Achieving uniform field emission from carbon nanotube composite cold cathode with different carbon nanotube contents: Effects of conductance and plasma treatment

A carbon nanotube (CNT) composite cold cathode was studied for field emission display application. The CNT composite cold cathode was composed of CNTs and silicon dioxide binder. Field emission from CNT composite cold cathode with different CNT contents was studied. It was found that with increase in CNT contents, the threshold field decreased. The conductance of the composite cathode was measured and with increasing CNT content, there was a critical CNT content where the conductance increased several orders of magnitude. Plasma etching using SF₆ as the etchant was adopted to treat the cathode. Improvement in emission uniformity was achieved. It was also found that after post-treatment the threshold field of the cathode decreased. The morphology of the etched cathode was analyzed and the improvement of uniformity and lowering of the threshold field was attributed to the exposure of CNTs after etching.     

Ionization gauge by carbon nanotube field emission

A newly developed ionization gauge using carbon nanotube (CNT) field emission effect has been designed and manufactured. The fabricated ionization gauge is of a triode type, consisting of a cathode (carbon nanotube field emitter arrays), a grid and a collector. The principle involved here is that for a constant number of electrons available for ionization emitted from carbon nanotube arrays by the grid potential, a constant fraction of gas will be ionized and the number of ions collected in the collector will be proportional to the number of gas molecules in the chamber traversed by the electrons. Due to the excellent field emission characteristics of CNT, it is possible to make a cost effective cold cathode ionization gauge. A screen-printing method has been used to make the CNT cathode. The glass grid with Cr deposited by E-beam has been put on the cathode with a gap of 200 μm between the two electrodes. Using the voltage applied to the grid, the electrons emitted from the carbon nanotube ionize gas molecules in the chamber and the ionized molecules are gathered in the collector. At this time, the collector voltage is maintained at a lower level than that of the grid voltage to obtain a large ionization ratio. The current detected in the collector is proportional to the pressure in the chamber. The ionization characteristics are dependent on the gas and the voltage applied to the grid and collector. In this paper we have shown the various metrological characteristics of the simple pressure sensor utilizing carbon nanotube.     

电刷镀镍/碳纳米管复合纳米镀层的结构与磨损性能

用含碳纳米管的快速镍电刷镀液制备了镍/碳纳米管复合纳米镀层,研究了热处理温度和镀液中碳纳米管含量对镀层平均晶粒尺寸、结构、力学性能及耐磨性能的影响。结果表明,镀层的晶粒大小随热处理温度的升高是先降低而后增大的;同样碳纳米管的加入对镍刷镀层的平均晶粒尺寸和微结构有显著的影响。镀层的硬度和耐磨性与镀层的平均晶粒尺寸有非常好的对应关系。热处理和碳纳米管的强化作用可导致镀层晶粒细化和结构致密化,从而有效地改善了镀层的力学性能和耐磨性能。     

碳纳米管增强铜基复合材料的研究进展

综述了碳纳米管增强铜基复合材料的预处理和制备方法,探讨了复合材料的组织、力学性能与摩擦学性能、电学性能和热学性能;最后指出了碳纳米管增强铜基复合材料今后的研究方向。     

Low background cold cathode ion source for molecular beam detection

An extractor gauge type electron bombardment ion source using carbon fiber bundles as field electron emitters is described. The cold cathode permits operation of the ionizer within a liquid He cooled cryopump. The high pumping speed for all molecules (except helium) together with its low background pressure make this ion source a very promising detector for crossed molecular beam scattering experiments.     

The effect of amorphous carbon layer on the field emission characteristics of carbon nanotube film

Carbon nanotube (CNT) has excellent field emission characteristics and could play as a good cold cathode in the application of vacuum electronic devices. However, the practical application faces a big obstacle regarding current fluctuation and deterioration of the CNT cathode. In this research, the formation of amorphous carbon (ac) layer between the CNT film and the substrate, and the effect of the existence of this layer on field emission stability of the CNT film are studied. The formation of the ac layer could be controlled by adjustment of growth temperature and hydrocarbon flow rate. The field emission character and current stability of the CNT film without ac layer are better than those of the CNT film with ac layer. The results attribute to the ac layer a thermal disequilibrium state under high current level. Moreover, adhesion capacity of the CNT film without ac layer is also better than that with the ac layer. It is concluded that the ac layer between the CNT film and substrate is a key factor in the stability of field emission characteristics and should be eliminated before applications.     

