Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials
Founded at 2009


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Comprehensive approach to studying fractal structures on iron surfaces

A.S. Antonov1, N.Yu. Sdobnyakov1, V.A. Anofriev1, M.S. Afanasiev2,3, E.M. Semenova1, V.V. Makaev1
1 Tver State University
2 MIREA – Russian Technological University
3 Fryazino Branch of V.A. Kotelnikov Institute of Radio Engineering and Electronics of RAS

Abstract: Nanoscale iron films of different thicknesses and at different spatial scales were studied using two alternative methods: atomic force microscopy and scanning tunneling microscopy. It was revealed that the surface morphology and fractal dimension depend not only on the film thickness but also on the deposition conditions and subsequent digital processing. It was concluded that the surface has a highly developed relief, which corresponds to high values of the fractal dimension. A hypothesis was put forward that the presence of iron oxides on the surface of the studied samples significantly affects their morphology, contributing to the formation of a complex and highly developed relief. These oxides lead to the formation of some structural inhomogeneities, which lead to the observation of agglomerates in a fairly wide range of fractal dimension values (from 2,49 to 2,94) on the film surface, i.e. oxides contribute to the aggregation of particles, creating a more complex surface structure. In addition, a method of separating agglomerates allowed us to record an increase in the value of the fractal dimension, which indicates the efficiency of separating and studying individual complex surface objects. Thus, for nanosized iron films, it becomes important to take into account the effects of oxidation and agglomeration of surface elements when analyzing them and choosing a method for obtaining them to identify structures with a certain value of the fractal dimension.
Keywords: atomic force microscopy, scanning tunneling microscopy, magnetron sputtering, fractal dimension, iron films

Effect of Bi-doping on the electrophysical properties of sodium niobate solid solutions

E.V. Barabanova, N.M. Ospelnikov, A.I. Ivanova
Tver State University

Abstract: Introduction of dopants is a classic method for modifying the properties of materials, in particular, complex oxides of the perovskite family with the general formula ABO3. Ions located in positions A and/or B are substituted. In this case, their valence can coincide with the valence of the basic ion (isovalent substitution) or differ (heterovalent substitution). Sodium niobate (NaNbO3) is a convenient basis for producing ferroelectric solid solutions. Doping changes the properties of sodium niobate in a wide range, allowing the production of functional materials for various applications. In this paper, the effect of Bi3+ doping upon substitution of niobium ion Nb5+ on the structure and electrophysical properties of sodium niobate is studied. It has been shown that such compositions are characterized by a significant increase in electrical conductivity with increasing the doping concentration, a decrease in the Curie temperature, and a change in the grain structure. The dopant concentration is more than 10 mol. % leads to the formation of some secondary phases.
Keywords: ionic conductivity, ferroelectric solid solutions, sodium niobate, dielectric permittivity

Investigation of optical properties of metal-doped CsPbX3 perovskite nanocrystals

V.P. Bezverkhniy, A.Y. Gagarina, E.N. Muratova, A.I. Maximov, V.A. Moshnikov
Saint Petersburg Electrotechnical University «LETI»

Abstract: As a part of the research work, inorganic lead-containing halide perovskite nanocrystals with the CsPbX3 structure were obtained by the hot injection. The alloying of single crystals of perovskites was carried out by solution methods, zinc and indium ions acted as dopants. The photoluminescence spectra and optical density spectra of the obtained colloidal solutions were studied. Our studies have shown that doping of perovskite nanocrystals with metal ions leads to an increase in photoluminescence as well as to a shift in the maximum of photoluminescence relative to the reference composition by 4 and 12 nm for bromides and iodides, respectively. Also, it has been shown that the magnitude of the shift does not depend on the type of dopant. It is noted that within the framework of this work, doping does not lead to a change in the position of the edge of its own absorption.
Keywords: perovskites, solar energy, nanocrystals, alloying, optical properties

Comparative studies of structural features of LiNbO3:Er:Zn crystals of different genesis

L.A. Bobreva1, R.A. Titov1, M.V. Smirnov1, I.V. Biryukova1, S.M. Masloboeva1, A.Yu. Pyatyshev2, N.V. Sidorov1, M.N. Palatnikov1
1 Tananaev Institute of Chemistry – Subdivision of the Federal Research Centre «Kola Science Centre of the RAS»
2 P.N. Lebedev Physical Institute of the RAS

