利用奥杰能谱学评价热阴极

已利用奥杰能谱学鉴定表面化学组成的能力,来评价大功率微波管浸渍钡钨阴极的好坏。用奥杰能谱学与逸出功测量法研究了发射好的阴极与发射差的阴极的表面,其结果解释了从行波管中、对由于发射特性差而剔除出的阴极的失效方式所作的分析。此计划所鉴定的发射差的阴极大多数取自制成的电子枪,它们曾经在为通讯技术卫星计划所研制的200瓦行波管上使用过,并已报废。测量结果表明,人们在发射差的阴极上至少观察到两种失效方式:①阴极表面的化学污染;②阴极表面层只有少数部分为钡所复盖。     

氧化物阴极的失效研究

一、前言 氧化物阴极已有几十年的应用和研究历史,是各类电真空器件中应用得最为广泛的一种阴极。几十年来人们对氧化物阴极的各种现象,诸如发射特性,涂层电导,中间层电阻,中毒、蒸发等等进行了较为详细的研究,通过这些研究人们对它的工艺和特性已有了较为透彻的了解,但由于氧化物阴极是一个十分复杂的发射体系,而电子发射又是一种表面现象。过去限于表面分析手段的不足,对氧化物阴极的发射本质还未能有完全的认识,对失效的氧化物阴极也难以去分析,判明它失效的原因。     

提高钼尖锥场致发射阵列阴极发射性能的研究

在利用微细加工技术和双向薄膜沉积工艺制得的钼尖锥场致发射阵列阴极进行实用化的过程中，目前存在的两个主要障碍是，阴极发射电流密度低和工作不稳定。通过对阴极发射失效机理和失效阴极的SEM照片进行研究认为，导致电流密度较低的原因是由于尖锥阵列的不均匀性造成只有部分尖锥发射电子；引起发射不稳定的主要因素是由于尖锥表面的微凸起和毛刺以及它吸附的各种影响有效功函数的污染物。采用电阻限流技术提高了阵列发射的均匀性，同时通过阴极老炼技术增强了场发射的稳定性，使其电流发射密度有很大程度的提高，而且电流波动也大为减小。研究结果对于该阴极在射频功率和平板显示等器件上的应用有着重要的意义。     

利用激光沉积研究镧钼阴极表面发射机制

为了研究镧钼阴极表面发射机制,采用专为研究阴极设计的与俄歇能谱仪相连的脉冲激光沉积装置制备薄膜阴极.通过测量阴极发射性能和原位分析表面成分(原子数分数),研究了阴极表面元素镧La和氧O变化对阴极发射性能的影响.实验发现随着阴极表面镧膜变薄,阴极发射性能逐渐减弱;阴极发射性能与表面元素La,O 的含量有关,表面层中La/O越高,阴极的发射性能越好.结果表明,传统的单原子层理论无法解释镧钼阴极的发射机制;超额镧在镧钼阴极的发射中起到了关键作用.     

造成发射衰落的CaO表面凝聚

在一定使用条件下,即使整个阴极有足够的发射,由于阴极表面上形成的高逸出功斑点,仍会导至阴极失效。这种失效在光导授象管使用的氧化物阴极中发现过,该管的电子束电流来自阴极表面的一小部分。利用奥杰电子谱仪和低能电子扫描探针配合等表面分析技术,揭示出高逸出功部分可能是与阴极表面钙的集中度高和钡的集中度低有关。奥杰溅射剖面也说明了,这个钙的富集区域(高逸出功斑点)实际上是厚度为100A数量级的表面簿层。而整个阴极组成是均匀的。这些斑点可能是BaO与BaCO_8转化的低共熔过程中产生的CaO熔渣。     

一种发射衰减的机构-CaO在表面的偏析

在某些应用中虽然阴极作为一个整体有良好的发射,但在阴极表面上形成一些高逸出功的小块可能导致阴极的失效。这种形式的失效曾在一种Vidion管的氧化物阴极中发现,在这种管子中来电流来自阴极表面一个很小的部份。表面分析技术AES和SLEEP联用指明高逸出功的区域是与高的表面钙浓度和低的表面银浓度联系在一起的。俄歇溅射剖面分析也揭示:这个富钙区域(高速出功小块)是一个很薄的表面层,厚度为100(?)的数量级而阴极的体成份似乎是均匀的。这种小块形成的一个可能的原因是在转控过程中由于形成Bao/Baco_3共晶熔化而使表面形成Cao熔渣。     

