V. S. Kharlamov

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 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.

Computer simulation of ferroelectric property changes in PLZT ceramics under neutron irradiation

The response of ferroelectric materials to high energy irradiation is of great interest because of their possible application in radiation environments such as thermonuclear reactors. In the present work a physical model for the defect evolution in PLZT ceramics under neutron irradiation and annealing is proposed. The influence of the defect system on the ferroelectric properties of these materials has been investigated. Satisfactory agreement between the theoretical estimated oxygen defect concentration after irradiation and annealing and the experimentally determined polarization has been obtained.

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.

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.

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.

Multi-scale simulation of MBE-grown SiC/Si nanostructures

The main obstacle for the implementation of numerical simulation for the prediction of the epitaxial growth is the variety of physical processes with considerable differences in time and spatial scales taking place during epitaxy: deposition of atoms, surface and bulk diffusion, nucleation of two-dimensional and three-dimensional clusters, etc. Thus, it is not possible to describe all of them in the framework of a single physical model. In this work there was developed a multi-scale simulation method for molecular beam epitaxy (MBE) of silicon carbide nanostructures on silicon. Three numerical methods were used in a complex: Molecular Dynamics (MD), kinetic Monte Carlo (KMC), and the Rate Equations (RE). MD was used for the estimation of kinetic parameters of atoms at the surface, which are input parameters for other simulation methods. The KMC allowed the atomic-scale simulation of the cluster formation, which is the initial stage of the SiC growth, while the RE method gave the ability to study the growth process on a longer time scale. As a result, a full-scale description of the surface evolution during SiC formation on Si substrates was developed.

Physical model of the formation of a periodic structure on the surface of pyrolytic graphite under high-energy ion bombardment

A physical model is proposed for the formation of a structure consisting of “micropoints” and “cavities” on the surface of pyrolytic graphite bombarded by 210 MeV Kr+ ions. This structure may be explained in terms of the depth distribution of the energy deposited by the bombardment.

Small defects in YBCO single crystals: Tc after neutron irradiation and annealing

Abstract Neutron irradiation of HTSs creates a wide spectrum of defect sizes. In this work, the influence of small defects on the critical temperature is investigated by sequential reactor neutron irradiation and annealing of a YBCO single crystal. The characteristic behaviour of T c under this treatment is satisfactorily explained by a theoretical model considering the creation, migration and annihilation of small defects in the oxygen sublattice.

Kinetic modeling of the growth of copper clusters of various heights in subsurface layers of lead

The growth of subsurface copper clusters of various shapes and heights during the deposition of copper onto lead has been studied by kinetic modeling. The heights and radii of clusters have been calculated. Based on a comparison with experimental data, it is established that significant differences in the heights of clusters possessing different shapes are determined by the specific elastic energy of the copper cluster–lead interface.