Colors of carbon nanotubes

Single-wall carbon nanotubes (SWCNTs) are graphitic materials whose colors are usually considered to be black. Actually, graphite-like black color is observed for as-synthesized SWCNT samples which are in the mixture state of the metallic and the semiconducting SWCNTs. However, after the separation of the metallic and the semiconducting types from the mixture, SWCNTs can exhibit various colors depending on their electronic types and diameters. These colorful colors are caused by the boundary conditions for the circumferential directions of the cylindrical structures. Here we discuss the underlying physical backgrounds of the colors of SWCNTs and the techniques to obtain such colorful SWCNTs.