纳米氧化锌的过饱和控制生长与大小分布控制.

"在非水介质中合成了纳米氧化锌,测定了纳米氧化锌的紫外吸收光谱,并用有效质量模型计算了粒子大小,开发并命名了一种称之为纳米粒子过饱和控制生长的技术,该技术涉及将小的纳米粒子悬浊液加入到大的粒子悬浊液中,结果因为不同大小粒子间的溶解度差异小的粒子将全部溶解,大的粒子将整体长大,大粒子悬浊液的粒子数将保持不变,大粒子的生长速度显著比Ostwald老化的高．该技术最显著的特征是只要最初两悬浊液粒子大小的差异足够大,分布不是太宽,则粒子大小的分布将会因为粒子如此长大而变窄．"     

Branching Features of a Polymer

Two parameters characterizing the branching features of polymers, branching density (BD), and branching completeness (BC), are proposed. Both have values of zero (0) for linear polymers. Branching density has the values of 1/2, 2/3, and (f – 2)/(f – 1) for the fully and densest branched polymers formed from tri-, tetra-, and f-functional monomers typed AB _{f –1}. Branching completeness will reach the value of one (1) for a completely branched polymer, where all possible branching monomeric units have reacted at least tri-functionally and all units are either terminal or dendritic. Branching density is close to the mole fraction of terminal units, and BC is close to the mole fraction of dendritic and terminal units in the branching polymers. The major advantage of these parameters is their independence of the degree of polymerization (dp). Branching density depends on the functionalities (f) of monomer units; BC does not. The higher the fraction of the dendritic unit monomerically bonded to a higher number of other units (the higher the terminal units fraction), the denser branched the polymer and the higher the BD. The BC and BD can be used in a simple way for describing multicharacter branching systems and for comparing the branching characters among them without any theoretical limitations. Physical quantities (namely, the number of dendritic and terminal units and the degree of polymerization) used for BD and BC evaluation can be determined directly from practical analyses, where NMR is most useful. The BC and BD, however, do not concisely describe branching characteristics for a polymer with cyclization or crosslinking in its structure.     

Effect of Nanocrystal Size on Anti-Stokes Photoluminescence in Lead Halide Perovskites

JETP Letters - We report size-dependent anti-Stokes photoluminescence (ASPL) of methylammonium lead bromide (MALB) perovskite nanocrystals (NCs) under resonant laser excitation. The ASPL efficiency...     

锐钛矿二氧化钛超细纳米晶的三声子互作用

本文通过对粒径为2.2-25.5nm的锐钛矿二氧化钛超细纳米晶在83-293 K温度范围内的变温拉曼光谱的研究,得到了三声子互作用对拉曼频率和线宽的贡献随粒径的变化关系。结果表明锐钛矿二氧化钛超细纳米晶的三声子相互作用随粒径减小而加强。     

Change in the Thermodynamic Properties of a Si–Ge Solid Solution at a Decrease of the Nanocrystal Size

Physics of the Solid State - The equation of state and the thermodynamic properties of the substitutional solid solution Si0.5‒Ge0.5 are calculated in the framework of the “ medium...     

Size dependence of Young's modulus in ZnO nanowires

We report a size dependence of Young's modulus in [0001] oriented ZnO nanowires (NWs) with diameters ranging from 17 to 550 nm for the first time. The measured modulus for NWs with diameters smaller than about 120 nm is increasing dramatically with the decreasing diameters, and is significantly higher than that of the larger ones whose modulus tends to that of bulk ZnO. A core-shell composite NW model in terms of the surface stiffening effect correlated with significant bond length contractions occurred near the {1010} free surfaces (which extend several layers deep into the bulk and fade off slowly) is proposed to explore the origin of the size dependence, and present experimental result is well explained. Furthermore, it is possible to estimate the size-related elastic properties of GaN nanotubes and relative nanostructures by using this model.     

