Addressing the lower limit of breakdown delay time in vacuum

Based on the Joule mechanism of vacuum breakdown initiation, the dependence of a pulsed electric strength on the high-voltage pulse duration at a finite rate of electric field buildup in the vacuum gap is calculated. The results of calculations are confirmed by experimental data available for subnanosecond pulses. It is shown that the breakdown delay time has no lower limit at an electric strength of up to ～3 × 10¹⁰ V/m observed in experiment. The independence of the breakdown delay time of the electric field strength for pulse durations comparable with the pulse front width is explained by the finite rate of applied voltage buildup.     

工频电场测量仪的校准装置

针对目前国内还没有在环境监测中广泛使用的对工频电场探头进行计量的检定规程或者校准规范,设计了一套工频电场探头校准装置,根据理论推导,确定所产生标准电场强度。通过高压源控制器来控制升压实现高压输出。校准所采用的电板满足所有工频电场测量仪校准需求,产生的电场强度范围从10 V/m到100 kV/m。最后,对溯源后的HI-3604分别进行电场强度测试与分析,实验数据表明:该校准装置可以用于工频电场探头校准,并给出了校准不确定度。     

A unified description of current-voltage characteristics in organic and hybrid photovoltaics under low light intensity

We develop a simple model that can explain the current-voltage ( J- V) curves of excitonic photovoltaic solar cells, spanning polymer:polymer, polymer:fullerene, and polymer:nanocrystal devices. We show that by subtracting out the dark current, we can explain apparent intensity-dependent characteristics and thus identify geminate recombination as the dominant loss mechanism and establish its electric field dependence. We present an analytic fit to the J- V curves of all measured devices based on a single fitted parameter, the electric field required to split 50% of geminate charge pairs, which we term the critical field. Devices of different material combinations and morphologies can all be described by this method and yield critical fields varying between >1 x 10(8) V/m for blends of poly(9,9'-dioctylfluorene- co-bis- N, N'-(4-butylphenyl)-bis- N, N'-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9'-dioctylfluorene- co-benzothiadiazole) (F8BT) and 8 x 10 (5) V/m for slow-grown blends of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). A comparison with material properties reveals that the primary route to improved photovoltaic materials is enhanced charge delocalization.     

Anharmonic character of the polarizing effect with the thickness modes of alpha-quartz plates

It is shown that for any thickness mode of vibrations the frequency change caused by a DC electric field applied to quartz plate resonators is only approximately proportional to the overtone frequency. It is shown that while this behavior can be predicted qualitatively, the deviations from proportionality are too irregular to claim a quantitative agreement. Concerning practical estimates of the magnitude of the frequency change for a chosen overtone, using the value known for the fundamental or another overtone, it appears that a field of 10(6 ) V/m the variation in Deltaf/f among overtones will only rarely exceed 10(-6). The highest value observed is 1.6x10(-6).     

Thermal stability of metal-silicide nanocrystal nonvolatile memory with barrier engineered tunnel layers

WSi2 nanocrystal nonvolatile memory devices were fabricated with a silicon oxide-nitride-oxide (SiO2: 2 nm/Si3N4:2 nm/SiO2:3 nm) tunnel layer. WSi2 nanocrystals of 2.5 nm diameters and a density of 3.6 x 10(12) cm(-2) were formed using radio frequency magnetron sputtering and annealing processes. The WSi2 nanocrystal nonvolatile memory device exhibited strong thermal stability during writing/erasing operations at temperatures up to 125 degrees C. When the writing/erasing voltages were applied at +10 V/-10 V for 500 ms, the memory window of the initial approximately 2.6 V decreased by approximately 1.1 V at 25 degrees C and 0.4 V at 125 degrees C after 10(4) sec, respectively. These results show that WSi2 nanocrystals with barrier-engineered tunnel layers are possible for application in nonvolatile memory devices.     

Spot measurements of intermediate frequency electric fields in the vicinity of compact fluorescent lamps

Starting in 2009, certain types of incandescent light bulbs will be withdrawn from the market in the European Union and elsewhere. However, compact fluorescent lamps that are among the candidates to replace them produce intermediate frequency electric fields (EFs) much higher than any other device or appliance previously available to the general public. Measurement results of these EFs showed that the maximum recorded EF strength in the 1.2-100 kHz frequency range in close proximity to the lamps was > 42 V m(-1) for all tested lamps. In nine cases, the field strength exceeded 87 V m(-1) and the highest measured value was 216 V m(-1).     

Quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics under both DC and AC bias

The basic quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) transparent ceramics have been studied under both DC and AC electric field bias. The contribution of piezoelectric resonance to electro-optic effect for this quadratic electro-optic ceramics material has been experimentally demonstrated and theoretically analyzed. It is found that, at the piezoelectric resonance frequencies, the piezoelectric induced electro-optic effect dominates and leads to a dramatically high sensitivity for weak electric signal detection. About 20 dB signal-to-noise ratio is attained when detecting AC electric field strength of 1 V/m with optimized DC bias. Besides, the effects of AC frequency and amplitude on halfwave voltage V(π) of PMN-PT are investigated.     

Electric fields within cells as a function of membrane resistivity--a model study

Externally applied electric fields play an important role in many therapeutic modalities, but the fields they produce inside cells remain largely unknown. This study makes use of a three-dimensional model to determine the electric field that exists in the intracellular domain of a 10-/spl mu/m spherical cell exposed to an applied field of 100 V/cm. The transmembrane potential resulting from the applied field was also determined and its change was compared to those of the intracellular field. The intracellular field increased as the membrane resistance decreased over a wide range of values. The results showed that the intracellular electric field was about 1.1 mV/cm for R/sub m/ of 10 000 /spl Omega//spl middot/cm/sup 2/, increasing to about 111 mV/cm as R/sub m/ decreased to 100 /spl Omega//spl middot/cm/sup 2/. Over this range of R/sub m/ the transmembrane potential was nearly constant. The transmembrane potential declined only as R/sub m/ decreased below 1 /spl Omega//spl middot/cm/sup 2/. The simulation results suggest that intracellular electric field depends on R/sub m/ in its physiologic range, and may not be negligible in understanding some mechanisms of electric field-mediated therapies.     

电泳沉积碳纳米管的微波等离子体改性

采用电泳法在Si基底上沉积了碳纳米管(CNTs)薄膜, 并利用Ar微波等离子体对CNTs薄膜进行了改性处理, 研究了改性前后CNTs的微观结构和场发射性能. 高分辨透射电子显微镜(HRTEM)和拉曼光谱的表征结果表明, 等离子体改性明显改变了CNTs的微观结构, 形成了大量的管壁结构缺陷、纳米级突起和“针形”尖端; 场发射测试结果表明, CNTs经Ar等离子体改性处理后开启电场较改性前?略有增大, 等离子体改性10min的CNTs薄膜表现出最佳的场发射J-E特性, 阈值电场由改性前的3.12V/μm降低到2.54V/μm, 当电场强度为3.3V/μm时, 场发射电流密度由改性前的18.4mA/cm²增大到60.7mA/cm². 对Ar微波等离子体改性增强CNTs薄膜场发射性能的机理进行了分析.     

微型大气电场监测装置的设计与实现

针对户外场磨式地面电场仪存在的输入阻抗高、感应电流信号弱、易受外界电磁波干扰、功耗大且无市电供电等问题,设计一种光伏发电加蓄电池储能供电的低功耗大气电场监测装置.为减小系统功耗,提高测量精度,设计微型低速双定子差分式电场传感器,传感器感应到的两路微弱电流信号经过T型反馈网络实现I/U变换.通过减法器和4 Hz低通滤波器...     

Design,construction and performance of a liquid xenon and liquid argon ionization chamber

We have constructed an ionization chamber for liquid xenon and liquid argon and have conducted studies of initial ion-electron recombination. Using a 392 keV ¹¹³Sn source, we find in xenon a charge collection of (90±5)% at an electric drift field of 1.6 kV/cm and (10±3)% at 10 V/cm. In argon we collect (78±5)% of the charge in a field of 1.6 kV/cm. We have developed a method for measuring the concentration of electronegative impurities in the detector liquid. The purity of the liquid was always better than 2 ppb O₂ equivalent. Under these conditions, the energy resolution observed with either liquid in the detector is (12±1)% FWHM at 380 keV in an electric drift field of 1.8 kV/cm for argon and 1.6 kV/cm for xenon. This appears to be a fundamental limit imposed by the statistics of delta electron production.     

