A. A. Schmidt

Modelling the Formation of Nano-Sized SiC on Si

Silicon carbide nano-clusters have some promising specific propert ies for microand optoelectronics. In this work the SiC clusters formation and the growt h n the silicon (111) surface during molecular beam epitaxy (MBE) have been investigated theor etically with implementation of the rate equations simulation model. The model was successfully appli ed to obtain the temperature dependence of the cluster concentration. The results were compared with the experimental data [1-3]. Furthermore, influence of the surface reconstruction tra nsition (7x7) → (1x1) on the temperature concentration dependence was investigated.

Linear alignment of SiC dots on silicon substrates

A linear alignment of self-assembled, cubic SiC dots grown by molecular beam epitaxy on Si substrates is demonstrated. The formation of well-ordered biatomic steps on (111) Si was used to control the nucleation sites. The resulting terraces promote an alignment along their step edges. SiC on Si represents self-organization in a system with chemical interactions. The resulting instability of the Si surface during the nucleation requires a precise control of the process conditions. By atomic force microscopy we demonstrate the achieved linear chains of SiC dots.

Supersonic motion of bodies in dusty gas

Abstract Supersonic dusty gas flows about the blunted bodies are considered. The effects of rigid particles on the shock layer parameters, drag and heat transfer are investigated within the frames of Euler and Navier-Stokes approaches. When formulating the closed set of gas-particles mixture conservation equations both phenomenological relations and kinetic theory are used. The problem is treated numerically by means of time-asymptotic method along with implicit finite-difference schemes.

Mathematical modeling of underwater explosion near free surface

The results of a numerical simulation of processes that accompany the local energy release in a liquid near the free surface (underwater explosion) are presented. Using the proposed mathematical model, it is possible to describe the propagation of compression and rarefaction waves in the liquid, their interaction with the free surface, and spreading in gas. The structure of flow initiated by the underwater explosion near the free surface is analyzed. The results of a numerical simulation are compared to the available experimental data and published results of calculations. It is shown that the proposed algorithm adequately describes the process under consideration.

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.

Initial Stages of the MBE Growth of Silicon Carbide Nanoclusters on a Silicon Substrate

The growth of silicon carbide (SiC) nanoclusters by molecular beam epitaxy on silicon substrates has been studied using a combination of experimental and theoretical methods. The first results concerning the initial stages of this growth are presented.

Numerical Analysis of Gasdynamic Aspects of Laser Propulsion

The paper is focused on numerical investigation of the gasdynamic processes accompanying laser beam energy deposition in nozzle of the laser propulsion engine (LPE). Various gasdynamic models were implemented in order to compare their applicability for simulation of the phenomena: (a) perfect ideal gas; (b) equilibrium plasma; (c) non‐equilibrium multi‐temperature plasma, and (d) two‐phase mixture. Numerical method of the simulation is based on high‐resolution Godunov‐type scheme and unstructured adaptive grid technique. Two types of LPE nozzles were considered: parabolic and “toroidal” parabolic. Non‐stationary gasdynamic function distribution and the thrust of the LPE were obtained. Time of gasdynamic parameter relaxation in the nozzle was estimated.

Using the Euler-Euler approach for mathematical modeling of turbulent flows in bubbly media

Results of the development of a mathematical model of turbulent flows in bubbly media are presented. The proposed model is based on the Euler-Euler approach to the description of multiphase flows, which is supplemented by the k-ω-SST model of turbulence with some modifications that make possible (i) the generation of turbulence due to the relative motion of phases and (ii) the turbulence-induced dispersion of bubbles. Investigations performed using the proposed model and the corresponding numerical code provided detailed information on the structure of turbulent flows in bubble columns. The results of calculations show good coincidence with experimental data.

Numerical modeling of flow in a differential chamber of the gas-dynamic interface of a portable mass-spectrometer

Mathematical modeling of flow in the differential chamber of the gas-dynamic interface of a portable mass-spectrometer was carried out to comprehensively study the flow structure and make recommendations for the optimization of the gas-dynamic interface. Modeling was performed using an OpenFOAM open computational platform. Conditions for an optimal operating mode of the differential chamber were determined.

SIMS profiling of GaAs/δ-AlAs/GaAs/… heterostructures using polyatomic ionized oxygen clusters

We have studied the possibility of using polyatomic ions as the primary projectile particles for the depth profiling of solid heterostructures by means of secondary ion mass spectrometry (SIMS) in combination with ion etching. Bombardment of a target by ionized oxygen clusters of the On+ (n=3, 4) type allows the specific impact energy per primary atom to be reduced, which significantly improves the depth resolution. It is shown that a beam of primary On+ (n=3, 4) clusters with the specific impact energy as low as 1 keV per oxygen atom can be obtained using a standard ion source with a magnetic mass separator. High-resolution depth profiles of a test heterostructure of the GaAs/δ-AlAs/GaAs/… type were obtained using a magnetic sector mass spectrometer and a primary beam of O3+ ions with a specific energy of 1 keV per oxygen atom. The experimental data are compared with the results of computer simulation of the ion sputtering process performed using the DITRIRS code.