Mie散射研究聚合物合金相结构的形成及相尺寸分布

本文应用Mie散射理论研究了聚丙烯 /尼龙 1 0 1 0合金的相结构与形态 ,计算了相尺寸分布。其结果与电子显微镜及Rayleigh散射结果进行了比较。     

Statistical Investigation of the Mean Size Distribution of AB2/B f Type Hyperbranched Polymer

A statistical method was applied to investigate the number of isomeric structures of hyperbranched polymers formed by the polymerization of an AB ₂ type moiety with B_f polyfunctional core moieties (abbreviation as AB₂/B _f type). By means of the kinetic model described by a Smoluchowski-like coagulation equation, the explicit expressions of z-average mean-square radii of gyration are evaluated as a function of the conversion of functional groups. The numerical calculation shows that the mean size of the AB ₂/B _f type hyperbranched polymers will increase with the increase of the conversion of A groups or the reaction time, furthermore increasing sharply at the end of the reaction. When the reaction is quantitatively completed, the z-average mean-square radii of gyration of AB ₂/B _f type hyperbranched polymers show a maximum. The results are similar to those for star branched polymers, rather than those of hyperbranched polymers made by the AB_f type monomers without cores; the former had finite values and the latter reached infinite values when the reaction was quantitatively completed. These theoretical analysis conclusions will be important for effectively controlling the mean sizes or the average degrees of hyperbranched polymers by varying the number of the B_f type polyfunctional core moieties in experimental research.     

Phonon-Assisted Photoluminescence in a Spherical Nanocrystal

Using the matrix density in the representation of path integrals for an electron, the multiphoton nonlinear absorption light coefficient in the second order of interaction energy with polar optical phonons is derived. This coefficient describes any electron interaction mechanism with phonons. From the interaction mechanism, the main role is played by dimensional resonance when the electron continuously absorbs energy from the field as a result of synchronizing its oscillation with the field. This dimensional resonance is possible when the frequency characterizing the laser field is a multiple of the phonon frequency. Whether a photon is absorbed or emitted, the initial level from where the transition occurs defines the temperature dependence. The absorption spectrum has the form of stripes whose intensity depends on the resonance character. The most pronounced absorption is at the triple resonance, where values of radiation and oscillatory and optical phonon frequencies are equal. __________ Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 654–659, September–October, 2005.     

Changes of the Thermodynamic Properties at Isochoric and Isobaric Decrease of the Silicon Nanocrystal Size

Physics of the Solid State - Equation of state P(ν/νo) and the baric dependences of the lattice and surface properties of silicon macro- and nanocrystals have been calculated using the...     

Size dependence of the mechanical properties of ZnO nanobelts

The Young's modulus of ZnO nanobelts was measured using an atomic force microscope following the modulated nanoindentation method. The nanobelts have a rectangular cross-section, with width-to-thickness ratios ranging 1–10 and lengths up to a few millimetres. The Young's modulus of two nanobelts with width-to-thickness ratio of 2.2 and 1.3 was measured at 55 and 108?GPa, respectively, indicating a size dependence of the elastic properties of the nanobelts.     

Wide-Range Spectral Diffusion in Single Mg-Tetraazaporphyrin Molecules in a Polymer Matrix at Cryogenic Temperatures

Zero-phonon spectral lines of single Mg-tetraazaporphyrin molecules in a polymer matrix and their spectral trails are recorded using cryogenic fluorescence nanoscopy at a temperature of 6 K. Spectral diffusion (stochastic jumps of zero-phonon lines) in an anomalously wide spectral range up to several tens of inverse centimeters is revealed. The structure of the vibronic band in the fluorescence excitation spectrum of single molecules, including both a narrow zero-phonon line and a broad phonon sideband, is directly observed.     

Influence of a Photoconductive Polymer Matrix on the Photoluminescence of Cationic Polymethine Dyes

Using symmetric cationic indopolycarbocyanines HIC and HIDC as an example, the authors detected the enhancement of their photoluminescence in films of photoconductive polymers poly–N–epoxypropyl carbazole and poly–N–vinyl carbazole as compared to nonphotoconductive polymers, i.e., polyvinyl butyral, polystyrene, and polyethylene. The excitation was carried out on the shortwave edge of the absorption band of the dye and did not affect the absorption region of the polymer. It is shown that the effect of enhancement of the luminescence increases with decrease in the excitation wavelength and becomes weaker with increase in the molecular mass of carbazole–containing polymers. Its enhancement is interpreted as the recombination luminescence of electron–hole pairs formed in photogeneration of charge from the dye molecules.     

