org/10.1039/D1RA08806H

А.С. Перепелица, О.В. Овчинников, М.С. Смирнов, И.Г. Гревцева, Т.С. Кондратенко, С.В. Асланов, С.Ю. Турищев, О.А. Чувенкова, Д.А. Бондаренко

Аннотация

Представлены результаты исследования закономерностей фотопроцессов, определяющих люминесценцию коллоидных квантовых точек Ag2S, при формировании оболочки из SiO2. Обнаружено, что формирование оболочки сопровождается значительным ростом квантового выхода рекомбинационной люминесценции (до 5 раз), менее заметным ростом времени затухания люминесценции, а также резким снижением концентрации одного типа мелких локализованных состояний с энергией ионизации около 0.14 эВ. Сделан вывод о том, что локализованные состояния с глубиной 0.14 эВ являются центрами безызлучательной рекомбинации носителей заряда.

Опубликовано 21 фераля 2022
DOI: 10.31857/S0367676522060217

A.A. Romanov, A.A. Silaev, N.V. Vvedenskii, A.V. Flegel, M.V. Frolov

Abstract

We analyze the polarization response of a single Ne atom in an intense infrared (IR) laser field and weak extreme ultraviolet (XUV) isolated attosecond pulse (IAP). The analysis is based on the numerical solution of the time-dependent Kohn–Sham equations and the recently developed perturbation theory in the XUV field for an atom subjected to an intense IR field. In our numerical results, we observe a significant increase in the magnitude of the atomic polarization response at the frequencies near the carrier frequency of the IAP and associate it with XUV-induced collective dynamics contributing to the polarizability of Ne. The specific interference between IR- and XUV-induced channels is discussed, and its utilization for retrieving the phase of the generated harmonics in the IR field is suggested.

Опубликовано: 17 июня 2022
https://doi.org/10.1364/OL.460076

S.S. Olshannikova, N.V. Malykhina, M.S. Lavlinskaya, A.V. Sorokin, N.E. Yudin, Yu.M. Vyshkvorkina, A.N. Lukin, M.G. Holyavka, V.G. Artyukhov

Abstract

Briefly, 2-(4-Acetamido-2-sulfanilamide) chitosan, which is a chitosan water-soluble derivative, with molecular weights of 200, 350, and 600 kDa, was successfully synthesized. The immobilization of ficin, papain, and bromelain was carried out by complexation with these polymers. The interaction mechanism of 2-(4-acetamido-2-sulfanilamide) chitosan with bromelain, ficin, and papain was studied using FTIR spectroscopy. It was found that the hydroxy, thionyl, and amino groups of 2-(4-acetamido-2-sulfanilamide) chitosan were involved in the complexation process. Molecular docking research showed that all amino acid residues of the active site of papain formed hydrogen bonds with the immobilization matrix, while only two catalytically valuable amino acid residues took part in the H-bond formation for bromelain and ficin. The spectral and in silico data were in good agreement with the catalytic activity evaluation data. Immobilized papain was more active compared to the other immobilized proteases. Moreover, the total and specific proteolytic activity of papain immobilized on the carrier with a molecular weight of 350 kDa were higher compared to the native one due to the hyperactivation. The optimal ratio of protein content (mg × g −1 of carrier), total activity (U × mL−1 of solution), and specific activity (U × mg−1 of protein) was determined for the enzymes immobilized on 2-(4-acetamido-2-sulfanilamide) chitosan with a molecular weight of 350 kDa.

