, which were first introduced by Iijima [31], are sheets of graphite rolled into circular tubes [32]. They can be synthesized as singular tubes called single walled nanotubes (SWNTs) with the diameter of about 1 nm, or as a series of concentric cylindrical shells of different diameters from 2 to 100 nm called multi walled nanotubes (MWNTs) and have the length of up to several micrometers [33], [34] and [35].