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1.
Field electron emission (FE) is a quantum tunneling process in which electrons are injected from materials (usually metals)
into a vacuum under the influence of an applied electric field. In order to obtain usable electron current, the conventional
way is to increase the local field at the surface of an emitter. For a plane metal emitter with a typical work function of
5 eV, an applied field of over 1 000 V/μm is needed to obtain a significant current. The high working field (and/or the voltage
between the electrodes) has been the bottleneck for many applications of the FE technique. Since the 1960s, enormous effort
has been devoted to reduce the working macroscopic field (voltage). A widely adopted idea is to sharpen the emitters to get
a large surface field enhancement. The materials of emitters should have good electronic conductivity, high melting points,
good chemical inertness, and high mechanical stiffness. Carbon nanotubes (CNTs) are built with such needed properties. As
a quasi-one-dimensional material, the CNT is expected to have a large surface field enhancement factor. The experiments have
proved the excellent FE performance of CNTs. The turn-on field (the macroscopic field for obtaining a density of 10 μA/cm2) of CNT based emitters can be as low as 1 V/μm. However, this turn-on field is too good to be explained by conventional theory.
There are other observations, such as the non-linear Fowler-Nordheim plot and multi-peaks field emission energy distribution
spectra, indicating that the field enhancement is not the only story in the FE of CNTs. Since the discovery of CNTs, people
have employed more serious quantum mechanical methods, including the electronic band theory, tight-binding theory, scattering
theory and density function theory, to investigate FE of CNTs. A few theoretical models have been developed at the same time.
The multi-walled carbon nanotubes (MWCNTs) should be assembled with a sharp metal needle of nano-scale radius, for which the
FE mechanism is more or less clear. Although MWCNTs are more common in present FE applications, the single-walled carbon nanotubes
(SWCNTs) are more interesting in the theoretical point of view since the SWCNTs have unique atomic structures and electronic
properties. It would be very interesting if people can predict the behavior of the well-defined SWCNTs quantitatively (for
MWCNTs, this is currently impossible). The FE as a tunneling process is sensitive to the apex-vacuum potential barrier of
CNTs. On the other hand, the barrier could be significantly altered by the redistribution of excessive charges in the micrometer
long SWCNTs, which have only one layer of carbon atoms. Therefore, the conventional theories based upon the hypothesis of
fixed potential (work function) would not be valid in this quasi-one-dimensional system. In this review, we shall focus on
the mechanism that would be responsible for the superior field emission characteristics of CNTs. We shall introduce a multi-scale
simulation algorithm that deals with the entire carbon nanotube as well as the substrate as a whole. The simulation for (5,
5) capped SWCNTs with lengths in the order of micrometers is given as an example. The results show that the field dependence
of the apex-vacuum electron potential barrier of a long carbon nanotube is a more pronounced effect, besides the local field
enhancement phenomenon. 相似文献
2.
利用场发射显微镜和四极质谱计研究了充入高纯O2的四极质谱和O2对单壁碳纳米管场发射的影响.单壁碳纳米管经过约1000℃的热处理得到清洁态场发射像后,充入O2,分别测量了O2吸附和脱附后场发射的I V特性.实验观测到在单壁碳纳米管上O2的吸附使场发射电流减小,说明逸出功增加.在10-4Pa的O2压强下对单壁碳纳米管进行约1000℃的热处理,可以产生氧化刻蚀作用,观测到场发射像的变化,并测量了氧化刻蚀产生的I V特性变化.
