Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials
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Editor’s column

Problems of the quantitative assessment of the friction couple contact area

V.O. Belavin, Yu.V. Brylkin, S.V. Zaletaev, A.L. Kusov, V.V. Pavlikov, A.A. Potapov, V.A. Tsarkova
Central Institute of Machine Building

Abstract: The results of our research of the surface of steel disks before and after friction are presented. Problems of the friction couple contact area estimation were under consideration. The results of searching a universal criterion of the friction couple contact area quantitative estimation are discussed. Using optical and scanning tunneling microscopy allows studying the surface profile at the micro- and nano-scales. An approach for determination of the contact area between bodies is proposed on the basis of the fractals theory. Such an approach allows to describe the heat transfer between bodies (conductive at contacts and radiant in pores heat exchange), to define the dependence of the friction force on the applied external force. The offered technique for the quantitative estimation of the surface structure at the micro- and nano-scales by means of the fractal theory will allow improving the accuracy of the spacecrafts thermal modes calculation as well as parameters of the knots of friction in them. This, in turn, will positively affect reliability and durability of the future spacecrafts. Improvement of methods in our further work will be aimed at studying tribological properties of the robotic products under the influence of the space factors and validation of the numerical modeling of the friction and heat exchange between mobile knots using results of experiments.
Keywords: tribology, thermal modes, robotics, steel surface, microscopy, fractal analysis, friction couple

On the nature of anomalously high value of yield stress of nanostructured magnetic fluid

A.N. Bolotov, O.O. Novikova
Tver State Technical University

Abstract: Based on magnetic fluids, new effective technical devices have been implemented, such as magnetic fluid bearings, seals, and dampers. The magnetic-viscous effect inherent in magnetic fluids can not only improve the properties of magnetic fluid units, but significantly complicate their operation after a long stop. This refers to the so-called «stop effect», which occurs due to an abnormally high limiting shear stress in a structured liquid. It is shown that, based on the existing ideas about the thixotropic properties of a magnetic fluid, it is not possible to convincingly explain the experimental value of the yield strength. Estimations according to the known formulas obtained for the chain model give a significantly underestimated value of the yield strength of a real magnetic fluid. A hypothesis is proposed according to which the rheological properties of the carrier medium change in the process of structure formation in the magnetic fluid under the action of compressive stresses created by a network of dispersed particles. Experiments have confirmed an increase in the density of a magnetic fluid in a magnetic field under the influence of such stresses. It can be assumed that the high value of the yield strength is due to the presence of the intrinsic yield strength of the dispersion medium, which is in a quasi-solid state.
Keywords: magnetic fluid, yield point, dispersed particles, magnetic interaction, chain model

Synthesis and study of the structure of lanthanum (III) compounds and cerium (III) with aspartic acid

V.A. Shkrumeliak, O.A. Golovanova
Dostoevsky Omsk State University

Abstract: A significant part of modern research is devoted to synthesis and study of the structure of compounds of rare earth elements with bioligands – these are those ligands that participate in biochemical processes. Compounds of rare earth elements with amino acids are of particular interest to study, since they are the most important bioligands, natural nanoscale molecules. In the course of the work, compounds of lanthanum (III) and cerium (III) with aspartic acid were synthesized. White crystalline precipitates were obtained for the «La-Asp» (1:2) and «Ce-Asp» (1:3) systems. With the help of optical microscopy, the fundamental difference between the crystals of synthesized compounds (in shape and size) from the crystals of the starting substances used for synthesis is proved. The results of IR-Fourier spectroscopy showed that metal ions interact with the carboxyl group of aspartic acid. The results obtained during the spectrophotometric analysis of the filler fluid for the «La-Asp» system (1:2) made it possible to simulate the spatial structure of this compound taking into account the amount of aspartic acid bound to lanthanum (III) ions. The synthesized compounds are promising for their further use in medicine.
Keywords: rare earth elements, complex compounds of lanthanum (III) and cerium (III), amino acids, aspartic acid, ligands

Gate dielectric nitrization and effect on changes in the density of interlayer states of MOS structures

N.V. Cherkesova1, G.A. Mustafaev1, A.G. Mustafaev2
1 KabardinoBalkarian State University
2 Dagestan State University of National Economy

