What are carbon nanotubes?

Carbon nanotubes are thin nanometre tubes composed of carbon atoms, the structure of which is similar to a honeycomb. Carbon nanotubes have shapes of empty cylinders and, depending on, whether nanotube walls are created by single layers or several graphene layers, we can distinguish several types of nanotubes. They include single wall nanotubes, double-wall nanotubes and multiwall nanotubes.