Continuing work first appearing in 2013 [1], the Bokor group at UC Berkeley has demonstrated FETs whose graphene nano-ribbon gates are precisely 9 and 13 atoms wide [2]. While the gate lengths are still defined lithographically, this line of development shows that two of the channel dimensions (width and thickness) can be exactly controlled. Some work remains to control device characteristic dispersion, but one expects that the chemical synthetic approach to gate definition is sound.
References:
[1] Bennett, et al., “Bottom-up graphene nanoribbon field-effect transistors”, Appl. Phys. Lett. 103, 253114 (2013), http://dx.doi.org/10.1063/1.4855116.
[2] Llinas, et al., “Short-Channel Field Effect Transistors with 9-Atom and 13-Atom wide Graphene Nanoribbons”, arXiv:1605.06730.