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1.
Jong-Hyun Lee Parlindungan Yonathan Hyun-Tae Kim Dang-Hyok Yoon Jaemyung Kim 《Applied Physics A: Materials Science & Processing》2008,93(2):511-516
The field emission properties of multi-walled carbon nanotubes were examined using a screen-printed thick film with a diode-type
configuration in a vacuum. The effects of various concentrations of two different ceramic fillers, indium tin oxide (ITO)
powder and a glass frit, on the emission current density and turn-on field were evaluated. The emission properties of both
pastes were dependent on the amount of filler. Considerably enhanced emission properties were obtained with the paste containing
5–10 wt.% of either ITO or the glass frit compared with those without a filler. The paste containing the ceramic filler showed
enhanced emission properties compared with that containing the 5 wt.% Ag conventionally used, which confirmed the importance
of the filler. The paste containing 10 wt.% ITO represented an emission current density of 176.4 μA/cm2 at 5 V/μA, a turn-on field of 1.87 V/μA for an emission current density of 1 μA/cm2 and a field enhancement factor of 7580. The paste formulation was also found to be suitable for fine patterning using UV-lithography
techniques. A long-term stability test for 110 h of a paste containing 10 wt.% ITO revealed a half-life of approximately 30000 h,
which is appropriate for commercial applications. 相似文献
2.
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
3.
Recent experiments have shown that carbon nanotubes exhibit excellent electron field emisson properties with high current densities at low electric fields. Here we present theoretical investigations that incorporate geometrical effects and the electronic structure of nanotubes. The electric field is dramatically enhanced near the cap of a nanotube with a large variation of local field distribution. It is found that deviation from linear Fowler-Nordheim behavior occurs due to the variation of the local field in the electron tunneling region. The maximum current per tube is of the order of 10 microA. Local and microscopic aspects of field emission from nanotubes are also presented. 相似文献
4.
It has been shown that the deposition of cesium atoms on multi-wall carbon nanotubes abruptly increases the current of the field electron emission, decreases the threshold electric field by a factor of three (to 0.8 V/m), and decreases the work function to 2.1–2.3 eV. It has been found that the flowing of the large emission current I ≥ 2 × 10?6 A leads to a change in the current-voltage characteristics and a decrease in the emission current. This effect has been explained by escape of cesium atoms from the tips of most nanotubes into the nanotube depth due to desorption or intercalation. At the same time, the low work function is retained for some nanotubes, probably, due to the stronger bonding of Cs atoms with these nanotubes. 相似文献
5.
研究了Ar离子束轰击及温度对多壁碳纳米管阵列场发射性能的影响.经Ar离子轰击35min后,发现阵列顶端的Fe催化剂颗粒明显减少,弯曲的顶部被轰击掉,使碳纳米管的场发射电流明显减小而场发射像无明显改变.温度的增加引起碳纳米管的场发射电流也随之增加.还研 究了在透明阳极技术中涂在阳极的荧光粉对场发射电流的影响.对同一碳纳米管阵列样品,发现涂有荧光粉的透明阳极使测量到的场发射电流大幅度减小,只是未涂荧光粉阳极电流的 1/30左右.直接用二氧化锡导电膜作阳极时,测得样品的开启场强为1.0V/μm.沉积了荧光粉的二
关键词:
多壁碳纳米管
场发射 相似文献
6.
Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H2, H2O, CO and O2 and then imaged in the field electron emission microscope. Only the samples exposed to O2 showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented. 相似文献
7.
《Current Applied Physics》2002,2(6):509-513
The overall aim of this work is to produce arrays of field emitting microguns, based on carbon nanotubes, which can be utilised in the manufacture of large area field emitting displays, parallel e-beam lithography systems and electron sources for high frequency amplifiers. This paper will describe the work carried out to produce patterned arrays of aligned multiwall carbon nanotubes (MWCNTs) using a dc plasma technique and a Ni catalyst. We will discuss how the density of the carbon nanotube/fibres can be varied by reducing the deposition yield through nickel interaction with a diffusion layer or by direct lithographic patterning of the Ni catalyst to precisely define the position of each nanotube/fibre. Details of the field emission behaviour of the different arrays of MWCNTS will also be presented. 相似文献
8.
9.
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
10.
The mechanism that limits the emission current of a carbon-nanotube-based cathode due to the temperature dependence of the emissivity of the nanotube is studied. This limitation has the character of thermal instability that shows up as an infinite increase in the emitter temperature after a certain emission current is exceeded. The heat conduction equation is solved for a nanotube at various model temperature dependences of the thermal and electrical conductivities of the nanotube in order to derive the limiting emission current as a function of the electrical conductivity of the nanotube. 相似文献
11.
Field emission from multi-walled carbon nanotubes and its application to electron tubes 总被引:5,自引:0,他引:5
Y. Saito K. Hamaguchi S. Uemura K. Uchida Y. Tasaka F. Ikazaki M. Yumura A. Kasuya Y. Nishina 《Applied Physics A: Materials Science & Processing》1998,67(1):95-100
Received: 5 December 1997 相似文献
12.
The present work describes the field emission characteristics of conducting polymer coated multi walled carbon nanotubes (MWNTs) field emitters fabricated over flexible graphitized carbon cloth. Nanocomposites involving the combination of MWNTs and conducting polymers polyaniline (PANI) and polypyrrole (PPy) have been prepared by in-situ polymerization method and have been characterized using scanning electron microscopy and transmission electron microscopy. Using spin coating method, field emitters based on PANI/MWNTs and PPy/MWNTs over flexible graphitized carbon cloth have been prepared. The field emission characteristics have been studied using an indigenously fabricated set up in a vacuum chamber with a base pressure of 2 × 10−5 Pa and the results are discussed. Our results display that the field emission performance of the emitters depends strongly on the work function of the emitting material. Low turn on emission field of 2.12 V/μm at 10 μA/cm2 and high emission current density of 1 mA/cm2 at 3.04 V/μm have been observed for PANI/MWNTs field emitter. 相似文献
13.
