Field-induced electron emission from broad-area YBaCuO high-T c electrodes

A transparent anode facility has been used to compare the field-induced electron emission characteristics of planar YBaCuO high-T _c electrodes at room temperature and in the superconducting state. It was found that virgin electrodes under ambient conditions exhibit an initial current switch-on event at typical field levels of 30 MV m^–1, with the emission coming from a single point site: a large hysteresis effect was also observed when the field was cycled. In contrast, at low temperatures, no switch-on events were observed, and the hysteresis effect was significantly smaller. Also, if an emission current in the nanoamp range was recorded under constant-field conditions as the temperature was lowered through T _c, there was an abrupt (i.e. step-like) fall in both the emission current and its associated noise at the superconducting transition.     

Novel design for accurate alignment of high voltage electrodes assembly

A design is described which enables the accurate alignment of high voltage plane parallel electrodes used in an ultra-high vacuum assembly. The main features of this design are that it effectively overcomes the eccentricities which are present in both the glass-to-metal graded seal used in the housing envelope and in the linear motion drives employed to vary the gap separation between the electrodes, as well as being relatively simple to fabricate. The present design has been successfully tested in two large chambers at applied voltages of up to 100 kV and at a background pressure of better than 10^?9 torr.     

A high resolution electron spectrometer facility for studying the spectra of microscopically localized field emission sites on planar cathodes

A high resolution (?30 me V) electron spectrometer originally designed for studying micropoint emitters, has been adapted to measure the electron spectra of the microscopically localized field electron emission processes that occur on broad-area high voltage electrodes. Details are given of the redesigned electron optical and mechanical systems, including a new electrostatic interfacing lens and a micromanipulator assembly for scanning the specimen cathode. The performance of the new facility has been evaluated, and its resolution has been estimated to be <80 meV.A micropoint anode probe and an associated image intensifier viewing system has been used for recording the complementary electroluminescent optical emission spectra. Facilities for the in situ treatment of electrode surfaces, viz, electron bombardment heating and ion etching, have also been incorporated and their effect on the emission characteristics of broad-area sites has been investigated.     

In-situ studies on phase transformations under electron irradiation in a high voltage electron microscope

High voltage electron microscopy (HVEM), using electron energies adequate for causing displacements of atoms from lattice sites, is a very effective technique for studying mechanisms of solid state phase transformations and for charting the path of phase evolution in real time. This has been demonstrated in studies on chemical ordering in nickel-molybdenum alloys and on theβ → Ω displacement ordering in zirconium-niobium alloys. The enhanced diffusivity due to electron irradiation makes it possible to explore a sequence of phase evolution at low enough temperatures where even some first-order transformations are driven by free energy (G) instabilities with respect to the relevant order parameter (η). Specific issues addressed in these studies are reviewed in this paper.     

压力管道泄漏声发射信号频谱特性实验研究

以水为实验介质,进行了充液压力管道泄漏声发射信号的实验研究。利用小波变换对不同流量、不同泄漏孔径条件下检测到的声发射信号频谱特性进行了分析研究,结果表明充液管道泄漏信号经小波分解后a6级信号的能量占总能量的绝大部分,信号的主要频率成分集中在3.05kHz-3.81kHz左右。     

A technique for studying the multiple emission sites on broad area electrodes in a vacuum

Observations of the transition radiation at the anode of a high voltage vacuum device using a low-light telescope have enabled the positions of the emission sites on the cathode to be determined accurately and have shown the way in which emitters are destroyed and sometimes produced at a breakdown. In addition, the electrical characteristics of the individual emission sites have been obtained by measuring the intensity of the transition radiation. This technique should allow the factors governing the voltage performance of industrial high voltage vacuum devices to be better understood.     