Опубликовано: 8 августа 2022
https://doi.org/10.3390/polym14153223

P.V. Seredin, D.L. Goloshchapov, N.S. Buylov, V.M. Kashkarov

Abstract

In our work, the influence of the coordination environment of the Ca atom states in biomimetic mineralizing composite dental materials integrated with dental tissue was investigated. Biomimetic composites as well as natural dental tissue samples were investigated using synchrotron X-ray absorption near edge structure (XANES) spectroscopy. Energy structure studies revealed a number of important features related to the different type of calcium atom environment. the surface of nanocrystalline calcium carbonate-substituted hydroxyapatite (nano-cHAp) crystals in natural enamel and dentin involved in the formation of bonds with the organic matrix is more characterized by the coordination environment of the calcium atom corresponding to its location in the CaI position, i.e. bound through common oxygen atoms with PO4 tetrahedrons. At the same time, on the surface of nano-cHAp crystals in bioinspired dental materials, the calcium atom is more characteristically located in the CaII position, bound to the hydroxyl OH group. The detected features in the coordination atomic environment in nano-cHAp play a fundamental role for engineering a biomimetic dental composite of the natural organomineral interaction in the mineralized tissue.

Опубликовано: 10 января 2022
https://doi.org/10.1016/j.rineng.2022.100337

P.V. Seredin, N.S. Buylov, D.L. Goloshchapov, S.A. Ivkov, E.P. Matyukhina, I.N. Arsentyev, A.V. Nashchekin, Sh.Sh. Sharofidinov, A.M. Mizerov, E.V. Pirogov, M.S. Sobolev

Abstract

In our study, we have analysed the effect of a non-polar m-plane of sapphire substrate on the features of HVPE growth as well as the structural, morphological, optical properties, and Raman scattering of the grown single crystal GaN epitaxial film.

We found that the chosen technological approach makes it possible to obtain samples of structurally high-quality semipolar gallium nitride with an S2 orientation (11‾22) on the m-sapphire. The S2 plane of (11‾22) GaN has a polar reversal of φ ∼ 75° relative to the non-polar (10‾10) m-plane of sapphire, as well as an azimuthal tilt. Under the selected conditions of epitaxial growth, the GaN film has the morphology of a stepped terrace formed during the growth of mesa-like crystal islands, and their coalescence determined the observed surface topography. Based on the data analysis obtained by complex structural-spectroscopic methods, the level of residual biaxial stresses and refractive index dispersion were determined, testifying to the high structural and optical quality of the epitaxial film of semipolar GaN. An analysis of Raman spectra revealed the presence of optical anisotropy depending on the polar angle when the heterostructure is rotated around the m axis of the sapphire substrate.

Optimisation of the technological methodology may in future lead to a promising approach for the growth of quality GaN structures on large area m-sapphire substrates as optoelectronic devices based on these layers will have excellent characteristics.

Опубликовано: 22 мая 2022
https://doi.org/10.1016/j.optmat.2022.112507

P.V. Seredin, D.L. Goloshchapov, V.M. Kashkarov, Yu.A. Ippolitov, J. Vongsvivut

Abstract

The application of biomimetic strategies and nanotechnologies (nanodentology) has led to numerous innovations and provided a considerable impetus by creating a new class of modern adhesion restoration materials, including different nanofillers. An analysis of the molecular properties of biomimetic adhesives was performed in this work to find the optimal composition that provides high polymerisation and mechanical hardness. Nanocrystalline carbonate-substituted calcium hydroxyapatite (nano-cHAp) was used as the filler of the light-cured adhesive Bis-GMA (bisphenol A-glycidyl methacrylate). The characteristics of this substance correspond to the apatite of human enamel and dentin, as well as to the biogenic source of calcium: avian eggshells. The introduction and distribution of nano-cHAp fillers in the adhesive matrix resulted in changes in chemical bonding, which were observed using Fourier transform infrared (FTIR) spectroscopy. As a result of the chemical bonding, the Vickers hardness (VH) and the degree of conversion under photopolymerisation of the nano-cHAp/Bis-GMA adhesive increased for the specified concentration of nanofiller. This result could contribute to the application of the developed biomimetic adhesives and the clinical success of restorations.

