CNTs (carbon nanotubes) have probably been around for a lot longer than was first realized, but ......... microscopy at that time was not advanced enough to distinguish them from other types of tubes.

The first method for producing CNTs and fullerenes in ......... quantities was by applying an electric current across two carbonaceous electrodes in an inert gas atmosphere.

This method is called plasma arcing: it involves the evaporation of one electrode as cations followed by ......... at the other electrode.

The carbon arc discharge method is the most common and easiest way to produce CNTs, but it produces a complex mixture of components and requires further purification to separate the CNTs from the soot and the ......... catalytic metals present in the crude product.

This method creates CNTs through arc-vaporization of two carbon rods placed end to end, separated by approximately 1mm, in an enclosure that is usually filled with ......... gas at low pressure.

Another method of nanotube synthesis involves plasma arcing in the ......... of cobalt with a 3% or greater concentration.

The nanotube product is a compact cathode deposit of rod-like ..........

However, when cobalt is added, the nature of the product changes to a web, with strands of 1mm or so thickness that stretch from the cathode to the walls of the reaction ..........

The ......... by which cobalt changes this process is unclear, however one possibility is that such metals affect the local electric fields and hence the formation of the five-membered rings.

Arc-discharge and laser vaporization are currently the principal methods for obtaining small quantities of high quality CNTs, but both methods suffer from .........: the CNTs are difficult to purify, manipulate, and assemble for building nanotube-device architectures for practical applications.