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

Double walled carbon nanotubes (DWNTs) were obtained by the are discharge technique 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 microscopy (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 diameters in the range 1.1-4.2 nm. As a rule, the DWNT tubes form into bundles. Occasionally single walled nanotubes (SWNTs) were observed by HREM although Raman spectroscopy did not reveal the presence of significant quantities of these tubules in the bulk product. (C) 2001 Elsevier Science Ltd. All rights reserved.