Опубликовано: 30 марта 2022
https://doi.org/10.3390/biomimetics7020035

P.V. Seredin, D.L. Goloshchapov, V.M. Kashkarov, A.A. Emelyanova, N.S. Buylov, K.F. Barkov, Yu.A. Ippolitov, T.N Khmelevskaia, I. Mahdy, T. Prutskij

Abstract

In this report, we demonstrated the formation of a biomimetic mineralizing layer obtained on the surface of dental enamel (biotemplate) using bioinspired nanocrystalline carbonate-substituted calcium hydroxyapatite (ncHAp), whose physical and chemical properties are closest to the natural apatite dental matrix, together with a complex of polyfunctional organic and polar amino acids. Using a set of structural, spectroscopy, and advanced microscopy techniques, we confirmed the formation of a nanosized ncHAp-based mineralized layer, as well as studying its chemical, substructural, and morphological features by means of various methods for the pretreatment of dental enamel. The pretreatment of a biotemplate in an alkaline solution of Ca(OH)2 and an amino acid booster, together with the executed subsequent mineralization with ncHAp, led to the formation of a mineralized layer with homogeneous micromorphology and the preferential orientation of the ncHAp nanocrystals. It was shown that the homogeneous crystallization of hydroxyapatite on the biotemplate surface and binding of individual nanocrystals and agglomerates into a single complex by an amino acid booster resulted in an increase (~15%) in the nanohardness value in the enamel rods area, compared to that of healthy natural enamel. Obtaining a similar hierarchy and cleavage characteristics as natural enamel in the mineralized layer, taking into account the micromorphological features of dental tissue, is an urgent problem for future research.

Опубликовано: 11 августа 2022
https://doi.org/10.3390/biomimetics7030111

A.S. Lenshin, P.V. Seredin, D.L. Goloshchapov, A.O. Radam, A.M. Mizerov

Abstract

In our study, for the first time we demonstrate the advantages of using a compliant hybrid substrate of porSi/SiC to grow high-quality ultra-thin nanostructured AlxGa1−xN/GaN heterostructures using molecular beam epitaxy with plasma-activated nitrogen. Comparison of our experimental results obtained by micro-Raman spectroscopy, deconvolution, and the fitting of the experimental Raman spectra and subsequent calculations with information from already established literature sources show that the use of such a hybrid SiC/porSi substrate has a number of undeniable advantages for the growth of ultra-thin AlxGa1−xN/GaN nanoheterostructures without requiring the use of thick AIIIN buffer layers. Direct growth on a hybrid compliant substrate of SiC/porSi leads to a substantial relaxation in the elastic stresses between the epitaxial film, porous silicon, and silicon carbide, which consequently affects the structural quality of the ultra-thin AlxGa1−xN/GaN epitaxial layers. The experimental and computational data obtained in our work are important for understanding the physics and technology of AlxGa1−xN/GaN nanoheterostructures and will contribute to their potential applications in optoelectronics.

Опубликовано: 3 мая 2022
https://doi.org/10.3390/coatings12050626

P.V. Seredin, D.L. Goloshchapov, V.M. Kashkarov, A.A. Emelyanova, N.S. Buylov, Yu.A. Ippolitov, T. Prutskij

Abstract

This pilot study presents a practical approach to detecting and visualising the initial forms of caries that are not clinically registered. The use of a laser-induced contrast visualisation (LICV) technique was shown to provide detection of the originating caries based on the separation of emissions from sound tissue, areas with destroyed tissue and regions of bacterial invasion. Adding microRaman spectroscopy to the measuring system enables reliable detection of the transformation of the organic–mineral component in the dental tissue and the spread of bacterial microflora in the affected region. Further laboratory and clinical studies of the comprehensive use of LICV and microRaman spectroscopy enable data extension on the application of this approach for accurate determination of the boundaries in the changed dental tissue as a result of initial caries. The obtained data has the potential to develop an effective preventive medical diagnostic approach and as a result, further personalised medical treatment can be specified.

