Abstract
Carbon nanotube is a rolled-up graphene sheet into a cylinder. The diameter of a carbon nanotube is 0.5-2nm and the length of the nanotube can be 100nm-10cm. Because of variety of possible helical geometries known as chirality, carbon nanotubes provide a family of structures that are expressed by two integers (n,m). In particular, depending on (n,m), a single-wall carbon nanotube is either metal or semiconductor. In this talk, we overview, for young scientists, the 33-years history since 1991 and propose five challenges of carbon nanotubes for now and future.