Symmetry-induced band-gap opening in graphene superlattices

Graphene, thanks to the exceptionally high mobility of its carriers, is very promising for high-performance interconnects in future carbon-based nanodevices. However, since its conductivity cannot be turned completely off, it is of limited help for logic applications. To this end a gap in the band structure is needed[1-2], and this is usually introduced via electron confinement (e.g. by cutting its edges to form nanoribbons or nanotubes [1]) or via symmetry breaking (e.g. through interaction with a SiC substrate [3]). Here we use symmetry arguments and electronic structure calculations to show[4], contrary to current opinion, that proper chemical functionalization may achieve this goal without breaking graphene symmetry. This has the advantage that new Dirac cones appear right close to the gapped region. Specifically, we study nxn honeycomb superlattices of defects in graphene. The considered defects are missing pz orbitals and can be realized by either introducing C atom vacancies (but also holes, aka “antidots” [5]) or chemically binding simple atomic species at the given sites. We find that the induced-gaps have an approximate square-root dependence on the defect concentration and compare favourably with those found in nanoribbons at the same length scale. All this suggests a route to novel graphene-based field-effect transistors, where a high “on/off” ratio is achievable and where the charge transport in the “on” state is predicted to be similar (pseudorelativistic) to the one found in pristine graphene. [1] P. Avouris, Z. Chen, and V. Perbeinos, Nat. Nanotech.2, 605 (2007). [2] K. Novoselov, Nat. Mater. 6, 720 (2007). [3] S. Y. Zhou et. al., Nat. Mater. 6, 770 (2007). [4] Martinazzo R., Casolo S. and Tantardini G.F. Submitted to Phys. Rev. B. Preprint at ArXiv:0910.2407. [5] J. A. Fu"rst et al., NewJ. Phys. 11, 095020 (2009). Abstract internet id 160