Fabrication of efficient field emitters with thin multiwalled carbon nanotubes using spray method Hee Jin Jeong, Ha Kyu Choi, Gil Yong Kim, Young Il Song, Yu Tong, Seong Chu Lim, Young Hee Lee * Department of Physics, Sungkyunkwan Advanced Institute of Nanotechnology and Center for Nanotubes and Nanostructured Composites, Sungkyunkwan University, Suwon 440-746, Republic of Korea Received 14 December 2005; accepted 4 April 2006 Available online 5 June 2006 Abstract Thin multiwalled carbon nanotube (t-MWCNTs)-based field emitters are made by use of a spray method. The number of tube walls is between 2 and 6, with the corresponding outer diameters between 3 and 6 nm. They were dispersed in dichloroethane and sprayed onto metal-deposited indium tin oxide glass. After heat treatment, they were found to be tightly adhered to metal electrode. Excellent field emission characteristics were exhibited, with a large field enhancement factor and low turn-on voltage, comparable to those of single- walled CNTs. However, the t-MWCNTs demonstrated a significantly lower degradation rate than SWCNTs in the emission current. This high emission stability was attributed to their stable edge structures, similar to conventional large-diameter MWCNTs. Therefore, t-MWCNTs could be utilized as an alternative material for field emitters. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Carbon nanotubes; Coating; Field emission 1. Introduction A large field enhancement factor, high electrical conduc- tivity, and environmental stability are prerequisites for an efficient field emitter. For this reason, carbon nanotubes (CNTs) have been considered as one of the best field emit- ters [1] due to their unique properties such as high aspect ratio, chemical inertness, high mechanical strength, and high electrical conductivity. Recently, singlewalled carbon nanotubes (SWCNTs) have been reported to have a large field enhancement factor, low threshold voltage, and high emission currents [2], but substantial degradation of emis- sion currents presents a serious drawback for application to the field emission displays [3]. In contrast to SWCNTs, multiwalled CNTs (MWCNTs) have shown high emission stability, however, a small field enhancement factor has resulted in low emission current [4]. Doublewalled carbon nanotubes have been studied for this purpose, but the poor production rate and following purification process of cata- lysts presents a serious bottleneck [5]. Thin multiwalled CNTs (t-MWCNTs) have been synthesized with high cata- lyst efficiency such that no further purification process is required [6]. Therefore, these t-MWCNTs, with small num- ber of walls of 2–6 and small diameters below 6 nm, could be an alternative for this purpose due to their intermediate structural properties between SWCNTs and MWCNTs [7]. CNT-based field emitters have been fabricated by vari- ous methods such as direct growth [8], suspension-filtering [3], electrophoresis [9], and screen printing [2]. One may easily control the alignment, density, diameter, and length of nanotubes using the direct chemical vapor deposition (CVD) growth method. However, this approach is often limited by the scalability of the substrate size and growth temperature. Whereas large area deposition of nano- tubes can be realized using the screen-printing method, a 0008-6223/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.04.009 * Corresponding author. Tel.: +82 031 299 6507; fax: +82 031 290 5954. E-mail address: leeyoung@skku.edu (Y.H. Lee). www.elsevier.com/locate/carbon Carbon 44 (2006) 2689–2693