基于CST软件的电火工品射频安全性分析

为了研究电火工品在复杂电磁环境下的射频安全性，针对某型电火工品建立了偶极子天线模型。基于CST电磁仿真软件，仿真得到了该天线模型的增益参数，进一步仿真计算得到了在频率为0．75GHz、电场强度为195V／m的电磁环境下，进入到该电火工品的射频功率，并与实际计算结果进行了对比验证。通过多频点仿真计算，得到了该天线模型的增益随频率变化的规律，即在0．5—2．0GHz的频率范围内，天线模型的增益随着频率的增大而增大。     

Low-frequency transient electric and magnetic fields coupling to child body

Much of the research related to residential electric and magnetic field exposure focuses on cancer risk for children. But until now only little knowledge about coupling of external transient electric and magnetic fields with the child's body at low frequency transients existed. In this study, current densities, in the frequency range from 50 Hz up to 100 kHz, induced by external electric and magnetic fields to child and adult human body, were investigated, as in residential areas, electric and magnetic fields become denser in this frequency band. For the calculations of induced fields and current density, the ellipsoidal body models are used. Current density induced by the external magnetic field (1 microT) and external electric field (1 V/m) is estimated. The results of this study show that the transient electric and magnetic fields would induce higher current density in the child body than power frequency fields with similar field strength.     

多氨基硅烷偶联剂改性碳纤维电场电极的制备及其电化学性能研究

利用硅烷偶联剂作为改性碳纤维的接枝材料,探索γ-氨乙基氨丙基三甲氧基硅烷(KH-792)改性前后碳纤维电化学性能和电场响应性能的变化。结果表明,改性后碳纤维电极的电化学性能显著提升,比容量为105.96 F/g,是未改性电极的4.58倍,未改性电极存在的低频容抗现象也得到改善。改性后,电极对的极差稳定性提高,日漂移量最低10μV/d,能够很好地响应1 m V/1 m Hz电场信号,电极对的电化学自噪声可低至1.7 n V/rtHz@1 Hz,与未改性电极对的自噪声相比明显降低。     

高场发射性能碳纳米管薄膜的沉积与表征

利用电泳法将碳纳米管（CNTs）沉积在表面镀覆了50～150 nm Ti薄膜的Si基底表面,900℃真空退火后形成了具有良好场发射性能的Ti-CNTs薄膜阴极.利用X射线衍射和扫描电子显微镜对制备的Ti-CNTs薄膜进行了表征.结果表明,高温退火过程中,CNTs的C原子和基底表面的Ti原子发生化学反应,在CNTs与基底之间形成了导电性钛碳化物,明显改善了CNTs与基底之间的电导性和附着力等界面接触性能;与Si基底表面直接电泳沉积的CNTs薄膜相比,制备的Ti-CNTs薄膜的开启电场从1.31 V/μm降低到1.19 V/μm;当电场强度为2.50 V/μm时,Ti-CNTs薄膜的场发射电流密度可达13.91 mA/cm^2;制备的Ti-CNTs薄膜显示出改善的发射稳定性.     

Electrical studies on sputtered CuCl thin films

CuCl is a wide-direct band gap semiconductor, lattice matched to Si and it possesses excellent ultra violet (UV) emission properties. It is thus a promising candidate for the next generation Si based UV optoelectronics. CuCl films were deposited using RF magnetron sputtering technique. X-ray diffraction analysis reveals that the grains are strongly <111> oriented. Triangular crystallites of CuCl were observed in the AFM surface topograph. Au–CuCl–Si–Au structures were fabricated and field dependent electrical studies were carried out in the electric field range of 1.25 × 10⁶ to 2.5 × 10⁷ V/m. I–V characteristics show that ohmic conduction prevails in low electric fields up to 2.5 × 10⁶ V/m. In the higher field range, from 2.5 × 10⁶ to 2.5 × 10⁷ V/m, the conduction mechanism was Schottky emission controlled. There was no trap related charge transport observed at higher electric fields. Preliminary electrical studies are reported in this article.     

