薄板型介质材料复介电常数的无损测量

采用带法兰结构的TE01n圆柱谐振腔,用无损检测的方法测量薄板型微波介质材料的复介电常数。利用轴向模式匹配法对谐振腔内的电磁场进行了求解,给出了相对介电常数和损耗角正切的计算公式,并利用矢量网络分析仪对几种常用微波介质材料进行了测量,其结果表明：该测量方法对相对介电常数的测量误差不超过1%,而对损耗角正切的测量误差不超过10%。该方法还具备一腔多模的测试能力,测量频率可调,可用于介质材料频率特性的测量。     

介电层表面直接生长石墨烯的研究进展

作为21世纪备受瞩目的材料,石墨烯兼具优异的电、热、光与力学性质,具有十分广阔的研究价值与应用价值.目前主要通过在金属基底上生长获得石墨烯,并将其转移至目标介电层基底上以构筑电子器件.转移过程不可避免地引入了褶皱、裂纹、破损以及聚合物/金属残留,严重损害了石墨烯的性能.因而直接在介电基底上制备高质量的石墨烯薄膜具有重要意义.本文总结了近年来在介电衬底上直接生长石墨烯的研究进展:阐述了金属辅助法、等离子体增强法以及热力学或动力学调控法等多种生长手段;介绍了多种介电/绝缘基底包括SiO_2/Si,Al_2O_3,SrTiO_3,h-BN,SiC,Si_3N_4以及玻璃表面生长石墨烯的特点与性能,分析了其可能的生长机理.根据拉曼谱图、薄层电阻、透光率、载流子迁移率等评估指标,将多种方法得到的石墨烯质量进行了总结与比较,并提出了直接在介电衬底上生成石墨烯的研究难点与趋势.     

聚酰亚胺/功能化石墨烯复合材料力学性能及玻璃化转变温度的分子动力学模拟

应用分子模拟方法,建立了聚酰亚胺(polyimide,PI),石墨烯及羧基、氨基、羟基功能化石墨烯模型,探究了聚酰亚胺和石墨烯,聚酰亚胺和功能化石墨烯共混后复合材料的力学性能和玻璃化转变温度(T_g).研究结果表明,羧基修饰的石墨烯与PI复合后材料力学性能增加显著,其杨氏模量和剪切模量分别为4.946 GPa和1.816 GPa.不同官能团修饰的石墨烯引入PI后材料的T_g均有不同程度下降;未修饰的石墨烯与PI复合后,其T_g(559.30 K)较纯PI的T_g(663.57 K)降幅最大;而羧基修饰的石墨烯与PI复合后T_g(601.61 K)降幅最小.计算比较了PI/石墨烯复合材料体系密度、溶解度参数、相互作用能、弹性系数和氢键平均密度,研究发现羧基修饰石墨烯/PI复合材料的密度为1.396 g·cm~(-3),溶解度参数为23.51 J~(1/2)·cm~(-3/2),其相互作用能与氢键平均密度最大,弹性系数显示羧基修饰石墨烯与PI组成的复合材料内部最均匀.计算结果表明,羧基功能化石墨烯可以大幅度提高PI的力学性能,增强石墨烯与PI之间的相互作用可以减少复合材料T_g的降幅程度.此基体间相互作用的研究方法可以作为预测聚合物基纳米复合材料结构与性能的有效工具,以期为材料的设计与应用提供理论指导.     

Electric permittivity and dielectric loss of castor oil during its transformation to the high pressure phase

Abstract

The changes of permittivity and dielectric loss of commercially pure castor oil observed during its transition to the high pressure phase are described. Discussion about physical properties of this phase is shortly presented too.     

含有偏心球形微粒介质球的有效介电常量

对于处在均匀外电场中含有偏心球形微粒的介质球,利用分离变量法求出球内外的电场,给出了球外电偶极矩和电四极矩的近似表达式.首次引入含有偏心球形微粒介质球的有效介电常量,它不同于同心多层介质球的等效介电常量,不仅与介质球内的介质有关,而且与球外介质有关.数值结果显示了有效介电量数随偏心距和球外介质介电常量的变化情况.     

Enhanced dielectric properties and energy storage density of interface controlled ferroelectric BCZT-epoxy nanocomposites

Polymer nanocomposites with ferroelectric fillers are promising materials for modern power electronics that include energy storage devices. Ferroelectric filler, Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) nanopowder, was synthesized by sol-gel method. X-ray diffraction (XRD) studies confirmed the phase purity and the particle size distribution was determined by transmission electron microscopy (TEM). Extended aromatic ligand in the form of naphthyl phosphate (NPh) was chosen for surface passivation of BCZT nanoparticles. Surface functionalization was validated by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy using slurry technique. The dielectric constant of surface-passivated BCZT nanopowder was ~155, whereas pristine BCZT nanopowder dielectric constant could not be assessed due to high innate surface conductivity. Furthermore, BCZT–epoxy nanocomposite films were prepared and analyzed by differential scanning calorimetry (DSC), dielectric spectroscopy, dielectric breakdown strength (DBS), and scanning electron microscopy (SEM). Owning to stronger polymer–particle interface, dielectric measurements of 5 vol.% NPh surface functionalized BCZT–epoxy nanocomposites indicated improved DBS and glass transition temperature (T_g), reduced dielectric loss, and enhanced energy storage density compared to untreated BCZT–epoxy composites and pure epoxy. The energy storage density of 30 vol.% NPh surface functionalized BCZT–epoxy nanocomposite of 20 μm film thickness was almost three times that of pure epoxy polymer of identical film thickness.     

