Direct Evidence for van der Waals Hetero-epitaxy of Graphene on Hexagonal Boron Nitride

We report on direct evidence for van der Waals (vdW) hetero-epitaxy of graphene grown on hexagonal boron nitride (hBN). Rotational misalignment of graphene on hBN produces a moir\'e pattern detectable by scanning probe microscopy (SPM) as a small modulation of the probe/surface friction. With the help of moir\'e interferometry and atomic resolution imaging, we obtained a fundamental insight into the growth behavior of single-crystalline graphene grown on h-BN substrates. It is found that the graphene grown by chemical vapor deposition mainly locks into one crystallographic orientation with respect to the h-BN substrate, while the graphene edges are parallel to armchair direction. The Moir\'e pattern on graphene/h-BN confirms that the rotational misalignment of graphene is definitely less than 0.05 $^{\circ}$ with respect to h-BN. It is also noticed that the vdW interaction plays a critical role in releasing the interfacial stress in the epitaxial graphene on h-BN. Our work shines light on creating artificial moir\'e interferometry in nanometer scale, which provides an invaluable scientific tool of atomic analyses on graphene based hetero-junction.