Field Emission from Multiwalled Carbon Nanotubes (original) (raw)
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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 properties of multiwalled carbon nanotubes
Ultramicroscopy, 1998
Field emission properties of multiwalled carbon nanotubes, in the form of both single tips and films, have been investigated. Nanotubes compare very favourably with other field emission sources, as they show low operating voltages and produce high current densities. Lifetimes in excess of 100 h in continuous operation at constant applied voltage were observed. Our measurements suggest that the good field emission properties are largely due to small tip size and to a nonmetallic density of states at the tip.
Field emission properties of as-grown multiwalled carbon nanotube films
Carbon, 2012
Multiwalled carbon nanotubes have been produced by ethylene catalytic chemical vapor deposition and used to fabricate thick and dense freestanding films ("buckypapers") by membrane filtering. Field emission properties of buckypapers have been locally studied by means of high vacuum atomic force microscopy with a standard metallic cantilever used as anode to collect electrons emitted from the sample. Buckypapers showed an interesting linear dependence in the Fowler-Nordheim plots demonstrating their suitability as emitters. By precisely tuning the tip-sample distance in the submicron region we found out that the field enhancement factor is not affected by distance variations up to 2µm. Finally, the study of current stability showed that the field emission current with intensity of about 3,3*10 -5 A remains remarkably stable (within 5% fluctuations) for several hours.
Controlled growth of carbon nanotube films for high-current field emission
Diamond and Related Materials, 2007
Carbon nanotubes (CNTs) offer great potential for numerous cold-cathode field emission applications. A less studied need is for high-current cathodes. While work to date has focused on the use of tangled webs of single-wall CNTs, much understanding about field emission has occurred from studies using multi-wall CNTs with controlled geometries. However, the crystalline nature of these multi-wall CNTs typically is far inferior to that of single-wall CNTs. We use high-resolution transmission electron microscopy to demonstrate that growth at temperatures ≤ 630°C via thermal chemical vapor deposition can produce highly crystalline multi-wall CNTs, with structures consisting entirely of concentric graphene cylinders. Conversely, growth at temperatures ≥ 650°C results in crystalline CNTs embedded in a nanocrystalline graphite, or glassy carbon, sheath. This sheath material is likely a poor electrical conductor, due to phonon scattering, and will have deleterious effects on field emission. Field emission measurements taken from such films are consistent with the best field-emitting multi-wall CNT films in the literature, in terms of total current for a given applied field, but without the benefit of the preferred perpendicular orientation. These results are promising toward the development of reliable high-current field emission cathodes.
Field Emission Properties of Single-Walled Carbon Nanotubes with a Variety of Emitter Morphologies
Japanese Journal of Applied Physics, 2008
Field emission properties of single-walled carbon nanotubes (SWCNTs), which were prepared through alcohol catalytic chemical vapor deposition for 10 -60 s, were characterized in a diode configuration. Protrusive bundles at the top surface of samples act selectively as emission sites. The number of emission sites was controlled by emitter morphologies combined with texturing of Si substrates. SWCNTs grown on a textured Si substrate exhibited a turn-on field as low as 2.4 V/mm at a field emission current density of 1 mA/cm 2 . Uniform spatial luminescence (0.5 cm 2 ) from the rear surface of the anode was revealed for SWCNTs prepared on the textured Si substrate. Deterioration of field emission properties through repetitive measurements was reduced for the textured samples in comparison with vertically aligned SWCNTs and a random network of SWCNTs prepared on flat Si substrates. Emitter morphology resulting in improved field emission properties is a crucial factor for the fabrication of SWCNT-electron sources. Morphologically controlled SWCNTs with promising emitter performance are expected to be practical electron sources.
Growth and field emission properties of small diameter carbon nanotube films
Diamond and Related Materials, 2005
Vertically aligned carbon nanotube films with diameters smaller than 5 nm, high densities up to 10 12 /cm 2 , and lengths of~5-8 Am were deposited by microwave plasma-assisted chemical vapor deposition. Experiments show that, by continuous reduction in the thickness of the iron film (i.e.,~0.3-0.5 nm), small diameter carbon nanotubes can be achieved with diameters that ranged from 1-5 nm, and the films are comprised of both single-and double-wall nanotubes. The electron field emission properties of the films were investigated by variable distance field emission and temperature-dependent field electron emission microscopy (T-FEEM). The films showed an emission site density of~10 4 /cm 2 and a threshold field of 2.8 V/Am similar to multiwalled nanotubes (1.9 V/Am). In addition, they also exhibited a temperature dependence of the emission site intensity.
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.
Enhancement of field emission characteristics of carbon nanotubes on oxidation
Journal of nanoscience and nanotechnology
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.
Increased field-emission site density from regrown carbon nanotube films
Journal of Applied Physics, 2005
Electron field emission properties of as-grown, etched, and re-grown carbon nanotube thin films were investigated. The aligned carbon nanotube films were deposited by the microwave plasma-assisted chemical vapor deposition technique. The surface of the as-grown film contained a carbon nanotube mat of amorphous carbon and entangled nanotubes with some tubes protruding from the surface. Hydrogen plasma etching resulted in the removal of the surface layer, and re-growth on the etched surface displayed that a new layer of carbon nanotube mat was formed. The emission site density and the current-voltage dependence of the field emission from all of the samples were analyzed. The results showed that the as-grown sample had a few strong emission spots and a relatively high emission current density (~ 20 µA/cm 2 at 1 V/µm), while the re-grown sample exhibited a significantly increased emission site density.
Effect of Substrate Morphology on Growth and Field Emission Properties of Carbon Nanotube Films
Nanoscale Research Letters, 2008
Carbon nanotube (CNT) films were grown by microwave plasma-enhanced chemical vapor deposition process on four types of Si substrates: (i) mirror polished, (ii) catalyst patterned, (iii) mechanically polished having pits of varying size and shape, and (iv) electrochemically etched. Iron thin film was used as catalytic material and acetylene and ammonia as the precursors. Morphological and structural characteristics of the films were investigated by scanning and transmission electron microscopes, respectively. CNT films of different morphology such as vertically aligned, randomly oriented flowers, or honeycomb like, depending on the morphology of the Si substrates, were obtained. CNTs had sharp tip and bamboo-like internal structure irrespective of growth morphology of the films. Comparative field emission measurements showed that patterned CNT films and that with randomly oriented morphology had superior emission characteristics with threshold field as low as *2.0 V/lm. The defective (bamboo-structure) structures of CNTs have been suggested for the enhanced emission performance of randomly oriented nanotube samples.