Опубликовано: 13 мая 2022
https://doi.org/10.3390/jimaging8050137

P.V. Seredin, D.L. Goloshchapov, V.M. Kashkarov, D.N. Nesterov, Yu.A. Ippolitov, I.Yu. Ippolitov, J. Vongsvivut

Abstract

(1) Objectives: This study is the first one to investigate the molecular composition of the dental biofilm during the exogenous and endogenous prophylaxis stages (use of dentifrice/drug) of individuals with different cariogenic conditions using molecular spectroscopy methods. (2) Materials and Methods: The study involved 100 participants (50 males and 50 females), aged 18–25 years with different caries conditions. Biofilm samples were collected from the teeth surface of all participants. The molecular composition of biofilms was investigated using synchrotron infrared microspectroscopy. Changes in the molecular composition were studied through calculation and analysis of ratios between organic and mineral components of biofilm samples. (3) Results: Based on the data obtained by synchrotron FTIR, calculations of organic and mineral component ratios, and statistical analysis of the data, we were able to assess changes occurring in the molecular composition of the dental biofilm. Variations in the phosphate/protein/lipid, phosphate/mineral, and phospholipid/lipid ratios and the presence of statistically significant intra- and inter-group differences in these ratios indicate that the mechanisms of ion adsorption, compounds and complexes arriving from oral fluid into dental biofilm during exo/endogenous prophylaxis, differ for patients in norm and caries development. (4) Conclusions: The conformational environment and charge interaction in the microbiota and the electrostatic state of the biofilm protein network in patients with different cariogenic conditions play an important role. (5) Clinical Significance: Understanding the changes that occur in the molecular composition of the dental biofilm in different oral homeostasis conditions will enable successful transition to a personalised approach in dentistry and high-tech healthcare.

Опубликовано: 26 июня 2022
https://doi.org/10.3390/pharmaceutics14071355

P. V. Seredin, Ali Obaid Radam, D. L. Goloshchapov, A. S. Len'shin, N. S. Buylov,
K. A. Barkov, D. N. Nesterov, A. M. Mizerov, S. N. Timoshnev, E. V. Nikitina,
I. N. Arsentyev, Sh. Sharafidinov, S. A. Kukushkin, I. A. Kasatkin

Abstract

In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid substrate containing layers of silicon carbide and porous silicon. Using X-ray diffractometry, Raman and photoluminescence spectroscopy, it is shown that thin films formed on a hybrid substrate have minimal residual stresses and intense photoluminescence.

Опубликовано: 29 июня 2022
DOI: 10.1134/S1063782622040030

D.V. Averyanov, I.S. Sokolov, A.N. Taldenkov, O.E. Parfenov, A.M. Tokmachev, V.G. Storchak

Abstract

Two-dimensional (2D) magnetic materials promise unconventional properties and quantum phases as well as advances in ultra-compact spintronics. Miniaturization of 2D magnets often reaches a single monolayer but in general can go beyond this limit, as demonstrated by 2D magnetism of submonolayer Eu superstructures coupled with Si. The question is whether the submonolayer magnetism constitutes a general phenomenon. Herein, we demonstrate that regular Eu lattices form a class of 2D magnets displaying various structures, stoichiometries, and chemical bonding. We synthesized and studied a set of Eu superstructures on Ge(001). Their magnetic properties are consistent with the emergence of a magnetic order such as ferro- or ferrimagnetism. In particular, control over the magnetic transition temperature by weak magnetic fields indicates the 2D nature of the magnetism. Taken together, Eu/Ge and Eu/Si superstructures seed a nucleus of the research area addressing the emergence of magnetism in submonolayer chemical species.

Опубликовано: 30 июля 2022
https://doi.org/10.1007/s12274-022-4694-7

D.V. Averyanov, I.S. Sokolov, A.N. Taldenkov, O.E. Parfenov, A.M. Tokmachev, V.G. Storchak

