共查询到20条相似文献,搜索用时 484 毫秒
1.
The magnitude of the local electric field and the electron emission current density for an array of aligned carbon nanotubes is estimated. For describing in detail the properties of the local electric field in the vicinity of the nanotube tips, a hybrid method allowing for the local determination of the field enhancement factor is introduced. The field factor consists of two parts: an internal factor which describes the structure of the carbon nanotubes and an external factor which represents the field screening effect due to neighboring nanotubes. The current density is obtained using the Fowler–Nordheim equation with the hybrid field enhancement scheme. As a result, the emission properties for an array of nanotubes with a given length are described satisfactorily, and an optimum value for the nanotube spacing is determined. PACS 85.45.Fd; 85.45.Db 相似文献
2.
V. R. Romanovskii 《Technical Physics》2009,54(11):1581-1585
The stability of resistive states in Bi2223 superconductor without a stabilizing matrix and with decreasing temperature dependence
of the resistive-transition index of its I–V characteristic is studied in a steady-state approximation. Analysis is carried out for a superconductor placed in a constant
magnetic field when it is slightly cooled by a coolant with a varying working temperature. It is shown that additional stable
resistive states may arise in the case of high electric fields and overheats. These (multistable) states are characterized
by stable steps in the electric field intensity and temperature, which do not transfer the supercon-ductor into the normal
state. The multistable resistive states may be related to the nontrivial variation of the superconductor’s differential resistance.
In this case, a decrease in the critical current density of the super-conductor and its related decrease in the resistive-transition
index of the I–V characteristic with increasing temperature play the key role in the formation of these states. Their presence should be taken
into consideration both in analyzing the stable conditions of high-temperature superconductors and in describing processes
observed in superconducting magnets when they pass into the normal state. 相似文献
3.
Effect of screening on the emissivity of field electron emitters based on carbon nanotubes 总被引:1,自引:0,他引:1
The effect of screening on the emissivity of a field cathode built around a carbon nanotube array is analyzed. A numerical method of solving the Laplace equation for intricate-shape cathodes is developed that makes it possible to relate the amplification factor to the nanotube spacing in arrays containing as many as 225 emitters. Mutual screening of the tubes, which shows up in the dependence of the field amplification factor on the average emitter spacing, is studied numerically. The optimal spacing between the tubes that provides an emission current maximum density at a given applied voltage is determined. The role of edge effects in carbon nanotube screening is established. 相似文献
4.
Sergei M. Pimenov Vadim D. Frolov Evgeny V. Zavedeev Nikolay P. Abanshin He-Yun Du Wei-Chao Chen Li-Chyong Chen Jih-Jen Wu Kuei-Hsien Chen 《Applied Physics A: Materials Science & Processing》2011,105(1):11-16
In this paper, we have studied field emission properties of highly dense arrays of multi-walled carbon nanotubes (CNTs) used
as cathodes in diode-type field emission devices with a phosphor screen. For the high-density CNT emitters it is demonstrated
that the emission sites are located on the CNT-cathode edges, which is direct experimental evidence of the ‘edge effect’.
The results of computer simulations (using ‘ANSYS Electromagnetic’ software) are presented to confirm the experimental data
and to analyze the effect of patterning on the electric field distribution for high-density CNT arrays. It is shown that selective-area
removal of nanotubes in the arrays leads to the formation of additional edges characterized by the high field enhancement
factor and enhanced emission from the CNT cathodes. In addition, scanning probe microscopy techniques are employed to examine
surface properties of the high-density CNT arrays. For CNT arrays of ‘short’ nanotubes, the work function distribution over
the sample surface is detected using a scanning Kelvin microscopy method. 相似文献
5.
