Long-term stability of various carbon-nanotube-based micro-tip emitters (original) (raw)
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2013
The CNT-inconel interface exhibhits good electrical contact as well as strong adhesion to be used directly as electrodes for super capacitors and field emitters without any post growth processing with respect to other metal substrate. Carbon nano tubes were synthesized on inconel substrate over the 10*10 mm 2 area by catalytic decomposition of ferrocene -Xylene mixture at 800°C. The growth process involved injecting a solution of particular concentration of ferrocene in xylene at a particular flow rate into a preheating zone of reactor. A mixture of argon and hydrogen was used to carry the xylene containing catalyst vapors upto substrate. Scanning electron microscopy (SEM) and Raman Spectroscopy investigations reveal that the nanotubes are multi-wall CNTs having about 40-70 nm diameter. The possibility of growing CNTs on the metal substrates other than silicon has been confirmed from the above results.
The Journal of Physical Chemistry C, 2010
Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission displays. CNT field electron emitters self-organized on substrates with an Fe/Al 2 O 3 catalytic/supporting layer, which accelerates CNT growth, are characterized using combinatorial libraries. A variety of morphologies are formed on single substrates by C 2 H 2 thermal chemical vapor deposition for 10 s at ambient pressure. Degradation of field emission decreases upon prolonged operation. Raman signals from thinner single-walled CNTs predominantly degrade during operation. Controlling the number of protruding thin CNTs is crucial to extracting current and ensuring sustainability. Thin CNTs protruding from CNT ensembles formed on a substrate with a multimodal distribution of catalyst particles show good field emission (FE) properties with practical sustainability. A potential design for self-organized thin CNTs fabricated by the current process is discussed on the basis of the combinatorial evaluation for field emission and 3D electric field simulations.
Electron field emission characteristics of carbon nanotube on tungsten tip
Journal of Physics: Conference Series, 2009
Electron field emission characteristic of carbon nanotubes on tungsten tip was investigated in 2x10 -6 Torr vacuum. The measurement results showed that the CNTs/W tip could emit electron at 0.7 V/µm (nearly 10 times lower than that of the W tip itself) and reach up to 26 µA at the electric field of 1 V/µm. The emission characteristic follows the Fowler-Nordheim mechanism. Analysis of the emission characteristic showed that the CNTs/W tip has a very high value of field enhancement factor (β = 4 1 4 .1 1 0 cm − × ) that is much higher than that of the tungsten tip itself. The results confirmed the excellent field emission behavior of the CNTs materials and the CNTs/W tip is a prospective candidate for advanced electron field emitter.
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.
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.
Applied Physics A: Materials Science & Processing, 2004
Using a chemical vapor deposition (CVD) method, multi-walled carbon nanotubes with uniform diameters of approximately 10 nm were synthesized on silicon substrates by the decomposition of acetylene using Fe, Co and Ni as the catalysts. Catalyst effects on the internal structures of the carbon nanotubes were evident in the Fe, Co and Ni catalyzed nanotubes. Although these nanotubes demonstrated similar morphologies, due to the variety of internal structures, the nanotubes synthesized from different catalysts demonstrated various electron field-emission characteristics including turn-on field, threshold field and field enhancement factor. Compared with carbon nanotubes from Ni catalyst, nanotubes from Fe and Co with the same diameters have better field-emission properties. Graphite layers in nanotubes from Fe and Co are much straighter and more parallel to the tube axis with fewer defects. For instance, the turn-on field and threshold field for nanotubes from Ni are 5 V/µm and 9 V/µm, respectively. These electric fields are much higher than those for nanotubes from Fe, which are 0.35 V/µm and 2.8 V/µm, respectively. This could be due to the effect of catalysts on the work function of nanotubes, since the catalyst particle usually terminates the free end of the nanotube, and the influence of internal structure on electron transportation along the nanotube axis. Therefore, this study suggests that besides a small diameter, good graphitization (crystallization) is an important prerequisite for a good carbon nanotube emitter.
Materials Chemistry and Physics, 2017
Exciting properties of carbon nanotube has proven it to be a promising candidate for field emission applications, if its processing cost can be reduced effectively. In this research, a new electrochemical technique is proposed for growing carbon nanotubes in selective areas by thermal chemical vapour deposition. In this process, electrochemical processing is used to create localized pits and deposition of catalysts, which act as roots to support growth and alignment of the CNTs on copper substrate. CNTs grown thus were characterized and studied using scanning electron microscope, transmission electron microscope and Raman spectroscopy, elucidating presence of multiwall carbon nanotubes (MWCNT). These CNT emitters have comparatively lower turn-on field and higher field enhancement factor.