This analysis, however, neglects the effects of curvature caused by rolling up the graphene sheet that converts all nanotubes with n-m=3i to small band gap semiconductors, with the exception of the armchair tubes (n=m) that remain metallic. Although the band gaps of carbon nanotubes with n-m= 3i and i\ne 0 are relatively small, some can still easily exceed room temperature, if the nanotube diameter is about a nanometer.
