Correlation between energy positions of deep intrinsic point-defect levels and a limiting fermi level in irradiated III–V semiconductors

The energy levels of neutral anion (V_A) and cation (V_C) vacancies and antisite defects are calculated for the anion C_A and cation A_C sublattices of III–V semiconductors. An averaged energy level position for these defects is estimated to be E_av ^abs = 4.9 eV. The position coincides with the local charge electroneutrality level. It is shown that the case, where the total energies of formation of V_A, V_C and antisite C_A, A_C defects in the sublattices of binary semiconductors are similar, corresponds to the point-defect equilibrium condition and stabilization of the Fermi level in the proximity of the local charge electroneutrality level. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 17–22, May, 2007.     

Electronic spectrum and ballistic transport in a helical nanotube

A model of a helical nanotube permitting analytical calculation of the spectrum and wave functions is proposed and studied. It is shown that the specific character of the symmetry of the Hamiltonian results in an electronic spectrum having no band structure despite the periodicity of the potential along the system axis. A two-dimensional ribbon rolled into a helix and a quasi-one-dimensional helix in a magnetic field are considered as limiting cases of the model. It is shown that the presence of additional local minima in the subbands of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential.     

Inclusion of cinnamaldehyde in modified γ-cyclodextrins

This work deals with the formation of inclusion complexes between cinnamaldehyde and two synthetic alkylcarbonates of γ-cyclodextrin, namely ethylcarbonate-γ-CD and octylcarbonate-γ-CD. Complexation was monitored by phase-solubility studies, by FT-IR spectroscopy and by DSC and TG analysis. The diffusion of cinnamaldehyde through a cellulose membrane was investigated in the absence and in the presence of each of the two γ-CD alkylcarbonates. Studies on photostability and stability over time were carried out on different cosmetic formulations containing pure cinnamaldehyde or an equivalent amount of cinnamaldehyde complexed with the two alkylcarbonates. Phase-solubility diagrams, DSC, FTIR and TGA analysis suggested the formation of inclusion complexes. The diffusion of cinnamaldehyde through the cellulose membrane decreased in the presence of the two alkylcarbonates confirming the interaction of this molecule with the inclusion agents. Moreover the stability of cinnamaldehyde to light and heat resulted increased by complexing this fragrance material with the two alkylcarbonates.     

Differentiation of species of the Baccharis genus by HPLC and chemometric methods.

Phytochemical investigation of the aerial parts of three Baccharis species (Asteraceae family) was performed using HPLC and chemometric methods, with the objective of distinguishing between three morphologically very similar species: Baccharis genistelloides Persoon var. trimera (Less.) DC, B. milleflora (Less.) DC and B. articulata (Lam.) Persoon. With the help of Principal Component Analysis (PCA) and variance weights, it was possible to characterize the chromatographic profiles of the alcoholic extracts of the three species. Application of Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN) methods on a training set of 74 extracts resulted in models that correctly classified all eight samples in an independent test set.     

Isotopic production cross sections of residues in reactions induced by relativistic heavy ions with protons and deuterons

The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets.     

Diffuse x-ray scattering study of the formation of microdefects in heat-treated dislocation-free large-diameter silicon wafers

Diffuse x-ray scattering (DXS) is used to study the formation of microdefects (MDs) in heat-treated dislocation-free large-diameter silicon wafers with vacancies. The DXS method is shown to be efficient for investigating MDs in silicon single crystals. Specific defects, such as impurity clouds, are found to form in the silicon wafers during low-temperature annealing at 450°C. These defects are oxygen-rich regions in the solid solution with diffuse coherent interfaces. In the following stages of decomposition of the supersaturated solid solution, oxide precipitates form inside these regions and the impurity clouds disappear. As a result of the decomposition of the supersaturated solid solution of oxygen, interstitial MDs form in the silicon wafers during multistep heat treatment. These MDs lie in the {110} planes and have nonspherical displacement fields. The volume density and size of MDs forming in the silicon wafers at various stages of the decomposition are determined.     

Quantum memory on the basis of photon echo in three-level optically dense gaseous media with the Ξ-configuration of atomic transitions

A new variant of realization of quantum memory based on the use of a photon echo in an optically dense three-level gaseous medium is proposed. The use of a long-lived highly excited optical level as a storage of quantum information is the characteristic feature of the scheme proposed. This scheme of quantum memory is distinguished by reduced optical noises owing to the possibility of realizing temporal, spectral, and spatial selection of weak quantum radiation relative to the accompanying laser pulsed fields.