Electric field-induced changes of W(110) and W(111) tips

Using field emission and scanning electron microscopy we have studied the influence of strong electric fields on the thermally induced growth behaviour of field emission tips. For smaller fields (i.e. smaller than needed for a satisfactory field emission image) we observe an enlargement of low-index faces, which for higher fields develops into a building-up of micro-structures and roughening on the initially spherical part of the tip surface. In an intermediate state only the region near the (111) directions contributes to the field emission pattern. For the highest fields employed the results indicate the growth of local protrusions preferentially near (100) faces. Our results show that in scanning tunnelling microscopy W(111) tips should be superior to the commonly used W(110) tips.     

碳纳米管场致发射特性的研究

详细论述了碳纳米管的场致发射特性，包括开启电场、阈值电场、发射电流密度、发射电流的稳定性及场发射电子能量分布等；阐述了场发射的机制；分析了发射特性与其几何结构、吸附态及尖端缺陷等因素的关系；并简要介绍了碳纳米管场发射特性在平板显示领域中的实际应用。     

热处理对钛掺杂类金刚石薄膜场发射性能的影响

采用多靶磁控溅射技术制备了钛掺杂类金刚石(Ti-DLC)薄膜,并在不同温度(300,350,400℃)下进行了热处理,研究了热处理温度对薄膜微观结构、成分、能带结构以及场发射性能的影响。结果表明:与热处理前的相比,300℃热处理后Ti-DLC薄膜中sp²-C团簇相对含量增大,光学带隙最小,开启场强最低,为5.43 V·μcm^-1,场发射性能最好;当热处理温度高于300℃时,薄膜的DLC含量减少,同时生成大量TiO₂,光学带隙增加,薄膜开启场强增大,场发射性能变差;薄膜的场发射电流基本不受热处理温度的影响。     

Visualization of individual emission sites on flat broad-area field emission cathodes

We introduce a novel scanning projection field emission microscope (SPFEM) designed to study flat broad-area field emission cathodes. The instrument merges capabilities of measuring the electron field emission current from an individual emitting site and genuine projection of electrons onto a luminescent screen. This is achieved by an optimized shape of the anode probe having a 0.04 mm aperture which generates an uniform macroscopic electric field across the investigated area of the cathode. This fact also enables presentation of the relation between the current density and the applied electric field. The magnification of the electron-optical system alone was calculated by computational modeling for some cathode-probe distances and for some voltages. The unique SPFEM performance is demonstrated on smooth sulfur-doped nanodiamond films synthesized on molybdenum substrates.     

用有限元方法计算X光源场发射阴极电流

针对场致发射阵列建立了有效的三维有限元模型来分析单个尖锥的发射电流.考虑到场致发射阵列的周期性和尖锥的轴对称性,仅对一个尖锥单元的1/4进行分析.对模型的表面施加电压边界条件,计算得到尖锥表面电场强度分布,电场强度在尖锥顶点最强,场发射电流在此处也最强.由Fowler-Nordheim函数可得到尖锥表面的场致发射电流密度分布,对整个尖锥表面进行积分后得到了单个尖锥的场致发射电流约为7μA.计算了在100V门电压下不同顶端半径的场致发射电流.结果显示,场发射对顶端半径有很强的依赖性.计算了100个顶端半径为8nm的尖锥在不同门电压下的总场致发射电流,发射电流与开启电压与实际测量值符合得很好.     

Magnetic field emission gun with zirconiated emitter

A magnetic-field-superimposed field emission gun with low aberrations and equipped with a zirconiated tungsten emitter has been developed for applications where very stable high probe currents are required. It has been tested on a conventional electron microscope at 10 kV and on an electron beam testing system at 1 kV. Probe current i = 250 nA in a probe size d = 0.4 μm is obtained at 10 kV; at 1 kV the resolution is 0.1 μm with i = 5 nA, and 0.4 μm with i = 30 nA. For these probe currents, the spatial broadening effect due to electron–electron interactions in the beam is the preponderant factor limiting the probe size.     

Analysis of Field Emission Properties of Carbon Nanocoils for Imaging Materials

Carbon nanotubes and nanocoils are expected as the charging materials and electron gun for the imaging devices. It is synthesized for carbon nanocoils with different diameters by the catalytic thermal decomposition of acetylene using iron-indium-tin-oxide catalysts. It is found that the turn-on voltage is decreased by decreasing the average diameter of the grown carbon nanocoils. The turn on voltage of as low as 30 V at the electrodes' gap of 130 μm has been achieved when the coil diameter is decreased to 60 nm. The calculation for the concentration of the electric field on the coil surface has been performed using a finite element method. It is obtained that the strength of electric field around the top ring of a coil is increased with the decrease of the tubular diameter of the coil and has a similar value for that at the tip of a carbon nanotube, suggesting that the efficiency of the field emission from nanocoils would be higher than that from nanotubes. These results can explain the good stability of field emission from carbon nanocoils.     

