Y. V. Vorobiev

Characterization of sol–gel glasses with different copper concentrations treated under oxidizing and reducing conditions

Abstract Using the sol–gel process SiO 2 coating and powdered samples doped with different concentrations of copper were prepared. Two sets of samples were made: one was thermally treated in air atmosphere, and the other, was annealed under a CO atmosphere. Both sets of samples were characterized using X-ray diffraction, optical transmission spectroscopy, photoacoustic absorption spectroscopy (PAS) in the visible and near infrared region and electron paramagnetic resonance (EPR). It is found that the chemical state of the copper depends on the type of treatment, amount of copper and the temperature of the treatment. The formations of CuO or Cu colloidal particles occur after the thermal treatments in air or in the CO atmosphere, respectively. In both cases, copper is found in the Cu 2+ state in interstitial positions and probably substituting the Si atoms in the SiO 2 matrix. The evolution of the optical absorption spectrum as function of the Cu content is a consequence of the changes in the composition and size of the colloidal particles. The optical and the PAS measurements are found to be complementary tools to elucidate the origin of the blue band in the absorption spectrum of these doped samples.

Peculiarities of Raman scattering in bioconjugated CdSe/ZnS quantum dots

The article presents the results of analysis of Raman scattering spectra of non-conjugated and bioconjugated CdSe/ZnS core-shell quantum dots (QDs). Commercial CdSe/ZnS QDs used covered by polymer are characterized by color emission with the maxima at 605-610 nm (2.03-2.05 eV). The bioconjugation process is performed to biomolecules-the antihuman Interleukin 10 (IL10) antibodies (mab). Raman scattering spectra measured at room temperature with excitation by a He-Ne laser line (632.8 nm) demonstrate two groups of peaks: (1) related to the Si substrate at 230-460, 522, 610, 670, 940-1040 cm(-1) and (2) to the PEG polymer on the QD surface in the range of 837-3320 cm(-1). It is revealed that the CdSe/ZnS QD bioconjugation to the antihuman Interleukin 10 antibodies is accompanied with the dramatic changes in the intensity of the Raman lines of both types: the intensity of the Si related line increases six- or ten-fold, but the intensity of the polymer related line decreases ten-fold. The models explaining the mentioned effects in Raman scattering spectra have been discussed.

Optimization of the solar energy collection in tracking and non-tracking photovoltaic solar system

Experimental and theoretical analysis is made of the conditions of collection of solar radiation in solar tracking system without concentration, and in non-tracking system with standard and bifacial photovoltaic solar panel. For the experiments with solar tracking, an original Sun tracker was developed. The tracking effect calculated and measured shows an increase in energy collection around 30 - 40 %; bifacial panels with a reflector collecting solar radiation for the rear face give the corresponding increase of 50 - 60 % for the same panel area.

Oxygen diffusion in silicon oxide films produced by different methods

Thin films of silicon oxide were prepared on copper substrates using several techniques, such as DC sputtering, sol-gel and microwave decomposition of gases (SiH4 and O2). The sol-gel films were made using a conventional mixture of tetraethoxysilane (TEOS), water and ethanol, with various TEOS/water ratios. The oxygen diffusion coefficient is found from the thickness of the copper oxide layer formed at the copper–SiO2 interface, which was estimated from reflectivity and Auger spectroscopy measurements. Thermal treatments at various temperatures allowed us to determine the temperature dependence of the diffusion coefficient. It is found that the diffusion coefficient depends on the method of preparation of the SiO2 layer, which could be related to differences in the structure of the oxide layer. This conclusion is confirmed by the dielectric breakdown measurements. It follows from the results obtained that the oxygen diffusion constants and the dielectric breakdown field could be the indicators of the structural quality of silica.

Semiconductor II-VI Quantum Dots with Interface States and Their Biomedical Applications