Effect of anodization voltage on electron field emission from carbon nanotubes in anodized alumina template

In this work, electron field emission from AAO-CNT structure is studied as a function of anodizing voltage. It is found that the turn-on electric field of AAO-CNTs reduces from 5 V/microm to 4 V/microm as anodization voltage increase from 20 to 30 V. On the other hand, CNTs the turn-on electric field of AAO-CNTs increases from 4 V/microm to 6 V/microm as anodization voltage increase from 30 to 40 V. Thus, anodization voltage of 30 V provides an optimal AAO-CNTs structure for electron field emission. The emission data have been analyzed based on the Fowler Nordhiem (F-N) model. AAO template prepared with 30 V anodization voltage is found to yield CNT nanoarray with optimum alignment and spacing that increase field enhancement factor by the lowering of field screening effect without significant lowering of CNTs density.     

Strain and temperature distribution in broad-area high-power laser diodes under operation determined by high resolution X-ray diffraction and topography

Broad-area lasers were investigated by high resolution X-ray diffraction (HRXRD) and topography, before and during laser operation. Rocking curves were taken at different positions of the 150 μm wide and 2 mm long laser stripe, using high-precision motorized slits with a spatial resolution of 40×40 μm². From the series of rocking curves recorded at different lateral positions and driving currents, the curvature and temperature profiles along the stripe could be estimated for different driving currents. X-ray topographs revealed regions with higher strain compared to the surrounding area. At lateral positions within the stripe, where the highest temperature was determined by HRXRD, regions of dark contrasts, indicating defects, were detected by cathodoluminescence. Transmission electron microscopy revealed that the highly strained regions act as sinks for point defects, since no dislocations or dislocation loops were detected. Thus, a clear correlation between temperature rise, high local strain and defect formation was found.     

高电位梯度ZnO压敏电阻的高压稳压性能研究

采用稀土掺杂和低温烧结的方法制备出高电位梯度的ZnO压敏电阻,并研究了Y2O3掺杂浓度对试样电位梯度和稳压性能的影响.结果表明,在800℃的烧结条件下,掺杂0.08%(摩尔分数)Y2O3后试样的电位梯度增加了49%,稳压系数达到1.99×10-2.从微观角度对ZnO压敏电阻烧结过程中的物化反应分析发现,较低的烧结温度能够抑制Y2O3的受主固溶和Bi2O3的挥发,减缓晶粒的生长速度,改善晶界质量,从而提高试样的电位梯度,实现高压稳压.     

Effect of annealing on diamond-like carbon characteristics by electron spin resonance spectral analysis

We have examined the effect of annealing on physicochemical properties of the diamond-like carbon (DLC) films to produce higher quality films by the electron spin resonance spectral analyses of the immobilized dangling-bond sites (DBS), since amount of DBS reflects the characteristics of DLC films. On heat treatment of DLC deposited from ethylene monomer under anaerobic condition, the DBS decay was clearly shown, as the temperature raised. The decay described by second-order kinetics indicated that the recombination reaction of DBS progressed on heat treatment, suggesting that annealing treatment would accelerate the carbon-carbon covalent bonding network to produce harder films. In fact, the resulted DLC film derived from ethylene monomer showed non-existence of any type of oxygen atom based on X-ray photoelectron spectrum measurement, and water contact angle measurement showed higher hydrophobic surface of the DLC films.     

In-situ devitrification of metallo-organic decomposition solutions in the high voltage electron microscope

The decomposition of metallo-organic compound films to yield ceramic oxides with a composition in the lead lanthanum zirconium titanate (PLZT) phase field has been observed using an environmental cell in the transition electron microscope. Diffraction pattern analysis indicates that the first formed phase is lead oxide but that this is rapidly followed by the formation of an homogeneous PLZT composition. The results are supported by differential thermal analysis (DTA)/thermogravimetric analysis (TGA) of the precursor solutions. These observations indicate that it may be practical to prepare thin films of this important electrooptic material by this route.     

