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


Accepted articles


Analysis of thermal stability of the internal structure of Ag-Cu nanoparticles

A.A. Cherepovskaya, S.L. Gafner, Yu.Ya. Gafner, D.A. Ryzhkova
Khakass State University

Abstract: Binary nanoparticles of the copper-silver alloy of are of great practical interest due to the possibility of fine-tuning their physical and chemical properties by changing the composition, size, shape and structure of nanoparticles. The processes of formation of the internal structure of Ag-Cu nanoparticles with a diameter from 2.0 to 8.0 nm during their crystallization with three different rates of thermal energy dissipation were studied by the molecular dynamics method. The features of this process were found to be dependent on the target chemical composition of nanoparticles, their size and the intensity of the thermal energy dissipation. The actual appearance and structure of the studied nanoparticles were determined using OVITO and xmakemol visualizers. It was shown that as a result of crystallization from the melt of binary Ag-Cu nanoparticles, metastable states that are sufficiently stable at room temperature (300 K), and the stability of such states after annealing at a temperature of 600 K is also evaluated.
Keywords: binary alloys, copper, silver, nanoparticles, structure, crystallization, metastable states, computer modeling, strong coupling

Kinetics of laser-induced crystallization of GeTe and Ge2Sb2Te5 chalcogenide phase-change material thin films

A.A. Burtsev , A.V. Kiselev , V.A. Mikhalevsky , V.V. Ionin , A.A. Nevzorov , N.N. Eliseev , A.A. Lotin
National Research Centre «Kurchatov Institute»

Abstract: The paper presents the results of theoretical analysis of crystallization of GeTe and Ge2Sb2Te5 thin films under the influence of pulse laser radiation. The phase transformations and the fraction of the crystalline phase was estimated on basis of the change of the probe optical reflection coefficient from the film sample surface. The formalism based on the Kolmogorov-Johnson-Mehl-Avrami theory was used to evaluate the kinetic behaviors of the phase transformation under the action of laser radiation. On the basis of experimental data of reflection changes during crystallization process of the researched materials, graphs were plotted and Avrami constants were determined. It is shown that GeTe exhibits a single step crystallization process associated with a high rate of nucleation and crystallite growth in all directions. The Ge2Sb2Te5 alloy is characterized by a two-step crystallization process with a change in the Avrami constant due to the influence of many factors such as the film geometry, sputtering characteristics, etc. Such type of crystallization is explained by the predominance of the high-stochastic nucleation.
Keywords: laser-induced crystallization, phase transitions, chalcogenides, phase-change materials, thin films, kinetics

Problems of 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 nanoscales. 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 nanoscales 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 the magnetic fluid in the magnetic field under the influence of such stresses. It can be assumed that high values of the yield strength are 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