具有一个环形阳极的马鞍场电子振荡微电离规

本文提出两种结构的具有环形阳极的马鞍场电子振荡微电离规(以下简称鞍场规),它其于可以产生电子路径,因而产生有效的气相电离的静电马鞍场约束的基础上。此种新颖、独特结构的鞍场规具有高灵敏度(500托~(-1))、量测范围宽(10~(-4)-10~(-10)托)、尺寸小(以柱型规管为例,外径约11～12mm,管长小于50mm)、功耗低(<0.15毫瓦),不需要任何去气电源,放气率极低,吸气率约为标准BA规的几十分之一。鞍场规与标准BA规和分离规的比较量测表明,在压强逐渐降低时,鞍场规不存在BA规由于电子诱导栅极正离子脱附产生的灵敏度异常现象,因此鞍场规特别适合于航天空间及密封器件内高真空和超高真空量测。     

环形阳极鞍场规发展前景的讨论

环形阳极鞍场规A型,全国鉴定会认为,与现有超高真空电离规相比,它的体积、重量、电极尺寸、功耗、吸放气率都小得多。而且,它的灵敏度高而稳定(没有发现像BA规所特有的严重灵敏度异常现象),使用时可不必进行电极除气。本文就这种规测量上下限扩展的可能性作一些初步讨论。一、环形阳极鞍场规量测上下限的扩展 1.压强上限的扩展     

场发射冷阴极电离规的研究进展

碳纳米管冷阴极具有优异的场致电子发射特性,在电子源应用方面具有很好的前景,被认为是很有希望取代热阴极的材料之一。本文回顾了20多年来场发射冷阴极电离规的发展。内容包括微尖型场发射阴极电离规和碳纳米管场发射阴极电离规的发展,从中可以看出场发射电离规的现状和发展趋势。最后对碳纳米管超高/极高真空电离规的发展进行了展望。     

电离规的新进展

介绍了传统热阴极电离规和冷阴极电离规的发展历程和研究现状、新型场发射阴极(微尖型阴极和碳纳米管阴极)在电离规中的应用、小型化电离规的发展和国内在超高/极高真空电离规研究方面取得的成果和现状。重点回顾了碳纳米管阴极电离规和小型化电离规在近年来取得的重大成就。由于碳纳米管具有长径比大、曲率半径小、机械特性强、导电性好和优异的场发射特性,使得其作为电离规阴极有望解决传统冷阴极电离规在低压下不能放电的困难和传统热阴极电离规的热出气效应,从而为极高真空测量提供一种解决途径。     

3D基底上碳纳米管场发射I-V特性建模与计算

利用有限元分析软件ANSYS分析了在平面上引入立体墙结构的阴极电场分布,给出了立体墙结构阴极表面的场强分布曲线,结合F-N方程计算了在立体结构上生长碳纳米管和平面型冷阴极上直接生长碳纳米管的电流密度,通过数值计算计算了总的场发射电流,结果表明,场发射电流随场强的变化非常大,立体墙结构型冷阴极场发射电流与平面型冷阴极发射电流相比,场发射能力得到极大的增强。     

NCG冷阴极规管放电性能的测试

在NCG冷阴极规管的研制工作中,精确测量真空度低于10~(-8)帕下的放电性能和起辉性能是一个关键的问题。利用了一台按国际标准ISO设计制造的比对系统满足了测量要求.首先介绍了比对测试系统的特点以及测试原理,然后根据测试结果给出了规管在压力下限的放电曲线和起辉性能.最后应用磁场和电场相匹配的原理,改进冷阴极规管的磁结构,使规管成本降低了30%—40%,有利于推广应用.     

极低压强传感器的设计和研制

为了测量极高真空的压强,尤其是航天飞机的极高真空分子屏后宇宙空间的压强,本文作者研制了一种类似静电鞍场规的极低压强传感器。ＸＨＶＳ型极低压强传感器的压强测量范围为１＊１０＾－４－１＊１０＾－１０Ｐａ,它具有灵敏度高,电极尺寸小,吸放气率降低,功耗低等特点。作者计算了ＸＨＶＳ型极低压强传感器模型的电场分布以及电子、离子的运动轨迹,利用蒙特卡罗方法对ＸＨＶＳ型极低压强传感器的灵敏度常数等特性参量进行了     

超高/极高真空测量发展综述

本文回顾了近50多年来在超高/极高真空测量方面所取得的重要进展.内容包括热阴极电离规和冷阴极电离规的研究进展、新型室温电子源(如Spindt阴极和碳纳米管场发射阴极)和真空的激光电离测量技术在超高/极高真空测量中的应用、小型化超高/极高真空电离规的发展以及我国在超高/极高真空测量方面的研究进展等,从中可对超高/极高真空测量的发展历史和现状有一个完整的了解.     

