Research

Modeling self-organization of nano-size vacancy clusters in stochastic systems subjected to irradiation

We study the self-organization of vacancy clusters in irradiated materials under reactor and accelerator conditions. Using a continuum stochastic model we take into account dynamics of point defects and their sinks with elastic interactions of vacancies. Dynamics of vacancy clusters formation is studied analytically and numerically. We have shown a difference in patterning dynamics at irradiation under reactor and accelerator conditions. The external noise influence related to fluctuation in a defect production rate is studied in detail. Applying our approach to pure nickel irradiated under different conditions we have shown that vacancy clusters having a linear size ∼eq 6 nm can arrange in a statistical periodic structure with nano-meter range. We have found that the linear size of vacancy clusters at accelerator conditions decreases down to 20%, whereas a period of vacancy clusters reduces to 6.5%.

D.O.Kharchenko, V.O.Kharchenko, A.I.Bashtova. Modeling self-organization of nano-size vacancy clusters in stochastic systems subjected to irradiation, Radiation Effects and Defects in Solids, 169(5), pp. 418-436 (2014)

Modeling of microstructure change in irradiated systems

We study a microstructure of systems with ballistic flux, describing formation of structure disorder under irradiation, using the phase field crystals method. It was found that due to competition between regular and stochastic components of the ballistic flux spatial patterns diffused atomic densities are realized. We have studied dynamics and statistics of defects during recrystallization of such systems. An influence of statistical properties of ballistic flux on a number of defects is analyzed. It was shown that spatial patterns formed under such flux during recrystallization are stable for thermal fluctuations with small intensity.

D.O.Kharchenko, V.O.Kharchenko, S.V.Kokhan, I.O.Lysenko. Modeling of microstructural changes in irradiated systems using the phase field crystal method, Ukr. J. Phys., 57, 1069 (2012).

Modeling of microstructure transformation in systems subjected to irradiation influence

We developed formalism for description microstructures transformations and phase separation in systems under irradiation .Investigation was made in a framework of a phase  field crystal method. This approach allows one to simulate materials on spatial scales of molecular dynamics and temporal scales of diffusive dynamics. Considering a model for a one component periodic system, driven by both stochastic thermally sustained flux and external (ballistic mixing) flux, we determined conditions of microstructure transformations appearance. Analysis of the system on a mesoscopic level, for a binary equiatomic system is performed. Reentrant processes of phase separation are discussed. We discuss pattern selection processes in systems with transient dynamics, characterized by memory effects.

Д.O.Харченко, І.O.Лисенко, В.О.Харченко. Моделювання мікроструктурних перетворень у системах, підданих радіяційному впливу, Usp. Fiz. Met., 13, 1001 (2012).

Stationary surface structures formation during ion beam sputtering

The formation of stationary surface structures during ion sputtering of materials was discussed. We generalize anisotropic Bradley-Harper model and study the behavior of the system described by the stochastic Kuramoto-Sivashinsky equation with multiplicative noise caused by fluctuations in the incidence. The dynamics of the stationary surface structures formation depending on the basic system parameters reduced to the angle of incidence and the properties of the target (the penetration depth of the ion into the target) was considered. We discussed growth and roughness exponents of the sputtered surface and the dynamics of the structural defects. An influence of the internal multiplicative noise intensity on the system dynamics is studied.

I.O. Lysenko, V.O. Kharchenko, S.V. Kokhan, A.V. Dvornichenko Stationary surface structures formation during ion beam sputtering, Metallofiz. Noveishie Tekhnol. V.35, ¹ 6, p.763 (2013)

Modeling of patterning at the surface during ion-beam sputtering

We study pattern formation processes in anisotropic system governed by the Kuramoto-Sivashinsky equation with multiplicative noise as a generalization of the Bradley-Harper model for ripple formation induced by ion bombardment. For both linear and nonlinear systems we study noise induced effects at ripple formation and discuss scaling behavior of the surface growth and roughness characteristics. It was found that the secondary parameters of the ion beam (beam profile and variations of an incidence angle) can crucially change the topology of patterns and the corresponding dynamics.

V.O.Kharchenko, D.O.Kharchenko, I.O.Lysenko. Modeling of ion-beam induced nano-size surface patterns in anisotropic systems. Nanotechnology Vol. 2: Synthesis and Characterization, Chapter 13, ed. by J.N.Govil, (Studium Press LLC, Houston, USA 2012) p.367.

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