Double-walled carbon nanotubes fabricated by a hydrogen arc discharge method

Double walled carbon nanotubes (DWNTs) were obtained by the are discharge t echnique in an atmosphere of Ar and H-2 mixture (1:1/v:v) at 350 Torr. The catalyst was prepared from a mixture of Ni, Co, Fe and S powders heated in an inert gas atmosphere at 500 degreesC for 1 h. High resolution electron m icroscopy (HREM) revealed that the dominant type of obtained nanotubes were DWNTs with outer diameter in the range of 1.9-5 nm and inner tube diameter s in the range 1.1-4.2 nm. As a rule, the DWNT tubes form into bundles. Occ asionally single walled nanotubes (SWNTs) were observed by HREM although Ra man spectroscopy did not reveal the presence of significant quantities of t hese tubules in the bulk product. (C) 2001 Elsevier Science Ltd. All rights reserved.