arXiv subjects

O. P. Konotop

Publications and source records attributed to O. P. Konotop.

6 recordsLinked to original sources

arXiv2026

Peculiarities Of Phase States In N2O-CO2 Cryoalloys According To Electron Diffraction Data

The structural characteristics of n2o-co2 alloys have been studied using transmission electron diffraction (THEED) across the entire range of their mutual concentrations at temperatures of 5 K and 65 K. The ranges in which regular solutions exist and intervals of alloy phase separation have been identified using the dependence of lattice parameters on composition and profile analysis of the diffraction pattern intensity distribution. It was found that maximum solubility values are up to 11 mol.% CO2 in the N2O matrix and up to 30 mol.% n2o in solid co2 at 65 K. The solubility limits for the components at 5 K are less 20 mol.% co2 in crystalline n2o and less than 35 mol.% n2o in a co2 crystal lattice. It was established that the character of n2o-co2 alloy separation corresponds to the mechanism of spinodal decomposition. The relative excess volumes that pertain to the admixture were determined for the CO2 impurity in solid n2o and for n2o impurity in co2 crystal. Conclusions regarding the character of n2o-co2 phase diagram have been made.

cond-mat.mtrl-sci↗

arXiv2026

Coexistence of close packed structures in large substrate-free Ar-Kr clusters according to THEED data

A quantitative phase analysis of substrate-free single-component and binary clusters of the Ar-Kr system obtained by adiabatic expansion of gas into vacuum through a supersonic nozzle was performed. The studies were carried out in-situ using transmission electron diffraction technique (THEED) on clusters with an average size ranging from 2000 to 100000 atoms/cluster and across the entire range of component concentrations. The independence of the threshold size of clusters, corresponding to the beginning of the formation of the hcp phase, from the component composition was revealed. It was established that clusters larger than this threshold size have a two-phase fcc-hcp structure with an identical concentration of components in each phase. The fraction of the hexagonal phase increases with the size of the aggregations and depends on the component content, reaching maximum in clusters with an equimolar composition. Arguments are presented in favor of the formation of two-phase clusters in the supersonic jet, rather than separate single-phase fcc and hcp ones. These findings are in good agreement with the previously proposed thermally activated diffusion mechanism for the nucleation and growth of the hcp phase in rare gas clusters.

physics.atm-clus↗

arXiv2022

Electron diffraction study of the formation and growth of clusters in supersonic binary N2-Kr gas jets

An electron diffraction diagnostics of substrate-free clusters formed in N2-Kr binary jets expanding through a supersonic nozzle into vacuum was carried out. Gas mixtures contained 0.5, 1, and 6 mol.% krypton, the measured average sizes of aggregations in the cluster beam varied from 500 to 30,000 molecules per cluster. A change in the nucleation mechanism in the jet from heterogeneous to homogeneous was revealed when the temperature of the gas mixture at the nozzle inlet T0 increased from 100 K to 120 K, which had a profound effect on the sizes, phase composition and component composition of the clusters. It was established that the intensification of cluster growth by inserted krypton nucleation centers at T0 = 100 K occurs through an increase in the fraction of the fcc phase. At T0 = 120 K, the effect of cluster growth suppression by the addition of an impurity with significantly stronger intermolecular forces was revealed for the first time. It is shown that the effect is manifested when the krypton gas content increases to 6 mol.% and is caused by the kinetics of gas condensation in a supersonic jet.

physics.atm-clus↗

arXiv2020

Quasicrystalline and crystalline rare-gas clusters produced in supersonic jets: Impact of the jet clustering level on cathodoluminescence spectra

The paper proposes a new approach to studying cathodoluminescence spectra of substrate-free rare-gas clusters produced in supersonic jets exhausting into a vacuum. The approach, which takes into account the fraction of the clustered substance in the jet, is applied to quantitatively analyze integrated intensities of the luminescence bands of the neutral and charged excimer complexes (Rg2)* and (Rg4+)* measured for nanoclusters of three rare gases (Rg = Ar, Kr, and Xe) with average sizes ranging from 100 to 18000 atoms per clusters (diameters varying from 2 to 13 nm). The amount of the clustered substance, which affects the absolute values of integrated intensity of the bands, is shown to be proportional to the logarithm of the average size of clusters in the jet. Analysis of normalized intensities allowed us to spectroscopically find two ranges of average sizes of Ar, Kr, and Xe nanoclusters which, in accordance with the electron diffraction studies, can be assigned to quasicrystalline icosahedral and crystalline fcc structures in clusters, as well as to find the cluster size range in which both structures coexist. We show that in fcc clusters the luminescence of the neutral molecules (Rg2)* comes from within the volume of the cluster, while the charged excimer complexes (Rg4+)* emit mostly from subsurface layers.

physics.atm-clus↗

arXiv2014

The fcc-hcp transition in single-component and binary van der Waals clusters from electron difraction data

An electron diffraction study of nucleation and growth of the hcp phase in large pure Ar and mixed Ar-Kr clusters formed by supersonic jet expansion is carried out. The threshold cluster size corresponding to the appearance of an hcp phase in addition to the fcc structure is determined. It is found that the relative volume of the hcp phase in clusters increases with their size. In very large aggregations, the percentage of hcp phase reaches its maximum and does not change with further cluster growth. The hcp phase relative volume in mixed clusters is almost double that in pure Ar clusters of the same size. A correlation between the hcp phase relative volume and the number of defective planes contained in the fcc matrix, which are the nuclei of the hcp phase, is established. A mechanism of nucleation and growth of the hcp phase in rare gas clusters is proposed.

physics.atm-clus↗

arXiv2014

Size and composition of clusters produced by supersonic expansion of binary gas mixtures

Size and composition of clusters produced by adiabatic expansion of binary gas mixtures (Ar-Kr, Kr-Xe, and N2-Ar) with various component concentrations are studied by using electron-diffraction technique. The resulting homogeneous and heterogeneous clusters are shown to have compositions substantially different from those of the primary gas mixtures and dependent on cluster size. We have found that the key parameters needed for an analysis of cluster composition are the critical cluster radius and the heavier component concentration in the gas mixture that can be used to establish the regions of existence of homogeneous and heterogeneous clusters. These critical values determine the coefficient of the enrichment of clusters with the heavier component with respect to its concentration in the primary gas mixture. Theoretical relations are obtained which provide a good quantitative description of the experimental results and can be expected to be also valid for finding the composition of binary clusters of other van der Waals systems.

physics.atm-clus↗