Electron field emission characteristics of carbon nanotube on tungsten tip (original) (raw)
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Applied Physics Letters, 2006
Vertically aligned multi-walled carbon nanotubes (CNTs) were grown on p-type silicon wafer using thermal chemical vapor deposition process and subsequently treated with oxygen plasma for oxidation. It was observed that the electron field emission (EFE) characteristics are enhanced. It showed that the turn-on electric field (E TOE of CNTs decreased from 0.67 (untreated) to 0.26 V/ m (oxygen treated). Raman spectra showed that the numbers of defects are increased, which are generated by oxygen-treatment, and absorbed molecules on the CNTs are responsible for the enhancement of EFE. Scanning electron microscopy and Transmission electron microscopy images were used to identify the quality and physical changes of the nanotube morphology and surfaces; revealing the evidence of enhancement in the field emission properties after oxygen-plasma treatment.
Electron field emission from carbon nanotubes
Comptes Rendus Physique, 2003
Carbon nanotubes (CNT) have recently emerged as a promising class of electron field emitters. They have a low threshold electric field for emission and a high emission current density which make them attractive for technological applications. In this article we review recent progress on understanding of CNT field emitters and discuss issues related to applications of CNTbased cold cathodes in vacuum microelectronic devices. The emphasis is on the emission characteristics of macroscopic CNT cathodes and their relations with the underlying materials properties. To cite this article: Y. Cheng, O. Zhou, C. R. Physique 4 (2003). 2003 Published by Elsevier SAS on behalf of Académie des sciences.
Thin Solid Films, 2008
Thin films (b 30 nm) of titanium carbide (TiC) are coated on carbon nanotubes (CNTs), directly grown on nano-sized (~500 nm in diameter) conical-type tungsten (W) tips, by employing an inductively coupled plasma chemical vapor deposition (ICP-CVD) technique. Modifications to structural properties (such as length to diameter ratio, crystal quality, and growth behavior) of CNTs due to TiC-coating are monitored using highresolution TEM, field-emission SEM, and Raman spectroscopy. The driving voltage required to obtain the same level of emission current in CNTs-emitter is significantly reduced by TiC-coating. It is also noted that the degradation of emission current due to prolonged operation (up to 30 h) is remarkably suppressed by TiC-coating.
Theory of Carbon Nanotube (CNT)-Based Electron Field Emitters
Theoretical problems arising in connection with development and operation of electron field emitters on the basis of carbon nanotubes are reviewed. The physical aspects of electron field emission that underlie the unique emission properties of carbon nanotubes (CNTs) are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include: the electric field amplification near a CNT tip with taking into account the shape of the tip, the deviation from the vertical orientation of nanotubes and electrical field-induced alignment of those; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the thermal effects resulting in degradation of nanotubes during emission. Simultaneous consideration of the above-listed effects permitted the development of the optimization procedure for CNT array in terms of the maximum reachable emission current density. In accordance with this procedure, the optimum inter-tube distance in the array depends on the region of the external voltage applied. The phenomenon of self-misalignment of nanotubes in an array has been predicted and analyzed in terms of the recent experiments performed. A mechanism of degradation of CNT-based electron field emitters has been analyzed consisting of the bombardment of the emitters by ions formed as a result of electron impact ionization of the residual gas molecules.
Characterization of the field emission properties of individual thin carbon nanotubes
Applied Physics Letters, 2004
Electron emission measurements were conducted on individual carbon nanotubes. The nanotubes had a closed end and their surfaces were thoroughly cleaned. It is shown conclusively that individual carbon nanotube electron emitters indeed exhibit Fowler-Nordheim behavior and have a work function of 5.1± 0.1 eV for the nanotubes under investigation, which had diameters of 1.4 and 4.9 nm.
