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. Moirre patterns are observed and the sensitivity of moirre interferometry proves that the graphene grains can align precisely with the underlying h-BN lattice within an error of less than 0.05 degree. The occurrence of moirre 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.s 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.

• The paper demonstrates a catalyst-free CVD technique to align graphene on h-BN with an error margin below 0.05°.
• Atomic-resolution imaging reveals moiré patterns and epitaxial relationships that yield carrier mobility over 20,000 cm²·V⁻¹·s⁻¹.
• The study advances practical pathways for engineering graphene-based devices via optimized synthesis and van der Waals epitaxy.

Precisely Aligned Graphene Grown on Hexagonal Boron Nitride by Catalyst-Free CVD

The paper presents a comprehensive study on the growth of precisely aligned graphene on hexagonal boron nitride (h-BN) substrates using a catalyst-free chemical vapor deposition (CVD) technique. The resultant graphene/h-BN heterostructure has been explored via atomic-resolution scanning probe microscopy, revealing important information about the material's properties and alignment accuracy.

The work primarily addresses the synthesis and precise alignment of graphene on h-BN without the use of metal catalysts, which has traditionally resulted in random orientations due to transfer processes. The precise alignment of graphene with the underlying h-BN lattice reported here is noteworthy, featuring an error margin of less than 0.05 degrees. The significance of such precision is underscored by the presence of moiré patterns, which indicate relaxed interfacial stress between the graphene and h-BN layers—a consequence of van der Waals epitaxy.

Several substantial results stand out in this research, including the achievement of high field-effect mobility exceeding 20,000 cm²·V⁻¹·s⁻¹ in the graphene flakes, a metric indicative of minimal carrier scattering and strong potential for high-performance electronic applications. Notably, the graphene grains exhibit edges oriented along the armchair direction, consistent with theoretical predictions for graphene grown on non-metallic substrates.

The research explores the epitaxial relationship between the graphene and h-BN lattices. The topology and orientation of the graphene are confirmed through comprehensive AFM imaging, elucidating the geometrical relationship between the moiré pattern and underlying graphene/h-BN lattices. This study also extends to polycrystalline graphene on h-BN, highlighting how temperature variations influence the polycrystallinity and domain orientations in the grown graphene, which typically results in large-angle grain boundaries.

The paper implications are multi-faceted, advancing both theoretical understandings of graphene epitaxy on insulating substrates and suggesting practical pathways for the atomic engineering of graphene-based electronic devices. The demonstrated methodology can potentially set benchmarks for future work in producing high-quality, large-scale graphene for technology applications. Future work could focus on further optimizing synthesis parameters and exploring the potential of such precisely aligned graphene/h-BN systems in novel electronic and optoelectronic devices, leveraging the weak van der Waals interactions to engineer desired material properties.

Overall, this research enhances the material science domain by illustrating the successful assembly of a graphene/h-BN structure with high alignment accuracy and remarkable electronic properties, underscoring the feasibility and prospects of using such high-quality heterostructures in device applications.