Field Emission Response from Multiwall Carbon Nanotubes Grown on Different Metallic Substrates
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Field emission response from multiwall carbon nanotubes grown on different metallic substrates Indranil Lahiri, Raghunandan Seelaboyina and Wonbong Choi Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33174, U.S.A.
ABSTRACT Carbon nanotubes (CNT) have seen a wide variety of applications, spread well beyond the semiconductor industries - especially in field emission related devices. For its widest possible application, it has become very much important to grow CNTs on a variety of metallic substrates and understand their field emission response. In the present study, multiwall CNTs (MWCNT), grown on pure metallic substrates like Cu, Al and W, were subjected to field emission tests under DC and AC bias. Choice of diffusion barrier layer and catalyst was also varied, to verify their effects on the emission response. Field emission behaviors from all such structures were compared with MWCNTs grown on Si. It was found that the MWCNTs grown on pure Cu substrate showed excellent field electron emission response, in terms of low turn-on field, high emission current, long time stability and very high field enhancement factor.
INTRODUCTION In recent years, cold field electron emitters have shown wide applications, from field emission displays [1], vacuum electronic devices [2,3], microwave power amplifiers [4] to electron microscopes [5] and x-ray tubes [6]. Due to its fine tip, high aspect ratio, good chemical resistance, efficient thermal conductivity and exceptional mechanical strength, carbon nanotube (CNT) array field emitter has remained the most popular choice [7-10]. Though CNTs are conventionally grown on Si wafers due to their excellent semiconducting properties, it is not the best substrate material for applications demanding high electrical and thermal conductivity. For such usages, CNTs are needed to be grown on metallic substrates, without compromising the properties required for the specific application. CNTs were directly grown on Inconel substrate by Talapatra et al. [11] and the immediate need of synthesizing CNTs on high conductivity metal surfaces were specifically pointed out. CNT growth on metallic surfaces reduces the interfacial resistance, though minimization of the contact resistance between a metallic film and CNTs is a well-known issue in nano-electronics [12]. CNTs can be semiconducting or metallic, thus type of CNTs, i.e., alignment of Fermi energy levels of CNTs and the substrate, plays an important role in contact resistance, apart from geometrical factors. A metallic substrate is expected to have least contact resistance with multiwall carbon nanotubes (MWCNT) as these are predominantly metallic. In the present study, we have focused our attention on growth of MWCNTs on different metallic substrates and their field emission response. Criteria for a good field emitter device are low turn-on field, high emission current and good stability of emission in long-time operation. Most of the researches in field emission from CNTs have, thu
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