Abstract: The processes occurring in the silicon-oxygen-nitrogen system are of great practical importance, since dielectric layers made from materials of this system are widely used as barriers to the penetration of impurities, elements of storage capacitors, field insulating layers, etc. Interest in the creation of such dielectrics has increased in connection with the use of the rapid thermal annealing stage in technological processes, which are accompanied by the appearance of fast surface states and mechanical stresses on the interface. As a result of the study, it was determined that the change in the threshold voltage in MDS structures is associated with the capture of electrons by the traps formed in the bulk of the semiconductor. MDS structures with nitrided oxide have better stability than conventional oxide. Studies have shown that the suppression of the formation of states at the interface depends on the degree of nitriding. The characteristics of MDS structures under the influence of irradiation substantially depend on the temperature and duration of fast thermal nitrization.
Keywords: metal–dielectric–semiconductor, silicon oxynitride, nitrization, gate dielectric, silicon dioxide, heat treatment

Effect of free valence on the electronic structure of n-alcohol radicals

V.V. Turovtsev1, E.M. Chernova2, E.A. Miroshnichenko3, Yu.D. Orlov2
1 Tver State Medical University
2 Tver State University
3 Semenov Research Center of Chemical Physics

Abstract: The paper presents the results of a study of the effect of free valence (when a hydrogen atom is separated) on the electronic structure of n-alcohol radicals by the example of radicals of nheptanol derivatives (C●H2(CH2)6OH, CH3C●H-(CH2)5OH, C2H5C●H-(CH2)4OH, C3H7C●H-(CH2)3OH, C4H9C●H-(CH2)2OH, C5H11C●H-CH2OH, C6H13C●H-OH, C7H15-O●). Geometry optimization and the electron density distribution in these compounds was obtained by the density functional method B3LYP/6-311++G(3df,3pd) 6d 10f. The electronic structure of the selected molecules and radicals was investigated within the framework of the «quantum theory of atoms in a molecule» (QTAIM): the electronic parameters of atoms and atomic groups were calculated, the spin density distribution was studied, the concepts of «radical center» and «free valence» were quantitatively characterized. The inductive effect and the tolerability of atomic groups are considered, and a qualitative scale of group electronegatives is compiled. The disturbing effect of various atomic groups, including those containing free valence, on the hydrocarbon chain is compared by comparing the integral parameters of the groups included in the compounds under study with the parameters of the «standard» groups.
Keywords: quantum theory of atoms in molecules, electron density, electronegativity, inductive effect, free valence, radical center

Green synthesis of silver nanoparticles. Complementary techniques for characterization

S.D. Khizhnyak, A.I. Ivanova, V.M. Volkova, E.V. Barabanova, P.M. Pakhomov
Tver State University

Abstract: The work presents the results of green synthesis (biosynthesis) of silver nanoparticles using aqueous extracts of maple and oak leaves. The efficiency of the synthesis, size and shape of the formed nanoparticles were studied using UV-visible spectroscopy, dynamic light scattering, atomic force microscopy and scanning electron microscopy techniques. It was found that the formation of silver nanoparticles is accompanied by the appearance of a plasmon resonance band in the electronic spectra of aqueous extracts, the maximum of which depends on the concentration of silver nitrate and is in the range of ~420-429 nm in the spectra of maple leaves, and in the spectra of oak extracts there is a shift towards longer wavelengths ~425-435 nm, which correspond to the formation of nanoparticles of larger size. According to the dynamic light scattering data, the size of nanoparticles in the maple extracts is of about 60-68 nm and in the oak samples of ~107 nm. The differences in the size and shape of nanoparticles obtained in the maple and oak phytoextracts detected by atomic force microscopy and scanning electron microscopy are explained by the different composition of bioactive substances in the plants involved in the reduction of silver ions and stabilization or modification of the surface of silver nanoparticles.
Keywords: green synthesis, silver nanoparticles, surface plasmon resonance, scanning electron microscopy

Evaluation of the properties of the fucoidan/Fe3O4 nanocomposite as a transport agent of covalently bound molecular cargo

V.E. Suprunchuk
North-Caucasus Federal University

Abstract: Magnetically controlled transport of drugs with targeted release of molecular cargo expands the possibilities of clinical therapy. This article explores the possibility of creating nanoparticles based on fucoidan modified with magnetite for biomedical purposes. The possibility of immobilizing a modelling fibrinolytic enzyme with a cross-linking agent was studied. The maximum loading of the enzyme is 2.06±0.09% of the mass. The particle size with immobilized alteplase according to scanningelectron microscopy was 94.4±24.3 nm, hydrodynamic diameter – 370 nm, zeta potential – -1.66±0.06 mV. The saturation magnetization of the sample is 6 emu/g. To understand the mechanisms of molecular load release, five kinetic models were applied to the results obtained: zero order, Weibull, Hill equation, Higuchi, Korsmeyer-Peppas. The use of mathematical modeling showed that the best model for describing this process is the Korsmeyer-Peppas kinetic equation (r2 = 0.97), and the release process is controlled by the Fick diffusion. The resulting biocomposite material is a promising candidate as a nanocarrier for an enzymatic agent.
Keywords: fucoidan, magnetite, magnetic nanoparticles, targeting, targeted delivery, alteplase, release kinetics, variable magnetic field

