Thermal degradation of ragged single-wall carbon nanotubes produced by polymer-assisted ultrasonication Akira Koshio a, * , Masako Yudasaka a , Sumio Iijima a,b,c a Nanotubulites Project, JST-ICORP, c/o NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan b Department of Physics, Meijo University, Tenpaku-ku, Nagoya 468-8502, Japan c NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan Received 27 February 2001 Abstract As-grown single-wall carbon nanotubes SWNTs) and a monochlorobenzene MCB) solution of polymethylmeth- acrylate PMMA) were sonicated using an ultrasonic processor. The SWNTs obtained were short and contained many holes and defects; therefore, they were called `ragged single-wall carbon nanotubes r-SWNTs)'. The r-SWNTs were degraded at and above 800°C in a vacuum 10 7 Torr). All the r-SWNTs disappeared after heat-treatment at 1200°C for 1 h. Since thermal degradation was not observed for as-grown SWNTs or for acid-puri®ed SWNTs, we suggest that the holes and defects in the r-SWNTs were formed by oxidation of chemically damaged sites formed during the polymer- assisted ultrasonication. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Since the discovery of single-wall carbon na- notubes SWNTs) [1] their nature, including their structure, and electronic and mechanical properties, has been revealed as a result of many investigations. However, many impurities, such as amorphous carbon, fullerenes, and metal catalysts, are pro- duced together with SWNTs. High-quality SWNTs need to be produced to study the detailed bulk properties of SWNTs and to develop applications for their use. Some methods for purifying SWNTs have been reported. Carbonaceous impurities can be removed by gas-phase oxidation [2], and metal impurities can be eliminated using a strong acid, followed by ®ltration and centrifugation [3]. The separation of SWNTs and impurities is more dicult than general separation techniques, largely because SWNTs of various lengths form bundles, to which impurities adhere. Ultrasonic irradiation is one eective method for dispersing, disentangling, and thinning bundles of SWNTs when SWNTs are puri®ed. Smalley and co-work- ers [4] reported purifying and cutting SWNTs by ultrasonically assisted ®ltration. Recently, our group has reported that ultrasonication and ®l- tration of a mixture of SWNTs and polymethyl- methacrylate PMMA) was a more eective method for removing carbonaceous impurities, and we also found a number of short SWNTs about 1 lm) and thin bundles containing one to three SWNTs [5]. In this study, we found that SWNTs puri®ed by polymer-assisted ultrasonication had worm-eaten- like holes and they rapidly sublimed at tempera- tures over 800°C. These were named `ragged 29 June 2001 Chemical Physics Letters 341 2001) 461±466 www.elsevier.nl/locate/cplett * Corresponding author. Fax: +81-298-50-1366. E-mail address: koshio@nlp.jst.go.jp A. Koshio). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4  0 1 ) 0 0 5 0 7 - 3