Comparative studies on the structure and electronic properties of carbon nanotubes prepared by the catalytic pyrolysis of CH4 and disproportionation of CO

A new type of carbon nanotubes prepared by catalytic decomposition of CH4 (CH4-CNT) was studied and compared with carbon nanotubes derived from CO-disproportionation (CO-CNT) and graphite. HRTEM observation reveals that the structural graphene sheets are in a conical hollow shape for CH4-CNT but in a cylindrical shape for CO-CNT. The valence band structure of CH4-CNT is similar to that of CO-CNT but with a lower density-of-state of 2p-pi valence electrons. Stronger plasma excitations and additional lower-energy transitions are observed for CH4-CNT by XPS investigations. A reduced work function and a more gradual Fermi edge for CH4-CNT are also detected by He I UPS. (C) 1999 Elsevier Science Ltd. All rights reserved.