Results are presented from studies to prepare carbon nanotubes of single geometry. Carbon nanotubes of certain stereochemistry have been found to be conductive. Others have been found to be excellent transistors, and together nanoelectronic devices have already been formed from them including logic gate circuits. Two synthetic approaches have been tried, namely plasma arcing in the presence of additives and ball milling. In plasma arcing, cathode deposits are altered by the presence of naphthalene in the feed material. The mixture of nanotubes so formed has a larger average void size than that formed in the absence of naphthalene. The results support proposed mechanisms of nanotube formation which involve growth by incorporation of carbon atoms into open tubes. They also show that naphthalene can be directly incorporated into fullerene black and thereby increase the number of hexagonal sheet structures in the carbon deposit. Work so far in ball milling has been confined to studies of the destruction of graphite crystalline phases.