HIERARCHICAL STRUCTURE OF CARBON NANOTUBES BASED FIELD EMITTER

Abstract

Field emitters (cold cathode) has been used in a wide variety of applications like field emission displays, X-ray sources, microwave amplifiers, satellite propulsion system, electron microscopes etc. With the advent of the nanotechnology, field emitter devices can be made much more efficient and useful. One dimensional nanomaterials have been widely investigated for this purpose owing to their unique properties. More specifically, carbon nanotubes have dominated the whole field emission research since its discovery by lijima in 1991. Carbon nanotubes have all the necessary properties required for a material to be a good field emitter i.e. high aspect ratio, high conductivity, high melting point, chemically inert, high mechanical strength. The excellent field emission characteristics shown by carbon nanotubes till now have further enhanced the expectations. High current density with better stability has been focus of many researchers. A lot of composites and designs have been reported to achieve high current density. Some of them have shown some good field emission results but still unable to find its way towards commercialization. In the present study, a 3-Dimensional hierarchical structure has been successfully synthesized and demonstrated. CuO nanostructure-CNT hierarchical field emitter was basically a two step process. First, CuO nanostructures were grown on a copper foil by chemical method. Then CNTs were synthesized over it using thermal chemical vapour deposition (CVD). To the best of author's knowledge, this hierarchical structure was demonstrated for the first time. High current density can be achieved by enhancing CNT density while avoiding screening effect. 3- Dimensional architecture has the advantage of the enhanced surface area so that more area is available for CNTs growth. Cupric oxide (CuO) nanotubes array and CuO nanorods were grown on copper substrate by simple chemical method. The surface area of these nanostructures was reported to be much higher than the corresponding 2-Dimensional structure. CuO nanotubes and nanorods show surface area of 1379.6 cm2 and 940.8 cm2 as compared to that of 2-Dimensional surface i.e. 2.25cm2. A comparative study was then made between 2-Dimensional structure i.e. Iv CNTs on copper foil and 3-Dimensional structure i.e CNTs on CuO nanotubes and CuO nanorods separately. The current density measured to be 0.87 mA/cm2, 3.11 mA/cm2 and 0.63 mA/cm2 for CNTs on copper foil, CNTs on CuO nanotubes and CNTs on CuO Nanorods respectively.