复合阴极材料发射特性分析

 基于对爆炸发射点火机制的分析,提出了介质增强场致爆炸发射的设想,研制并实验研究了金属-介质复合阴极的电子发射特性;同时,基于对表面闪络爆炸发射机制的分析,研制出了石墨-碳纤维复合阴极并进行了初步实验研究。研究结果表明,金属-介质复合阴极与石墨 碳纤维复合阴极电子发射密度均超过17 kA/cm²,使用寿命预计超过10⁵次。     

碳纳米管阴极的强流脉冲发射性能研究

采用丝网印刷和涂敷方法制备了两种碳纳米管阴极，并研究了两种阴极的强流脉冲发射特性，表征了阴极表面碳纳米管的形貌及分布.研究结果表明在脉冲宽度为100 ns、电压为1.64×10⁶ V的脉冲电场下，涂敷法制备阴极的场发射电流最高达5.11 kA，最高发射电流密度达260 A/cm².丝网印刷法制备阴极的场发射稳定性优于涂敷法制备阴极，但其发射电流低.阴极表面发射体的形貌与分布影响了阴极的脉冲发射性能.碳纳米管阴极的脉冲发射机理为爆炸电子发射.碳纳米管阴极可以作为强 关键词： 碳纳米管 阴极 脉冲发射 强电流     

重复频率爆炸发射阴极现状及展望

重复频率爆炸发射阴极(EEC)是产生高功率重复频率强流电子束的关键。阐述了爆炸发射的尖端场增强和闪络引发机制,分析了影响EEC重复频率运行的因素,综述了EEC研究现状并总结了几种EEC特性,指出实现重复频率发射阴极的方法在于探索新型材料和改进结构。提出采用六硼化镧(LaB6)作为EEC材料和适用于单焦斑多幅闪光照相工业冷阴极二极管(IXD)的新型阴极结构轮辐状金属-铁电陶瓷复合阴极,并对其前景进行展望。     

中间层Re的加入对覆膜钡钨阴极性能的改善

研究了一种新型的覆膜钡钨阴极——双层膜(Os-W/Re膜)钡钨阴极.对这种新型阴极的发射性能进行了测试，重点对其老炼前后表面薄膜的微观形貌进行了分析，表明中间层Re膜的加入使覆膜钡钨阴极的性能得到了改善.通过对Os-W双元合金膜钡钨阴极和Os-W/Re双层膜钡钨阴极发射特性的比较，发现Os-W/Re双层膜阴极的直流发射性能好于Os-W合金膜阴极.对两种阴极激活后发射表面的X射线光电子能谱分析表明，Os-W/Re双层膜阴极激活后表面形成的三元合金膜是其发射特性优于Os-W合金膜阴极的主要原因.应用扫描电子显微镜分析比较两种阴极激活老炼后的表面状态，结果表明：Os-W合金膜阴极在老炼一段时间后，其表面薄膜出现开裂，这会导致阴极发射均匀性下降；而Os-W/Re双层膜阴极在同样老炼条件下，发射表面薄膜均匀并保持完整，从而确保覆膜钡钨阴极发射均匀性和工作可靠性. 关键词： 双层膜钡钨阴极 Os-W/Re膜 Os-W膜 薄膜开裂     

平面二极管爆炸发射阴极特性实验研究

 在电压0.6~1.0 MV,脉冲重复频率为100 Hz条件下,实验研究了爆炸发射阴极的有效发射面积、平均发射电流密度、二极管阻抗、电子束能量损耗机制等特性。结果表明：阴极有效发射面积随时间呈方波变化,在脉冲开始后5 ns内有效发射面积基本达到稳定。在碳纤维、天鹅绒、石墨、不锈钢4种阴极材料中,碳纤维阴极有效发射面积最大且变化相对稳定,并且碳纤维阴极具有最大的平均发射电流密度。二极管阻抗随着阴阳极间隙的增加并非呈平方关系增加,而是呈线性增长,阻抗失配是降低电子束能量传输效率的主要机制。     

