The influence of P<Superscript>+</Superscript>, B<Superscript>+</Superscript>, and N<Superscript>+</Superscript> ion implantation on the luminescence properties of the SiO<Subscript>2</Subscript>: nc-Si system

The possible mechanisms of the influence of implanted impurities of Group III and V elements on the luminescence properties of a system consisting of silicon nanocrystals in SiO₂ are considered and generalized. The effect of boron and nitrogen ion implantation on the photoluminescence intensity is investigated experimentally. The experimental results and previously reported data on the ion-implantation doping with phosphorus are discussed in terms of the mechanisms under consideration. The state of implanted phosphorus is determined using x-ray photoelectron spectroscopy. It is shown that the enhancement and degradation of the photoluminescence depend on the type of implanted impurities and the conditions of postimplantation heat treatment.     

Formation and decay kinetics of nickel nitrides resulting from nitrogen ion implantation. The nickel–nitrogen phase diagram

Structural transformations in nickel films exposed to N⁺ ions were investigated through the use of electron diffraction, electron microscopy, Rutherford backscattering (RBS) of He⁺ ions, thermal desorption spectroscopy (TDS).

With an increasing exposure dose, there occurred a smooth transition of the FCC structure of Ni to the HCP phase -Ni₃N with the lattice parameters a=0.266 nm and c=0.430 nm. The completion of the transition was observed once the implanted nitrogen concentration corresponding to the stoichiometric ratio of Ni₃N was attained, this giving evidence for the chemical nature of the structural change observed.

During annealing, structure variations were traced, enabling one to observe the following four nickel nitrides: (1) -Ni₃N with a disordered arrangement of nitrogen atoms (HCP-phase with a=0.266 nm and c=0.430 nm), (2) β-Ni₃N with an ordered arrangement of nitrogen atoms (two hexagonal lattices: one with a=0.266 nm, c=0.430 nm, and the other with a=0.466 nm and c=0.43 nm), (3) Ni₄N having a primitive cubic lattice structure with a=0.377 nm, (4) Ni₈N having the FCC structure with a=0.725 nm.

The results of an investigation have led to building up a phase diagram for the Ni–N system.     

Σ-Definability of countable structures over real numbers, complex numbers, and quaternions

We study Σ-definability of countable models over hereditarily finite {ie193-01} superstructures over the field ℝ of reals, the field ℂ of complex numbers, and over the skew field ℍ of quaternions. In particular, it is shown that each at most countable structure of a finite signature, which is Σ-definable over {ie193-02} with at most countable equivalence classes and without parameters, has a computable isomorphic copy. Moreover, if we lift the requirement on the cardinalities of the classes in a definition then such a model can have an arbitrary hyperarithmetical complexity, but it will be hyperarithmetical in any case. Also it is proved that any countable structure Σ-definable over {ie193-03}, possibly with parameters, has a computable isomorphic copy and that being Σ-definable over {ie193-04} is equivalent to being Σ-definable over {ie193-05}. Supported by RFBR-DFG, grant No. 06-01-04002 DFGa. __________ Translated from Algebra i Logika, Vol. 47, No. 3, pp. 335–363, May–June, 2008.     

Some Properties of Solutions to a Second Order Elliptic Equation with Principal Part of Divergence Form with Potential Concentrated on a Hypersurface

A number of classical results of the theory of second order elliptic equations of divergence form in ℝ ^d, d ⩾ 2, is generalized to problems with singular potential concentrated on a hypersurface of codimension 1. Such results are required, for example, for describing photon crystals. Bibliography: 8 titles. __________ Translated from Problemy Matematicheskogo Analiza, No. 31, 2005, pp. 25–37.     

The invariance of order parameter and temperature redefinition in helix-coil transition theory of circular closed DNA

The order-disorder (helix-coil) transition in circular closed DNA (ccDNA) is described on the basis of the open chain DNA (ocDNA) model, proposed earlier, which considers the transition as loop formation. The Hamiltonian of the ccDNA model is constructed on the basis of the open chain model taking into account topological restrictions. These restrictions are taken into account through hydrogen bond reduced energy dependence on the fraction of broken hydrogen bonds in the macromolecule. The invariance of the order parameter (helicity degree) has been shown for ocDNA and ccDNA. This invariance results in the interdependence between temperatures of ocDNA and ccDNA with the same value of helicity degree. The dependence can be obtained with the help of the derivative of reduced energy of hydrogen bonding dependence on instantaneous denaturation degree. Thus, it has been shown that the melting curve of ccDNA can be obtained from the consequent curve of ocDNA through the redefinition of temperature scale. The calculated and experimentally measured melting curves have been compared under inversion conditions and qualitative agreement between them is found.     

Plasticization of NaCl crystals under the combined action of short mechanical and magnetic pulses

The dynamic yield stress of NaCl crystals is found to decrease under loading with a mechanical pulse of submicrosecond duration initiated by an electron beam preceded by a pulse of a vortex electromagnetic field (the time delay is 10^?6 s). This effect becomes more pronounced as the intensity of loading increases.