Carbon Nanotube
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure.
Some allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d-f) fullerenes (C60, C540, C70); g) amorphous carbon; h) carbon nanotube.
http://en.wikipedia.org/wiki/Carbon_nanotube