Current-controlled nanotube growth and zone refinement

We describe methods by which the growth of a single carbon nanotube (CNT) can be precisely controlled by an electrical current. In one method a CNT is grown to a predetermined geometry inside another nanotube, which serves as a reaction chamber. Another method allows a preexisting marginal-quality multiwall CNT to be zone refined into a higher-quality multiwall CNT by driving a catalytic bead down the length of the nanotube. In both methods, the speed of nanotube formation is adjustable, and the growth can be stopped and restarted at will. (c) 2005 American Institute of Physics.