Raman spectroscopy of doubly aligned bilayer graphene

Graphene aligned with hexagonal boron nitride (hBN) undergoes significant structural reconstruction due to the formation of a moiré superlattice. Here, we look at the effect of such structural reconstruction on the Raman spectroscopy of bilayer graphene for both singly aligned and doubly aligned heterostructures. The G peak is found to be particularly sensitive to the hBN alignment as it broadens in doubly aligned bilayer graphene compared to that of singly aligned bilayer graphene. This broadening is attributed to the variation in the phonon frequency as a result of the lattice reconstruction of the bilayer graphene responding to the periodic potential exerted by hBNs on either side of the bilayer graphene. In addition, the position of the G-peak and 2D peak follows a slope of 2.2, which implies the formation of strain in the bilayer graphene, validating the argument of lattice reconstruction.