D. V. Kulikov

Atomic assembly during ion-beam assisted growth: Kinetic modeling

The influence of an additional bombardment with low-energy ions during conventional molecular beam epitaxy deposition is studied. A model is proposed describing the initial growth stages during conventional molecular beam epitaxy and ion-beam assisted molecular beam epitaxy. The additional bombardment with low-energy ions leads to a transformation of the growth mode from island growth to layer-by-layer growth. In the first stages of film growth, the hyperthermal ion bombardment causes an increasing detachment of atoms from the tops of the growing islands. Based on the model, using simulation by the kinetic-equation method, the size distribution function of growing clusters is calculated. The theoretical results are in good agreement with experimental results obtained upon the deposition of GaN films.

Changes in the transition temperature after irradiation and annealing in single crystalline YBa2Cu3O7−δ

Abstract We present a model for the defect dynamics in YBa 2 Cu 3 O 7− δ crystals elucidating the changes in the transition temperature after neutron irradiation and subsequent annealing. These changes are found to be closely related to the calculated concentration of vacancies at the Cu–O chain sites.

Computer simulation of transition from h-BN TO c-BN during ion beam assisted deposition☆

A model is proposed of c-BN growth during the ion Beam assisted deposition procces. This phase appears when N and B atoms in h-BN create inserted ab-planes that increase the density of the material, resulting in transition from h-BN to c-BN. The aim is to simulate the processes that occur in growing BN films that lead to the phase transition. The ballistic processes caused by ion beam have been simulated by means of Monte Carlo computer codes TRIRS and DYTRIRS. With the help of computer code GEAR the annealing of the profiles of bombarding particles (Ar, N, B) have been modelled. The sink strengths of dislocation loops and migration energies of Ar, B and N atoms in BN have been estimated. These loops can act as nuclei of inserted ab-planes consisted of B and N, leading to formation of c-BN. It is shown that, according to our model, the transition from h-BN to c-BN is indeed possible, under certain conditions.

Kinetic model of growth of GaAs nanowires

A kinetic model of growth and formation of the crystal structure of gallium arsenide nanowires by molecular beam epitaxy on surfaces activated by Au drops is developed. The thicknesses of alternating layers of cubic and hexagonal phases formed due to fluctuations of the solution composition in the drop are calculated and compared with experimental data.

Theoretical Study of Ferroelectric Properties Degradation in Perovskite Ferroelectrics and Antiferroelectrics under Neutron Irradiation

In present study the influence of neutron irradiation on different types of ferroelectric perovskite structures is theoretically investigated. The changes of polarization of PLZT ceramics after irradiation are caused by oxygen vacancies with special reordering of the crystal lattice around a vacancy. This reordering leads to about zero value of local polarization which results in zero polarization of the whole sample when a sufficient number of such vacancies are created. Oxygen vacancies formed by irradiation may also serve as a source of charge carriers in the ferroelectric perovskite materials. In the case of antiferroelectric lead-zirconate thin films the influence of oxygen vacancies on polarization is suppressed and it is possible to clarify the influence of radiation charged defects on the material properties. We associate the decrease of the Curie-Weiss temperature in lead-zirconate thin films under neutron irradiation with the charges located near film surfaces where Schottky junction on the contact between antiferroelectric and metal is formed. In this case the relative decrease of the Curie-Weiss temperature is proportional to the neutron fluence. However the charges possibly remaining in the bulk of the film may change this proportionality to the quadratic law.

The influence of the implantation sequence on the (SiC)1−x(AlN)x formation

Abstract The influence of the implantation sequence on the defect and implant distribution during (SiC) 1− x (AlN) x formation was studied by Rutherford backscattering spectrometry/ion channelling (RBS/C) and elastic recoil detection. It is shown that the implantation sequence aluminum followed by nitrogen lead to an improved crystallinity compared to the reverse implantation sequence for implantation temperatures above 400°C. The results obtained are discussed in relation to the defects distributions calculated by using a developed model which includes the effect of stress self-consistently.

Diagnostics of bubble-mode vortex breakdown in swirling flow in a large-aspect-ratio cylinder

We report for the first time on the possible formation of regions with counterflow (bubble-mode vortex breakdown or explosion) at the center of strongly swirling flow generated by a rotating endwall in a large-aspect-ratio cylindrical cavity filled with a liquid medium. Previously, the possibility of bubble-mode breakdown was studied in detail for cylindrical cavities of moderate aspect ratio (length to radius ratios up to H/R ∼ 3.5), while flows in large-aspect-ratio cylinders were only associated with regimes of self-organized helical vortex multiplets. In the present study, a regime with nonstationary bubble-mode vortex breakdown has been observed in a cylindrical cavity with H/R = 4.5.

A physical model of the oxygen subsystem evolution in PLZT ceramics under neutron irradiation and annealing

A physical model describing the evolution of defects in the oxygen subsystem of ferroelectric PLZT ceramics under neutron irradiation and isochronous annealing conditions is proposed. The model takes into account the dependence of the material properties on the lanthanum content. The oxygen vacancy concentration variations calculated using this model agree with the experimental data on the polarization behavior in annealed ceramics.

High-temperature high-dose implantation of N+ and Al+ ions in 6H-SiC

A series of experimental and theoretical investigations has been initiated for 6H-SiC samples sequentially implanted with high doses of N+(65 keV) + N+(120 keV)+Al+(100 keV)+Al+(160 keV) ions at temperatures between 200 and 800 °C. Nitrogen and carbon distribution profiles are measured by ERD and structural defect distributions are measured by Rutherford backscattering with channeling. A comparison between the experimental data and the results of computer simulation yields a physical model to describe the relaxation processes of the implanted SiC structure, where the entire implanted volume is divided into regions of different depth, having different guiding kinetics mechanisms.

Computer simulation of the growth of GaAs nanowhiskers with inhomogeneous crystal structures

A physical model is proposed for the growth of GaAs nanowhiskers (NWs) with inhomogeneous crystal structures during the molecular beam epitaxy. Numerical calculations performed using this model give the temporal variation of the growth rate and the height of NWs and indicate the moments of switching from one crystal phase to another. The results of calculations coincide with the available experimental data.