The structure of nanotubes fabricated by carbon evaporation at high gas pressure

Nanotubes were fabricated by carbon evaporation at high gas pressure (gas-n itrogen or nitrogen-argon, pressure up to 1300 atm). Three main types of tu bes were observed and are characterised as follows: (1) Multilayered surfac e modulated micro- and nanotubes (SMMTs and SMNTs, respectively) with fluct uating diameters caused by periodically interrupted movement of catalytic p articles during tube formation. All tubes of this type have a common princi ple of structural organization: the main part of the walls is formed by con tinuous graphene layers to which the side layers of inner caps are connecte d. An extreme form of SMNTs was observed in which the carbon nanotube walls were spheroidal. (2) Stacked conical layer carbon nanotubes (CLNTs). These nanotubes have open edges and were found to readily absorb argon. (3) Mult iple walled carbon nanotubes (MWNTs) consisting of concentric cylindrical l ayers. The inner channels of these nanotubes were sometimes observed to be filed with Fe carbides. The growth of (1) and (2) type nanotubes is promote d by Fe catalytic particles. At reduced catalyst concentration and at high temperature, most of the observed nanotubes are type (3). In addition the p resence of N-2 in the gaseous mixture was found to enhance the rate of grap hite evaporation and increased the nanotube yield. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.