The synthesis and properties of CaCu3Ti4O12 thin films

The CaCu₃Ti₄O₁₂ (CCTO) thin films were synthesized via a metal‐organic solution containing stoichiometric amounts of the metal cations at 700 °C for 1 h. The stable metal‐organic solution was prepared by dissolving calcium nitrate, copper nitrate, and tetrabuty titanate in grain alcohol. The phases, microstructures, and electric properties of CCTO thin films were characterized by X‐ray diffraction, scanning electron microscopy, atomic force microscope, and electric measurements. The results show that the CCTO thin films have homogeneous microstructure, smooth surface, low leakage current, and high values of dielectric constant. The low leakage current can be attributed to the small surface roughness. The high value of dielectric constant can be attributed to the internal barrier layer capacitor mechanism and metal‐insulator‐semiconductor junction of CCTO thin films. Copyright © 2013 John Wiley & Sons, Ltd.     

A polarizable empirical force field for molecular dynamics simulation of liquid hydrocarbons

Electronic polarizability is usually treated implicitly in molecular simulations, which may lead to imprecise or even erroneous molecular behavior in spatially electronically inhomogeneous regions of systems such as proteins, membranes, interfaces between compounds, or mixtures of solvents. The majority of available molecular force fields and molecular dynamics simulation software packages does not account explicitly for electronic polarization. Even the simplest charge‐on‐spring (COS) models have only been developed for few types of molecules. In this work, we report a polarizable COS model for cyclohexane, as this molecule is a widely used solvent, and for linear alkanes, which are also used as solvents, and are the precursors of lipids, amino acid side chains, carbohydrates, or nucleic acid backbones. The model is an extension of a nonpolarizable united‐atom model for alkanes that had been calibrated against experimental values of the density, the heat of vaporization and the Gibbs free energy of hydration for each alkane. The latter quantity was used to calibrate the parameters governing the interaction of the polarizable alkanes with water. Subsequently, the model was tested for other structural, thermodynamic, dielectric, and dynamic properties such as trans/gauche ratios, excess free energy, static dielectric permittivity, and self‐diffusion. A good agreement with the experimental data for a large set of properties for each considered system was obtained, resulting in a transferable set of polarizable force‐field parameters for CH₂, CH₃, and CH₄ moieties. © 2014 Wiley Periodicals, Inc.     

Selective switching of individual multipole resonances in single dielectric nanoparticles

Following Mie theory, nanoparticles made of a high‐refractive‐index dielectric, such as silicon, exhibit a resonator‐like behavior and very rich resonance spectra. Which electric or magnetic particle mode is excited depends on the wavelength, the refractive‐index contrast relative to the environment, and the geometry of the nanoparticle itself. In addition, the spatial structure of the impinging light field plays a major role in the excitation of the nanoparticle resonances. Here, it is shown that, by tailoring the excitation field, individual multipole resonances can be selectively addressed while suppressing the excitation of other particle modes. This enables a detailed study of selected individual resonances without interference by the other modes.

     

电子能量对沿面介质阻挡放电等离子体化学产物的影响

基于光电倍增管研制了一套无触发信号的双通道光学探测系统, 并组装了测试样机, 实现了对沿面介质阻挡放电(SDBD)等离子体约化电场的测量, 进而通过BOLSIG+软件获得了电子能量. 采用原位紫外吸收光谱和傅里叶变换红外光谱, 研究了SDBD等离子体在不同电压和频率下的化学产物的浓度变化, 并结合空气等离子体化学反应揭示了产物相互作用的微观机理. 结果表明, 电子能量能够改变电子碰撞反应的速率系数, 调控化学反应的源头活性粒子的浓度, 进而影响到化学产物的生成和猝灭.     

Synthesis and characterization of fluorine functionalized graphene oxide dispersed quinoline-based polyimide composites having low-k and UV shielding properties

Polyimide nanocomposites having low-k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior.     

