Figure 4. Investigation of the morphology of bilayer graphene grown on h-BN.

(a) A typical bilayer graphene on h-BN. Both the top and bottom layer of the bilayer are in hexagonal shape with the opposite sides parallel. The nearly perfect alignment between top- and bottom-layer hexagons can be observed. Dashed red line marks the grain edges of the bottom layer. To be noted that the right-up part of the top layer marked between two white dashed lines is a graphene domain with different lattice orientation; (b) Magnified friction image from the black box in panel (a) is shown. Moiré pattern on both terraces exhibits uninterrupted periodicity across the step edge; (c) Magnified friction image from the white box in panel (a) is shown. The dashed white lines represent the tilted interfaces of different domains in the top layer. Continuous moiré pattern was also observed on the graphene domains stitched together at tilted interfaces. Regular hexagons demonstrate the patterns; The friction images (d), (e), (f) and (g) show the (scan 5 nm × 5 nm) atomic lattices taken from the blue, pink, orange and green dots in panel(a), (b) and (c), some regular hexagons demonstrate the lattice of graphene and h-BN, respectively. Zigzag directions (in dashed line) and lattice vectors (in solid line) are indicated by arrows. The images are filtered to improve clarity; (h) All model hexagons in previous panels (except (g)) are rescaled for comparison and they are well aligned with each other. Hexagon model in (g) is obviously anticlockwise tilted for 30° from other one. It reveals that the graphene domain is twisted with its neighbor at almost 30°. Above images are measured under the same scan angle. The corresponding unfiltered raw images of (e–g) are shown in Fig. S8; (i) The boundaries of domains in the top layer of bilayer graphene were unveiled after powerful laser treatment under ambient condition, as the boundaries are more chemically reactive than the pristine graphene lattice.