Effect of carbon nanotube structural parameters on field emission properties

Experimental studies were devoted to the effect of structural parameters, i.e., tube diameter and density, on the field electron emission characteristics of carbon nanotubes. Thermal chemical vapor deposition system was employed to synthesize carbon nanotubes. Nanotubes with different diameters and densities were obtained by adjusting the thickness of the iron (Fe) catalyst film. The morphologies of the Fe and carbon nanotube film were characterized by scanning electron microscopy respectively. Further field emission measurement confirmed that the tube diameter and density could significantly affect the electron emission properties of the carbon nanotube. Possible physical reasons for the effect are discussed.     

Nanomaterials for field electron emission: preparation,characterization and application

We review the current development in synthesis and deposition techniques of quasi-one-dimensional nanomaterials and recent achievements in the study of the field electron emission properties of these materials. Major findings are given from our recent experimental study of the field electron emission characteristics of carbon nanotubes, copper sulfide and silicon carbide nanorods. The study reveals that the above nanomaterials are promising candidates as cold cathode electron emitters. Furthermore, we review the recent development of techniques for growing and depositing the above nanomaterials in device structures. Typical device structures and their performance are also shown.     

A series of tufted carbon fiber cathodes designed for different high power microwave sources

We report the fabrication technique of tufted carbon fiber cathodes for different microwave sources. Three carbon fiber cathodes were constructed, including a planar cathode, an annular cathode, and a cylindrical cathode for radial emission. Experimental investigations on these cathodes were performed in a reflex triode virtual cathode oscillator (vircator), a backward wave oscillator (BWO), and a magnetically insulated transmission line oscillator (MILO), respectively. The pulse duration of microwave emission from the reflex triode vircator was lengthened by using the planar carbon fiber cathode. In the BWO with the annular carbon fiber cathode, the uniform electron beam with a kA/cm(2) current density was observed. In addition, carbon fiber has great promise as field emitter for MILOs. These results show that the carbon fiber cathodes can be utilized for electron emission in high power diodes with different structures.     

Application of response surface methodology in the optimization of laser treatment in buckypaper lighting for field emission displays

Carbon nanotube field emission backlight (CNT-BLU) is promising to replace traditional backlighting devices in liquid crystal display (LCD) industry. This study reports a laser irradiation process to enhance field emission properties of buckypaper, a thin sheet of high-loading carbon nanotube network. The scanning laser treated the selected region of buckypaper to activate CNT emitters. The improvement of phosphorescence luminance intensity, uniformity, and the reduction of turn-on field were achieved by adjusting machining parameters of laser power, laser lens motion speed, laser resolution, laser beam size, and pattern orientation. Design of experiment and response surface methodology provided ways to rapidly search the feasible laser parameter setting for processing buckypaper field emitters and improving field emission properties within fewer experimental runs. 2^5?1 Fractional fracotrial design presented the initial models of five repsponses. In addition, the face-centered central composite design is applied since the 2^5?1 factional factorial design showed curvature significance. It assisted to give the scientifical insight of the following conclusions. High-energy laser treatment damages and burns the CNTs into carbon oxide materials; furthermore, it loses the effective CNTs. Low-energy laser treatment performs CNT activation and produced low field emission performance. In this study, we succeeded to apply statistical analysis methods to understand the physics and mechanics of laser-activated buckypaper field emission and, furthermore, improve, optimize, and demonstrate performance by material selection, process development, and characterization.     

Field emission from individual multiwalled carbon nanotubes prepared in an electron microscope

Individual multiwalled carbon nanotube field emitters were prepared in a scanning electron microscope. The angular current density, energy spectra, and the emission stability of the field-emitted electrons were measured. An estimate of the electron source brightness was extracted from the measurements. The results show that carbon nanotubes are promising candidates to replace existing sources in high-resolution electron beam instruments.     

巴基管增强铜基复合材料的磨损性能研究

对催化热分解法制备的巴基管进行表面预处理化学镀、巴基管增强铜基复合材料粉末冶金法制备工艺作了的研究。对制备的复合材料的磨损试验表明 :磨损过程存在磨台阶段和稳态磨损阶段。最后对主要因素对磨损的影响作了研究 ,并与一般碳纤维材料进行了对比试验 ,表明巴基管具有良好的抗磨性     

Electron irradiation-induced destruction of carbon nanotubes in electron microscopes

Observations of carbon nanotubes under exposure to electron beam irradiation in standard transmission electron microscope (TEM) and scanning electron microscope (SEM) systems show that such treatment in some cases can cause severe damage of the nanotube structure, even at electron energies far below the approximate 100 keV threshold for knock-on damage displacing carbon atoms in the graphene structure. We find that the damage we observe in one TEM can be avoided by use of a cold finger. This and the morphology of the damage imply that water vapour, which is present as a background gas in many vacuum chambers, can damage the nanotube structure through electron beam-induced chemical reactions. Though, the dependence on the background gas makes these observations specific for the presently used systems, the results demonstrate the importance of careful assessment of the level of subtle structural damage that the individual electron microscope system can do to nanostructures during standard use.     