关键词:
单壁碳纳米管
场发射显微镜
场发射
四极质谱 相似文献
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Interference fringes are obtained in a field-emission microscopy
(FEM) study of a multi-walled carbon nanotube (MWCNT) with two
open-ended branches. The FEM pattern, which is composed of three
parallel streaks, can be interpreted by using classical Young's
double-slit interference with the ends of the two MWCNT branches
treated as two secondary sources of the electron wave. The origin of
the coherency of the electron beams from the two branches is
discussed on the basis of the quantitative analysis of the FEM
pattern. The result suggests a new approach to obtaining a coherent
electron source. 相似文献
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对热扩散阴极表面微区发射状态进行原位观察和分析一直是热阴极研究的重要课题.本文着重介绍深紫外激光光发射电子/热发射电子显微镜的基本原理及其在热扩散阴极研究中的典型实例.系统配备了高温激活所用的加热装置,样品可被加热至1400℃.系统具有光发射电子、阴极热发射电子、光发射电子和阴极热发射电子联合三种电子成像模式.应用表明,对于热扩散阴极而言,深紫外激光光发射电子像适于呈现阴极表面的微观结构形貌;热发射电子像适于反映阴极表面的本征热电子发射及均匀性;光电子和热电子联合成像适于对阴极表面的有效发射点做出精确定位. 相似文献
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将单根多壁碳纳米管(multi-walled carbon nanotube,MWCNT)组装在W针尖上并送入超高真空场发射/场离子显微镜(Ultrahigh Vacuum Field-emission/Field-Ion microscope,UHV-FEM/FIM)进行场蒸发及场发射研究.结果表明,场蒸发可以降低MWCNT的逸出功,从而增强其场发射能力.估算MWCNT的蒸发场低于1.3×108V·cm-1,且在此场强下的平均蒸发速率为9.4nm·min-1.定性讨论了MWCNT的蒸发场大大低于C的理论值的原因.首先,通过场解吸获得的清洁端口上有较多悬挂键,平均每个C原子的配位数较小,所以升华热较低.其次,可能存在于MWCNT中的H原子会在强场下碰撞端口的C原子,使其更易蒸发.以上结果显示了利用场蒸发剪短碳纳米管从而改善其场发射特性的可行性.
关键词:
碳纳米管
场蒸发
场发射 相似文献
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对闭口碳纳米管(CNT)顶端分层掺氮及吸附不同数目水分子体系,运用第一性原理研究了有电场存在时的电子场发射性能.结果表明:掺氮并吸附水分子的CNT结构稳定;外电场愈强、水分子数愈多,体系态密度(DOS)向低能端移动幅度愈大且最高分子占据轨道(HOMO)/最低分子空轨道(LUMO)能隙愈小.吸附能,DOS/LDOS,HOMO/LUMO及其能隙分析一致表明,第三层氮掺杂CNT吸附不同数目水分子体系的场发射性能最佳.
关键词:
氮掺杂
水吸附
密度泛函理论
电子场发射 相似文献
11.
Influence of high-energy electron irradiation on field emission properties of multi-walled carbon nanotubes (MWCNTs) films 总被引:1,自引:0,他引:1
Sandip S. PatilPankaj M. Koinkar Sanjay D. DholeMahendra A. More Ri-ichi Murakami 《Physica B: Condensed Matter》2011,406(9):1809-1813
The effect of very high energy electron beam irradiation on the field emission characteristics of multi-walled carbon nanotubes (MWCNTs) has been investigated. The MWCNTs films deposited on silicon (Si) substrates were irradiated with 6 MeV electron beam at different fluence of 1×1015, 2×1015 and 3×1015 electrons/cm2. The irradiated films were characterized using scanning electron microscope (SEM) and micro-Raman spectrometer. The SEM analysis clearly revealed a change in surface morphology of the films upon irradiation. The Raman spectra of the irradiated films show structural damage caused by the interaction of high-energy electrons. The field emission studies were carried out in a planar diode configuration at the base pressure of ∼1×10−8 mbar. The values of the threshold field, required to draw an emission current density of ∼1 μA/cm2, are found to be ∼0.52, 1.9, 1.3 and 0.8 V/μm for untreated, irradiated with fluence of 1×1015, 2×1015 and 3×1015 electrons/cm2. The irradiated films exhibit better emission current stability as compared to the untreated film. The improved field emission properties of the irradiated films have been attributed to the structural damage as revealed from the Raman studies. 相似文献
12.
H. J. Kreuzer 《Micron (Oxford, England : 1993)》1995,26(6):503-509
The setup of the LEEPS (low energy electron point source) microscope is described and images of carbon fibres and nanotubes are shown and compared to simulated images. We used a Kirchhoff-Helmholtz type transform to reconstruct the (wave front at the) object. We also showed that this transform can be used to reconstruct optical in-line holograms. 相似文献
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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 相似文献