基于CVD直接生长法的碳纳米管场发射阴极

碳纳米管(CNT)场发射阴极具有启动快、分辨率高、寿命长、功耗小等优点,在多种真空电子设备与器件上,包括平板显示器、真空测量、微波管、X射线管等得到了应用。本文讨论了碳纳米管阴极的主要制备方法以及存在的问题,介绍了基于化学气相沉积法和阳极化工艺、在含催化金属基底直接制备碳纳米管冷阴极所具有强附着力特点,以及应用在X射线管等强流真空电子器件上的优势。文章介绍了在不锈钢基底直接生长CNT阴极的场发射性能,其开启电场为1.46 V/μm。与常规催化金属镀膜层上生长的CNT阴极相比,大电流发射与稳定性显著提高。金属基底阳极化工艺显著改善碳纳米管结构与场发射性能。直径2 cm的不锈钢基底上生长的CNT具有晶体性好、分布均匀等特点,场发射性能提高。在镍基底上生长的CNT阴极电流密度可以达到500 mA/cm~2以上。     

易激发的冷阴极电离计

这只高真空规测量10~(-4)～10~(-8)托。规的特点是在阴极上装了一个点火器。冷规在-2.5KV直流高压下引燃。通常反应时间小于1分钟。线性范围在5×10~(-3)到5×10~(-8)托。并且计算了在各个压强下的最大正负偏差数值。这个数值小于百分之五十。冷阴极电离真空计(以下简称冷规),因无热灯丝,不会因系统突然漏气而烧毁;规管租电源结构简单,且规管灵敏度高。但是普遍认为,冷规在上下限的扩展上比较困难。为解决在低压强下激发和下限的延伸,以激发电离为例曾对潘宁规采取过加辅助针尖、加     

碳纳米管表面化学镀银及场发射性能研究

利用化学镀方法对碳纳米管(carbon nano-tubes,CNTs)表面金属化镀银,研究表面化学镀银碳纳米管的场发射性能。碳纳米管经氧化处理后,表面存在一些羰基(CO)、羧基(—COOH)和羟基(—OH)等活性基团,经敏化、活化处理后,形成金属钯活化中心,进而还原金属银离子,从而获得表面化学镀银的碳纳米管。表面化学镀银碳纳米管阴极的开启电场约为0.19V/μm,当电场强度为0.37V/μm时,最大发射电流达6mA/cm2,场增强因子约为25565。实验结果表明,化学镀银层可以提高碳纳米管的电子传输和热传输能力,提高碳纳米管的场发射电流和发射稳定性,有利于碳纳米管在场发射平板显示领域的应用。     

衬底电极对丝网印刷CNT阴极场发射性能的影响

通过丝网印刷技术,将碳纳米管(carbon nanotube,CNT)浆料直接转移到CrCuCr薄膜衬底电极、掺Sn的In_2O_3(indium tin oxides,ITO)透明导电薄膜衬底电极和Ag浆导电厚膜衬底电极上,高温烧结后得到CNT阴极,并对CNT阴极进行表面形貌和场发射性能的研究.结果表明,不同衬底电极对CNT阴极场发射性能的影响不一样,CrCuCr薄膜衬底电极CNT阴极、ITO透明导电薄膜衬底电极CNT阴极及Ag浆厚膜导电衬底电极CNT阴极场发射的开启电场分别为0.99、2.05和2.46V/μm;当电场为3.0V/μm时,它们的亮度分别为2472、1889、587cd/m~2.CrCuCr薄膜衬底电极CNT阴极的场发射性能最优,ITO透明导电薄膜衬底电极CNT阴极次之,Ag浆厚膜导电衬底电极CNT阴极最差,并根据金属-半导体理论模型分析了原因.     

A new formulation of the magnetic vector potential method for three dimensional magnetostatic field problems

A novel formulation of the magnetic vector potential method for three dimensional magnetostatic field calculations is derived. Rigorously defining the interface and boundary conditions of the gauge of the vector potential, the new method gives a unique solution to the problem. The new field equation does not contain the gauge condition against the usual formulations[1], [2], [3], and takes the form of the diffusion equation. Computed results are favorably compared with the analytic solution of a test problem. This formulation is directly applicable to three dimensional eddy current problems.     

