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B-J. Li Materials Research Laboratories, Industrial Technology Research Institute, 195-5 Chung Hsing Road, Section 4 Chutung, Hsinchu, Taiwan

R.P.H. Changa) Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (Received 23 July 2002; accepted 27 January 2003)

A modified high-temperature arc furnace was used to produce carbon nanotubes from carbon black by a solid-state transformation without a catalyst. The layer of carbon nanotubes thus formed was nearly pure with only a minor amount of carbon black particles. The properties of these nanotubes were found to be very similar to those produced by the conventional arc synthesis. Based on this process, a mechanism for the growth of these nanotubes is proposed. In addition, field-emission properties of these nanotubes were comparable to the properties of arc-grown carbon nanotubes.

I. INTRODUCTION

The discovery of carbon nanotubes (CNTs) by Iijima in 19911 has created a great amount of interest due to their remarkable mechanical2 and electrical3 properties. Nanotubes have already been widely used as field emitters4 and scanning microscope probe tips.5 In addition, nanotubes have potential applications in hydrogen storage,6 electronic devices,7,8 and composite materials.9 The most significant challenge for the industrial use of CNTs is the ability to produce large-scale quantities of high-crystalline nanotubes. This requires the development of rapid, efficient, and low-cost processing methods. The three most common production techniques for CNTs are arc discharge, laser ablation, and chemical vapor deposition (CVD). During the production of CNTs by arc discharge between a pair of graphite electrodes, graphitic species are evaporated from the anode as a result of high-temperature heating by the arc and deposited by rapid solidification on the water-cooled cathode.10 The resulting condensed material contains highly crystalline multiwall nanotubes (MWNTs) along with multilayered polyhedral graphitic particles. Single-wall nanotubes (SWNTs) can be produced by adding a metal catalyst to the system. Laser ablation uses an intense

a)

Address all correspondence to this author. e-mail: [email protected] This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/jmr/policy.html. J. Mater. Res., Vol. 18, No. 4, April 2003

laser pulse to ablate a graphite target containing a catalyst.11 During laser ablation, the evaporated carbon species flow downstream in an oven and condense on a cold finger where carbon nanotubes are formed. The CVD method involves flowing a hydrocarbon gas over a heated layer of catalyst particles.12 The carbon nanotubes grow on the catalyst particles by a vapor-liquid-solid (VLS) formation process. All of these synthesis methods rely on the formation of nanotubes from a carbon vapor source. Each method has its own set of parameters that determines the t