A.S. Berdinsky A.V. Shaporin J.-B. Yoo J.-H. Park P.S. Alegaonkar J.-H. Han G.-H. Son 《Applied Physics A: Materials Science & Processing》2006,83(3):377-383
The simulation results of the electric field intensity and the enhancement factor, γ, for an individual CNT imaged as a conducting
rod is presented. The field enhancement factor, γ̄, for the CNT paste array is evaluated experimentally by varying the cathode-anode
(CA) spacing, d. The simulations indicate that the distribution of electric field intensity and the enhancement factor as
a function of cathode-anode spacing, d, could be divided into the two parts: strong (d<100 μm) and weak (d>100 μm) dependences
of the enhancement factor γ(d). Furthermore, the field enhancement factor, γ̄, estimated experimentally for the CNT paste
FEA indicates that the two-region field emission model (TRFE) is adequate for estimation of the field enhancement factor,
γ̄. Moreover, the effective enhancement factor, γ̄, for the CNT paste FEA was found to be ≈50γ and is attributed to the additions
of the emission currents from the individual CNTs in an array. In addition, the empiric functions of the geometrical enhancement
factor, β̄(d), and γ̄(d) were estimated from the Fowler–Nordheim plot for the CNT paste FEA. One can use the empiric functions
β̄(d) and γ̄(d) for the design and fabrication of the devices based on the CNT paste FEA with a variable CA spacing.
PACS 81.07.De; 85.35.Kt; 79.70.+q; 85.45.Fd; 72.80.Tm 相似文献
6.
建立一种平行背栅极碳纳米管阵列阴极,基于电场叠加原理,利用镜像电荷法对其进行计算,给出碳纳米管顶端表面电场增强因子。在此基础上,进一步分析器件各类参数对电场增强因子的影响。分析表明,碳纳米管阵列阴极具有最佳阵列密度,其对应碳纳米管间距大约为碳纳米管高度的两倍,靠阴极阵列边缘部位的碳纳米管发射电子能力比其中心部位的大。除了碳纳米管的长径比之外,栅极宽度、栅极厚度和栅极间距等也对电场增强因子有一定的影响:栅极越宽,场增强因子越大;而栅极厚度、栅极间距越大,场增强因子就越小。 相似文献
7.
采用丝网印刷工艺制作了碳纳米管(CNTs)薄膜阴极.经适当能量激光烧蚀后,相互粘连的CNTs随表面粘附有机物的蒸发而分散开,管间隙增加、屏蔽效应减小,使得场发射性能大幅度提高,开启场强降低、场倍增因子β增大.Raman光谱分析表明,随激光能量增加,CNTs表面缺陷增多,成为新的场发射点,对其β增大的贡献加强.相对于两电极结构,三电极中平栅极结构场发射性能经激光烧蚀有更显著的改善.这说明激光烧蚀是提高CNTs场发射性能的有效方法.
关键词:
碳纳米管薄膜
场发射
激光烧蚀
Raman光谱 相似文献
8.
建立一种平行栅碳纳米管阵列阴极,利用悬浮球模型和镜像电荷法进行计算,给出碳纳米管顶端表面电场与电场增强因子的解析式. 在此基础上,进一步分析器件各类参数以及接触电阻对阴极电子发射性能的影响. 分析表明,碳纳米管间距大约为2倍碳纳米管高度时阵列阴极的分布密度最佳,靠边缘部位的碳纳米管发射电子能力比其中心部位的大;除碳纳米管的长径比之外,栅极宽度和栅极间距也对电场增强因子有一定作用;接触电阻的存在大幅度降低碳纳米管顶端表面电场与发射电流,而接触电阻高于800 kΩ时,器件对阳极驱动电压的要求更高.
关键词:
平行栅碳纳米管阵列
悬浮球
场增强因子
接触电阻 相似文献
9.
The dynamics of a flat isotropic brane Universe with two-component matter source —perfect fluid with the equation of statep = (γ − 1)ρ and a scalar field with a power-law potentialV ∼ φα is investigated. We describe solutions for which the scalar field energy density scales as a power-law of the scale factor.
