Graphene, the bottom up way

15 June 2013 - Nano

bottom up graphene.PNGGraphene can famously be produced from simple graphite and sticky tape stripping of layer after layer but that does not mean new production methods are continuously investigated. Take for example recent work from Lang Jiang et al. in JACS (DOI). They opted for a bottom-up approach starting from hexabromobenzene. The rationale: by heating a thin layer of the compound on a copper surface, all bromine will be expelled and in a series of Ullmann couplings a graphene chickenwire framework will form with potentially infinite size.
In the experimental implementation hexabromobenzene was sublimed in a furnace 120°C, then the radical intermediates were transported in a carrier gas and deposited on a copper foil kept at 250°C. In this way the production of 3 by 3 square centimetre pieces with 1 nm thickness have been reported.
In AFM mode the process could be followed in more detail: bromine is not just expelled, it first forms little bromine islands in a carbon sea. EPR spectra confirm the radical nature of the process although the evidence for a C6 hexaradical as suggested in the illustration is thin.