The research of defect formation and clusterization processes by means of a molecular dynamics method both in nc-TiN nanocrystals and amorphous a-Si3N4 matrix, as the constituents of nc-TiN/a-Si3N4 nanocomposite, under exposure to Xe implantation was the aim of the present study. Dependences of the clustered Xe atoms fraction on their concentration and temperature of post-irradiation annealing were analyzed. At defect formation process in nc-TiN nanocrystals, there is a size effect consisting in intensification of the radiation point defects formation with the reduction of nc-TiN nanocrystals size and concurrent predominant formation of the dangling Si- and N-bonds in a-Si3N4 matrix. Accumulation of these defects at the irradiation leads to amorphization of nc-TiN nanocrystals with the size less than 8 nm and to formation of the nanopores in a-Si3N4 matrix. The important role of the radiation defects subsystem in transport processes of implanted Xe both in TiN close-packed lattice as well as in a-Si3N4 amorphous matrix is shown. There is a much higher extent of intensity of xenon atoms clusterization processes in the amorphous matrix. The results of the simulation are compared to existing experimental data. (C) 2017 Elsevier B.V. All rights reserved.

In the present work the influence of nc-TiN nanocrystals on the elastic properties of nc-TiN/a-Si3N4 nanocomposite is discussed. The elastic moduli (shear modulus, compression modulus, Young’s modulus) for both amorphous matrix a-Si3N4 and nc-TiN nanocrystals of different size were calculated by first-principles method and molecular static method correspondingly. The Volkov-Stavrov approach was applied for modeling elastic properties of nanocomposite taking into account size and volume fraction of the TiN inclusions. The results of modeling showed the increase the effective elastic moduli of the nc-TiN/a-Si3N4 nanocomposite with nc-TiN inclusions size and volume fraction growth. The obtained results are compared to the experimental data.

Today submicron silicon-on-insulator (SOI) MOSFET structures are widely used in different electronic components and also can be used as sensing elements in some applications. The development of devices based on the structures with specified characteristics is impossible without computer simulation of their electric properties. The latter is not a trivial task since many complicated physical processes and effects must be taken into account. In current study ensemble Monte Carlo simulation of electron and hole transport in deep submicron n-channel SOI MOSFET with 100 nm channel length is performed. The aim of the study is investigation of the influence of interband impact ionization process on the device characteristics and determination of the transistor operation modes when impact ionization process starts to make an appreciable influence on the device functioning. Determination of the modes is very important for adequate and accurate modeling of different devices on the basis of SOI MOSFET structures. Main focus thereby is maid on the comparison of the use of two models of impact ionization process treatment with respect to their influence on the transistor current-voltage characteristics. The first model is based on the frequently used Keldysh approach and the other one utilizes the results obtained via numerical calculations of silicon band structure. It is shown that the use of Keldysh impact ionization model leads to much faster growth of the drain current and provides earlier avalanche breakdown for the SOI MOSFET. It is concluded that the choice between the two considered impact ionization models may be critical for simulation of the device electric characteristics.

The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the "loop of extrema" both in the valence and conduction bands near the center of the cubic Brillouin zone.

A theoretical modeling of the formation of Frenkel pairs and the diffusion of a self-interstitial atom in silicon crystals at normal and high (hydrostatic) pressures has been performed using molecular dynamics, semiempirical quantum-chemical (NDDO-PM5, PM6), and ab initio (SIESTA) methods. It is shown that, in a silicon crystal, the most stable configuration of a self-interstitial atom in the neutral charge state (I 0) is the split configuration 〈110〉. The shifted tetrahedral configuration (T 1) is stable in the singlet and triplet excited states, as well as in the charge state Z = +2. The split 〈110〉 interstitial configuration remains stable under hydrostatic pressure (P ≤ 80 kbar). The activation barriers for diffusion of self-interstitial atoms in silicon crystals are determined to be as follows: ΔE a (Si)(〈110〉 → T 1) = 0.59 eV, ΔE a (Si)(T 1 → T′1) = 0.1 eV, and ΔE a (Si)(T 1 → 〈110〉) = 0.23 eV. The hydrostatic pressure (P ≤ 80 kbar) increases the activation barrier for diffusion of self-interstitial atoms in silicon crystals. The energies of the formation of a separate Frenkel pair, a self-interstitial atom, and a vacancy are determined. It is demonstrated that the hydrostatic pressure decreases the energy of the formation of Frenkel pairs.

By means of first principles calculations, we have investigated the band structures of different phases of higher manganese silicides ($\mathrm{Mn}{\mathrm{Si}}_{x}$ with $x$ ranging from 1.73 to 1.75). In this family, ${\mathrm{Mn}}_{11}{\mathrm{Si}}_{19}$, ${\mathrm{Mn}}_{15}{\mathrm{Si}}_{26}$, and ${\mathrm{Mn}}_{27}{\mathrm{Si}}_{47}$ have been found to behave like degenerate semiconductors and, at the same time, like metals because the Fermi level stays partly in the energy gap and partly in the valence band close to its top. The spin-polarized calculations have revealed that these phases can be also treated as half-metals displaying 100% spin polarization of holes at the Fermi energy. On the contrary, ${\mathrm{Mn}}_{4}{\mathrm{Si}}_{7}$ is shown to be a semiconductor with the indirect band gap of $0.77\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Its dielectric function possesses some anisotropy effects with respect to different light polarizations. We have also discovered that the $\mathrm{Mn}{\mathrm{Si}}_{1.75}$ stoichiometry provides semiconductor properties without degeneracy. The role of stacking faults in the gap reduction of higher manganese silicides is discussed.