Synthesis and improved electron field emission characteristics of Au-coated nano-carbon needle films

Nano-carbon needle films (NCNFs) coated with a 5-nm Au layer were prepared on p-type Si (100) substrates by means of quartz-tube type microwave plasma chemical vapor deposition (MWPCVD) at different total gas pressures and an electron beam (EB) method. The NCNF deposited at the total gas pressure of 60 Torr had better field emission (FE) characteristics due to the dense structure of carbon sheets, good direction and high density of carbon needles. The FE properties were obviously improved due to depositing Au thin layer on NCNFs. The FE current density at a macroscopic electric field, E, of 10 V/μm was increased from 68.2 mA/cm² to 154.6 mA/cm² and the threshold field was decreased from 2.4 V/μm to 2.1 V/μm for the Au-coated NCNF deposited at the total gas pressure of 60 Torr. The three-region E model was employed to reasonably explain the FE data.     

Current voltage characteristics of composite superconductors with high contact resistance

An experimental study has been made of current-voltage characteristics of composite superconductors with contact resistance between superconducting filaments and normal metal with high electrical conductivity. It is shown that stable resistive states exist in such conductors over a wide range of currents. The presence of resistive states is interpreted in terms of the resistive domain concept. The minimum and maximum currents of resistive states are found to be dependent on the electrical resistance of normal metal and magnetic field.     

Synthesis and improved electron field emission characteristics of Au-coated nano-carbon needle films

Nano-carbon needle films (NCNFs) coated with a 5-nm Au layer were prepared on p-type Si (100) substrates by means of quartz-tube type microwave plasma chemical vapor deposition (MWPCVD) at different total gas pressures and an electron beam (EB) method. The NCNF deposited at the total gas pressure of 60 Torr had better field emission (FE) characteristics due to the dense structure of carbon sheets, good direction and high density of carbon needles. The FE properties were obviously improved due to depositing Au thin layer on NCNFs. The FE current density at a macroscopic electric field, E, of 10 V/μm was increased from 68.2 mA/cm² to 154.6 mA/cm² and the threshold field was decreased from 2.4 V/μm to 2.1 V/μm for the Au-coated NCNF deposited at the total gas pressure of 60 Torr. The three-region E model was employed to reasonably explain the FE data.     

MgO纳米线的制备及其电子发射性能的研究

采用碳热还原-氧化法成功制备大小均匀的MgO纳米线,采用场致发射电子显微镜(FESEM)和X射线衍射(XRD)表征其形貌及晶体结构。采用丝网印刷将MgO纳米线转移到阴极电极,并将阴极电极与印刷有荧光粉的阳极电极组装成二级场致发射器件。场致电子发射测试表明MgO纳米线具有较好的电子发射特性:其阈值电场强度仅为3.82V/μm(1mA/cm2),最高电流密度达到2.68mA/cm2(4.01V/μm),发光亮度为1152cd/m2,4h内没有明显的衰减。MgO有望作为冷阴极材料在场致发射器件上得到应用。     

A study of the electron emission characteristics of a triggered vacuum switch

Details are given of the construction and operational characteristics of a triggered vacuum switch suitable for operation over a wide range of voltage. To gain an insight into the physical basis of the performance of the device, two in situ analytical techniques have been employed to study the electron emission characteristics. Firstly, an anode probe hole technique, incorporating a new automated two-dimensional electrode scanning facility, has been used to display the spatial distribution of the electron emission associated with the ‘firing’ mode of the triggered vacuum switch. Secondly, the energy spectrum of this emission has been recorded using a high resolution electron spectrometer that is interfaced with the above facility. In conclusion, a qualitative discussion aims to interpret the physical significance of the experimental findings.     

岩石声发射信号能量分布特征的EMD分析

冲击荷载作用下岩石声发射信号具有瞬态性和多样性的特点,属于典型的非平稳信号。利用EMD方法对岩石声发射信号进行分解,得到一系列具有不同特征时间尺度的IMF分量,对每一个平稳的IMF分量提取能量特征。分析结果表明：冲击荷载作用下岩石声发射信号能量主要分布在前4个IMF分量内,且分布不均匀;岩石声发射信号各IMF分量的频谱与原始信号的频谱基本一致;随着岩石的密度、纵波波速、弹性模量的降低,冲击荷载作用下岩石声发射信号的优势频率越来越集中,且其优势频率有往低频发展的趋势;相比小波包分析,EMD分析法对于非平稳信号而言更具适应性。