Abstract

2D magnetic materials are at the forefront of research on fundamentals of magnetism; they exhibit unconventional phases and properties controlled by external stimuli. 2D magnets offer a solution to the problem of miniaturization of spintronic devices. A technological target of materials science is to find suitable magnetic materials and scale their thickness down as much as possible, a single monolayer being a natural limit. However, magnetism does not halt at one monolayer – it may persist beyond this boundary, to sparse but regular lattices of magnetic atoms. Here, we report 2D magnetic phases of Eu on the Ge (110) surface. We synthesized two submonolayer structures Eu/Ge(110) employing molecular beam epitaxy. The phases, identified by electron diffraction, differ in the surface density of Eu atoms. At low temperature, they exhibit magnetic ordering with magnetic moments lying in-plane. Strong dependence of the effective magnetic transition temperature on weak magnetic fields points at the 2D nature of the observed magnetism. The results are set against those on the Eu/Si system. The study of Eu/Ge(110) magnets demonstrates that a variety of substrates of different structure and symmetry can host submonolayer 2D magnetic phases, suggesting the phenomenon to be rather general.

Опубликовано: 30 августа 2022
DOI: 10.1039/d2nr02777a

D.V. Averyanov, I.S. Sokolov, A.N. Taldenkov, O.E. Parfenov, I.A. Karateev, O.A. Kondratev, A.M. Tokmachev, V.G. Storchak

Abstract

The inherent malleability of 2D magnetism provides access to unconventional quantum phases, in particular those with coexisting magnetic orders. Incidentally, in a number of materials, the magnetic state in the bulk undergoes a fundamental change when the system is pushed to the monolayer limit. Therefore, a competition of magnetic states can be expected in the crossover region. Here, an exchange bias state is observed at the crossover from 3D antiferromagnetism to 2D ferromagnetism driven by the number of monolayers in the metalloxene GdSi2. The material constitutes a stack of alternating monolayers of Gd and silicene, the Si analogue of graphene. The exchange bias manifests itself as a shift of the hysteresis loop signifying coupling of magnetic systems, as evidenced by magnetization studies. Two features distinguish the phenomenon: (i) it is intrinsic, i.e. it is detected in an individual compound; (ii) the exchange bias field, 1.5 kOe, is unusually high, which is conducive to applications. The results suggest magnetic derivatives of 2D-Xenes to be prospective materials for ultracompact spintronics.

Опубликовано: 24 октября 2022
https://doi.org/10.1021/acsnano.2c09452

O.E. Parfenov, A.N. Taldenkov, D.V. Averyanov, I.S. Sokolov, O.A. Kondratev, M.M. Borisov, S.N. Yakunin, I.A. Karateev, A.M. Tokmachev, V.G. Storchak

Abstract

Silicene, a Si-based analogue of graphene, holds a high promise for electronics because of its exceptional properties but a high chemical reactivity makes it a very challenging material to work with. The silicene lattice can be stabilized by active metals to form stoichiometric compounds MSi2. Being candidate topological semimetals, these materials provide an opportunity to probe layer dependence of unconventional electronic structures. It is demonstrated here that in the silicene compound SrSi2, the number of monolayers controls the electronic state. A series of films ranging from bulk-like multilayers down to a single monolayer have been synthesized on silicon and characterized with a combination of techniques – from electron and X-ray diffraction to high-resolution electron microscopy. Transport measurements reveal evolution of the chiral anomaly in bulk SrSi2 to weak localization in ultrathin films down to 3 monolayers followed by 3D and 2D strong localization in 2 and 1 monolayers, respectively. The results outline the range of stability of the chiral state, important for practical applications, and shed light on the localization phenomena in the limit of a few monolayers.

Опубликовано: 30 августа 2022
https://doi.org/10.1039/D2MH00640E

V. K. Makarov, R. G. Chumakov, A. M. Lebedev, V. G. Stankevich

Abstract

A submonolayer film of fullerene fluoride C60F18 on the surface of an Au(111) single crystal has been analyzed by excitation-energy-resolved X-ray photoelectron spectroscopy. An analysis of the experimental data according to the model taking into account the photoelectron escape depth from the sample makes it possible to identify the orientation of C60F18 dipole molecules with respect to the substrate surface.