钪型阴极表面微观发射结构的模拟计算

在阴极研究领域,钪型阴极因其大发射电流密度受到广泛关注,但其发射机制仍不明确。普遍认为表面发射层为BaxScyOz-W结构,但发射表面是动态变化的,很难确认其最佳表面发射结构。本文对钪型阴极表面BaxScyOz-W的理想发射结构进行了建模,并利用密度泛函方法对其功函数进行了计算。计算得到Ba-O-Sc-O-W表面结构的最小功函数为1.186eV。通过对计算结果的分析,讨论了不同表面原子结构对应的功函数变化。     

待定系数法计算场致发射体阴极表面场强和发射电流密度

在计算场致发射体阴极发射电流时 ,影响发射电流的主要因素是阴极表面的电场强度。由于发射电流密度的大小和阴极表面场强呈指数关系 ,阴极表面场强很小的变化将引起发射电流的剧烈变化 ,所以提高阴极表面场强的计算精度是至关重要的。本文提出了一种计算阴极表面场强的新方法——待定系数法 ,并用该方法计算了一个二极管场致发射体的阴极表面电场强度和电流密度。     

阴极蒸发物电子发射现象的研究

为研究钡钨阴极蒸发物的电子发射现象,采用一种新设计的测试装置,对沉积在多晶钨表面上阴极蒸发物的电子发射曲线进行了采集,利用电子发射显微镜和扫描电镜对蒸发物沉积层的电子发射像、表面形貌和成分进行了分析。结果表明,电子发射曲线分3段,即陡升段、快升段和缓升段。分析认为,发射曲线的3段依次对应着多晶钨表面的晶界及划痕发射、晶面发射和3维岛状发射。实践证明,在覆膜阴极表面构造均匀弥散分布的岛状晶体发射点,可大幅度提高阴极的电子发射性能。     

掺氧化钇钡钨阴极的表面特性研究

以掺氧化钇的钡钨阴极作为研究对象,利用现代表面分析技术,包括发射式电子显徽镜、扫描电子显微镜、俄歇电子谱仪和高分辨率x射线光电子谱仪等,进行了综合研究,获得了阴极发射性能、表面形貌和表面化学等实验结果,并对实验结果进行了讨论。     

Vacuum arcs and switching

This paper is a review of vacuum-arc phenomena which are related to switching devices. Despite the device overtones, the approach adopted for this paper is fundamental. Topics discussed include the drawn arc, the triggered arc, the power input to the cathode spot, cathode-spot division, arc stability, substructure of the cathode spot, dielectric recovery processes, and breakdown between electrodes subjected to repeated arcing. Frequent reference to the recent literature is made. Due to the somewhat specialized nature of certain parts of the discussion, introductory and appended sections of the paper present supplementary remarks on the concept of plasma and electrical conduction in gases, electron emission processes, and electrical contact phenomena.     

The Numerical Simulation Study of Pseudospark Hollow Cathode Discharge

Pseudospark discharges are sources of intense electron beams. Reported in this paper are theoretical studies of the Pseudospark discharges. A theoretical and computational model has been adopted to study the initiation phase of Pseudospark discharges via a two-dimensional electrostatic particle-in-cell plus Monte Carlo (PIC-MCC) collision method. From the numerical results, a sequence of physical events has been identified. It has been found that the ionization processes determined by local electric field and hollow cathode effect. The growth phenomena is dependent of α ionization multiplication due to local space charge from initial ionization growth to onset of the hollow cathode effect, and then hollow cathode effect become leading factor.     

浸渍钪酸盐钡钨阴极的次级发射特性的研究

本文利用扫描电子束探针法,研究了渍制钪酸盐钡钨阴极在室温下的次级发射特性,观察了激活程度对该阴极的次级发射特性、次级发射图象和次级发射面分布的影响。激活最佳时,可获m=3.56(Epm=700V)。在温度高于1100℃下激活,对的影响较大。该阴极表面的分布是不均匀的。面分布曲线的峰值半高宽度为0.4。本文结合国内外对该阴极表面分析研究的结果,对实验现象进行了讨论。从理论上推导出的二项式面分布曲线能与实验结果较好地符合。     

