Large intrinsic energy band gaps in annealed nanotube-derived graphene nanoribbons*

The usefulness of graphene for electronics is diminished by an absent energy bandgap. While graphene nanoribbons have non-zero bandgaps, lithographic fabrication methods introduce defects which decouple the bandgap from electronic properties and compromise performance [1]. Here, we present direct measurements of a large intrinsic energy bandgap of approximately 50 meV in 100 nm-width level nanoribbons fabricated by high-temperature annealing of unzipped carbon nanotubes [2]. The activation energy is seven times greater than those in [1], and is close to the width of the transport gap in the differential conductance. This similarity suggests that the activation energy is in fact the intrinsic bandgap. High-resolution TEM and Raman spectroscopy, along with an absence of hopping conductance and stochastic charging effects, suggest a low defect density. [1] M.Y. Han, P. Kim et al., PRL 104, 056801 (2010) [2] J.Haruyama, J.M.Tour, et al., Nature Nanotech. (December 2010)