Carbon nanotubes are relatively new, having come about less than two decades ago. Or rather, the ability to see them was made possible by advances in microscopes. Nanotubes are usually 10 nanometers in diameter and can be up to a millimeter in length.
Nanotubes have interesting properties, because they can conduct large currents, are impermeable (so far), and are extremely strong. Consequently, many researchers are working to make large scale nanotubes for construction of any number of things, as well as nano-electronics. A nanotube usually consists of a graphite sheet containing 60 carbon atoms wrapped into a tube and sealed at the ends.