双层复合栅介质膜的制备及电学性能研究

介电常数分别为2.6的聚甲基丙烯酸甲酯(PMMA)及介电常数为16的偏氟乙烯-三氟乙烯共聚物(P(VDF-TrFE))两种不同的有机绝缘材料,通过溶液旋涂的方法在P型硅衬底上制备了不同结构的复合栅介质膜并测试了它们的高频C-V特性及漏电特性。实验结果表明Si-PMMA-P(VDF-TrFE)-Ag结构绝缘膜上单位面积电容达到了35nF/cm2,40V电压下漏电流随着扫描次数的增加逐渐由7.29×10-7 A/cm2降低至3.44×10-7 A/cm2。而Si-P(VDF-TrFE)-PM-MA-Ag结构栅介质膜测得的单位面积电容仅为15nF/cm2,在相同电压下的单位面积漏电流为1.93×10-8 A/cm2。在此基础上分析了电子陷阱以及电场强度对双层栅绝缘膜C-V、I-V特性的影响。     

Dielectrophoretic and electrothermal effects at alternating current heated disk microelectrodes

When a disk microelectrode is polarized with an alternating potential of very high frequency (0.1-2 GHz) and a high amplitude (up to 2.8 V rms), the electrode is heated up, and at the same time, a very intense electric field is created around the electrode (>10(6) V/m for electrodes 1 microm in radius). This strong electric field gives rise to positive or negative dielectrophoretic effects. Positive dielectrophoretic effects can be used to assemble nanowires from nanoparticles at the electrode edge. On the other hand, a negative dielectrophoretic effect is probably responsible for "jet boiling" observed at overheated microelectrodes. In addition, a combination of a high temperature gradient and a high potential gradient generates an intense electrothermal flow of solution which very strongly enhances the mass transport and is responsible for intense convection in such systems. The electrothermal flow and dielectrophoretic forces can be generated directly on a microelectrode employed in electrochemical detection because the high frequency ac polarization of the electrode does not interfere with the acquisition of analytical signals.     

基于(100)定向金刚石薄膜的辐射探测器研究

采用微波等离子体化学气相沉积（MPCVD）方法制备了100μm米厚高质量(100)定向金刚石薄膜. 利用(100)定向金刚石薄膜成功制备了α粒子探测器, -100V偏压下电荷平均收集效率为37.7%, 最大的电荷收集效率达到60%以上. 在此基础上, 通过在α粒子探测器条状电极面蒸镀一层合适厚度的硼(10B)膜转化层, 成功研制了金刚石中子探测器. 镀硼之后探测器对中子有明显的响应, 在1V/μm电场下, 对252Cf中子的能量分辨率达到9.3%,探测效率达到1.67%. 同时还研究了电场强度和硼(10B)层厚度对器件探测效率的影响规律. 在厚度<1.5μm时, 随着厚度的增加, 探测效率上升, 当厚度>1.5μm时, 探测效率下降.     

Energy distribution of trapping and transport states in MDMO-PPV ([poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene)

We have investigated charge carrier transport and trapping in the layers of [poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene (MDMO-PPV). To reveal distribution of the trapping states the thermally stimulated current method was applied using the varying excitation conditions by light and applied voltage. To assure the selective excitation of the defect states close to the band gap edges, both extrinsic and intrinsic excitation by the light passed through the long-pass color filters with the cut-off energies ranging from 1.77 eV up to 3.1 eV was employed. Carrier transport conditions were varied by increasing applied electric field from 5 x 10(4) V/cm up to 6 x 10(5) V/cm. The effective thermal activation energy of material conductivity was dependent both on the spectral region of the exciting light and applied electric field. The superposition of several thermally activated processes, i.e., carrier generation from the trapping states and thermally stimulated mobility growth according to the Gaussian disorder model, was revealed. The energy distribution of the trapping state density was shown to follow the Gaussian distribution function. We had demonstrated that carrier trapping is effectively influenced by the extended defect states with the effective activation energy values ranging from 0.05 eV up to 0.15 eV with maximum located at about 0.07-0.08 eV. Moreover, deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.