Effect of few-walled carbon nanotube crystallinity on electron field emission property
Carbon letters, 2011
We discuss the influence of few-walled carbon nanotubes (FWCNTs) treated with nitric acid and/or sulfuric acid on field emission characteristics. FWCNTs/tetraethyl orthosilicate (TEOS) thin film field emitters were fabricated by a spray method using FWCNTs/TEOS sol one-component solution onto indium tin oxide (ITO) glass. After thermal curing, they were found tightly adhered to the ITO glass, and after an activation process by a taping method, numerous FWCNTs were aligned preferentially in the vertical direction. Pristine FWCNT/ TEOS-based field emitters revealed higher current density, lower turn-on field, and a higher field enhancement factor than the oxidized FWCNTs-based field emitters. However, the unstable dispersion of pristine FWCNT in TEOS/N,N-dimethylformamide solution was not applicable to the field emitter fabrication using a spray method. Although the field emitter of nitric acid-treated FWCNT showed slightly lower field emission characteristics, this could be improved by the introduction of metal nanoparticles or resistive layer coating. Thus, we can conclude that our spray method using nitric acid-treated FWCNT could be useful for fabricating a field emitter and offers several advantages compared to previously reported techniques such as chemical vapor deposition and screen printing.
Modeling of the electron field emission from carbon nanotubes
Journal of Vacuum Science & Technology B, 2001
Using a tunneling approach for the field emission from a single carbon nanotube, expressions for the emission current as a function of the anode voltage and of the emitted electron energy spectrum are obtained. The low dimensionality of the electronic system of a carbon nanotube is taken into account. The extraction field on the nanotube's tip is evaluated using numerical computations. For nanotubes of practical interest, having large enough diameters, it is demonstrated that the influence of the detailed form of the electron energy dispersion relations is not of major importance. This influence could be generally embedded in a numerical factor entering the expression of the emission current. The influence of the various tube parameters on the characteristics is also identified and analyzed. An approximate formula for use in practical analysis in field emission is deduced and its validity for different nanotube sizes is verified.
Electron field emission from multi-walled carbon nanotubes
Films of aligned multi-walled carbon nanotubes (MWNT) are produced by two different methods, thermal chemical vapour deposition (thermal CVD) and plasma chemical vapour deposition (plasma CVD), on silicon substrates. Electron field emission measurements on these films show that the thermal CVD produced films have excellent emission properties, while the plasma CVD films seem to give a lower electron emission with lower threshold and turn-on fields on the initial voltage scan. The electron emission for some of the films is accompanied by light emission from the carbon nanotubes at high emission current densities. The light emission is a result of strong ohmic heating and can be explained in terms of the one dimensional heat equation. This heating effect in the nanotube film is more important for the thermal CVD films than for the plasma films and can be qualitatively explained by considering the nanotube morphology in each case.
Field emission and electron deposition profiles as a function of carbon nanotube tip geometries
Journal of Applied Physics, 2007
We present an analysis to explore the electron distribution within a workpiece subjected to field emission from the tip of a carbon nanotube. By calculating the field emission current density at sites on the periphery of the tip and by mapping this current density towards the surface using the trajectories followed by the electrons, we are able to determine the shape of the electron beam profile on the surface. Once this profile is obtained we can solve electron-beam transport equation by means of Monte Carlo simulation to determine the electron distribution inside the workpiece. We repeat these simulations for various applied voltages, gap distances, and for different tip shapes in order to understand the effects that these parameters may have on the distribution of the deposited electrons. These distributions are needed to investigate the field emission based nanomachining process.
Modeling the electron field emission from carbon nanotube films
Ultramicroscopy, 2001
A theoretical framework for the electron field emission from carbon nanotubes (CNTs) is discussed. Using the tunneling theory, the influence of the detailed electron energy dispersion is proven to be of little importance for the electron field emission. By means of numerical computations in a simplified model, the influence of the environment on the local field on a CNT is discussed for an aligned CNT film. In a simple triangular model for the potential energy barrier at the tube end, a tunneling probability was obtained. A statistical model was developed for the structural and functional parameters of aligned CNT films. Practical CNT films of excellent alignment, obtained directly on a tungsten wire by plasma-enhanced chemical vapor deposition, were analyzed by this statistical model. Their distribution in the enhancement factors was thus deduced. An indirect method to get the average electrical parameters of the film using only a limited amount of experimental data was thus established. r (D. Nicolaescu). 0304-3991/01/$ -see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -3 9 9 1 ( 0 1 ) 0 0 1 0 7 -3