IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 18 (2007) 395702 (5pp) doi:10.1088/0957-4484/18/39/395702 Improved field emission properties of thiolated multi-wall carbon nanotubes on a flexible carbon cloth substrate F T Chuang 1 , P Y Chen 2 , T C Cheng 2 , C H Chien 3 and B J Li 4 1 Department of Material Science and Engineering, National Chiao-Tung University, Hsinchu 30050, Taiwan, Republic of China 2 National Nano Device Laboratories, Hsinchu 30078, Taiwan, Republic of China 3 Department of Electronics Engineering, National Chiao-Tung University, Hsinchu 30050, Taiwan, Republic of China 4 Industrial Technology Research Institute (ITRI), Hsinchu 30050, Taiwan, Republic of China E-mail: pychen@mail.ndl.org.tw Received 1 May 2007, in final form 22 July 2007 Published 4 September 2007 Online at stacks.iop.org/Nano/18/395702 Abstract In this paper we report the observation of enhanced field emission properties from thiolated multi-wall carbon nanotubes (MWCNTs) produced by a simple and effective two-step chemical surface modification technique. This technique implements carboxylation and thiolation on the MWCNTs synthesized by microwave plasma chemical vapor deposition (MPCVD) on the flexible carbon cloth substrate. The resulting thiolated MWCNTs were found to have a very low threshold field value of 1.25 V μm −1 and a rather high field enhancement factor of 1.93 × 10 4 , which are crucial for applications in versatile vacuum microelectronics. (Some figures in this article are in colour only in the electronic version) 1. Introduction Since carbon nanotubes (CNTs) were discovered by Iijima in 1991 [1], there has been increased interest in the study of electron field emission of CNTs, in particular for potential applications in field emission displays (FEDs), vacuum flat lamps, vacuum microelectronic sources, etc. [2–4]. Some unique physical properties, such as high aspect ratio, a whisker- like shape for optimum geometrical field enhancement, high electrical conductivity and extraordinary environmental stability, make CNTs promising candidates for cold cathode materials. In the past, field emission from patterned CNT thin films on silicon and various types of rigid substrates had been extensively studied [5–8]. However, these sorts of substrates are vulnerable to breaking. Therefore, the lighter, more durable and longer lifespan field emitters made on flexible substrates have recently attracted significant attention. In 2004, Jo et al [9] and Banerjee et al [10] reported, respectively, the growth of CNTs or ZnO nanowires (ZnO NWs) on carbon cloth by thermal chemical vapor deposition (thermal CVD). We find that carbon cloth is intrinsically a plastic and electrically conducting substrate, allowing the practical implementation of flexible electron sources for versatile vacuum microelectronics applications. In addition, carbon cloth is also considered to be a good cathode substrate due to its woven geometry, which provides an additional geometric enhancement effect to the overall field emission properties [9]. In this work, we report a study on surface chemical modifications on MWCNTs with the aim of improving the field emission properties of the MWCNTs grown on the flexible carbon cloth. Our experimental results obtained using a two- step chemical process show that thiolation of MWCNTs could significantly improve the field emission efficiency, and thus be very promising for the fabrication of low turn-on field and highly efficient electron emitters for flexible electronics. 2. Experimental details All MWCNT samples were grown by MPCVD on the flexible carbon cloth substrate [11]. A Fe film of 20 nm was used as a catalyst and patterned with a size of 0.5 × 0.5 cm 2 . The 0957-4484/07/395702+05$30.00 1 © 2007 IOP Publishing Ltd Printed in the UK