Spindt型与薄膜场致发射的数值模拟与特性比较

采用质点网格法（particle-in-cell）,利用MAGIC软件模拟了场致发射的物理过程.对两 种典型的场致发射模型（Spindt阴极发射体和金刚石薄膜发射体）分别进行了模拟.对Spind t阴极发射，研究了发射特性与尖端尺寸，尖端与栅极面的相对高度的关系.对金刚石薄膜发 射，比较了三极管和四极管的发射特性，以及薄膜面积对发射特性的影响，得出金刚石薄膜 发射体优于Spindt发射体的特性. 关键词： 场致发射 MAGIC程序 Spindt发射体 金刚石薄膜发射体     

丝网印刷制备碳纳米管阴极的强流脉冲发射特性研究

采用丝网印刷法制备了一种大面积的碳纳米管阴极,表征了阴极表面碳纳米管的形貌及分布.研究了该阴极在不同脉冲条件下的高压脉冲发射特性,分析了发射时阴极面等离子体产生和发射点的分布.研究表明：碳纳米管阴极的脉冲发射机制为爆炸电子发射,在平均场强为16.7V/μm的单脉冲电场下,阴极的最高发射电流密度为99 A/cm².在平均场强为15.4 V/μm的双脉冲电场下,阴极的最高发射电流密度为267 A/cm².碳纳米管阴极可以作为强流电子束源在高能微波器件中得到应用. 关键词： 强流脉冲电子束 碳纳米管 阴极 丝网印刷     

碳纳米管阴极强流脉冲发射放气质谱分析

借助2 MeV直线感应加速器注入器平台,利用四极质谱仪研究了碳纳米管阴极的强流脉冲发射放气质谱特性. 研究结果表明:在脉冲高压电场下,碳纳米管阴极材料释放出较多的吸附气体,解吸气体又以CO₂,N₂(CO),H₂三种气体居多,这些解吸气体在阴极等离子体形成过程中起着重要的作用. 通过分析解吸气体成分的含量,证明碳纳米管阴极强流脉冲电子发射过程为场致等离子体发射,而不是场致爆炸发射. 关键词： 碳纳米管阴极 强流脉冲发射 质谱分析 场致等离子体发射     

表面微结构对碳化硅晶须掺杂石墨阴极爆炸电子发射性能的影响

爆炸发射阴极已广泛应用于高功率微波源,但常规场致爆炸发射阴极存在使用寿命短或电子发射不均匀的问题,改善阴极材料是解决这一问题的有效途径.本文将碳化硅晶须掺杂到石墨中制备得到阴极,从二极管电流波形上升沿和输出微波脉宽产生的变化着手,分析了碳化硅晶须掺杂石墨阴极表面材料成分和微观形貌对其电子发射性能的影响机理.研究发现,碳化硅晶须的存在,不仅有利于阴极场发射的快速启动、发射微点数目增多,还有利于降低等离子体膨胀速度、抑制脉冲缩短现象,使得输出微波脉宽增大.随着脉冲发射数量增多,碳化硅晶须掺杂石墨阴极表面被等离子体不断"抛光",微凸起形状因子减小、均匀性提高,场发射启动速度减慢,但输出微波脉宽增大.     

爆炸电子发射初期阴极表面电场的研究

为了研究二极管爆炸电子发射初始阶段阴极表面复杂的物理现象及规律, 建立了由场致电子发射阴极构成的一维平板真空二极管物理模型,通过自行编程数值求解泊松方程, 考虑了发射出的电子对阴极表面电场的非线性影响,自洽模拟得到了阴极表面电场随时间的变化情况. 模拟结果表明,爆炸电子发射初期,阴极表面电场随时间的增加而呈现出不断振荡的规律, 且振荡幅度越来越小,最终到达一个稳态的值,二极管两极板之间的外加电场越大, 阴极表面稳态电场的绝对值越大;电场增强系数越大,阴极表面稳态电场的绝对值越大. 在整个时间演变过程中,阴极表面的实际电场强度决定着阴极发射的电流密度大小, 反过来阴极发射的电流密度又会影响到阴极表面的电场.     