Опубликовано: 15 марта 2022
DOI: 10.1134/S1063774522060165

D.V. Sivkov, O.V. Petrova, S.V. Nekipelov, A.S. Vinogradov, R.N. Skandakov, K.A. Bakina, S.I. Isaenko, A.M. Ob'edkov, B.S. Kaverin, I.V. Vilkov, V.N. Sivkov

Abstract

The results of the comparative quantitative study of oxygen-containing groups adsorbed on the surface of carbonized sponge scaffold (CSS), highly oriented pyrolytic graphite (HOPG), fullerite C60 and multi-walled carbon nanotubes (MWCNTs) introduced into a high vacuum from the atmosphere without any pre-treatment of the surface are discussed. The studied materials are first tested by XRD and Raman spectroscopy, and then quantitatively characterized by XPS and NEXAFS. The research results showed the presence of carbon oxides and water-dissociation products on the surfaces of materials. It was shown that main source of oxygen content (~2%) on the surface of HOPG, MWCNTs, and C60 powder is water condensed from the atmosphere in the form of an adsorbed water molecule and hydroxyl group. On the CSS surface, oxygen atoms are present in the forms of carbon oxides (4–5%) and adsorbed water molecules and hydroxyl groups (5–6%). The high content of adsorbed water on the CSS surface is due to the strong roughness and high porosity of the surface.

Опубликовано: 1 августа 2022
https://doi.org/10.3390/app12157744

V.V. Punegov, S.I. Kolosov

Abstract

The dynamical diffraction of spatially restricted X-ray beams in a thick perfect crystal is studied using two-dimensional recurrence relations and the Takagi–Taupin (T-T) equations. It is shown that the two-dimensional recurrence relations are transformed into T-T equations when passing from a crystal with an array of discrete lattice planes to a model of continuous periodic electron density. The results of calculations of the X-ray diffraction field inside the crystal and the angular distribution of the scattering intensity in reciprocal space based on these two approaches are presented. It is shown that, when using the two-dimensional recurrence relations and T-T equations, the calculated contours of reciprocal-space maps and their qx sections are similar to each other, and the qz sections completely coincide.

Опубликовано: 11 февраля 2022
https://doi.org/10.1107/S1600576722001686

N.A. Zhuk, M.G. Krzhizhanovskaya, S.V. Nekipelov, V.N. Sivkov, D.V. Sivkov

Abstract

SA continuous series of solid solutions (Bi_1.5Mg_0.75-xFe_xTa_1.5O₇±Δ (x = 0–0.75)) with the pyrochlore structure were synthesized with the solid-phase method. It was shown that iron, like magnesium, is concentrated in the structure in the octahedral position of tantalum. Doping with iron atoms led to an increase in the upper limit of the thermal stability interval of magnesium-containing pyrochlore from 1050 °С (x = 0) up to a temperature of 1140 °С (x = 1). The unit cell constant a and thermal expansion coefficient (TEC) increase uniformly slightly from 10.5018 Å up to 10.5761 Å and from 3.6 up to 9.3 × 10^-6 °С^–1 in the temperature range 30–1100 °С. The effect of iron(III) ions on the thermal stability and thermal expansion of solid solutions was revealed. It has been established that the thermal stability of iron-containing solid solutions correlates with the unit cell parameter, and the lower the parameter, the more stable the compound. The TEC value, on the contrary, is inversely proportional to the cell constant.

Опубликовано: 31 октября 2022
https://doi.org/10.1107/S1600576722004319

K.A. Bakina, N.A. Zhuk, V.N. Sivkov, S.V. Nekipelov

Abstract

Solid solutions of bismuth-magnesium tantalates and bismuth-zinc tantalates doped with 3d-metal atoms were studied by XPS and NEXAFS. It was shown that atoms of bismuth, magnesium and zinc in all the compounds under consideration have the charge states Bi3+, Mg2+ and Zn2+, respectively, and the tantalum atoms, in turn, have an effective charge of +(5–δ).

Опубликовано: 23 августа 2022
https://doi.org/10.18721/JPM.153.207