Mechanism behind structural changes accompaning the solid-state polymerization in the molybdenumvanadium mixed oxide films

T.V. Sviridova, Z.A. Yakubovskaya, V.B. Odzhaev, D.V. Sviridov
Belarusian State University

Abstract: In this paper we investigate the changes in the surface topology of inorganic polymerderived films resulted from photostimulated polymerization. With the use of the atomic-force microscopy, the surface structure changes of mixed molybdenum-vanadium oxide thin films (V2O5:MoO3 = 3:2) resulted from the UV light-induced polymerization was investigated. The analysis of atomic-force images evidenced that the solid-state polymerization in the mixed oxide films obtained by condensation of corresponding oxoacids occurs through 3D mechanism. As the result of exposure, MoO3/V2O5 films lose the intrinsic anisotropy which is due to the directional agglomeration of belt-like mixed oxide oligomers. The photopolymerization processes in the mixed oxide film yield agglomerates of nuclei built from the faceted nanometer-sized pseudocrystallites. The exposure is also accompanied with solid-state recrystallization of initially amorphous oxide resulting in the rougher relief of the exposed film. The selective acidic etching uncovers the latent structure of the film, this etching being accompanied with pseudocrystallite dispergation that results in the smoothing of the microrelief of the oxide film surface. These structural features of photosensitive mixed oxide MoO3/V2O5 films facilitate their application as the inorganic photoresists.
Keywords: photopolymerization, molybdenum-vanadium mixed oxides, thin films, nanostructure, inorganic photoresists, atomic force microscopy

Peculiarities of texture formation in strontium hexaferrite-based materials when produced from organic nitrate precursors

A.A. Ostroushko1, M.O. Tonkushina1, T.Yu. Zhulanova1,2, E.V. Kudyukov1, A.Ya. Golub1, O.V. Russkikh1
1 Ural Federal University named after the first President of Russia B.N. Yeltsin
2 Institute of High Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences

Abstract: The processes of strontium hexaferrite (permanent magnet material) fabrication in combustion reactions followed by heat treatment of organic nitrate precursors containing glycine or polyvinyl alcohol have been studied. The formation of iron-glycine complexes of organic precursor components affects the formation of the morphology of the obtained samples. When using glycinecontaining systems during combustion, a branched fibrous texture of the material with extended internal cavities with elongated oxide particles emerges. Such samples have a higher coercivity; the external magnetic field has no significant influence on the texture formation during combustion. It was established that charges are generated in precursors during their combustion, which manifests itself in the appearance of a potential difference between the ground and the precursor. In this case, the appearance of lower intensity charges allows us to obtain samples with higher magnetization, as well as with a greater ability to increase the magnetic characteristics during further thermomagnetic processing.
Keywords: strontium hexaferrite, synthesis, organic nitrate precursors, magnetic properties, texturing

Synthesis and diagnostics of gas-sensitive nanostructures based on molybdenum compounds

S.S. Nalimova1, Z.V. Shomakhov2, A.D. Chuprova1, A.M. Guketlov2
1 Saint Petersburg Electrotechnical University «LETI»
2 KabardinoBalkarian State University

Abstract: In recent years, various transition metal dichalcogenides have been widely investigated, which are of interest for many applications, including gas sensors. In this work, some gas-sensitive nanostructures based on molybdenum disulfide and molybdenum oxide were synthesized by hydrothermal method. The surface chemical composition of the samples was studied by X-ray photoelectron spectroscopy. The gas-sensitive properties of the synthesized structures to isopropyl alcohol and acetone vapors at different working temperatures were analyzed. It was shown that as a result of heat treatment at 150°C, partial oxidation of molybdenum disulfide occured. Annealing of MoS2 samples at 400°C led to complete oxidation to MoO3. Analysis of the gas-sensitive properties of the structures showed that molybdenum oxide has the maximum response to isopropyl alcohol and acetone vapors in the entire temperature range under study. Both molybdenum disulfide and molybdenum oxide show a better response to isopropyl alcohol vapors compared to acetone vapors.
Keywords: chemisorption gas sensors, molybdenum disulfide, molybdenum oxide, X-ray photoelectron spectroscopy