Combinatorial Evaluation for Field Emission Properties of Carbon Nanotubes Part II: High Growth Rate System (original) (raw)
Related papers
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.
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.
Carbon Nanotubes For Field Emission Displays
AIP Conference Proceedings, 2003
Display structures suitable for direct growth of CNT films by thermal CVD are described. The CNT film specifications for TV application are the following: a threshold field for emission higher than 3 V/µm, a current density of 140mA/cm 2 and an emission site density around 10 7 cm -2 . The major difficulty encountered with the deposited films is to reach the specified emission site density. These films present an exponential distribution of the amplification factor controlling the current emission. Small 1 cm 2 working displays with CNTs grown by using the decomposition of C2H2 over Ni catalyst have been done. These samples show that the three major locks of conventional FED technology, namely large size compatibility, simple low cost cathode and good reliability, are now opening thanks to CNTs.
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.
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.
Large field emission current density from well-aligned carbon nanotube field emitter arrays
Current Applied Physics, 2001
We have grown well-aligned carbon nanotube arrays by thermal chemical vapor deposition at temperatures below 800°C on Fe nanoparticles deposited by a pulsed laser on a porous Si substrate. Porous Si substrates were prepared by the electrochemical etching of p-Si (1 0 0) wafers with resistivities of 3±6 X cm. These well-aligned carbon nanotube ®eld emitter arrays are suitable for electron emission applications such as cold-cathode¯at panel displays and vacuum microelectronic devices like microwave power ampli®er tubes. Field emission characterization has been performed on the CNT-cathode diode device at room temperature and in a vacuum chamber below 10 À6 Torr. The anode is maintained at a distance of 60 lm from the carbon nanotube cathode arrays through an insulating spacer of polyvinyl ®lm. The measured ®eld emitting area is 4X0 Â 10 À5 cm 2 . Our carbon nanotube ®eld emitter arrays emit 1 mAacm 2 at an electric ®eld of 2 Valm; they emit a large current density as high as 80 mAacm 2 at 3 Valm, which is orders of magnitude higher than any other results reported so far. The open tip structure of our carbon nanotubes and their good adhesion through Fe nanoparticles to the Si substrate are part of the reason why we can attain a large ®eld emission current density within a low ®eld. The ®eld emitter arrays in our diode device are vertically well-aligned carbon nanotubes on the Si-wafer substrate. Ó
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.
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.