共查询到19条相似文献,搜索用时 76 毫秒
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采用自悬浮定向流法制备了金属纳米粉体并采用真空手套箱专利技术和冷压法在高压(1.5 GPa)作用下保压40 min后,成功制备出了相对密度达97%和显微硬度达1.85 GPa的金属Cu纳米晶材料。经XRD分析,其晶粒大小为20 nm。正电子湮没(PAS)实验结果表明,其空隙大小和数量与采用惰性气体冷凝法原位压制(IGC)的样品相比,空位簇数量较多,微空隙的大小和数量基本相当。激光惯性约束聚变(ICF)模拟实验表明:采用该方法制备的纳米Cu块体材料靶的激光转换效率比常规Cu材料靶高5倍。 相似文献
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纳米锗颗粒镶嵌薄膜的吸收光谱研究 总被引:1,自引:0,他引:1
用离子束溅射技术和热处理方法,制备出颗粒尺寸和镶嵌密度均可控制的高质量Ge-SiO2纳米颗粒镶嵌薄膜,在室温下测量了不同粒度纳米锗颗粒镶嵌薄膜样品的吸收光谱,观测到在可见光区有较强的光吸收和吸收带边蓝移。研究表明:镶嵌在经缘介质薄膜中的纳米锗颗粒的能量带是量子化的,随着纳米锗粒子平均尺寸的减小,其吸收带隙增加,吸收带边蓝移的程序相应增大。 相似文献
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利用自组装的嵌段聚合物有序图案为模板来制备有序金属颗粒纳米阵列是人们关注的热点之一。本文概述了最近利用团簇束流沉积系统将银团簇淀积在聚苯乙烯-聚丁二烯-聚苯乙烯(SBS)三嵌段聚合物自组装形成的有序图案上,制备了有序的银纳米颗粒阵列材料,如线形银团簇颗粒阵列和二维银团簇颗粒阵列。利用自编的径向分布函数计算程序对线形银团簇颗粒阵列进行了定量分析,进一步定标了这种线形阵列的有序度,发现在同一线形阵列内有小部分银团簇是近接排列的,大部分团簇颗粒是等间距排列的。同时探讨了这些有序阵列形成的机制。并讨论了利用紫外-可见分光光度计和拉曼谱仪研究这些有序阵列所得到的相关性质。 相似文献
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We present a study on dielectric response of Ag14 nanocluster dimer using first principles methods. The interaction energy, (hyper)polarizability of dimer are predicted under various separations of the two identical Ag14 nanoclusters. The appropriate separation makes the second-order hyperpolarizability of Ag14 dimer is about 70 times larger than the Ag14 monomer. The increase of polarizability and hyperpolarizability is ascribed to reconfiguration of molecular electronic state from Ag cluster monomer to dimer. Nonlinear response is more susceptible to the steady intermediate state compared to linear response. The crucial transitions contributed to hyperpolarizability are assigned to be from highest occupied molecular orbitals to the lowest unoccupied molecular orbital (HOMOs-LUMO) of nanocluster dimer. Binding character of LUMO plays an important role in determining nonlinear optical properties. 相似文献
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Optical properties of nanocrystalline silver halides 总被引:4,自引:0,他引:4
Michal Ilana Freedhoff Alfred P. Marchetti George L. McLendon 《Journal of luminescence》1996,70(1-6):400-413
A review of quantum confinement effects in nanocrystals of silver bromide (AgBr) and silver iodide (AgI) is presented. AgBr is an indirect gap semiconductor while AgI has a direct band-to-band lowest energy transition. An examination of the low-temperature optical properties of quantum confined AgBr grown using a variety of synthetic techniques will be made. The dynamics of some of the involved excitonic processes will be measured and discussed in reference to a possible breakdown in the momentum selection rules as the nanocrystals are made smaller. Other explanations for this behavior such as impurity exclusion and surface effects will also be considered, as will the dynamics associated with the trapping of excitons at intrinsic iodide impurities in AgBr. Absorption measurements on AgI nanocrystals will be discussed and compared with the exciton photophysics in AgBr. Both AgBr and AgI display an increasing blue shift of their luminescence, arising from the recombination of excitons, as the crystallite size decreases. The luminescence intensity arising from this process increases with decreasing size in AgBr but it disappears in small crystals of AgI. This leads to the conclusion that in the latter material nonradiative decay channels are opening up as the size decreases. 相似文献
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Silver nanoparticles have been prepared using hydrogen gas as the reducing agent for silver nitrate and poly(vinyl pyrrolidone) as the capping agent; the reaction was carried out at 70 °C for 3 h. The size of the nanoparticles was found to be about 20 nm as analyzed using transmission electron micrographs. The X-ray diffraction pattern revealed the face-centered cubic (fcc) structure of silver nanoparticles. The linear absorption of Ag nanoparticles, α, is obtained about 3.71 cm−1. The non-linear refractive indices of silver nanoparticles were defined by the z-scan technique using CW He-Ne laser (λ = 632.8 nm) at different incident intensities. The magnitude of non-linear refractive index (n2) was measured to be in the order of 10−7 (cm2/W) with a negative sign. Therefore self-defocusing phenomena is taking placed for Ag nanoparticles. 相似文献
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The silver chromate self-assembly necklace structures were synthesized using high-active acrylicamide template. The whole
length of the necklace structure was between 1.2 and 1.5 μm. The product was composed of single crystalline nanorods with
diameters of about 40 nm and lengths of 300 nm. The synthetic mechanism and product’s optical properties were also studied. 相似文献
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R.A. Ganeev M. Baba A.I. Ryasnyansky M. Suzuki H. Kuroda 《Optics Communications》2004,240(4-6):437-448