The effective stiffness of an embedded graphene in a polymeric matrix

Modeling the real sizes of an embedded graphene and the surrounding polymer of a representative volume element in a molecular dynamics simulation is a tedious task. The less computational limitations made the continuum-based method a good candidate for modeling of nanocomposites. However, having a good knowledge of mechanical properties of the embedded graphene in a polymeric matrix is a challenge for employing a continuum-based method. Since the applied stress on the graphene/epoxy nanocomposites has not been directly transferred to the embedded graphene, it brings the following question to mind. Is the stiffness of the embedded graphene different from that of the isolated one? To answer to this question, a model was developed by combining the molecular dynamic simulation and the finite element method to calculate the stiffness of an embedded graphene in a polymeric matrix. The results show that the longitudinal stiffness of the embedded graphene is different from that of the isolated graphene and is a function of its length. The use of this relationship in the micromechanical method leads to consider the nanosize effect in macroscale. The results were compared with some available experimental data to validate the model.     

不同电介质结构下介质阻挡放电特性研究

设计制作了单面有氧化铟锡(ITO)导电介质层的双玻璃介质层的介质阻挡放电装置,研究了其放电特性,并将其与双玻璃介质层和单玻璃介质层的介质阻挡放电进行了比较.从电荷输运的角度分析,上述三种装置分别实现了电荷的二维、零维和三维输运.采用两种不同的双玻璃介质层装置,获得了单个稳定的放电丝.与无ITO导电层的双玻璃结构得到的单个放电丝相比,单面有导电ITO介质的双玻璃结构中,单放电丝呈"T"字型,其光晕是前者光晕的2倍,其放电电流大于前者电流,其放电时间间隔长短交替现象更为明显,且存在强度大小交替的现象.分析表明,壁电荷输运及二次电子发射的不同导致了不同电介质结构放电特性的不同. 关键词： 介质阻挡放电 壁电荷 二次电子发射     

Electrical characteristics of etched ion-tracks in polyimide filled with silver nanoparticles

Silicon ions, of energy 150?MeV and fluence ～10¹²?ions/cm², were used to register latent tracks in 40?µm thick polyimide samples. Different sizes of tracks were obtained by etching the ion irradiated polyimide samples, in chemical solutions, by varying the temperature and etching period. Silver nanoparticles were diffused into the etched tracks by immersing the polyimide samples in silver solution and then irradiating with 6.5?MeV electrons at different fluences varying from 1?×?10¹⁵ to 5?×?10¹⁵?cm^?2. Results of morphological and elemental analysis, carried out by Scanning Electron Microscopy and Energy Dispersive X-ray. Analysis revealed that the conical tracks could be fully filled with silver nanoparticles at electron fluence of 5?×?10¹⁵?cm^?2. The minimum d. c. resistance of an array of tracks, filled with silver nanoparticles and measured across the polyimide film, was orders of magnitude higher as compared to that of silver wires of equivalent sizes connected in parallel. In addition, these silver nanoparticles filled tracks exhibited rectifying I–V behavior and frequency dependent a. c. resistance, characteristic of metal–polymer nano-composites. Possible mechanisms have been discussed, which can justify the asymmetric current–voltage characteristics in such nano-composites.     

Comprehensive studies on dielectric properties of p-methoxy benzylidene p-decyl aniline with function of temperature and frequency in planar geometry: A potential nematic liquid crystal for display devices

The dielectric properties of the nematic mesophase, p-methoxy benzylidene p-decyl aniline(MBDA), measured in planar geometry with a function of frequency and temperature are investigated in detail. The complex dielectric permittivity(ε' and ε') is also studied at a bias voltage of 10 V for planar aligned sample cell of nematic mesophase. The dielectric permittivity with bias voltage attains a higher( 2 times) value than that without bias voltage at a temperature of 56℃,which is due to the fact that the linking group of nematic molecules is internally interacted with an applied bias voltage.This is supported by observing an enhanced dielectric permittivity of nematic liquid crystal(LC) in the presence of bias voltage, which can be fully explained as the increasing of the corresponding dipole moment. The dielectric relaxation behaviors of nematic LC are also demonstrated for planar aligned sample cell. The remarkable results are observed that the relaxation frequency shifts into low frequency region with the increase of the bias voltage applied to the planar aligned sample cells. The dielectric relaxation spectra are fitted by Cole–Cole nonlinear curve fitting for nematic mesophase in order to determine the dielectric strength.     

Secondary electron emission characteristics of graphene films with copper substrate

For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield (SEY) material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25℃ and vacuum pressure of (2-6)×10^-9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6-8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators.     

