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991.
992.
Light emitting diodes (LEDs) based on GaN/InGaN material suffer from efficiency droop at high current injection levels. We propose multiple quantum well (MQW) GaN/InGaN LEDs by optimizing the barrier thickness and high–low–high indium composition to reduce the efficiency droop. The simulation results reflect a significant improvement in the efficiency droop by using barrier width of 10 nm and high–low–high indium composition in MQW LED. 相似文献
993.
The modified Jain–Khare semi-empirical formalism for the evaluation of differential and integral electron impact ionization cross sections for molecules has been extended to the evaluation of cross sections for the electron ionization of CO2 clusters: (CO2)240 and (CO2)1700. The energy dependent differential cross sections are evaluated at the incident electron energies of 50, 100 and 200 eV. The integral total ionization cross sections have been calculated in the energy range varying from ionization thresholds to 1000 eV which revealed a good agreement with the available experimental and the theoretical data. The ionization rate coefficients have also been evaluated using the presently calculated ionization cross sections and Maxwell–Boltzmann energy distributions. 相似文献
994.
A general synthetic route to beta-lactam-fused enediynes by intramolecular Kinugasa reaction has been successfully developed. The method has widened the scope of Kinugasa reaction in the synthesis of sensitive systems like the one described in this communication. 相似文献
995.
Salazar-Villanueva M Hernandez Tejeda PH Pal U Rivas-Silva JF Rodríguez Mora JI Ascencio JA 《The journal of physical chemistry. A》2006,110(34):10274-10278
We present a detailed structural analysis for small Tin (n = 2-15) clusters based on ab initio quantum mechanical calculations of their binding energies, frontier orbital gaps, and second energy derivatives. Local density approximation calculations revealed that while the smaller clusters (n < or = 8) prefer hexagonal atomic arrays with bulklike crystal symmetry, the bigger clusters prefer pentagonal atomic arrays. From the stability criteria of the magic number clusters we could identify three magic number clusters Ti7, Ti13, and Ti15. While the most stable configuration of Ti7 is a decahedral bipyramid induced by tetrahedral atomic arrays, the most stable configuration of Ti13 is an icosahedron. The other stable cluster Ti15 takes a closed-shell icosahedron-like configuration with both pentagonal and hexagonal symmetries. The stability of the Tin clusters strongly depends on their geometries and charge states. The HOMO-LUMO gap of the Tin clusters approaches its bulk value for n > 8. While there is not much difference between the HOMO and LUMO isosurface charge distributions for the Ti7 and Ti13 clusters in their most stable configurations, they are very different in the case of Ti15. Such a distinct charge distribution in Ti15 indicates its singular chemical selectivity over the other two magic number clusters. 相似文献
996.
997.
Self-assembly of silver nanoparticles: synthesis, stabilization, optical properties, and application in surface-enhanced Raman scattering 总被引:1,自引:0,他引:1
Panigrahi S Praharaj S Basu S Ghosh SK Jana S Pande S Vo-Dinh T Jiang H Pal T 《The journal of physical chemistry. B》2006,110(27):13436-13444
Silver nanoparticle aggregates were synthesized in large scale using resorcinol under alkaline condition to obtain an assembly of silver clusters. Stable dispersion of the cluster in aqueous medium has been examined out of resorcinol-capped silver nanoparticle assemblies. The UV-vis spectroscopy during the particle evolution has been studied in detail. From the high-resolution TEM (HRTEM) image and XRD pattern it was confirmed that the particles are made of pure silver only. The capping action of resorcinol has been authenticated from the FTIR spectra. UV-vis spectroscopy and TEM images reveal that the temperature, effect of vibrational energy, heat shock, and time-dependent particle evolution have unique bearing on the stability and surface properties of the clusters. The concentrations of silver nitrate, resorcinol, and NaOH have important influence on the particle evolution and its size. TEM images incite us to examine the aggregates to capitulate surface-enhanced Raman scattering (SERS) to the single molecular level using crystal violet (CV) and cresyl fast violet (CFV) as molecular probes. The SERS intensity of CV increases with increasing the size of the silver aggregate. 相似文献
998.
Pande S Ghosh SK Nath S Praharaj S Jana S Panigrahi S Basu S Pal T 《Journal of colloid and interface science》2006,299(1):421-427
This article reports the reduction of methylene blue (MB) by thiocyanate ions (SCN(-)) in aqueous and micellar solutions. Thiocyanate ions are found to be an effective reducing agent for the decolorization of methylene blue under ambient condition. Effects of salting-in and salting-out agents have been investigated for real-time application in the reduction process. The salting-in agent urea has been found to uniquely enhance the rate of the reduction of MB by thiocyanate ion in the presence of micelles. Again, the catalytic activity of nanoparticles in the reduction of MB has also been studied. Detailed kinetic and thermodynamic aspects have been considered to realize the interaction between methylene blue and thiocyanate. Kinetic studies revealed that the reaction is reversible and follows first-order reaction kinetics. 相似文献
999.
Papsai P Aldag J Persson T Elmroth SK 《Dalton transactions (Cambridge, England : 2003)》2006,(29):3515-3517
The anticancer active complex cisplatin interacts preferentially with the common, G-C rich, wobble base pair region of both tRNA(Ala) and Mh(Ala) in a reaction that at pH 6.3 is rate limited by the acid hydrolysis of the metal complex. 相似文献
1000.
The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB7) using ground-state absorption as well as steady-state and time-resolved fluorescence measurements. The results are contrasted to those previously obtained for beta-cyclodextrin (beta-CD; Singh et al. J. Phys. Chem. A 2004, 108, 1465). Both the neutral (NR) and cationic (NRH+) forms of the dye formed inclusion complexes with CB7, with the larger binding constant for the latter (K = 6.5 x 10(3) M(-1) versus 6.0 x 10(5) M(-1)). This result differed from that for beta-CD, where only the neutral form of the dye was reported to undergo sizable inclusion complex formation. From the difference in binding constants and the pK(a) value of protonated neutral red in the absence of CB7 (6.8), an increased pK(a) value of the dye when complexed by CB7 was projected (approximately 8.8). This shift differed again from the behavior of the dye with beta-CD, where a decreased pK(a) value (ca. 6.1) was reported. The photophysical properties of both NR and NRH+ forms showed significant changes in the presence of CB7. Fluorescence anisotropy studies indicated that the inclusion complexes of both forms of the dye rotate as a whole, giving rotational relaxation times much larger than that expected for the free dye in aqueous solution. The thermodynamic parameters for the NRH+.CB7 complex were investigated in temperature-dependent binding studies, suggesting an entropic driving force for complexation related to desolvation of the cation and the removal of high-energy water molecules from the CB7 cavity. 相似文献