A theoretical modeling of the diffusion of self-interstitials in silicon and germanium crystals both at normal and high hydrostatic pressure has been carried out using molecular mechanics, semiempirical (PM3, PM5) and ab-initio (SIESTA) methods. According to the simulation for the Si and Ge neutral interstitials (I0) both in silicon and germanium crystals more stable configuration is <110> split interstitial. T is the stable configuration for the double positive interstitial I++, but the interstitial is displaced from the high-symmetry site. Stability of <110> splitinterstitial is not changed under hydrostatic pressure. The activation barriers for the diffusion of interstitials were determined and equal to ΔEa(Si)(<110> -> T1)=0.69 eV; ΔEa (Ge)(<110> -> T1)=1.1 eV. For mixed interstitials the calculated activation barriers equal Si Emix = 1.06 eV, Ge Emix = 0.86 eV. Hydrostatic pressure decreases the activation barriers ΔEa(Si), ΔEa (Ge).

By means of ab initio calculations we have revealed a newly discovered Ca3Si4 compound to be a semiconductor. It is characterized by an indirect transition of 0.35 eV. A peculiar dispersion of the last valence band and the first conduction band, displaying a loop of extrema, has been found. This feature leads to large anisotropy of the mobility of holes and electrons. We also present the dielectric function of this material in comparison with data for another semiconducting calcium silicide Ca2Si.

First‐principles calculations of the band structure and the dielectric function of Ir 3 Si 5 are presented. We find this compound to be characterized by an indirect band gap of 0.97 eV. A number of direct transitions of about 1 eV have been also determined. Features in the dependence of the imaginary and real parts of the dielectric function on photon energy are discussed in comparison with data for some other semiconducting silicides. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The formalism of the linear augmented Slater-type orbital method in the LDA + U approximation is described. All the expressions necessary for the program implementation of this method are derived, and the electronic structure of the ferromagnetic compounds MeB6 (Me = La, Gd) is calculated. The results obtained can be used in analyzing experimental data for rare-earth hexaborides.

Certain aspects of spin-dependent kinetic theory of conductivity for Fe-containing graphite composites have been considered, in particular those concerning charge transport along carbon nanotubes. Band structure simulations have been performed taking into account spin polarization and assumption of ferromagnetic ordering of Fe atoms in graphite composite. It has been demonstrated that infinite log-like barriers which corresponded to Coulomb screening potential in 1D wires are partially penetrable for stochastically driven particle in diffusion approximation.

The long-range charge transfer correlated with the existence of fractal nanostructure for thin Fe-containing Langmuir-Blodgett (LB) films of thiophene derivatives has been experimentally observed. Band structure of the film with hexagon crystal structure has been simulated assuming 26 carbon atoms and one(or two) Fe atom in cluster in elementar cell and validity of adiabatic approximation. The simulations display, that the energy of the structure is reduced when taking into account the ferromagnetic ordering. This leads to the stabilization of the structure. Dynamically invertible instability of band structure at changes of spin polarization is considered as appearance of photo-induced quasi-steady states of nanostructured LB-films. Temperature Green function method has been proposed to examine relativistic corrections for Fermi system which are caused by non-sphericity of atom potential in leaky packed solids. The origin of quasi-stationary modes in Dirac problem is considered for an electron in the vicinity of the ionization threshold in a strong oscillating magnetic field.

The physical properties of the stoichiometric compounds in the series Ti-Zr-N are studied theoretically, including electronic structure calculations by the linear augmented Slater orbitals method, as well as calculation of the bulk elastic moduli and the equilibrium lattice constant. The results obtained can be used for determining the phases of the materials used for protective coatings.

Theoretical findings supporting semiconducting properties of the ReSi1.75 phase were originally obtained by ab initio Linear muffin-tin orbital method. The material was shown to be a narrow-gap semiconductor with indirect transition value of 0.16 eV. The first direct transition with appreciable oscillator strength at 0.30 eV is predicted.

Electronic band structure calculations of Nowotny ``chimney-ladder'' isostructural ruthenium and osmium silicides and related germanides have been performed by the linear muffin-tin orbital method within the local density approximation. Both silicides have been found to be direct gap semiconductors with energy gaps of 0.41 and 0.95 eV in ${\mathrm{Ru}}_{2}{\mathrm{Si}}_{3}$ and ${\mathrm{Os}}_{2}{\mathrm{Si}}_{3},$ while the band gaps in the germanides have a competitive indirect-direct character with gaps of about 0.3 and 0.9 eV in ${\mathrm{Ru}}_{2}{\mathrm{Ge}}_{3}$ and ${\mathrm{Os}}_{2}{\mathrm{Ge}}_{3},$ respectively.

The Green function method based on the proposed modified numerical methods of tetrahedrons in the case of nonlocal distribution of electron density in solids and nonspherical interatomic potential in complex energy-momentum space has been developed.