Field emission from single-walled carbon nanotube (SWNT) nonwoven has been
investigated under high vacuum with different vacuum gaps. A low turn-on
electric field of 1.05\,V/$\mu $m is required to reach an emission current
density of 10 $\mu $A/cm$^{2}$. An emission current density of 10
mA/cm$^{2}$ is obtained at an operating electric field of 1.88\,V/$\mu $m. No
current saturation is found even at an emission current of 5\,mA. With the
vacuum gap increasing from 1 to 10 mm, the turn-on field decreases
monotonically from 1.21 to 0.68\,V/$\mu $m, while the field amplification is
augmented. The good field-emission behaviour is ascribed to the combined
effects of the intrinsic field emission of SWNT and the waved topography of
the nonwoven. 相似文献
14.
15.
The spatial distribution of light emission has been studied in planar field electron emitters with long and sparse carbon nanofilaments/nanotubes. The photographic recording of light emission of the emitting nanofilaments/nanotubes is shown to be efficient to determine the position of individual nanofilaments/ nanotubes in different emitter surface areas, as well as to highlight the nanofilaments/nanotube agglomerate distribution over the emitter surface, which mainly contributes to its emission. 相似文献
16.
Effect of adsorbates on field emission from carbon nanotubes 总被引:1,自引:0,他引:1
Recent experiments indicate that water molecules adsorbed on carbon nanotube tips significantly enhance field-emission current. Through first-principles density-functional theory calculations we show that the water-nanotube interaction is weak in zero electric field. However, under emission conditions large electric field present at the tube tip: (a) increases the binding energy appreciably, thereby stabilizing the adsorbate; and (b) lowers the ionization potential (IP), thereby making it easier to extract electrons. Lowering of IP is enhanced further through the formation of a water cluster on the nanotube tip. 相似文献
17.
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
18.
S. Groudeva-Zotova R. Kozhuharova D. Elefant T. Mühl C.M. Schneider I. Mönch 《Journal of magnetism and magnetic materials》2006
The work addresses the correlation between the phase composition and the magnetic characteristics of aligned Fe-filled multi-walled carbon nanotubes (Fe-MWCNTs) grown by pyrolysis of ferrocene on oxidized Si substrates. In a combinatorial approach we exploited the extremely high gradients of the technological parameters temperature and ferrocene flow across the surface of a substrate positioned close to the reactor wall to obtain a large variation in the structural and magnetic properties of the Fe-MWCNTs. In this way, we established several clear correlations between the Fe-filling phase composition and the overall magnetic characteristics of the aligned Fe-MWCNTs. The α-Fe rich samples, which possess a more ordered graphitic sheet structure, a higher degree of preferred crystalline orientation of the metal filling and much larger metal crystallites in comparison with the carbide-rich samples, show a much stronger magnetic anisotropy with easy axis perpendicular to the substrate and unusually high values of the coercive field Hc and the saturation field Hs. The changes in the measured saturation magnetisation Ms and the Hc values correlate well with the variation of the α-Fe content and the filling crystallinity. A special annealing treatment of the samples causes a distinct increase of the α-Fe quantity and an increase of the measured average grain size. The respective magnetic characteristics show a significant increase of the overall magnetic moment and decrease of the coercive field. The correlation between the structural and the magnetic characteristics of the annealed samples matches quite well the respective correlations in the case of as-deposited samples. 相似文献
19.
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
20.
Electron irradiation-induced change of structure and damage mechanisms in multi-walled carbon nanotubes 下载免费PDF全文
《中国物理 B》2015,(11)
Owing to their unique structure and excellent electrical property, carbon nanotubes(CNTs) as an ideal candidate for making future electronic components have great application potentiality. In order to meet the requirements for space application in electronic components, it is necessary to study structural changes and damage mechanisms of multi-walled carbon nanotubes(MWCNTs), caused by the irradiations of 70 and 110 ke V electrons. In the paper, the changes of structure and damage mechanisms in the irradiated MWCNTs, induced by the irradiations of 70 and 110 ke V electrons, are investigated.The changes in surface morphology and structure of the irradiated MWCNT film are characterized using scanning electron microscopy(SEM), x-ray photoelectron spectroscopy(XPS), Raman spectroscopy, x-ray diffraction analysis(XRD), and electron paramagnetic resonance(EPR) spectroscopy. It is found that the MWCNTs show different behaviors in structural changes after 70 and 110 ke V electron irradiation due to different damage mechanisms. SEM results reveal that the irradiation of 70 ke V electrons does not change surface morphology of the MWCNT film, while the irradiation of 110 ke V electrons with a high fluence of 5 × 1015cm-2leads to evident morphological changes, such as the formation of a rough surface, the entanglement of nanotubes and the shrinkage of nanotubes. Based on Raman spectroscopy, XPS, and XRD analyses, it is confirmed that the irradiation of 70 ke V electrons increases the interlayer spacing of the MWCNTs and disorders their structure through electronic excitations and ionization effects, while the irradiation of 110 ke V electrons obviously reduces the interlayer spacing of the MWCNTs and improves their graphitic order through knock-on atom displacements. The improvement of the irradiated MWCNTs by 110 ke V electrons is attributed to the restructuring of defect sites induced by knock-on atom displacements. EPR spectroscopic analyses reveal that the MWCNTs exposed to both70 ke V electrons and 110 ke V electrons suffer ionization damage to some extent. 相似文献