涡场中黏附性颗粒团聚体粒径分布的预测

黏附性颗粒团聚现象在自然界和工业界普遍存在,扰动流场中黏附性颗粒间的碰撞、摩擦和吸附等动力学行为,导致团聚体形态不断演化,准确预测黏附性颗粒团聚体的粒径分布是调控颗粒团聚过程的重要前提。本文通过二维泰勒格林涡场中黏附性颗粒团聚的数值模拟研究,明确了利用Monte Carlo模型预测团聚体粒径分布的可行性及其适用范围,发现当黏附性颗粒间内聚数小于3.5×10^?4时,Monte Carlo模型可较好的预测团聚体粒径分布,且相对误差小于±30%;而当内聚数大于3.5×10^?4后,Monte Carlo模型不再适用。     

PbS纳米晶修饰的ZnO/PVP复合电双稳器件阻变机制

采用简单旋涂工艺制备了具有ITO/PVP/ZnO NCs/PbS NCs/PVP/Al 夹心结构的有机/无机复合电双稳存储器件,与没有PbS纳米晶修饰层的器件ITO/PVP/ZnO NCs/PVP/Al相比,PbS纳米晶的引入使目标器件的开关比提高了2个数量级。结合器件的I-V曲线和能级结构分析了PbS 纳米晶修饰层对器件阻变和载流子传输的影响。结果显示,PbS纳米晶层的加入不仅优化了器件能级结构,有利于载流子的俘获和释放,还修饰了ZnO纳米晶的表面缺陷,降低了器件载流子的复合损耗。     

Fisher Information Matrix of Husimi Distribution

We calculate the Fisher information matrix of Husimi distribution in the Fock–Bargmann representation. It turns out that the Fisher information of the position and that of the momentum move in opposite directions, and that a weighted trace of the Fisher information matrix is a constant independent of the Husimi distribution. This may be interpreted as a kind of uncertainty relation (in the spirit of Heisenberg uncertainty principle) from the statistical inference point of view.     

无源矩阵驱动高分子发光显示屏的典型串扰分析

无源驱动对高分子发光显示屏质量要求较高,每个像素都应具有完好的二极管特性。为了在选通像素时,消除D．Braun串扰,无源驱动必须断绝选通像素与非选通像素之间的关联,所以需空闲行列上加以反向偏压。但研究表明,对于整流特性比较低的像素,在行扫描的空闲时间内,使驱动IC的VDD与VEE短路,产生相当大的漏电流并在显示屏的电阻网络上形成异常的压降,从而改变空闲行列上的原有电位。这样也就改变了非选通像素的偏置状态,使之正偏导通发光,形成了新的串扰。其表现为两种亮线：一是列串扰。亮度分布与阳极ITO及金属引线电阻有关;二是行串扰。从实验上讨论此两种串扰的产生原因,并提出减缓串扰的可能性。     

Micromechanical Behavior of Carbon Nanotube-Covered SiC Fibers in Polymer Matrix Composites

The incorporation of nanotube-covered fibers in continuous fiber/epoxy composites has been shown to influence the mechanical, electrical, and thermal properties of the composite. Increased interlaminar shear stress, flexural strength and modulus have been reported in such composites over composites containing bare fibers. In this study, the microstructure and interfacial shear strength (ISS) of continuous silicon carbide fiber/epoxy composites with and without nanotubes grown from the SiC fiber surface were investigated with micro-Raman spectroscopy (MRS) and microscopy. The fibers with nanotubes grown from the surface were found to have a reduced ISS compared with the bare fibers. Electron microscopy showed good wetting of epoxy in the nanotube forests, but poor attachment of the nanotube forests to the fibers. These results suggest that the mechanism leading to improvements in bulk composite properties is not due to an improvement in the fiber/matrix ISS.