Visible Luminescence of SiGe/Si Quantum Wells Under an External Anisotropic Deformation

We realize for the first time an experimental investigation of the IR and visible luminescence of SiGe/Si heterostructures with quantum well subjected to an external anisotropic deformation. We show that tensile strain along the [100] direction enhances the absolute and relative intensities of visible luminescence by a factor of 7/3 at a temperature of 5 K. This effect is absent for a tensile strain along the [110] direction. We explain the phenomenon observed in view of the model of single-photon biexciton recombination for the system in which the bottom of the conduction band is formed by only two opposite electronic valleys.     

Visible luminescence enhancement methods in SiGe/Si heterostructures

The possibility of increasing the photoluminescence signal of Si1?xGex/Si quantum wells in the visible spectral range due to a change in the conduction band structure and the interaction of many-body states with plasma oscillations of metal nanoparticles is studied. The sample band structure was controlled using a uniaxial strain of ～10?4. It is found that such an approach allows an increase in the emission intensity of biexcitons in the quantum well (x = 9%) by a factor of 2.4 at a temperature of 5 K. Metal nanoparticles deposited on the sample surface with a protective layer thickness of 20 nm allowed us to increase the luminescence intensity of quantum wells approximately by a factor of 2.7.     

TeV-scale leptoquarks from GUTs/string/M-theory unification

The question of a possible existence of the “baroleptons” (leptoquarks) at the TeV energy scale is considered. Leptoquark mass and coupling bounds coming from rare meson decays are briefly reviewed.     

Impurity–defect emission from undoped Cd<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Zn<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te single crystals near the fundamental absorption edge

Shallow impurity–defect states in undoped Cd_1–xZn_xTe (x ～ 3–6%) single crystals have been studied using low-temperature photoluminescence measurements. It has been found that the effect exerted by zinc is mainly reduced to a rigid shift of all the specific features associated with the exciton radiation, which made it possible, with a high (～0.3 meV) accuracy, to measure the band gap and the zinc concentration in solid solutions. Hydrogen-like donors with the ground-state energy of ～14 meV and four types of acceptors with average activation energies of 59.3 ± 0.6 meV, 69.6 ± 1.5 meV, 155.8 ± 2.0 meV, and 52.3 ± 0.6 meV have been identified in all the crystals studied. Based on a comparison with the results of the analysis of the impurity background and the data available in the literature on impurity–defect emission in undoped CdTe, the first three acceptors can be assigned to the substitutional impurities Na_Cd, P_Te, and Cu_Cd, respectively. The most shallow acceptor (52.3 ± 0.6 meV) is a complex defect in which there is a nonstandard excited level separated by only 7 meV from the ground level. This level is formed apparently due to the removal of degeneracy, which is characteristic of T_D acceptors, by the low-symmetry potential of the complex defect.     

Catalytic properties of Pd-containing systems based on SBA-15 molecular sieve modified with imidazolium ionic liquid

Palladium(II) ions were incorporated in SBA-15 molecular sieve modified with imidazolium-based ionic liquids. The synthesized materials were characterized using differential thermic analysis, low-temperature nitrogen adsorption, transmission electron spectroscopy and elemental analysis. The materials obtained basing on a grafted ion liquid, in 1-hexene hydrogenetion were shown to exhibit the catalytic activity significanly higher than those prepared via ion liquid adsorption on supports.     

Nonstandard Features of the Interaction of Single Luminescent Centers Formed by Partial Dislocation Cores in CdTe and ZnSe with Longitudinal Optical Phonons

JETP Letters - Low-temperature (5 K) microphotoluminescence has been measured in order to study individual luminescent centers formed by the cores of partial dislocations in a CdTe/Si film and a...     

The center of a rational cohomology algebra for some loop spaces with respect to the Pontryagin product

We solve the problem of calculation of the center of the rational cohomology algebra H*(ΩX;?) of the loop space of simply connected four-dimensional manifolds with the Pontryagin product. The well-known results of Milnor and Moore represent H*(ΩX) as a universal enveloping Lie algebra π*(ΩX) endowed with the Whitehead-Samelson bracket. Neisendorfer obtained a representation of the algebra Π*(ΩX) ? ? in terms of generators and relations for the case when X is a simply connected four-dimensional manifold. In this paper, the center Z(H*(ΩX;?)) is calculated using this representation.