High-temperature electron backscatter diffraction and scanning electron microscopy imaging techniques: in-situ investigations of dynamic processes

In-situ heating experiments have been conducted at temperatures of approximately 1200 K utilising a new design of scanning electron microscope, the CamScan X500. The X500 has been designed to optimise the potential for electron backscatter diffraction (EBSD) analysis with concomitant in-situ heating experimentation. Features of the new design include an inclined field emission gun (FEG) column, which affords the EBSD geometrical requirement of a high (typically 160 degrees) angle between the incoming electron beam and specimen surface, but avoids complications in heating-stage design and operation by maintaining it in a horizontal orientation. Our studies have found that secondary electron and orientation contrast imaging has been possible for a variety of specimen materials up to a temperature of at least 900 degrees C, without significant degradation of imaging quality. Electron backscatter diffraction patterns have been acquired at temperatures of at least 900 degrees C and are of sufficient quality to allow automated data collection. Automated EBSD maps have been produced at temperatures between 200 degrees C and 700 degrees C in aluminium, brass, nickel, steel, quartz, and calcite, and even at temperatures >890 degrees C in pure titanium. The combination of scanning electron microscope imaging techniques and EBSD analysis with high-temperature in-situ experiments is a powerful tool for the observation of dynamic crystallographic and microstructural processes in metals, semiconductor materials, and ceramics.     

磁声发射检测系统的设计与研究

磁声发射利用了铁磁材料中的磁畴壁在外磁场作用下往复震荡和磁化矢量的转动而产生应力波从而导致声发射现象.介绍了一款磁声发射检测仪的设计,对各主要硬件部分的电路工作原理及其设计思想进行了分析与讨论.     

Application of ion-beam etching techniques to the fine structure of biological specimens as examined with a field emission SEM at low voltage

The term “etching,” in electron microscopy, refers to the removal of specimen surface layers and includes chemical, electrolytic, and ion-beam methods. The ion-beam etching process is used to remove layers of a target material by bombarding it with ionized gas molecules. Recently, the method has been applied to the field of biological specimens; however, the practical procedures for such organic materials have not been developed. In the present study, we used an apparatus in which a beam of argon ions is collimated and focused by electrostatic lenses onto an appropriate target. We demonstrated the optimum conditions to observe biological specimens that were treated with osmium tetroxide and tannic acid. The specimens were examined uncoated at low accelerating voltage using a field emission scanning electron microscope. According to our experiments, when a biological specimen was observed under high-resolution conditions at over 50,000x magnification, the optimum condition of ion-beam etching consisted of an accelerating voltage of E = 1 keV and an ion-beam dose of It = 360 ～ 400 μA. min, depending on parts of the specimens. In order to decrease overetching, we had to choose factors such as E = 1 ～ 2 keV and It = 500 μA. min.     

Characterization system based on image mapping for field emission devices

Field Emission devices (FE) have been proposed as efficient electron sources for several applications such as electron microscopy and vacuum sensors. Evidently, characterization methods applied during development phase of FE devices are crucial to evaluate aspects related with their working stability, homogeneity, and efficiency. However, the traditional methods provide only overall information about such characteristics, which difficult to improve the performance of these devices and their integration with electronics. To overcome this problem, this work presents an alternative system to characterize FE devices through electron emission imaging in real-time. The proposed system acquires I-V features of FE devices, while a video camera captures the emission image from a phosphor screen. Virtual instrumentation based on LabVIEW manages the whole system including measurement instruments, image capture, and data processing. As a result, histograms, 3D maps, and other FE analyses provide information about emitting characteristics of selected regions of interest. The main contribution of this work is to offer an important tool for the analyses of electron emission, by the association of captured images with the localized emission current. The extracted information from our system can efficiently support the characterization and the development of FE devices.     

不同技术路线Warp Air Clean材料对机动车尾气减排效果研究

传统机动车尾气减排技术经过长期发展,取得了较好效果,但在短期难以获得更大的突破。Warp Air Clean(WAC)技术通过对发动机的进气进行净化,提高发动机内燃烧效率,从而减少尾气排放,是解决机动车尾气排放的新途径。本研究对比了四种不同合成方案WAC材料的减排效果,为该技术的进一步完善优化提供了基础。研究发现:采用加成型硅橡胶合成方案的合成材料效果最好,在怠速与高怠速工况下均能有效降低机动车排放的CO、THC和NO。     

Growth and field emission properties of ZnO nanostructures deposited by a novel pulsed laser ablation source on silicon substrates

