And here I always thought that Graphene is a zero-gap semiconductor, because its conduction and valence bands meet at the Dirac points. The Dirac points are six locations in momentum space, on the edge of the Brillouin zone, divided into two non-equivalent sets of three points. The two sets are labeled K and K’. The sets give graphene a valley degeneracy of gv = 2. By contrast, for traditional semiconductors the primary point of interest is generally Γ, where momentum is zero. Go figure.
But Carbon itself is considered a very high bandgap semiconductor. Perhaps when you whittle down Carbon to single-atom width, it goes from high bandgap to lowbandgap semiconductor.