Abstract: Comparative studies of double-doped LiNbO3:Er:Zn crystals of different genesis have been carried out using infrared absorption spectroscopy (in the region of OH-group stretching vibrations) and Raman spectroscopy. A LiNbO3:Er(0,53 mol.%):Zn(4,02 mol.%) crystal obtained by solid-phase doping and a LiNbO3:Er(0,75 mol.%):Zn(3,82 mol.%) crystal obtained by homogeneous doping were used in the study. No significant changes have been recorded in the infrared absorption spectra and Raman spectra of crystals obtained using different technologies. Minor changes in the main parameters of the absorption bands with frequencies of 3483 and 3492 cm-1 have been detected in the infrared absorption spectra. This may be due to the higher concentration of zinc dopant in the LiNbO3:Er (0,53 mol.%):Zn(4,02 mol.%) crystal. Measuring the half-width parameter of the band with a frequency of 271 cm-1 in the Raman spectra of the studied crystals helped to establish that the LiNbO3:Er(0,53 mol.%):Zn(4,02 mol.%) crystal has a higher ordering of the structural units of the cation sublattice compared to the LiNbO3:Er(0,75 mol.%):Zn(3,82 mol.%) crystal.
Keywords: lithium niobate, solid phase doping, homogeneous doping, erbium, zinc, double doping, Raman scattering, complex defects, infrared spectroscopy

Comparative studies of photoluminescent and optical properties, concentration of OH groups in double-doped LiNbO3: Er:Zn crystals

L.A. Bobreva1, R.A. Titov1, M.V. Smirnov1, I.V. Biryukova1, S.M. Masloboeva1, A.Yu. Pyatyshev2, O.V. Palatnikova1, N.V. Sidorov1, M.N. Palatnikov1
1 Tananaev Institute of Chemistry – Subdivision of the Federal Research Centre «Kola Science Centre of the RAS»
2 P.N. Lebedev Physical Institute of the RAS

Abstract: A comparative analysis of the photoluminescent properties, concentration of OH-groups and optical quality of double-doped crystals obtained from charges of different genesis has been performed. In a LiNbO3:Er(0,53 mol.%):Zn(4,02 mol.%) crystal obtained by solid-phase doping, the content of OH-groups is higher than in a LiNbO3:Er(0,75 mol.%):Zn(3,82 mol.%) crystal obtained by homogeneous doping. These changes occur as a result of the simultaneous formation of two types of complex defects in the LiNbO3:Er (0,53 mol.%):Zn(4,02 mol.%) crystal structure: ZnNb3--OH and VLi- OH. It has been established that photoluminescence in the visible region is caused by radiative transitions of Er3+ without the manifestation of the host’s own luminescence in the studied crystals. For the LiNbO3:Er:Zn crystal obtained by solid-phase doping, the luminescence intensity is 77% higher than in the crystal obtained by homogeneous doping. This may be due to the participation of OH-groups in the energy transfer between the host and the Er3+ ions.
Keywords: lithium niobate; double doping; photoluminescence; hydroxyl groups; rare earth and non- photorefractive dopant; point and complex defects

Switching processes in alanine doped triglycine sulfate crystals

N.N. Bolshakova1, A.I. Ivanova1, N.Yu. Druginina2, E.M. Semenova1, S.S. Schipilov1
1 Tver State University
2 Military Academy of Air and Space Defense named after Marshal of the Soviet Union G. K. Zhukov

Abstract: The paper presents the results of an experimental study of the dielectric and switching characteristics of some initial and annealed alanine-doped crystals of the triglycine sulfate group at room temperature. The results of measurements and calculations of the effective permittivity, switchable polarization, coercive and bias fields, unipolarity coefficient and dielectric loss tangent are presented. It was found that for most samples before and after annealing, the dielectric hysteresis loops are unipolar and shifted along the abscissa axis. This indicates a preferential orientation of domains and the presence of bias fields. As a result of annealing, the values of the coercive field and the unipolarity coefficient of the crystals decrease, and the switchable polarization increases. It is shown that the field dependences of the effective permittivity of the crystals before annealing have extrema lying in the field range of (5-7,5) ∙ 104 V∙m-1 and in the range (5-12) ∙ 104 V∙m-1 after their annealing.
Keywords: triglycine sulfate crystals, hysteresis, switching processes, permittivity

Analysis of domain structure parameters of RFe11Ti (R = Y, Gd, Ho, Er) single crystals based on magnetic force microscopy data

A.M. Guseva, A.I. Sinkevich, S.D. Smetannikova, E.M. Semenova, Yu.G. Pastushenkov
Tver State University

Abstract: The results of an experimental study of the magnetic domain structure on the basal plane of RFe11Ti single crystals (R=Y, Gd, Ho, Er) by magnetic force microscopy are presented. At room temperature, the compounds are characterized by magnetocrystalline anisotropy of the «easy axis» type. Based on the magnetic force microscopy data, the sizes of domains on the basal plane of the samples were determined. Using the Bodenberger-Hubert method, the surface energy density of domain walls γ was determined for all compounds based on the magnetic force microscopy data: YFe11Ti – 4,05 mJ/m2, GdFe11Ti – 5,93 mJ/m2, HoFe11Ti – 4,97 mJ/m2, ErFe11Ti – 2,98 mJ/m2. The cube counting method was used to calculate the fractal dimension DL of the stray fields of the domain structure at different heights from the surface (0,1 – 9 μm). DL on the surface of the z(0) sections has values of 2,62 for compounds with R = Y, Gd, Ho and 2,72 for R=Er. For all samples, DL has a maximum near the surface.
Keywords: rare earth intermetallic compounds, domain structure, magnetic force microscopy, fractal dimension

