Study of J-E Curve with Hysteresis of Carbon Nanotubes Field Emitters (original) (raw)
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Study of J-E Curve with Hysteresis of Carbon Nanotubes Field Emitters Academic Editors
We observe hysteresis in J-E plot during field emission measurement of CNTs grown by LPCVD technique. CNTs are synthesized on Fe-coated Si substrate at 650 • C. SEM and Raman study confirm that CNTs are successfully grown on Si substrate by LPCVD technique. In this study, we find that ramp-down curve has higher value of current density than ramp-up curve which indicates that CNTs show positive hysteresis. Our results show that a high current density at low turn-on voltage is obtained in ramp-down step of J-E plot which may be since not all CNTs contribute in ramp-up step process. But in ramp-down step all CNTs contribute as field emitters due to high electric field treatment. We also performed stability analysis of CNTs with current at constant applied voltage for 5 hrs and find that the sample shows long-term stability due to increase in emitting site density since a large number of CNTs participate in field emission.
A stable high power carbon nanotube field-emitter device
Diamond and Related Materials, 2004
We report a new fabrication process for carbon nanotube field emitters with high performance and their superior emission properties. The process employs spin-on-glass coating and chemical-mechanical polishing to realize mechanical stability and leveling of the carbon nanotubes. The morphology of the emitter devices revealed a high stability and performance in the emission properties. Particularly in the device scale measurement, an absolute turn-on voltage of 4.5 V was measured, which corresponds to a turn-on voltage per distance less than 1.5 Vymm. The device also revealed an extremely high current density of ;3 Aycm . 2 This value was observed from the proximity of the electrode to the tip of the carbon nanotubes. ᮊ
Elimination of Current Non-Uniformity In Carbon Nanotube Field Emitters
Journal of Materials Science-materials in Electronics, 2007
Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown, patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up. The sudden increase in current resulted in region of
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.
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.
Optimization of Vertically Aligned Nature of CNTs for Improved Field Emission Behavior
Fullerenes, Nanotubes and Carbon Nanostructures, 2009
For improved field emission behavior, we demonstrate the PECVD technique to grow highly ordered, selectively grown, vertically aligned carbon nanotubes (CNTs) with optimum density. We report the optimization of vertically aligned CNTs by optimizing catalyst thickness, dot size of catalyst and the spacing between them. We made an attempt to optimize the catalyst thickness to understand the effect over density, diameter and height of CNTs. SEM images reveal that the catalyst thickness as well as the dot size and the spacing is helpful in optimizing the vertical alignment of CNTs. The vertically aligned CNTs provide a large number of tips as compared to horizontally aligned CNTs over an area. Also, the high value of the enhancement factor required to achieve a better FE behavior is also plausible with vertical CNTs. The field emission results confirm that the vertically aligned CNTs bring a large current density at relatively low threshold field. We were able to achieve a current density of 100 mA/cm 2 at a field of 6 V/mm. Density and therefore screening effect also becomes important factors that hinder the performance of CNT-based emitters. However, in our typical samples we observed less discrepancy in the density, and the density so calculated was in the order of 10 9 /cm 2 .
Field Emission from Multiwalled Carbon Nanotubes
2002
Films of multi-walled carbon nanotubes are very efficient cathodes for field emission devices. Films are grown by thermal chemical vapour deposition on silicon substrates with iron as a catalyst particle. Different types of films are investigated: vertically aligned MWNT with clean and coated nanotube sidewalls. SEM, TEM and Raman spectroscopy has been used in order to determine the structure of the different films. The results show that the aligned MWNT films have excellent field emission properties with high emission current densities and low turn-on and threshold fields. They also show that the presence of a surface coating with amorphous carbon has no impact on the efficiency of the field emission. The current density as a function of applied electric field (on multiple cycles) is reproducible up to a value of 1 mA/cm 2. Exceeding this value leads to light emission from the carbon nanotube film at the investigated spot. Spectral measurements of this light shows a purely blackbody radiation effect with a temperature around 1550 K for the onset current density but temperatures over 2000 K are also seen for higher current densities. In addition, there is a strong correlation between the light intensity and the current density.