Carbon nanotubes are an allotrope of carbon with a cylindrical nanostructure. These cylindrical carbon molecules have unusual properties, which make them potentially useful in a wide variety of applications in nanotechnology, electronics, optics and other fields of materials science. They exhibit extraordinary strength and stiffness, as well as unique electrical and thermal properties. Additionally, owing to their hollow structure and high aspect ratio, carbon nanotubes can be used as nanoscale reservoirs for other molecules.