Towards the investigation of the magnetization processes of uniaxial magnetic materials by means of the analysis of transformation of their domain structure: experiment and computer modeling

G.G. Dunaeva, A.Yu. Karpenkov
Tver State University

Abstract: This paper presents the results of complex studies, including direct experiment and computer modeling, of the magnetization reversal processes of a SmCo5 single crystal and a (GdBiLu)3(FeGa)5O12 ferrite-garnet film. The analysis of images of the domain structure in the external magnetic field of both samples allowed us to construct the field dependences of magnetization. It was found that the field dependence of the magnetization of the ferrite-garnet film coincides with the magnetometry data. For the SmCo5 single crystal the saturation field of the surface corresponds to the saturation field obtained from the measurements on a vibrating sample magnetometer, however, the view of the field dependence M(H) differs. Image analysis of the main domains of a single crystal in an external magnetic field and computer modeling have shown that the values of the domain structure disappearance fields on the surface of the film located above the single crystal are significantly less than the saturation fields according to magnetometry data. The application of an external magnetic field of 0,02 T leads to saturation of the entire volume of the ferrite-garnet film in the direction of the field, which does not allow further observation of the transformation of the main domain structure of the bulk sample and limits the applicability of the indicator film method.
Keywords: ferrite-garnet film, single crystal, magnetic domain structure, Kerr effect, magnetization reversal processes

Structural features and properties of the Sn-Zn-Si-Al system alloys obtained by the method of rapid solidification from the melt

D.A. Zernitsa1, V.G. Shepelevich2
1 Mozyr State Pedagogical University named after I.P. Shamyakin
2 Belarusian State University

Abstract: The article presents the results of studying the microstructure of rapidly solidified foil of Sn55,18Zn44,50Si0,23Al0,09 alloy. The phase composition of rapidly solidified foil was studied. A uniform distribution of alloying silicon and aluminum in tin in the form of a solid solution was established. The formation of the (100) texture of tin and (1010) of zinc was revealed, associated with the predominant growth of crystallites, in which the close-packed planes of tin and zinc are perpendicular to the direction of heat removal during crystallization. An analysis of the structure and properties of the foil during isothermal annealing and natural aging was performed, with a description of the processes occurring. Formation of a dispersed structure due to high degree of supercooling of liquid phase with increase of degree of dispersion of zinc during isothermal annealing (average chord d on sections of zinc phases is 1,24 μm before heat treatment and 0,42 μm after isothermal annealing for 170 min at 150°C) along with invariance of texture during heat treatment is established. Change of the microhardness of foil during natural aging, noticeable formation of large number of clusters of precipitations of tin and zinc phases due to their supersaturation, as well as reinforcing action of alloying elements (Si, Al) are explained. During heat treatment zinc dissolves in the matrix phase, with decrease of its volume, while share of softening phase of tin increases which leads to a decrease in the microhardness.
Keywords: rapidly solidified structures, multicomponent alloy, zinc, tin, supersaturated solution, structure, isothermal annealing, silicon, aluminum

Study of potassium intercalated graphite by Raman spectroscopy

Z.A. Akhmatov1,2, A.Kh. Khokonov2,3, I.N. Sergeev2, M.G. Ambartsumov4
1 Kabardino-Balkarian State University named after H.M. Berbekov
2 Institute of Nuclear Research of RAS
3 Kabardino-Balkarian Scientific Center of RAS
4 Leading Researcher of North-Caucasus Federal University

Abstract: In this paper, a study of a graphite intercalation compound by potassium was carried out using Raman spectroscopy. The purpose of the study was to determine the intercalation stage and study the influence of intercalated atoms on the vibrational properties of highly oriented pyrolytic graphite lattice. The intercalation of highly oriented pyrolytic graphite by potassium was performed using a two-zone method. Raman spectra were obtained for both pure and intercalated highly oriented pyrolytic graphite. The experiments carried out to identify the synthesized structures showed the formation of sixth stage graphite intercalation compound. Knowledge of the stage of the intercalated graphite compounds is important for its use as a superconducting material, as well as in supercapacitors. In addition, the intercalation stage is a key factor in obtaining graphene by chemical exfoliation of graphite intercalation compound, since the number of graphene layers will directly depend on the intercalation stage. In the obtained Raman spectra, the effect of G-peak splitting is observed, indicating a change in the vibrational properties of the graphite lattice during its intercalation due to the charge transfer from the intercalate to the carbon layers. The value of the transferred charge is determined using first-principles calculations.
Keywords: Raman spectroscopy, highly oriented pyrolytic graphite, alkali metals, intercalation, two- zone method, first-principles calculations