Simon Salleh Atri

1 Introduction A pair of graphene layers can stack in two high-symmetry arrangements, forming metastable periodic crystals. In a stack of N layers (with N-1 interfaces), this results in a total of 2N-1 possible configurations. Of these, 2N-3 + 2(N-4)/2 and 2(N-3) + 2(N-3)/2 represent inequivalent crystal structures for even and odd, respectively.[1] For instance, tri-layer graphene (N = 3) has two metastable polytypes (Figure 1a,b), while tetralayer graphene (N = 4) has three.