Nanocrystals of group II-VI semiconductors, known as quantum dots (QDs), in which electrons and holes are three dimensionally confined within the exciton Bohr radius of the material, are characterized by the exceptional optical properties, such as broad absorption and sharp emission bands as well as size-tunable photoluminescence in the visible spectral range. The most popular are CdSe/ZnS QDs due to their bright and unique emission with the wide excitation spectra and narrow emission bandwidths (Bailey et al., 2004; Dybiec et al., 2007; Jamieson et al., 2007; Kune et al., 2001; Norris et al., 1996; Tessler et al., 2002). The II-VI QDs have been investigated in versatile photonic applications including solar cells (Choi et al., 2006; Kongkanand et al., 2008; Lopez-Luke et al., 2008), optical fibre amplifiers (Liu et al., 2007), color displays using light-emitting diode arrays (Huang et al., 2008: Klude et al., 2002; Zhao et al., 2006), optical temperature probes (Liang et al., 2006; Walker et al., 2003), as well as in biology and medicine (Alivisatos et al., 2005; Grodzinski et al., 2006; Hoshino et al., 2007; Murcia et al., 2008; Portney & Ozkan, 2006; Wang et al., 2007). Note that metal, semiconductor, polymer and ceramic nanoparticles in general have gained essential interest for biological and medical applications (Brigger, et al., 2002). Polymer and ceramic nanoparticles have been widely used as drug carriers, whereas metal nanoclusters and semiconductor QDs have been applied mainly for imaging and therapy. Among various nanoparticles, semiconductor QDs attracted much attention due their exceptional optical properties. In comparison with organic dyes and fluorescent proteins, the semiconductor quantum-confined core/shell nanostructures, such as CdSe/ZnS QDs, are brighter, more stable against photo bleaching, have multicolor emission in dependence on core sizes and can be excited for this emission with a single light source. The size-tunable properties allow one to choose an emission wavelength that is well suited to experimental conditions and to synthesize the QD-based probe by using an appropriate semiconductor materials and nanocrystal sizes. In biology and medicine the semiconductor QDs have been used: for the fluorescence resonance energy transfer (FRET) analysis (Bailey et al., 2004; Jamieson et al., 2007; Zhang et al., 2005), in gene technology (Gerion et al., 2002; Han et al., 2001; Pathak et al., 2001), fluorescent labeling of cellular proteins (Dubertret et al., 2002; Dubertret et al., 2003; Hanaki

The effects of porosity on optical properties of semiconductor chalcogenide films obtained by the chemical bath deposition

This paper is dedicated to study the thin polycrystalline films of semiconductor chalcogenide materials (CdS, CdSe, and PbS) obtained by ammonia-free chemical bath deposition. The obtained material is of polycrystalline nature with crystallite of a size that, from a general point of view, should not result in any noticeable quantum confinement. Nevertheless, we were able to observe blueshift of the fundamental absorption edge and reduced refractive index in comparison with the corresponding bulk materials. Both effects are attributed to the material porosity which is a typical feature of chemical bath deposition technique. The blueshift is caused by quantum confinement in pores, whereas the refractive index variation is the evident result of the density reduction. Quantum mechanical description of the nanopores in semiconductor is given based on the application of even mirror boundary conditions for the solution of the Schrödinger equation; the results of calculations give a reasonable explanation of the experimental data.

Automatic sun tracking solar electric systems for applications on transport

Technical and economical aspects of application of solar electric systems in city transport are discussed, with the possible use of Sun tracking; the effect of the latter on the solar energy conversion efficiency is analyzed in application to stationary and moving platforms with photovoltaic solar panels. The option of using grid-connected solar panels is taken into account. An analysis made shows that introduction of the “green” systems discussed will have not only positive ecological impact, but it can also be economically justified.

Analytical solution of the Schrödinger equation for an electron confined in a triangle-shaped quantum well

For the triangular-shaped quantum well, the electron wave functions and energy values are found by analytical solution of the Shrodinger equation. In approximation of impenetrable walls, two sets of solutions are obtained, one corresponding to the symmetric, and the other to antisymmetric wave functions. The distributions of the probability density give a clear picture of standing waves in a triangular-shaped plate. The comparison of the system energy levels with those obtained for quasi-periodic boundary conditions give reasonable coincidence. The results obtained proved to be useful in explanation of electronic optical absorption spectra of some of the organic colorants, on the basis of FEMO approach (free electron molecular orbitals); it could be used for other nanosystems with particles of triangular shape.

Structural Evolution of Colloidal Particles in Porous SiO2 Coatings.

The sol-gel method has been used to produce samples having colloidal copper-based particles embedded in a SiO2 matrix. The particle composition depended on: the atmosphere in which the samples were annealed, the annealing temperature and the time after the treatment. The optical properties of the colloidal system were determined, as a function of the sample history. For that, the model proposed by Mie was used with effective values for the optical constants of the colloidal particles. From this analysis, characteristic parameters of the colloidal system and particle composition were determined.

Electric and photoelectric properties of semi-insulating crystals of CdTe:Pb

Abstract CdTe:Pb monocrystals were grown by the Bridgemann method. The impurity concentration in the melt was in the ranges of N Pb 0 =10 18 –5×10 19 cm −3 . From the electric measurements it turns out that the lead creates deep levels with E V +0.43 eV in CdTe. At the mentioned concentrations, N Pb 0 the hole concentration is (6.11×10 9 –1.98×10 13 ) cm −3 . From the photoelectric measurements it follows that recombination processes in CdTe:Pb could be explained by the presence of the defects with significantly different trapping cross-sections of electrons and holes ( S pr ≫ S nr ). The trapping asymmetry of the mentioned centers was defined to be S pr / S nr >10 6 .