The optical, structural, and nonlinear optical properties of silver nanoparticles prepared by laser ablation in various liquids were investigated at 397.5, 532, and 795 nm. The TEM and spectral measurements have shown temporal dynamics of size distribution of Ag nanoparticles in solutions. The thermal-induced self-defocusing dominated in the case of high pulse repetition rate as well as in the case of nanosecond pulses. In the case of low pulse repetition rate, the self-focusing (γ = 3 × 10−13 cm2 W−1) and saturated absorption (β = −1.5 × 10−9 cm W−1) of picosecond and femtosecond radiation were observed in these colloidal solutions. The nonlinear susceptibility of Ag nanoparticles ablated in water was measured to be 5 × 10−8 esu (at λ = 397.5 nm). 相似文献
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Summary The theory of the RPA optical response of a solid has been generalized in order to take into account also the possible presence
of spatially nonlocal potentials in the Hamiltonian. Explicit expressions for first- and second-order susceptibilities are
given in the new framework. The expressions obtained depend on the matrix elements of operators of the form of a commutator
of a component of the position operatorr and an operator that commutes with the lattice translations. The problem of the evaluation of these matrix elements is solved
in a simple manner by introducing an auxiliary, periodic position operator,XXXr. In such a way a general formulation is obtained that preserves the gauge invariance. As an application of the new theory,
the second harmonic generation (SHG) from a semiconductor in a simple two-band model has been studied. The differences between
our correct gauge-invariant results and those obtained in the usual local approximation is an indication of a slow convergence
of the expressions obtained in the local approximation. 相似文献
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The metal-assisted chemical etching of silicon in an aqueous solution of hydrofluoric acid and hydrogen peroxide is established for the fabrication of large area, uniform silicon nanowire (SiNW) arrays. In this study, silver (Ag) and gold (Au) are considered as catalysts and the effect of different catalysts with various thicknesses on the structural and optical properties of the fabricated SiNWs is investigated. The morphology of deposited catalysts on the silicon wafer is characterized by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). It is shown that the morphology of the fabricated silicon nanostructures remarkably depends upon the catalyst layer thickness, and the catalyst etching time directly affects the structural and optical properties of the synthesized SiNWs. FESEM images show a linear increment of the nanowire length versus time, whereas the etching rate for the Au-etched SiNWs was lower than the Ag-etched ones. Strong light scattering in SiNWs caused the total reflection to decrease in the range of visible light, and this decrement was higher for the Ag-etched SiNW sample, with a longer length than the Au-etched one. A broadband visible photoluminescence (PL) with different peak positions is observed for the Au- and Ag-etched samples. The synthesized optically active SiNWs can be considered as a promising candidate for a new generation of nano-scale opto-electronic devices. 相似文献
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This paper describes the structural, morphological and optical properties of the nano-composite of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and quantum dots (QDs). The ZnSe and CdSe QDs have been synthesized, with the aid of Mercaptoacetic acid (MAA), by a colloidal method with an average size of ~5 to 7 nm. QDs have been embedded in PEDOT:PSS using a simple solution processing approach and has been deposited as thin films by spin coating technique. The QDs embedded PEDOT:PSS enhances the light absorption spectra of samples, prominently in terms of absorption intensity which may consequently improve sensitivity of the optoelectronic devices. 相似文献
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Ion-conducting polymer electrolyte films based on a copolymer poly(methyl-methacrylate-co-4-vinyl pyridine N-oxide) [P(MMA-CO-4VPNO)]
complexed with potassium chlorate (KClO3) were prepared by solution cast technique. The complexation of KClO3 salt with the polymer was confirmed by X-ray diffraction and infrared studies. The electrical conductivity and optical absorption
of pure and KClO3-doped P(MMA-CO-4VPNO) polymer electrolyte films have been studied. The electrical conductivity increased with increasing
dopant concentration, which is attributed to the formation of charge transfer complexes. The variation of electrical conductivity
with temperature shows two regions with two activation energies. Optical properties like direct band gap, indirect band gap,
and optical absorption edge were investigated for pure and doped polymer films in the wavelength range 300–550 nm. It was
found that the energy gaps and band edge values shifted to lower energies on doping. The behavior is in an agreement with
the activation energies obtained from the conductivity data. 相似文献