Carbon nanotubes are tubes made of carbon atoms with a diameter of nanometer order (typically in the range from 0.4 nm to 40 nm) and an optional length (carbon nanotubes up to 550 mm in length have been grown). Carbon nanotubes can be viewed as rolled graphene-fragments (graphene is a single carbon layer of the graphite structure, describing its nature by analogy to a polycyclic aromatic hydrocarbon of quasi infinite size). Different graphene-fragments rolled at different angles and curvatures result in different nanotubes with varying properties.
Carbon nanotubes can be categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs) where SWNTs have a single layer of carbon atoms while MWNTs have multiple layers of them.
Unique structural, chemical, mechanical, thermal, optical and electronic properties of nanotubes have attracted lots of interest in their exploration and exploitation.