Graphene nanoribbons can be formed in three ways:

- Top-down cutting out of extended graphene (by e.g. e-beam lithography, minimum width is limited by beam resolution, typically 15 nm)

- Unzipping of carbon nanotubes (chemical attack and subsequent opening of tubes, problem here is the unknown edge termination and the missing selectivity with respect to width and direction of the ribbon axis)

- Surface-assisted bottom-up fabrication of graphene nanoribbons by covalently bonding molecular precursors that carry the full information about width and growth direction for the ribbon. This fabrication leads to atomically defined ribbons of width below 1 nm. However, only for very selected ribbons, the appropriate molecular monomers have been reported that can be reacted on the surface to the desired ribbon geometry.

Based on the bottom-up process a possible route for the formation of 'intraribbon' quantum dots has recently been shown (see link below). In this case, varying properties along the ribbon axis is achieved by a not fully completed dehydrogenation step which yields covalently coupled ribbon segments of different effective width and thus different electronic band gaps.

http://pubs.acs.org/doi/abs/10.1021/nn203129a