On the possible use of a commercial Penning gauge as a magnetic field sensor

Penning sensors were originally conceived to extend the measurement range of cold-cathode gauges in the direction of low pressures by introducing an additional constant magnetic field. This paper examines the possibility of using a commercially available sensor to measure magnetic field by keeping pressure constant. For the preliminary tests reported, a commercial Penning gauge was exposed to magnetic fields in the range of a few tens of mT to 1.1 T. Three different regimes were identified. In the first, up to 150 mT, the measured current increases linearly with the applied magnetic field. Following a very irregular transition region of the order of 50 mT, for fields between 200 mT and 1.1 T, the measured current decays relatively smoothly. The results suggest that the principle may be applicable for the measurement of steady-state fields in harsh environments, with high temperature and neutron fluence.     

基于两种数值模拟方法的ASDEX电离规灵敏度研究

ASDEX电离规因其特殊的电极结构,可在高磁场、高温等离子体的聚变复杂环境下工作,被广泛应用于国内外核聚变装置。本文基于蒙特卡洛模拟法与电子路径积分法的数值模拟方法,分别研究了电极电压和磁场环境对电离规灵敏度及其电子运动轨迹的影响。研究表明：在无磁场条件下,随着加速栅极电压从160 V增加到430 V,灵敏度和电子平均轨迹长度先增大后减小;随着控制极电压从75 V增加到180 V,灵敏度先增加而后持续减小,电子发散程度先减小后增大。在磁场条件下,各电极的电子收集率随磁感应强度的增加急剧变化,并在0.1 T后趋于稳定。磁感应强度为0.1 T时,随着磁场偏移角度从0°增加到30°时,灵敏度缓慢衰减20%;若磁场偏移角度超过30°时,则灵敏度的衰减幅度迅速增加。     

Structure refinement of pure Mg under pulsed magnetic field

Abstract

A pulsed magnetic field (PMF) was introduced into the solidification of pure Mg. Fine uniform equiaxed grains are acquired in the whole ingot from the PMF treatment, in contrast with the coarse columnar grains observed in conventional casting, and the average grain size is refined to 260 μm with a 200 V PMF treatment. Pulsed magnetic field increases melt convection during solidification, and the violent agitation causes warmer liquid to fracture the tip of columnar dendrites or to break off dendrite branches to promote the formation of an equiaxed structure, with the broken pieces transported into the bulk liquid acting as nuclei. In addition, the uniform temperature field resulting from the stirring increases the likelihood of nuclei survival. The Joule heat effect also participates in the structure refinement. The pure Mg produced with a 200 V PMF treatment exhibits improved mechanical properties, such as the ultimate compressive strength (227 MPa) and fracture strain (33·2%).     

Preparation and field emission properties of titanium polysulfide nanobelt films

TiS₃ nanobelt films, with widths of about 0.1–12 μm, thickness of about 20–250 nm, and lengths of up to 200 μm, have been grown on Ti substrates by a surface-assisted chemical-vapor-transport at 450 °C for 8 h. The TiS₃ nanobelt films were converted into TiS_1.71 nanobelt films by pyrolysis in a vacuum at 600 °C for 2 h. The work functions of the two films were determined by ultraviolet photoelectron spectroscopy measurements to be 4.60 and 4.44 eV, respectively. Preliminary field emission experiments using the nanostructures as cold electron cathodes showed that both materials gave significant emission currents. The turn-on fields (defined as the electric field required to produce a current density of 10 μA/cm₂) were about 1.0 and 0.9 V/μm, respectively, whereas the threshold fields (defined as the electric field required to produce a current density of 1 mA/cm₂) were about 5.6 and 4.0 V/μm, respectively. These data reveal that both materials have potential applications in field emission devices. This article is published with open access at Springerlink.com     

Direct observation of field emission in a single TaSi2 nanowire

The electric potential change in a single TaSi2 nanowire during field emission was visualized by means of electron holography. During the field emission, the interference fringes of the electron hologram were blurred locally between the TaSi2 nanowire and anode. This phenomenon was interpreted as being due to a change in the electric potential of approximately 1 V in the TaSi2 nanowire after each ballistic emission. The experiments on the single TaSi2 nanowire field emission behavior provide the useful information for understanding the field emission in the nano-field-emitting device.     

Fabrication of In-doped SnO2 nanowire arrays and its field emission investigations

The field emission of In-doped SnO₂ wire array has been performed in parallel plate diode configuration. A maximum current density of 60?µA/cm² is drawn from the emitter at an applied field of 4?V/µm. The nonlinearity in the Fowler–Nordheim plot, characteristics of semiconductor emitter has been observed and explained on the basis of electron emission from both the conduction and the valence bands. The current stability recorded at a preset value of 1?µA is observed to be good. The high emission current density, good current stability and mechanically robust nature of the wires offer unprecedented advantages as promising cold cathodes for many potential applications based on field emission.