排序方式: 共有173条查询结果,搜索用时 31 毫秒
81.
M. Esmaeili M. Gholami H. Haratizadeh B. Monemar P. O. Holtz S. Kamiyama H. Amano I. Akasaki 《Opto-Electronics Review》2009,17(4):293-299
We report the results from detailed optical spectroscopy from MOCVD grown GaN/AlGaN multiple quantum wells (MQWs), as opposed
to most previous studies where MBE was employed by means of photoluminescence (PL) technique. In this paper we will present
theoretical and experimental results demonstrating how polarization induced electric fields and bound interface charges in
GaN/AlGaN MQWs affect the emission peak energy, PL line shape, as well as the emission line width. Theoretically estimated
fields in this work are consistent with experimental data. Transition energy of the heavy hole and electron ground state Ee-hh
in GaN/AlGaN MQWs were calculated and it is found that it stays in good agreement with the experimental data. 相似文献
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Herein, one-pot synthesis of pyrimido[4,5-b]quinoline and indenopyrido[2,3-d]pyrimidine derivatives was developed by the three-component reaction of aldehydes, 6-amino-1,3-dimethyluracil, and 1,3-dicarbonyl compounds in the presence of glycolic acid-supported cobalt ferrite CoFe2O4@SiO2@Si (CH2)3NHCOOCH2COOH as a novel magnetic catalyst in ethanol at reflux conditions. Glycolic acid-supported cobalt ferrite was characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). Moreover, the catalyst was easily recovered with magnetic separation and recycled at least for five times without significant loss of its catalytic activity. The products were formed in excellent yields over appropriate reaction times under environmentally friendly conditions. The high efficiency and easy isolation of catalyst from products with an external permanent magnet are some of the remarkable advantages of this method. 相似文献
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Due to many important applications, the group III-nitride semiconductors have recently attracted remarkable attention among the semiconductor researchers and engineers. In this paper, we report on the impact of the extrinsic and temporal carriers on the screening of the polarization internal fields. The optical efficiency of GaN/AlGaN multiple quantum well (MQW) nanostructures were studied by means of photoluminescence (PL) and time-resolved PL measurements. Extrinsic carriers come from Si doping in the barriers while temporal carriers originate when the samples are excited by the laser beam. The emission peaks of MQWs in PL spectra of the undoped and low-doped samples show a shift towards higher energy levels as excitation intensity increases, while the other samples do not exhibit such a phenomenon due to the dominance of the extrinsic carriers. The transient data confirm the results of the PL measurements. 相似文献
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New dichromophoric cyanine dyes based on benzothiazol‐2‐amines as push? pull systems were synthesized in two series of disperse and cationic forms (see 4 in Scheme 1 and 5 in Scheme 2, resp.). Their thermal stabilities, UV/VIS, fluorescence, and solvatochromic behavior, which are important parameters in push? pull systems, were also studied. 相似文献
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Kuki Á Nagy L Shemirani G Memboeuf A Drahos L Vékey K Zsuga M Kéki S 《Rapid communications in mass spectrometry : RCM》2012,26(3):304-308
Dissociation of doubly cationized polyethers, namely [P + 2X]2+ into [P + X]+ and X+, where P = polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetrahydrofuran (PTHF) and X = Na, K and Cs, was studied by means of energy‐dependent collision‐induced dissociation tandem mass spectrometry. It was observed that the collision voltage necessary to obtain 50% fragmentation (CV50) determined for the doubly cationized polyethers of higher degree of polymerization varied linearly with the number of degrees of freedom (DOF) values. This observation allowed us to correlate these slopes with the corresponding relative gas‐phase dissociation energies for binding of alkali ions to polyethers. The relative dissociation energies determined from the corresponding slopes were found to decrease in the order Na+ > K+ > Cs+ for each polyether studied, and an order PPG ≈ PEG > PTHF can be established for each alkali metal ion. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Morteza Gholami Alireza Ghassempour Reza Alizadeh Hassan Y. Aboul‐Enein 《Journal of separation science》2009,32(7):918-922
Vancomycin crystalline degradation products (CDPs) have been introduced as one of the newest and most interesting derivatives of vancomycin for enantiomer separation of a wide variety of chiral compounds. In this attempt, a chiral stationary phase (CSP) has been prepared using diol silica gel based on vancomycin CDPs which led to a new chiral selector with new functionality of functional groups on a microcolumn LC. Different kinds of mobile phases were examined to realize the behavior of the chiral selector in separation of atropine, fluoxetine, amlodipine, mandelic acid, alanine, and phenylalanine which were separated successfully on this column. Good results were obtained by using a polar mobile phase containing water, methanol, and acid additives for separation of chiral acidic compounds and amino acid samples. Considerable results were obtained for analysis of basic compounds by using polar organic mobile phase (POP) containing methanol, acid and base additives. These results can be associated with the presence of the carboxylic acid groups present in new CSP by using a diol silica gel. 相似文献
90.
Harifi-Mood AR Habibi-Yangjeh A Gholami MR 《The journal of physical chemistry. B》2006,110(13):7073-7078
The solvatochromic parameters (ET(N), normalized polarity parameter; pi*, dipolarity/polarizability; beta, hydrogen-bond acceptor basicity; alpha, hydrogen-bond donor acidity) were determined for binary solvent mixtures of 1-(1-butyl)-3-methylimidazolium tetrafluoroborate ([bmim]BF4) with water, methanol, and ethanol at 25 degrees C over the whole range of mole fractions. In nonaqueous solutions, the value of the mixture increases with mole the fraction of [bmim]BF4 and then decreases gradually to the value of pure [bmim]BF4. Positive deviation from ideal behavior was observed for the solvent parameters ET(N), pi*, and alpha, whereas the deviation of the beta parameter is negative. The applicability of the combined nearly ideal binary solvent/Redlich-Kister equation for the correlation of various solvatochromic parameters with solvent composition was proved too for the first time. This equation provides a simple computational model to correlate and/or predict various solvatochromic parameters for many binary solvent systems. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute-solvent and solvent-solvent interactions have been applied for interpretation of the results. 相似文献