Carbon Evaporation from Carbon Nanotube Field Emitters Studied by Conductivity Change of CNT Anode (original) (raw)
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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.
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.
physica status solidi (a), 2012
Carbon nanotubes (CNTs) are considered very promising for the realization of low-cost field emission electron sources. However, despite intensive research and development efforts, the fabrication of reliable CNT cathodes for high current density (>100 mA/cm 2 ) applications remains a formidable challenge. In this study we use scanning anode field emission microscopy (SAFEM) to investigate the microscopic origins of macroscopic emission performance variations in chemical vapor deposition (CVD) grown CNT planar field emission cathodes. The field enhancement distributions are determined and the field emission properties of individual emission sites on the cathodes are probed. Contact I(V) measurements are carried out to estimate the resistance of individual emitters. The degradation behavior of individual sites is also studied and can be related with the macroscopic cathode performances. Scanning (SEM) and transmission electron microscopy (TEM) provide additional information on the contact and structural properties of the cathodes. Our results indicate that the sample macroscopic performances depend strongly on the individual emitter field emission properties in terms of maximum current before degradation and contact resistance.
Field electron emission properties of carbon nanotube films deposited by electrophoresis
2011
The merit of various kinds of carbon nanotubes as field electron emission cathode materials has been studied. The field electron emission characteristics of electrophoretically deposited films of single walled carbon nanotubes, multiwalled carbon nanotubes of diameter between 10 and 20 and >50 nm and carbon nanofibres with diameters between 200 and 600 nm were investigated. Results of the measurements revealed that the field enhancement factor beta, the turn on electric field and the threshold electric field were strongly dependent on the size of carbon materials, where single walled carbon nanotubes produced the best results in terms of lowest electric field values, highest field enhancement factor and highest current density.
Electron field emission from a single carbon nanotube: Effects of anode location
Applied Physics Letters, 2005
Electron field emission from an isolated carbon nanotube ͑CNT͒ was performed in situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1-60 m. The threshold field required for an emission current of 100 nA was seen to decrease from a value of 42 V m −1 at an anode to CNT tip separation of 1 m, asymptotically, to approach 4 V m −1 at a separation of 60 m. It is proposed that at low D, the electric field enhancement factor ͑͒ reduces as the anode electrode approaches the CNT mimicking a parallel plate configuration. Under "far field" conditions, where D Ͼ 3 h, where h is the CNT height, the CNT enhancement factor is no longer dependant on D, as shown by the asymptotic behavior of the threshold field, and is purely a factor of the CNT height and radius. For each CNT to tip separation, measured emission current data together with the threshold field and enhancement, are consistent with a Fowler-Nordheim analysis for the far field conditions, and dispels the need for a novel emission mechanism to explain the results as has been proposed recently.
Operating voltage diminution of field emission cathodes based on carbon nanotubes
IOP Conference Series: Materials Science and Engineering
The possibility of minimizing the operating voltages of the diode structure with a field emission cathode based on an array of carbon nanotubes is investigated. The numerical simulation method was used to perform theoretical calculations that showed the potential for an unlimited reduction in the operating voltage by reducing the diameter of the emitters, increasing the height of the emitters and reducing the value of the interelectrode gap. Established deviation of the experimental values of the operating voltage from theoretically calculated when approaching in the interelectrode gap near to values commensurate with the height of the emitters. It is shown that the observed effect is caused by low conductivity of multi-walled carbon nanotubes, high contact resistance with a substrate, as well as micro-and macroinhomogeneities of the structure of an array of carbon nanotubes.
Field emission properties of the graphenated carbon nanotube electrode
Applied Surface Science, 2015
Reduced graphene oxide-coated carbon nanotubes (RGO-CNT) electrodes have been prepared by hot filament chemical vapour deposition system in one-step growth process. We studied RGO-CNT electrodes behaviour as cold cathode in field emission test. Our results show that RGO-CNT retain the low threshold voltage typical of CNTs, but with greatly improved emission current stability. The field emission enhancement value is significantly higher than that expected being caused by geometric effect (height divided by the radius of nanotube). This suggested that the field emission of this hybrid structure is not only from a single tip, but eventually it is from several tips with contribution of graphene nanosheets at CNT's walls. This phenomenon explains why the graphenated carbon nanotubes do not burn out as quickly as CNT does until emission ceases completely. These preliminaries results make nanocarbon materials good candidates for applications as electron sources for several devices.
Field Emission Cathodes Based on Structured Carbon Nanotube Arrays
Abstract— Field emission properties of the structured carbon nanotube cathodes were investigated by field emission scanning microscopy, scanning electron microscopy and integral field emission measurements with luminescence screen. The carbon nanotube arrays were synthesized by the atmospheric pressure floating catalyst chemical vapour deposition method under the high temperature pyrolysis of ferrocene/xylene solution. Varying arrays of carbon nanotube columns and blocks were fabricated on Si, SiO 2 and porous anodic alumina substrates. Well-aligned field emission from nearly 100% of the patches at electric field <10 V/µm in direct current and pulsed mode integrally and locally was observed. High current capabilities up to mA currents for structured carbon nanotube cathodes were achieved. Integral field emission measurements with luminescence screen and processing under N 2 and O 2 exposures of up to 3×10 −5 mbar demonstrated homogeneous current distribution and long-term stability of the structured carbon nanotube cathodes. Index Terms— carbon nanotubes, field emission catchodes, structured carbon nanotube arrays, field emission scanning microscope.
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.
Carbon nanotube films as electron field emitters
Carbon, 2002
Carbon nanotubes have been recognized as one of the most promising electron field emitters currently available. We review the state of the art of current research on the electron field emission properties of carbon nanotube films and present recent results outlining their potential as field emitters as well as illustrating some current concerns in the research field.