天鹅绒与碳纳米管阴极强流脉冲发射特性

在2 MeV直线感应加速器注入器平台上开展了天鹅绒阴极与碳纳米管阴极的强流脉冲发射特性综合实验。研究结果表明:天鹅绒阴极与碳纳米管阴极均具有强流脉冲发射性能,在1.61 MV的二极管电压下,天鹅绒阴极与碳纳米管的发射电流密度分别为84,108 A/cm2;启动时间分别为21,40 ns;放气量分别为0.29,0.91 PaL;放出气体分子数目与发射电子数目之比分别为64,225;两种冷阴极强流脉冲发射时的放气质谱相似。     

The volt-ampere characteristics of the leakage and emission current of sandwich cathodes

The study of the properties of a metal-dielectric-metal system in a strong electric field has so far led to heterogeneous results. Their agreement with theory is unsatisfactory or lacking entirely. The theoretical conceptions are based on the assumption of the field emission of electrons from the surface of metals to the conduction band of the dielectric and from there by passage through the second metal electrode to vacuum. A perfect dielectric is assumed here. This assumption is probably not fulfilled when realizing the cathodes, as can be estimated from a comparison of the technology of producing a dielectric, for example, with the preparation of intrinsic semi-conductors. The presence of defects in the dielectric layer may have a decisive influence on the properties of the cathodes. In this way we can obtain different results even when using the same materials for making the cathodes.The present paper deals with the influence of the thickness of the dielectric on the electrical properties of cathodes. Two different dielectrics were used, produced in different ways: a dielectric dependent on the metal electrode (oxidizing cathodes) and independent (evaporated cathodes).In conclusion, the author thanks L. Sodomka and K. Frainic for assistance in the experiments.     

Physical operating principles of scandate cathodes for microwave devices

The electronic structure of barium oxide crystallites determining the emission properties of both dispenser and scandate cathodes has been studied using electron spectroscopy for chemical analysis, electron energy loss spectroscopy, and optical spectroscopy. It has been established that the other elements (calcium, aluminum, scandium, and tungsten) contained in cathode materials are diluted in barium oxide and significantly affect its electronic structure and, consequently, emission properties. The obtained results give an idea about the physical and physicochemical mechanisms of the effect of scandium on the reduction of the work function of scandate cathodes relative to that of the cathodes of other types.     

Composition,structure, and performance of Ni-based cathodes in lithium ion batteries

With the rapid development of electric vehicles, Ni-based cathodes attract increasing attention as used in power batteries due to their high capacity and low cost. However, Ni-based cathodes are faced with several problems, such as Li/Ni disorder, cycle capacity degrading, poor storage in air, and thermal instability. This review carefully compared the structure difference between LiNiO₂ and LiCoO₂ and concluded that the electronic structure of Ni³⁺ determined the instability of LiNiO₂. The degrading mechanism during long cycle was discussed in the second part and it could be attributed to the surface properties. Moisture sensitive severely restricts the application of Ni-based cathodes due to the gelation in slurry making and gas released in batteries. Some possible mechanisms proposed by previous researchers were reviewed in the third part and a new interpretation on the basis of diffusion was also suggested. Lastly, the nature of thermal instability of Ni-based cathodes was presented.     

