Improved performance of silicon‐nanoparticle film‐coated dye‐sensitized solar cells

Silicon (Si) nanoparticles with average size of 13 nm and orange–red luminescence under UV absorption were synthesized using electrochemical etching of silicon wafers. A film of Si nanoparticles with thickness of 0.75 µm to 2.6 µm was coated on the glass (TiO₂ side) of a dye‐sensitized solar cell (DSSC). The cell exhibited nearly 9% enhancement in power conversion efficiency (η) at film thickness of ～2.4 µm under solar irradiation of 100 mW/cm² (AM 1.5) with improved fill factor and short‐circuit current density. This study revealed for the first time that the Si‐nanoparticle film converting UV into visible light and helping in homogeneous irradiation, can be utilized for improving the efficiency of the DSSCs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of YBa2Cu3O7−x films at various stages of their growth by medium-energy ion scattering

The initial stages in the formation and growth of yttrium-barium cuprate films have been studied in the course of magnetron sputtering of a ceramic target by combining medium-energy-ion scattering (MEIS) and scanning-electron microscopy. The growth mechanisms of YBa₂Cu₃O_7−x films on MgO and substrates having the perovskite structure, SrTiO₃ and LaAlO₃, at deposition temperatures of 700–780 °C and (Ar+O₂) pressure of ∼70 Pa were found to be essentially different. Simulation of MEIS spectra (H⁺ or He⁺ ions with initial energies of 150–250 keV) and comparison of these results with experimental data revealed that in the first case a film forms from pyramid-shaped islands and, in the second, it grows by a two-dimensional layer-by-layer process starting practically with the first monolayer. For the island mechanism, MEIS permitted determination of the substrate surface coverage and showed the growth of the YBa₂Cu₃O_7−x phase to be paralleled by formation of epitaxial nuclei of a Cu₂O phase. After the first, initial stage in the film formation, the second stage, regular growth within reduced thicknesses of 7–15 nm, sets in. This stage is characterized by a practically complete coverage of the substrate and a stable composition. The third stage, regular growth, of an apparently helical nature, was observed to set in at thicknesses above 100 nm. In this stage, the quality of film structure in the bulk and on the surface was found to be somewhat inferior to that of YBa₂Cu₃O_7−x single crystals and did not depend on substrate type. Fiz. Tverd. Tela (St. Petersburg) 41, 588–595 (April 1999)     

Electronic structure and spatial distribution of the spin density of shallow nitrogen donors in the SiC lattice

The discovery of unique magnetooptical properties of paramagnetic centers in silicon carbide, which make it possible to control spins of small arrays of centers of atomic sizes to single centers at room temperatures, using the techniques of optical detection of the magnetic resonance, posed a number of problems, among which one of the main ones is the creation of conditions under which spin relaxation effects are minimized. As studies of properties of spin nitrogen-vacancy centers in diamond showed, the main contribution to spin relaxation is made by the interaction with nitrogen donors, being a major impurity in diamond. A similar problem exists for silicon carbide, since nitrogen donors are also basic background impurities. The objective of this work is to study the spatial distribution of the spin density of nitrogen donors in two basic silicon carbide polytypes, i.e., 4H-SiC and 6H-SiC, to use this information for minimizing the interaction of nitrogen donors with paramagnetic centers in silicon carbide. The results of the study are analyzed by magnetic resonance methods; the spin density distribution on the nearest coordination spheres of nitrogen donors occupying carbon sites in silicon carbide is determined. It is concluded that paramagnetic centers in the 4H-SiC polytype, including silicon vacancies, can be more stable to the interactions with unpaired donor electrons, since electrons are not localized on the coordination sphere closest to the paramagnetic center in this case.     

Raman spectroscopic studies of vibrational relaxation and non‐coincidence effect in substituted benzaldehyde binary mixtures

The molecular interaction in the binary mixture of 3‐phenoxybenzaldhyde (3Phbz) and 4‐ethoxybenzaldehyde (4Etob) was analysed in four different solvents. The concentration dependence of vibrational relaxation of the CO stretching band of 3Phbz in different solvents was investigated by varying the concentration of the solute molecule in the solvents by performing Raman spectroscopic measurements. The self‐associated nature and the formation of hydrogen‐bonded complexes in the solute molecule, 4Etob, were considered to analyse the wavenumber separation between the peaks of hydrogen‐bonded and free carbonyl groups. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis theory of random energy of train derailment in wind

Based on the analysis theory of random energy of train derailment, an analysis theory of random energy of train derailment in wind is suggested. Two methods are proposed -the time domain method and the frequency domain method of analysis theory of random energy of train derailment in wind. The curves of σ pw -v under various wind speeds are obtained through the computation. The original curve of σ p -v is expanded, which turns the analysis theory of random energy of train derailment into the all-weather theory. Train derailment condition has been established under wind action. The first and second criterions of train derailment have been proposed in light of wind action. The analysis of train derailment cases at home or abroad is made, in- cluding the first analysis of Xinjiang train derailment case encountered 13-level of gale, which explained the inevitability of train derailment. The analysis theory of random energy of train derailment in wind shows its validity and accuracy. The input energy σ pw of the transverse vibration of train-track(bridge)-wind system is linked to train speed. With the establishment of the analysis theory of random energy of train derailment in wind, It is likely to initiate an all-weather speed limit map for a train or any high-speed train.