We also describe solutions existing in regions of the parameter space where these scaling solutions are unstable or do not
exist. 相似文献
10.
Self-sustained electron emission from a silicon-polymer planar structure is studied experimentally. It is found that emission
can be initiated by a short-term action (e.g., a vacuum microdischarge). The I–V characteristics and time dependence of the emission current are recorded. It is shown that the value and stability of the
emission current depend on the thickness of the polymer film. A model explaining the origin of and conditions for self-sustained
electron emission is proposed. It is based on today’s concepts of electron emission from insulating layers (Malter effect)
with regard to the structure and properties of polymer films. 相似文献
11.
Jianfeng Dai Xiaowen Mu Xiaoting Chen Junhong Wang Bi Fu 《Physica E: Low-dimensional Systems and Nanostructures》2011,44(1):152-155
The field emission performances of normal-gate cold cathode, which is composed of different multi-wall carbon nanotubes (MWCNTs) bundles array are calculated. The device parameters such as the arrangement of bundles, array density, gate location, gate voltage, anode voltages and anode–cathode distance affect the field emission properties, which is discussed in detail. The results reveal that the hexagon bundles array needs a lower threshold voltage than square array to reach high field enhancement factor and large emission current density. The emission current density is two orders larger than that of the oxide emitter. The optimal bundles array densities of hexagon and square array to get field enhancement factor are 0.0063 and 0.00375 μm−2, respectively. Meanwhile, the field emission performances are impacted critically by gate location and gate voltage. Field emission properties changed little while the anode–cathode distance varies within tens of micrometers, which increases the process-friendliness of CNTs field emission devices. 相似文献
12.
《Physica E: Low-dimensional Systems and Nanostructures》2009,41(10):3166-3169
In order to optimize the field emission from carbon nanotubes (CNTs) array by the emission current density, the calculation of the field emission was extended with the floating sphere model and the Fowler–Nordheim equation, and the trend of the emission current density versus the intertube distance (the distance between the nearest CNTs) was mainly discussed in this paper. Only considering the field enhancement factor in the previous works, the field emission from CNTs array was optimized only by possibly decreasing the intertube distance with the maximal field enhancement factor. Herein, both the field enhancement factor and the emission current density were taken into account, the field emission from CNTs array could be optimized analytically with the intertube distance of 10th of the tube height, which was much smaller than the estimated value and the experiment result. 相似文献
13.
Zero-field current-voltage (I–V) characteristics of various high-temperature superconductor samples are analyzed in the context of the current-temperature
(I−T) phase diagram. After establishing the validity and relevance of the phase diagram to these materials, the anisotropy factor
is extracted from the slope ofI
c
1
(T) (the current defined by the onset of resistance). It is concluded that studying theI−V characteristics of amples in the context of theI−T phase diagram is a simple, useful tool for comparing samples.
Work supported by the Office of Naval Research. 相似文献
14.
The degradation rate of carbon nanotubes (CNTs) in an electron field emitter is calculated. The degradation mechanism is taken to be the sputtering of the CNT surface by the ions that result from the ionization of residual gas molecules by an electron impact. The degradation rate and the corresponding CNT lifetime are calculated as a function of the nanotube geometry, the applied voltage, the pressure and kind of a residual gas, the interelectrode gap, and the nanotube array density. The obtained strong dependence of the degradation rate on the applied voltage is caused by a sharp character of the I?CV emission characteristic determined by the Fowler-Nordheim relationship. The dependence of the degradation rate on the interelectrode gap is induced by the corresponding dependence of the probability of reaching the CNT surface. 相似文献
15.
16.