X射线二极管在2～6keV能区的灵敏度退化研究

利用北京同步辐射装置4B7B束线,在2.1~5.9 keV能区,对"强光一号"加速器Z箍缩实验中常用的Al和Au阴极X射线二极管进行了谱响应标定。对比了不同阴极材料(Au和Al)、加工方式(蒸镀Al和机械加工固体Al)及使用条件(参与实验发次)对探测器谱响应分散性及退化程度的影响。长期储存后的镀Au阴极仍有较好的谱响应一致性,但灵敏度退化明显,比文献报道新鲜Au阴极数据低70%以上,使用中还会进一步降低。Al阴极在保存和使用中的灵敏度退化相对较轻。新鲜的固体Al阴极谱响应分散性较小,灵敏度较文献报道数据略高,使用过10~40发次并保存9个月后灵敏度平均下降约20%~30%。镀Al阴极的谱响应分散性较大,相对偏差可达20%。初步探讨了定期更换以减轻灵敏度退化影响的可行性。     

掺镧锆锡钛酸铅陶瓷极化强度变化量对电子发射电流强度的影响

铁电阴极因其优异的电子发射性能在高功率微波管的电子束源、平板显示技术以及宇航推进器等领域 有着广阔应用前景而日益受到人们的重视.大量研究表明,铁电阴极电子发射性能受阴极材料性能的影响. 在激励电场作用下,铁电阴极材料会产生表面非屏蔽电荷而引起极化强度的变化, 这表明铁电阴极电子发射性能可能与阴极材料的极化强度变化量存在着某种关系. 为研究阴极材料极化强度变化量对铁电阴极电子发射性能的影响,以掺镧锆锡钛酸铅铁电和反铁电陶瓷样品 作为阴极材料,通过正半周电滞回线测试得到阴极材料在不同电场强度下的极化强度变化量, 测量得到电子发射电流强度随激励电场的变化曲线,并分析了电子发射电流强度与极化强度变化量的关系. 结果表明,两种样品电子发射电流强度与极化强度变化量正相关.     

Influence of the spot field on field emission from composites

Field emission from composite cathodes made of materials with greatly differing work functions (lanthanum hexaboride-pyrographite and hafnium carbide-pyrographite) and also from homogeneous lanthanum hexaboride cathodes, is studied experimentally. The effective emission from the composite cathodes the constituents of which differ greatly in work function and much worse emission properties of the homogeneous cathode are explained by making allowance for the influence of high (≥2 × 10⁷ V/cm) fields of spots arising at the contact of materials with different work functions on the field emission. The emission current density and the flow of electrons emitted under the action of the spot fields toward the anode are estimated by numerical computation.     

Efficient electron sources utilizing the effect of field emission

W-Cs₃Sb, W-TiO₂, and W-TiO₂-Cs field emission cathodes are fabricated and studied. All these cathodes outperform the conventional tungsten cathode in emission properties: the emission current is very stable and one-and-a-half to two orders of magnitude higher. Physical models of the new emitters are suggested and experimentally verified.     

LaB6与TaC混合涂层热阴极

研究了一种LaB6与TaC混合涂层热阴极,其发射层通过均匀混合LaB6与TaC粉末得到。比较了该阴极在LaB6与TaC混合比例为1∶1, 2∶1和3∶1下的发射特性,发现混合型LaB6阴极的功函数与多晶LaB6阴极的非常接近,在3∶1的混合比例下,电极的发射电流稳定,得到的电流密度为30 A/cm2。该电极可被应用于需要大电流密度和超大面积阴极的真空电子器件及动态真空电子束设备中。     

Carbon nanotube field emission cathodes fabricated with trivalent chromium conversion coated substrates

The properties of carbon nanotube (CNT) field emission cathodes fabricated by a dip coating method with trivalent chromium conversion coated substrates are studied. Two kinds of substrates with different morphologies, one with a rough crackled surface and the other with a smooth surface, were used for making the CNT cathodes, and their I-V curves and emission patterns were evaluated. The results show that, as compared to the smooth substrate surface, the rough surface with self-assembled sub-micro-cracks on the substrate can dramatically enhance the uniformity of the emission pattern and the emission efficiency. The cathode fabricated with the crackled substrate shows good field emission properties such as high brightness, good uniformity, a low turn-on field (0.86 V/μm) and a high current density of 10 mA/cm² at 2.5 V/μm.