Influences of Sr2+ Doping on Microstructure,Giant Dielectric Behavior,and Non-Ohmic Properties of CaCu3Ti4O12/CaTiO3 Ceramic Composites

The microstructure, dielectric response, and nonlinear current-voltage properties of Sr²⁺-doped CaCu₃Ti₄O₁₂/CaTiO₃ (CCTO/CTO) ceramic composites, which were prepared by a solid-state reaction method using a single step from the starting nominal composition of CCTO/CTO/xSrO, were investigated. The CCTO and CTO phases were detected in the X-ray diffraction patterns. The lattice parameter increased with increasing Sr²⁺ doping concentration. The phase compositions of CCTO and CTO were confirmed by energy-dispersive X-ray spectroscopy with elemental mapping in the sintered ceramics. It can be confirmed that most of the Sr²⁺ ions substituted into the CTO phase, while some minor portion substituted into the CCTO phase. Furthermore, small segregation of Cu-rich was observed along the grain boundaries. The dielectric permittivity of the CCTO/CTO composite slightly decreased by doping with Sr²⁺, while the loss tangent was greatly reduced. Furthermore, the dielectric properties in a high-temperature range of the Sr²⁺-doped CCTO/CTO ceramic composites can be improved. Interestingly, the nonlinear electrical properties of the Sr²⁺-doped CCTO/CTO ceramic composites were significantly enhanced. The improved dielectric and nonlinear electrical properties of the Sr²⁺-doped CCTO/CTO ceramic composites were explained by the enhancement of the electrical properties of the internal interfaces.     

Dielectric Spectroscopy Analysis of Liquid Crystals Recovered from End-of-Life Liquid Crystal Displays

In the present work, the dielectric properties of recycled liquid crystals (LCs) (non-purified, purified, and doped with diamond nanoparticles at 0.05, 0.1, and 0.2 wt%) were investigated. The studied LC mixtures were obtained from industrial recycling of end-of-life LC displays presenting mainly nematic phases. Dielectric measurements were carried out at room temperature on a frequency range from 0.1 to 10⁶ Hz using an impedance analyzer. The amplitude of the oscillating voltage was fixed at 1 V using cells with homogeneous and homeotropic alignments. Results show that the dielectric anisotropy of all purified samples presents positive values and decreases after the addition of diamond nanoparticles to the LC mixtures. DC conductivity values were obtained by applying the universal law of dielectric response proposed by Jonscher. In addition, conductivity of the doped LC mixtures is lower than that of the undoped and non-purified LC.     

太赫兹波段Smith-Purcell辐射的介质加载光栅高频特性

提出了一种用于Smith-Purcell效应器件的介质加载光栅慢波结构,通过研究该结构的注-波互作用过程,推导出带电子注的色散方程,并数值求解出波的线性增长率.利用色散方程,结合电磁场传播的边界条件,推导出Smith-Purcell效应振荡器工作所需的起振电流.详细研究了高频结构长度、电子注主要参数和介质相对介电常数对起振电流的影响,并与普通金属光栅结构进行了比较.结果表明:保持其他参数不变时,高频结构长度越短,起振电流越大;保持高频结构参数不变时,起振电流随电子注厚度和注-栅距离的增大而增大,随电子注电压的增大而减小;与金属光栅相比,介质的引入提高了注-波互作用的增长率,有效减小了振荡器的起振电流.理论计算结果与软件CHIPIC的模拟结果比较符合.     

Preparation of Low-dielectric Permittivity Polyimide Resins with High Surface Activity from Chemically Bonded Hyperbranched Polysiloxane

Thermosetting resin matrix is the key component of advanced wave-transparent composites,where low dielectric constant,excellent processability,high thermal stability,as well as good bonding ability are required for resins.Herein,we prepared a series of phenylethynyl terminated polyimide(PI)resins by grafting amine-functionalized hyperbranched polysiloxane(HBPSi)to PI chains during the in situ polymerization.The effects of HBPSi on the processability of oligomers,molecular packing,thermal stability,dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail.The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability.Meanwhile,the 10 wt％HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the interfacial shear strength(IFSS)of 37.64 MPa,compared with that of neat PI-6 matrix(27.34 MPa),and better adhesion to metal with the lap shear strength of 10.48 MPa,50％higher than that of neat resin PI-6(6.98 MPa).These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties,indicating their great potential as low-dielectric constant resin matrix in radar radome.