Structure changes of single-wall carbon nanotubes and single-wall carbon nanohorns caused by heat treatment

Raman spectra and transmission electron microscope images showed that diameter enlargement of HiPco, a kind of single-wall carbon nanotube, accompanied by tube-wall corrugation was caused by heat treatment (HT) at 1000 to 1700 degreesC. Further enlargement accompanied by straightening of the tube walls and incorporation of carbon fragments within the tubes became obvious after HT at 1800 to 1900degreesC. The transformation of some single-wall carbon nanotubes into multi-wall nanotubes was observed after HT at 2000degreesC, and most single-wall tubes were transformed into multi-wall ones by HT at 2400 degreesC. What influence the Fe contained in the HiPco tubes had on these structure changes was unclear; similar changes were observed in single-wall carbon nanohorns that did not contain any metal. This indicates that thermally induced changes in the structure of single-wall carbon nanotubes can occur without a metal catalyst. Heat treatment increased the integrity of the nanotube-papers. and this increase may have been due to tube-tube interconnections created by HT. (C) 2003 Elsevier Science Ltd. All rights reserved.