Low-energy, high-current, ion source with cold electron emitter

An ion source based on a two-stage discharge with electron injection from a cold emitter is presented. The first stage is the emitter itself, and the second stage provides acceleration of injected electrons for gas ionization and formation of ion flow (<20 eV, 5 A dc). The ion accelerating system is gridless; acceleration is accomplished by an electric field in the discharge plasma within an axially symmetric, diverging, magnetic field. The hollow cathode electron emitter utilizes an arc discharge with cathode spots hidden inside the cathode cavity. Selection of the appropriate emitter material provides a very low erosion rate and long lifetime.     

Influence of the multi-walled carbon nanotube and short carbon fibre composition on tribological properties of epoxy composites

The present research work deals with the development of a novel polymer composite for brake pad applications. The composite that was used consists of epoxy resin, carbon fibre and carbon nanotubes in varying weight percentage. The tribological performance of three different samples was tested using a pin-on-disc under dry contact condition. The results indicated that the sample filled with short carbon fibres (SCF), and multi-walled carbon nanotube (MWCNT) had superior performance. Reduction in wear rate was observed due to synergism between SCF and MWCNT as compared to SCF only. Scanning electron microscopy was subsequently performed on all samples. The micrographs show changes in the structural formation after the incorporation of SCFs and MWCNT. This increased composite structural strength and explains why SCF and MWCNT’s hybrid-filled composite material has better tribological properties.     

Effect of carbon nanotube addition on the tribological behavior of carbon/carbon composites

Carbon nanotube composite coatings were applied onto carbon/carbon composites to improve wear properties. Carbon nanotubes have been prepared by catalytic pyrolysis of hydrocarbons. The nanotube slurry was prepared by addition of phenolic resin and solvent to infiltrate into C/C composites. The nanotube added composites were then carbonized in a nitrogen atmosphere. Ball-on-disc type wear tests were performed to evaluate the tribological properties of the carbon nanotube added carbon composites. The result showed that addition of nanotube has the potential to increase the wear resistance of carbon composites. Changes in Raman spectra, morphology and surface damage were studied to explain observed wear behavior.     

一种基于金阴极MCP的冷阴极电子源的研制

采用深紫外光子激发金阴极产生的冷阴极电子源具有诸多优点,将其应用于电子轰击离子源(EI)有助于获得高质量的离子源。本实验分别采用在JGS2石英玻璃上蒸镀金薄膜构成透射式金阴极、在微通道板(MCP)输入面蒸镀金薄膜构成反射式金阴极,将二者以不同的组合方式装配在一起,通过施加不同的间隙电压,从而获得较大范围的电子流输出,研制出电子束流可调(10^-11～10^-5 A)、均匀分布(非均匀度6.5%)的稳定输出(稳定工作时间大于5 h)电子源,有望在高质量EI源中得到推广和应用。     

Field-dependent electron emission patterns from individual SWCNTs simulated with a multi-scale algorithm

The electron distribution of open-ended single-walled carbon nanotubes (CNTs) with chirality indexes (7,0) and (5,5) in field emission conditions was calculated via a multi-scaled algorithm. The field emission images were produced numerically. It was found that the emission patterns change with the applied macroscopic field. Especially, the symmetry of the emission pattern of the (7,0) carbon nanotube is breaking in the lower field but the breaking is less obvious in the higher field. The magnification factor increases with the applied macroscopic field.     

Microstructure and wear resistance of nickel–carbon nanotube composite coating from brush plating technique

This paper investigates the microstructure and wear resistance of nickel–carbon nanotube (CNT) composite coating deposited by brush plating technique. The Ni/CNT coating deposited with a pulse current source has less porosity, higher hardness and higher wear resistance than that with a DC source. CNTs greatly improve the coating performance. The wear mechanism is mainly the smearing of the Ni/CNTs coatings, instead of the fracture for the Ni coatings.     

巴基管粒度对其复合镀层摩擦学性能影响的研究

用无电解复合镀方法,在４５号钢基体上镀了一层镍－磷－巴基管复合镀层。本文详细实验研究了粒度对镍－磷－巴基管复合镀层摩擦学性能的影响。结果表明：巴基管复合镀层具有极优的摩擦学性能,而且巴基管的粒径愈小,复合镀层的摩擦学性能则愈优。