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91.
Zinc oxide nanoparticles were synthesized using chemical method in alcohol base. During synthesis three capping agents, i.e. triethanolamine (TEA), oleic acid and thioglycerol, were used and the effect of concentrations was analyzed for their effectiveness in limiting the particle growth. Thermal stability of ZnO nanoparticles prepared using TEA, oleic acid and thioglycerol capping agents, was studied using thermogravimetric analyzer (TGA). ZnO nanoparticles capped with TEA showed maximum weight loss. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for structural and morphological characterization of ZnO nanoparticles. Particle size was evaluated using effective mass approximation method from UV-vis spectroscopy and Scherrer's formula from XRD patterns. XRD analysis revealed single crystal ZnO nanoparticles of size 12-20 nm in case of TEA capping. TEA, oleic acid and thioglycerol capped synthesized ZnO nanoparticles were investigated at room temperature photoluminescence for three excitation wavelengths i.e. 304, 322 and 325 nm, showing strong peaks at about 471 nm when excited at 322 and 325 nm whereas strong peak was observed at 411 for 304 nm excitation. 相似文献
92.
K. Hyomi 《Journal of luminescence》2009,129(12):1715-1717
We present a micro-photoluminescence (m-PL) study of electron-spin injection under magnetic fields in self-assembled semiconductor quantum dots (QDs) of CdSe. A characteristic band line-up of the CdSe QDs coupled with a diluted magnetic semiconductor quantum well (DMS-QW) of ZnCdMnSe through a ZnSe barrier layer enabled us to inject the electron spins from the DMS-QW into QDs. An experimental evidence of the electron-spin injection was provided by observations of circularly polarized m-PL spectra from individual QDs in this coupled QD structure. We find anti-correlation of PL intensity in between the DMS-QW (spin injector) and the individual QDs (spin receiver). 相似文献
93.
Dandan Wang Jinghai Yang Guozhong Xing Lili Yang Ming Gao Tom Wu 《Journal of luminescence》2009,129(9):996-22735
Single-crystalline ZnO nanowires (NWs) were synthesized by a facile vapor transport method. The good orientation and high crystal quality were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) measurements. Excitation-power-dependence photoluminescence spectra of ZnO NWs show that the UV emission displayed an evident blueshift with increasing excitation power and the corresponding energy shift might be as large as 10 meV. This anomalous phenomenon correlates to the band bending level caused by the surface built-in electric field due to the existence of substantial oxygen vacancies. By increasing the excitation power, the enhanced neutralization effect near the surface will reduce the built-in electric field and lead to a reduction of band bending which triggers the blueshift of the UV emission. 相似文献
94.
We have studied luminescence enhancement of zinc oxide (ZnO) nanoparticles with the average size of 30 nm on several metal surfaces at low temperatures. Bandedge luminescence originated from bound exciton (BE) annihilation is observed at 3.360 eV, and strongly depends on the kind and surface roughness of metal. The luminescence intensity is about 10 times larger for Ag surface than that for quartz surface. Furthermore, the luminescence increases remarkably when the roughness of Ag surface is almost the same as the particle size. The intensity ratio of the fast decay component to the slow one decreases for Ag surface compared with quartz. These results suggest that the luminescence enhancement is partially attributed to suppressing of the nonradiative recombination process in ZnO nanoparticles on metal surface. 相似文献
95.
R. Deng B. Yao Y.F. Li B.H. Li Z.Z. Zhang H.F. Zhao J.Y. Zhang D.X. Zhao D.Z. Shen X.W. Fan L.L. Yang Q.X. Zhao 《Journal of Crystal Growth》2009,311(19):4398-4401
The polar and non-polar ZnO thin films were fabricated on cubic MgO (1 1 1) and (0 0 1) substrates by plasma-assisted molecular beam epitaxy. Based on X-ray diffraction analysis, the ZnO thin films grown on MgO (1 1 1) and (1 0 0) substrates exhibit the polar c-plane and non-polar m-plane orientation, respectively. Comparing with the c-plane ZnO film, the non-polar m-plane ZnO film shows cross-hatched stripes-like morphology, lower surface roughness and slower growth rate. However, low-temperature photoluminescence measurement indicates the m-plane ZnO film has a stronger 3.31 eV emission, which is considered to be related to stacking faults. Meanwhile, stronger band tails absorbance of the m-plane ZnO film is observed in optical absorption spectrum. 相似文献
96.
