Continuous and Scalable Fabrication of Transparent Conducting Carbon Nanotube Films Budhadipta Dan, † Glen C. Irvin, ‡ and Matteo Pasquali †, * † Department of Physics and Astronomy, Department of Chemical and Biomolecular Engineering, and Department of Chemistry, The Smalley Institute for Nanoscale Science & Technology, Rice University, 6100 Main Street, Houston, Texas 77005, and ‡ Unidym Inc., 1430 O’Brien Drive, Suite G, Menlo Park, California 94025 C arbon nanotubes (CNTs) combine nanoscale size with high aspect ratio (1000) and unique electri- cal, optical, mechanical, and electrochemi- cal properties, 1-6 making them ideal candi- date materials for high-impact applications in various fields. 7 Yet, much as in polymer science and engineering, such applications can only be attained by developing appro- priate scalable processes that translate the properties of the elemental molecules (SWNTs) or particles (CNTs) into macro- scopic materials. Scientific knowledge about processing SWNTs into macroscopic and commercially useful products is still scarce and is a topic of extensive current re- search. An important recent success in this area has been the fabrication of optically transparent and electrically conducting thin films of pure SWNTs. Such transparent and conductive thin films or coatings may re- place indium tin oxide (ITO) in a wide range of applications, for example, in touch screens, flat panel displays, image record- ers, optical communication devices, and so- lar cells. 8,9 Nanotube films have been fabricated by vacuum filtration, 10-12 transfer printing onto various substrates, 13,14 drawing from vertically oriented nanotube forests, 15 spin coating, 16 drop casting from SWNT disper- sions, 17 quasi-Langmuir-Blodgett deposi- tion, 18 dip-coating, 19 direct CVD growth, 20 air-spraying, 21,22 and, after suitable function- alization, wire-wound rod coating, 23,24 and slot coating. 25 However, most of the pro- cesses proposed so far cannot be ported easily to large scale production-with the ex- ception of air-spraying, which has the draw- back of forming sparse and relatively non- uniform networks, 22 and rod and slot coating, which are scalable methods but have so far have required functionalized CNTs. 23-26 Here we report the fabrication of films of SWNT films by “draw-down Mayer rod coating” (rod coating) process using pristine SWNTs. Draw-down rod coating is a well-known coating technique widely used by laborato- ries in the coating industry for making liq- uid thin films in a continuous and controlled manner. 27 Fluids that can be coated effec- tively by the Mayer rod method can then be readily adapted to more controllable, higher throughput methods such as slot, slide, and roll coating. 28,29 Figure 1a shows a schematic diagram of the rod coater with the wire-wound Mayer rod. The coating ap- paratus consists of a stainless steel rod wound tightly with stainless steel wire and a smooth and flat glass pad. The substrate is held down on the drawdown glass pad us- ing heavy duty clips; the Mayer rod rolls over the substrate, doctoring off the coat- ing fluid. Part of the liquid flows through the grooves in the wire-wound rod and forms the thin liquid film. The diameter of the wound wire determines the size of the grooves and, hence, it controls the final *Address correspondence to mp@rice.edu. Received for review December 3, 2008 and accepted March 26, 2009. Published online April 8, 2009. 10.1021/nn8008307 CCC: $40.75 © 2009 American Chemical Society ABSTRACT We report an industrially scalable, fast, and simple process for the large scale fabrication of optically transparent and electrically conducting thin films of single-walled carbon nanotubes (SWNT). Purified, pristine HiPco SWNTs were dispersed in water at high concentrations with the help of surfactants, rod-coated into uniform thin films, and doped by various acids. We show how to combine different surfactants to make uniform dispersions with high concentration of SWNTs and optimal rheological behavior for coating and drying, including preventing dewetting and film rupture that has plagued earlier attempts. Doping by fuming sulfuric acid yielded the films with best performance (sheet resistance of 100 and 300 /sq for respective transparency of 70% and 90%). We use a figure of merit (FOM) plot for an immediate evaluation and comparison of the performance and microstructure of CNT films produced by different methods. Further scientific engineering will pave the way to the deployment of CNT films in commercial applications. KEYWORDS: single walled carbon nanotubes · SWNT films · transparent · conductive · coatings · wire-wound rod coating · rheology. ARTICLE www.acsnano.org VOL. 3 ▪ NO. 4 ▪ 835–843 ▪ 2009 835 Downloaded by NEW YORK UNIV on September 3, 2009 | http://pubs.acs.org Publication Date (Web): April 8, 2009 | doi: 10.1021/nn8008307