Precisely aligned graphene grown on hexagonal boron nitride by catalyst free chemical vapor deposition

Abstract

To grow precisely aligned graphene on h-BN without metal catalyst is extremely important, which allows for intriguing physical properties and devices of graphene/h-BN hetero-structure to be studied in a controllable manner. In this report, such hetero-structures were fabricated and investigated by atomic resolution scanning probe microscopy. Moiré patterns are observed and the sensitivity of moiré interferometry proves that the graphene grains can align precisely with the underlying h-BN lattice within an error of less than 0.05°. The occurrence of moiré pattern clearly indicates that the graphene locks into h-BN via van der Waals epitaxy with its interfacial stress greatly released. It is worthy to note that the edges of the graphene grains are primarily oriented along the armchair direction. The field effect mobility in such graphene flakes exceeds 20,000 cm2·V−1·s−1 at ambient condition. This work opens the door of atomic engineering of graphene on h-BN, and sheds light on fundamental research as well as electronic applications based on graphene/h-BN hetero-structure.

Graphene on boron-nitride: Moiré pattern in the van der Waals energy

“…These dielectric properties of h-BN are comparable with that of SiO 2 making h-BN a promising alternative substrate for graphene with improved high-temperature and high-electric field performance. The latter is due to almost twice larger surface optical phonon frequency of h-BN than similar modes in SiO 2 [4].Moiré patterns are observed in aligned graphene on h-BN. It was found that graphene flakes can align with the underlying h-BN lattice within an error of less than 0.05 o [4,7].…”

Graphene on hexagonal lattice substrate: Stress and pseudo-magnetic field

“…The B-N bond length is close to that of C-C with only a very small (1.6%-2%) lattice mismatch [4,5] which results in the appearance of a Moiré pattern (MP) when GE is put on top of BN. It was found that GE flakes can align with the underlying h-BN lattice within an error of less than 0.05 o [4,6]. Ab-initio and semi-empirical van der Waals studies showed that the interaction between GE flakes and the h-BN substrate is similar to that of a GE-GE stacked structure [7].…”

“…For example, hexagonal boron nitride has turned out to be an ideal dielectric substrate which is atomically flat and improves graphene's mobility by more than two orders of magnitude [2,3]. The B-N bond length is close to that of C-C with only a very small (1.6%-2%) lattice mismatch [4,5] which results in the appearance of a Moiré pattern (MP) when GE is put on top of BN. It was found that GE flakes can align with the underlying h-BN lattice within an error of less than 0.05 o [4,6].…”

“…We found that the symmetry of the out-of-plane deformation in the GE lattice is similar to the MP structure [14]. Therefore the Fourier transform (FT) of ∆h should correspond to six Moiré pattern vectors [4,13,15]…”

Spontaneous strains and gap in graphene on boron nitride

“…- 15 and experimentally. [16][17][18][19][20] The earliest experiments on different samples showed conflicting results on the existence of an insulating state at the neutrality point. Some experiments 21 suggested the existence of an electronic gap of about ∼ 30 meV, while others do not see any clear evidence of it.…”