Lewis acidic ionic liquids were used to catalyze the reaction of epoxypropane with POCl3.Considering the lower cost and catalytic activities,we concluded that[Et3NH]Cl/AlCl3 was the most attractive ionic liquid from an economical point of view.But it would be easily inactivated because of sensitive to water and air.Moreover,it could not be reused easily because of difficulty recovery in the reaction.However,supporting[Et3NH]Cl/AlCl3 catalyst could resolve above problems.Supporting[Et3NH]Cl/ AlCl3 catalyst could be separated by filter easily and reused 5 times in 98%yield.Furthermore,the catalyst was applicable to other epoxy ether cleaving reactions. 相似文献
97.
98.
We present comparative measurements of two Mach–Zehnder interferometers, one with Y-junction couplers and the other with MMI couplers, both developed in silicon-on-insulator technology and using plasma dispersion
effect for light phase modulation. Measurements of fiber-to-fiber losses, absorption coefficient, output intensity vs. time
and extinction ratio vs. frequency have been performed at λ=1.3 μm and at λ=1.55 μm. Results are reported and discussed in
this paper.
Received: 18 May 2001 / Revised version: 24 September2001 / Published online: 30 October 2001 相似文献
99.
Y. Gottesman E.V.K. Rao D. Piot E. Vergnol B. Dagens 《Applied physics. B, Lasers and optics》2001,73(5-6):609-612
This paper describes a comprehensive report on the high potential of optical low-coherence reflectometry (OLCR) measurements
to assist the design optimization and performance evaluation of symmetric MMI couplers. Using three sets of deep-ridge InGaAsP–InP
couplers on InP and by performing OLCR measurements simultaneously in reflection and transmission modes, the nature and origin
of all reflections in MMI have first been identified with respect to a deliberately chosen design parameter, namely, the coupler
length. In addition, and in total agreement with the self-imaging principle and also the BPM simulations, the back reflections
in combiner mode are shown to be prominent even in fully optimized devices. Finally, a simple design artifact has been proposed
and demonstrated experimentally for the first time to suppress back reflections.
Received: 16 May 2001 / Published online: 2 November 2001 相似文献
100.
G. Srinivasan T.P. Mullin D. Hanna A. Manivannan M.S. Seehra 《Applied Physics A: Materials Science & Processing》2001,72(3):333-339
The nature of the double-exchange (DE) interaction in lanthanum manganites is studied through chemical substitutions, Cs for
La, and high-pressure measurements. Static and high-frequency magnetic measurements and high-pressure electrical transport
studies were carried out on bulk polycrystalline and radio-frequency sputtered thin films of La0.7-xCsxCa0.3MnO3 for x=0-0.1. The samples are found to be cubic. Curie temperature Tc measurements provide evidence for bond-length-related weakening of DE as x is increased from 0 to 0.03. For higher x, the
bond-angle-related changes lead to an increase in the strength of DE. High-pressure mangetoresistance data indicate both bond
length and bond-angle-related increase of 10–20 K/GPa in Tc with pressure, with the largest increase measured for x=0.03. The rate of increase in the Curie temperature with pressure
decreases with increasing Tc. Anomalies are observed in the magnetic parameters for x=0.03. The Cs-concentration dependence of the low-temperature saturation
magnetization shows a minimum close to x=0.03. Ferromagnetic resonance studies at x-band reveal a 5% decrease in the g-value
for x=0.03 relative to the end members (x=0 and 0.1). The low-field magnetostriction for x=0.03 indicates a relatively strong
electron–phonon spin coupling compared to neighboring compositions.
Received: 15 May 2000 / Accepted: 24 July 2000 / Published online: 9 November 2000 相似文献