Dielectric permittivity, density, viscosity and refractive index of binary mixtures of anisole with methanol and 1-propanol at different temperatures

Static dielectric permittivity, density, viscosity, and refractive index of anisole (AN), methanol (MeOH), 1-propanol (1-PrOH) and binary mixtures of AN with MeOH and 1-PrOH at nine different concentrations, were measured at 303, 313 and 323 K temperatures. Measured properties of pure AN, MeOH and 1-PrOH were compared with literature values and they were found in good agreement. The investigation of binary mixtures showed a systematic change in static dielectric permittivity, density and viscosity with change in concentration of anisole in the mixture. Measured properties of liquid samples were used to calculate Kirkwood correlation factor and excess parameters such as excess dielectric permittivity, excess molar volume and excess viscosity. Determined parameters have been interpreted in terms of molecular interaction among the molecular species of the binary mixtures.     

Enhanced dielectric properties of polyvinylidene fluoride with addition of SnO2 nanoparticles

In this letter, SnO₂/polyvinylidene fluoride (PVDF) nanocomposites with outstanding dielectric properties were fabricated. The SEM and TEM images showed that SnO₂ nanoparticles with size of 5–7 nm dispersed homogeneously in polymer matrix. The significantly improved dielectric constant was well explained by percolation theory. The nanocompo‐ sites can retain a certain value of breakdown field. The maximum energy density of SnO₂/PVDF nanocomposites was 5.4 J/cm³, two times that of the pure polyvinylidene fluoride. These findings suggest that SnO₂/PVDF nanocomposites are suitable candidates for energy storage applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Raman analysis of amorphous silicon ruthenium thin films embedded with nanocrystals

We report the Raman analysis of both as‐deposited and annealed amorphous silicon ruthenium thin films embedded with nanocrystals. In the Raman spectra of as‐deposited films, variations of TO peak indicate a short‐range disorder of a‐Si network with an increase of Ru concentration. The substitutional Ru atoms lower the concentration of Si―Si bonds and suppress the intensity of TO peak, but have less effect on TA, LA and LO peaks. In the Raman spectra of annealed films, characteristic parameters confirm the upgrade of a‐Si network at a low annealing temperature and the emergence of both ruthenium silicide and silicon nanocrystals at 700 °C. Although ruthenium silicide nanocrystals present no Raman peaks in the Raman spectra of as‐deposited samples, the non‐linear variations of intensity ratios I_{LA + LO}/I_TO and I_TA/I_TO still suggest their existence, and these nanocrystals are subsequently verified by high‐resolution transmission electron microscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced piezoelectric properties of sodium bismuth titanate (Na0.5Bi4.5Ti4O15) ceramics with B‐site cobalt modification

The piezoelectric properties of the cobalt‐modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics were investigated. The piezoelectric properties of NBT ceramics were significantly enhanced by cobalt modification. The Curie temperature T_C and piezoelectric constant d₃₃ for the 0.3 wt% cobalt‐modified NBT ceramics (NBT‐C3) were found to be 663 °C and 30 pC/N, respectively. Thermal annealing studies presented that the cobalt‐modified NBT ceramics possess stable piezoelectric properties, demonstrating that the cobalt‐modified NBT‐based ceramics are promising candidates for high temperature piezoelectric applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

HfO2顶层多层介质膜脉宽压缩光栅的Piranha溶液清洗

为了提高HfO2顶层多层介质膜脉宽压缩光栅（PCG）的抗激光损伤性能,使用Piranha溶液（浓硫酸和双氧水的混合液）清洗PCG去除其制作工艺和使用过程中残留在表面的污染物,包括CHF3作为工作气体对HfO2进行反应离子束刻蚀生成的碳氟化合物及金属氟化物。对Piranha溶液的清洗温度、组成成分、清洗时间、清洗遍数等参数进行了系统研究,用扫描电子显微镜（SEM）观察清洗前后的PCG表面形貌,用X射线光电子能谱仪（XPS）检测清洗前后PCG表面的元素成分及其原子分数的变化,并分析了各残留污染物的去除机理。实验结果表明：Piranha溶液能有效去除PCG表面污染物,而且清洗温度越高,清洗遍数越多,对PCG表面残留污染物的去除效果越显著。在90 ℃下60 min有效活性时间内,使用浓硫酸和双氧水体积比为2∶1的Piranha溶液清洗3遍以上,PCG表面残留的F元素的原子分数接近0.1%（XPS的分辨极限）,达到良好的清洗效果。     

HfO2顶层多层介质膜脉宽压缩光栅的Piranha溶液清洗

为了提高HfO2顶层多层介质膜脉宽压缩光栅(PCG)的抗激光损伤性能,使用Piranha溶液(浓硫酸和双氧水的混合液)清洗PCG去除其制作工艺和使用过程中残留在表面的污染物,包括CHF3作为工作气体对HfO2进行反应离子束刻蚀生成的碳氟化合物及金属氟化物.对Piranha溶液的清洗温度、组成成分、清洗时间、清洗遍数等参...