Yu. V. Trushin

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.

Computer simulation of ion sputtering of polyatomic multilayered targets

Abstract The novel binary collision approximation Monte Carlo (BCA-MC) computer codes TRIRS and DYTRIRS for simulating ion sputtering of polyatomic nonuniform amorphous targets are presented. TRIRS simulates the collision cascade in a target and related secondary processes, including sputtering, damage generation etc., being more realistic than similar MC-BCA codes in modeling low-energy interatomic collisions. These improvements ensure better simulation of low-energy atomic collision processes in nonuniform targets, like sputtering, and ultra-low energy ion implantation. DYTRIRS is the extension of TRIRS which simulates the dynamics of the ballistic stage of ion-induced modification and sputtering for a target under high-fluence ion irradiation. The efficiency of DYTRIRS is verified by comparing the simulation of sputtering and secondary-ion mass-spectrometry in-depth compositional profiling of molecular-beam epitaxy grown two-dimensional (Al,Ga)AsGaAs (001) heterostructures, including structures with silicon and aluminum marker layers.

Computer simulation of the sputtering of polyatomic multilayered materials with consideration of the spatial overlapping of the collision cascades

Abstract The special dynamic computer code DYTRIRS for the simulation of the sputtering and modification phenomena in multilayered compound materials under high-fluence ion irradiation was developed on the basis of the Monte Carlo computer code TRIRS for the collision cascade calculation. In the computer simulation technique, the spatial overlap of ion-induced atomic collision cascades in a modified material are taken into account. This simulation technique was tried out on the specially grown multilayered structures. the results of the simulation of the sputtering phenomena of the Fe and Cu targets protected by carbon layer under high fluence ion irradiation are demonstrated.

The transition from 2D to 3D nanoclusters of silicon carbide on silicon

We have evaluated the critical average distance between the nanoclusters of silicon carbide grown by molecular beam epitaxy on silicon and estimated the time of the transition from two-to three-dimensional growth.

Concentration Profiles in Laser‐Deposited Ni/C and W/C Multilayers

Experimental studies of concentration profiles in W/C and Ni/C multilayers prepared by pulsed laser deposition are compared with ballistic simulations of the deposition process by means of the computer code TRIDYN. One part of the deposited particles possesses kinetic energies of about 100 eV and leads to a ballistic mixing of the deposited layers. As a consequence, diffuse interface concentration profiles arise and the concentrations within the individual layers depend on the layer thickness. The concentration profiles can be highly asymmetric between adjacent interfaces as observed e.g. in W/C multilayers. Simulations predict that the interface width for the deposition of W onto C is up to 3.5 times larger than in the opposite case. Differences between simulation results and HREM, AES, X-ray and XPS studies suggest that the resulting interface concentration profiles are essentially influenced by compound formation as well as by demixing of components occurring during deposition.

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.

Study of Si and C adatoms and SiC clusters on the silicon surface by the molecular dynamics method

Individual Si and C adatoms, as well as SiC clusters, on a Si surface are simulated by the molecular dynamics method in the course of investigation of the initial stages of formation of a SiC layer on silicon with the help of molecular beam epitaxy. The potential energy surfaces for Si and C adatoms on the (2 × 1) reconstructed Si(001) surface and on the nonreconstructed Si(111) surface, as well as on the Si(111) surface with a SiC cluster, are calculated and analyzed. The values of migration barriers for adatoms on these surfaces are calculated. The effect of the SiC cluster on deformation of the surface region of Si(111) and on the migration of adatoms is investigated. The deep minima observed on the potential energy surfaces immediately above a cluster and at its boundaries can trap diffusing adatoms. The distributions of stresses and strains in the silicon lattice under a cluster on the surface are studied and described.

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.