Field Emission from the Carbon Nanotubes Grown over Cylindrical Surface
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Field Emission from the Carbon Nanotubes Grown over Cylindrical Surface D. Sarangi* and A. Karimi Institute of Physics of the Complex Matter (FSB-IPMC), Swiss Federal Institute of Technology (EPFL), CH 1015 Lausanne, Switzerland.
ABSTRACT
Carbon nanotubes are excellent field emitters due to their high aspect ratios and small radii of curvature. These properties of the nanotubes offer tremendous possibilities for the realization of field emission devices. For the realization of the field emission devices controlled placement and alignment of the nanotubes over the substrate surface is desirable. Furthermore, field emission of the nanotubes in cylindrical geometry has added advantages over planar geometry. But, it is difficult to grow nanotubes uniformly over non-planar substrates such as long metallic cylinders by conventional CVD techniques. In the present investigation we have adopted a very simple technique called as Cold Plasma Chemical Vapor Deposition (CP-CVD) to grow carbon nanotubes over a catalyst-supported metallic wire by resistive heating in hydrocarbon atmosphere at about 750oC. The localized dissociation of the hydrocarbon gas over metallic wire allows well controlled growth of the nanotubes. The field emission performance of these nanotube coated wires was measured in a cylindrical geometry where the aluminum tube was used as an anode. Emission site density is found to be the most important parameter to control the field emission performance. Comparisons of the field emission properties were made using nanotubes grown in different hydrocarbon gases such as methane and acetylene. The effects of other parameters, such as growth time, was also investigated.
INTRODUCTION
Carbon nanotubes (CNTs) are increasingly becoming popular as electron emitters for field emission (FE) based devices due to their high aspect ratios and good mechanical and chemical stability. A large number of devices have already been demonstrated and/or proposed based on CNTs field emitters. Saito et al. [1] produced and commercialized nanotube based lighting devices. Jung et al. [2] demonstrated triode-type CNTs based 5” color display with high brightness and good color purity at video-speed operation. Other proposed applications based on nanotube field emission includes a microwave amplifier [3], as electron source to generate X-rays [4], as electron gun for the cathode ray tubes (CRTs) [5], etc. Very recently Croci et al. [6] demonstrated a 40 cm fully sealed luminescent tube where carbon nanotube coated metallic wire acts as a cathode. To realize these kind of devices, controlled and wellaligned growth of the nanotubes is essential. We have previously demonstrated a way of *
Present Address: Micro and Nanosystems, ETH Zentrum –CLA H 1, Tannenstrasse 3, 8092 Zurich, Switzerland. Email: [email protected]
A5.66.2
controlling the placement and physical characteristics of nanotubes grown by a very simple technique called Cold Plasma Chemical Vapor Deposition (CP-CVD) [7-9]. This paper mainly deals with the fiel
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