Nature Commun. 4, 2074 (2013)

An energetically stable graphene bilayer can be realized in only one way: the 'AB' stack, in which the two layers are shifted with respect to each other. If a third graphene sheet is added, it can be positioned above the first layer (the ABA stack); or shifted again (to produce an ABC stack). Although the former is slightly more stable, domains of both stacking types occur in samples of trilayer graphene.

Wenjing Zhang and colleagues have now discovered a trick that can induce the transformation of ABC-stacked into ABA-stacked domains. It involves triazine molecules, which have the structure of benzene but with three of the carbon–hydrogen units replaced by nitrogen atoms. Simply evaporating triazine molecules onto a graphene trilayer at 150 °C for 8 hours effects the ABC–ABA change.

Zhang et al. calculated and compared the formation energies of different kinds of ABA–ABC domain boundaries. They found that the likeliest scenario is that the top graphene layer has a 'wrinkle': on one side of the wrinkle the structure is ABA-stacked; on the other, ABC-stacked. Molecular dynamics simulations show that the adsorbed triazine molecules effectively 'iron out' the wrinkle, driving it away from the domain boundary and resulting in an ABA-stacked structure.