Anode/cathode make and break phenomena in a model of defibrillation

The goal of this simulation study is to examine, in a sheet of myocardium, the contribution of anode and cathode break phenomena in terminating a spiral wave reentry by the defibrillation shock. The tissue is represented as a homogeneous bidomain with unequal anisotropy ratios. Two case studies are presented in this article: tissue that can electroporate at high levels of transmembrane potential, and model tissue that does not support electroporation. In both cases, the spiral wave is initiated via cross-field stimulation of the bidomain sheet. The extracellular defibrillation shock is delivered via two small electrodes located at opposite tissue boundaries. Modifications in the active membrane kinetics enable the delivery of high-strength defibrillation shocks. Numerical solutions are obtained using an efficient semi-implicit predictor-corrector scheme that allows one to execute the simulations within reasonable time. The simulation results demonstrate that anode and/or cathode break excitations contribute significantly to the activity during and after the shock. For a successful defibrillation shock, the virtual electrodes and the break excitations restrict the spiral wave and render the tissue refractory so it cannot further maintain the reentry. The results also indicate that electroporation alters the anode/cathode break phenomena, the major impact being on the timing of the cathode-break excitations. Thus, electroporation results in different patterns of transmembrane potential distribution after the shock. This difference in patterns may or may not result in change of the outcome of the shock.     

Vacuum arc ion currents and electrode phenomena

Properties of dc vacuum arcs between copper electrodes are studied in both a vacuum interrupter and a metal walled arc chamber. Maximum ion currents of ∼8 to 20 percent of the arc current (100 to 3000 A) are drawn from the diffuse arc plasma when the bounding metal wall or shield is biased negative. This maximum ion current is a fundamental arc property independent of wall diameter, anode diameter, and electrode spacing. The geometric dependence of the wall ion current, together with observations of isotropic vapor and ion emission from the cathode, indicates that the cathode regions adjacent to the cathode spots are the predominant sources of ionization for the plasma. Assuming single ionization, 55 percent of the vapor leaving these regions is ionized. Starvation phenomena in the anode region remote from the cathode spots lead to anode voltage drop and anode spot formation. Post arc currents reveal a mean ion speed during arcing of ≈8×10⁵cm/s. This mean speed may be acquired in the cathode region by acceleration from a potential maximum.     

在沉铜层上镀铜的阴极初始过程研究

针对印制电路板沉铜后进行一次铜电镀时,作为阴极的电路板的电镀初期的过程进行研究并阐明其发生机理。     

AN INVESTIGATION ON SECONDARY EMISSION PROPERTIES OF IMPREGNATED BARIUM SCANDATE DISPENSER CATHODE

A scanning electron probe is used to study the secondary emission properties of the im-pregnated barium scandate dispenser cathode, the influence of the activation on the secondary emis-sion property, the secondary emission image and the secondary emission distribution over the surfaceof the cathode. At optimal activation, δ_m=3.56 (E_(pm)=700eV). The activation has a larger effect onδ when the activation temperature is higher than 1100℃. The distribution over the surface of thecathode is non-uniform. The half-peak width of the distribution curve over the surface is 0.4. Theexperimental phenomena are discussed in relation to surface analysis of the cathode. The theoreticallyderived binomial distribution curves over the surface fit much better with the experimental results.     

The effect of space charge on shot noise in crossed-field electron guns

The two-dimensional electronic behavior of the crossed-field potential minimum is analyzed by means of a feedback network which provides a vehicle for understanding the complex phenomena, while allowing quantitatively accurate numerical calculations. The solutions, limited to the low-frequency range where transit time may be neglected, Show shot-noise smoothing as a function of magnetic field and cathode length. For low magnetic fields and short cathodes, the smoothing approaches the results of the North theory for zero magnetic field. It is also shown that if the cathode length is greater than about 11 normalized (Kino) units or 0.55 of the cycloid length for the existing field conditions, an initial perturbation of the emission current will lead to growing fluctuations of the beam current. This instability is considered to be responsible for the observation, in some crossed-field tubes, that the output noise increases when the cathode is heated sufficiently to form a potential minimum in front of the cathode. This criterion for the existence of excess noise is applied to all the experiments for which sufficient data have been published and no disagreement is found.     

测量热阴极次级电子发射的新方法及其应用

本文利用相关检测技术,并对测试管结构作了改进,很好地抑制了热电子本底及空间电荷效应,构成一种测量热阴极在工作温度下次级电子发射性能的新方法。以浸渍钪酸盐阴极为样品,测得在低的轰击电子能量和电子流情况下次级电子发射系数占随温度指数上升;轰击电子能量或轰击电子流较大时,温度对没有很大的影响。研究表明高温下钪酸盐阴极存在电子轰击热发射增大效应,对此本文提出内建场模型加以解释。     

Dynamic cathode boundary fields and transferred electron oscillators

The evolution of a generalized time-dependent cathode boundary field model is discussed, and calculations are presented which demonstrate its applicability for explaining such diverse phenomena as 1) the appearance of anomalously high efficiency oscillations in InP and 2) the more moderate oscillatory behavior associated with GaAs.