采用悬浮球模型,结合对称的镜像电荷层方法,对静电场中纳米碳管阵列的场增强因子进行了计算,并在考虑极板间距的情况下,对其计算结果做了修正.结果表明:纳米碳管阵列的间距对纳米碳管阵列的场发射性能影响很大.当纳米碳管阵列中碳管间距小于碳管高度时,场增强因子随间距的减小而急剧减小;而当碳管间距显著大于碳管高度时,场增强因子几乎不变.但当考虑阴阳极之间单位面积通过的场发射电流时,可论证当管间距与管高度相若时,能使场发射电流密度最佳(最大).另外,极板间距对场增强因子的影响很小,但是可以通过减小极板间距,来降低纳米碳管作为场发射体的场发射的开启电压,优化纳米碳管的场发射性能.
关键词:
纳米碳管阵列
场增强因子
开启电压 相似文献
17.
X.Q. Wang M. Wang H.L. Ge Q. Chen Y.B. Xu 《Physica E: Low-dimensional Systems and Nanostructures》2005,30(1-2):101-106
To optimize the field emission of the infinite carbon nanotubes (CNTs) array on a planar cathode surface, the numerical simulation for the behavior of field emission with finite difference method was proposed. By solving the Laplace equation with computer, the influence of the intertube distance, the anode–cathode distance and the opened/capped CNT on the field emission of CNTs array were taken into account, and the results could accord well with the experiments. The simulated results proved that the field enhancement factor of individual CNT is largest, but the emission current density is little. Due to the enhanced screening of the electric field, the enhancement factor of CNTs array decreases with decreasing the intertube distance. From the simulation the field emission can be optimized when the intertube distance is close to the tube height. The anode–cathode distance hardly influences the field enhancement factor of CNTs array, but can low the threshold voltage by decreasing the anode–cathode distance. Finally, the distribution of potential of the capped CNTs array and the opened CNTs array was simulated, which the results showed that the distribution of potential can be influenced to some extent by the anode–cathode distance, especially at the apex of the capped CNTs array and the brim of the opened CNTs array. The opened CNTs array has larger field enhancement factor and can emit more current than the capped one. 相似文献
18.
Takashi Yasuda Masayoshi Tonouchi Shuzo Takano 《Czechoslovak Journal of Physics》1996,46(Z3):1265-1266
Current-voltage (I–V) characteristics are studied in the intrinsic Josephson junctions of Bi2Sr2CaCu2Oy single crystals. In order to examine the influence of self-heating, a current pulse (∼0.2 μsec) is applied to the mesas of
40 μmϕx0.15 μm patterned on the crystal. As a consequence, in contrast to small characteristic voltageV
c in the continuous-current measurement, theV
c data is found comparable to the BCS value. Moreover, theI–V curve is nearly ohmic forl>l
c
, implying that the nonlinearity under the continuous current is due to heating. The quasiparticle resistance forT<T
c
is also presented by an estimate from the characteristic voltage. 相似文献
19.
利用化学镀方法对多壁碳纳米管(multi-walled carbon nanotubes,MWNTs)表面金属化镀镍(MWNTs/Ni),采用丝网印刷制备MWNTs/Ni场发射阴极,并在磁场辅助下热处理所得阴极,研究磁场辅助热处理对MWNTs/Ni阴极的场发射性能的影响,经300mT磁场辅助热处理的MWNTs/Ni的场发射阴极开启场强约为0.80V·μm~(-1),场增强因子β约为16068,对单根MWNTs/Ni在磁场中的受力情况进行建模分析,实验结果表明:磁场辅助热处理有助于提高MWNTs/Ni在阴极表面的直立分布,提高了MWNTs/Ni的场发射性能。 相似文献
20.
A low energy electron accelerator has been constructed and tested. The electron beam can operate in low energy mode (100 eV
to 10 keV) having a beam diameter of 8–10 mm. Thin films of CdS having thickness of 100 nm deposited on ITO-coated glass substrate
by thermal evaporation method have been irradiated by electron beam in the above instrument. The I–V characteristic is found to be nonlinear before electron irradiation and linear after electron irradiation. The TEP measurement
confirms the n-type nature of the material. The TEP and I–V measurements also confirm the modification of ITO/CdS interface with electron irradiation.
相似文献