Zinc oxide (ZnO) nanostructures were produced using a novel pulsed laser ablation apparatus comprising in-situ analysis of the plume by reflection time-of-flight mass spectrometry. Various morphologies of nano and microstructures were obtained for laser wavelengths of 1064 and 355 nm, and oxygen ambient pressures of 10⁻⁶ and 10⁻² mbar, respectively. None of the produced structures exhibited a particular type of self-organisation whereas all of them showed low aspect ratios and good field emission properties. Optimum values of 5.2 V μm⁻¹ and 2060 were obtained for the turn-on field and Fowler–Nordheim enhancement factor, respectively, for deposited nano-tipped microstructures presenting a high coverage of the substrate. The experimental data showed that for a given laser wavelength, higher field enhancement factors were obtained for the samples grown at the lower pressure of 10⁻⁶ mbar. In these conditions, the deposited materials showed distinct nanostructuring and comparison with existing data showed the corresponding ablation plumes to contain (ZnO)_n clusters, up to n=13. This work also shows that the electronic properties of the nanostructured ZnO produced in our conditions, as determined by the oxygen concentration during deposition, have an influence on the field emission properties in addition to the nanostructure morphology.     

Intravacuolar network may act as a mechanical support for Toxoplasma gondii inside the parasitophorous vacuole

The intravacuolar network inside the parasitophorous vacuole of Toxoplasma gondii consists of an intricate system of membrane-limited tubules of uncertain role in parasite development. We propose that it is an important structural support to the maintenance of the parasites in the characteristic rosette arrangement of parasites inside the vacuole, rather than being associated with the nutrient acquisition from the host cell, as previously suggested. We based our assumptions on observations made by field emission scanning electron microscopy of an epithelial cell line (LLCMK2) infected at various time intervals. Scraping the surface of infected monolayers with Scotch tape exposed the inner organization of the parasitophorous vacuole. Ultrathin sections and freeze-fracture replicas of analogous samples were correlated with field emission observations and added new data on tubular membranes and general organization of the parasitophorous vacuole.     

Investigation of the relationship between internal fluid leakage through a valve and the acoustic emission generated from the leakage

The detection of acoustic emission (AE) signals produced by liquid and gas leakage through valves can be related directly to the qualitative leakage rate. This allows for cost estimation of losses in processes for several industries. However, to find out the relationship between qualitative leakage rate and AE signal large amounts of experimental data is needed. This paper presents a theoretical investigation of the acoustic emission to detect the internal leakage rate through a valve and experimental validation. The AE signals generated by internal liquid and gas leakage through valves were characterised. The effect of the influenced factors of leakage rates, inlet pressure levels, valve sizes and valve types, on AE parameter, AE_RMS, were studied and explained. The results of theoretical and experimental showed that AE signal power computed from the power spectral density (PSD) correlated well with influenced factors of leakage rates. Finally, a novel and inexpensive AE instrument has been invented for predicting qualitative leakage rate using a micro processor and derived relationship.     

分散剂对电泳沉积制备碳纳米管薄膜形貌和场发射性能的影响

采用丙酮、异丙醇、丙酮/无水乙醇混合溶液3种不同的分散剂,利用电泳沉积法在硅基底上制备了碳纳米管(CNTs)薄膜;采用超景深光学显微镜和电子显微镜观察了不同薄膜的表面形貌,并在高真空中对碳纳米管薄膜阴极进行了场发射特性测试。结果表明:以异丙醇作分散剂制备的CNTs薄膜表面均匀连续,场发射性能较好,开启电场和阈值电场分别为0.188V.μm-1和2.8V.μm-1。     

真空微电子压力传感器的研制

提出了一种带过载保护功能的真空微电子压力传感器.对传感器的压力敏感膜尺寸、阴阳极间距等结构参数进行了分析计算;针对过载保护的问题,在结构上设计了过载保护环,实现了真空微电子压力传感器的过载自保护功能.采用硅的干、湿法结合的腐蚀、氧化锐化和真空键合等工艺技术,成功地研制出传感器实验样品.对传感器实验样品的参数进行了测试分析,其场致发射阴极锥尖阵列密度达24000个/mm²,起始发射电压为0.5～1V,反向电压≥25V,当正向电压为5V时,单尖发射电流为0.2nA,压力灵敏度为0.1μA/KPa.     

LEO SUPRA系列热场发射扫描电子显微镜

本文介绍LEOSUPRA系列热场发射扫描电子显微镜的性能及特点 ,主要包括肖特基场发射电子源、电子光学系统以及检测器等。     

Evaluation of measurement uncertainty using mixed distribution for conducted emission measurements

For evaluation of measurement uncertainty for conducted emission measurements, we propose a new model which uses mixed distribution. Namely, evaluation of probability density function (PDF) for the measurand has been done using a Monte Carlo method and a modified least-squares method. As the Monte Carlo method required numerical calculation of approximate PDF values, pseudorandom number generator (PRNG) was developed for these requirements. For illustration, this work presents mixed distributions of two normal distributions, normal and rectangular distributions, and normal and also triangular distributions in case of conducted emission measurements. The results obtained by the Monte Carlo method and the modified least-squares method are compared to the corresponding results when applying the standard Guide to the Expression of Uncertainty in Measurement (GUM) procedure.