Which crystal plane of the AlN substrate is a good choice for the growth of graphene films, m-plane or c-plane?

Graphene, as a typical two-dimensional material, has demonstrated transformative application potential in fields such as electronic devices, energy storage, and catalysis due to its outstanding carrier mobility, mechanical strength, and excellent thermal conductivity. However, traditional methods for preparing graphene on non-metallic substrates typically adopt a “growth-transfer” strategy: graphene is synthesized on metal substrates, such as copper or nickel, via CVD and subsequently transferred to the target substrate. This process has certain limitations: mechanical transfer can introduce wrinkles, contamination, and defects, leading to degraded electrical performance; simultaneously, the van der Waals interface formed is less stable and prone to delamination, thereby affecting the device reliability. Although numerous studies have reported the graphene growth on non-metallic substrates (e.g., h-BN, quartz glass, SrTiO₃, SiO₂/Si, and Al₂O₃), core challenges in nucleation control and lateral growth kinetics persist. To overcome this bottleneck, researchers have proposed several strategies for directly growing graphene on non-metallic substrates: pre-depositing a metal film (Ni/Cu) on the substrate surface, growing graphene, and subsequently removing the metal layer via corrosion, or placing a metal foil (Cu/Ni) upstream of the substrate and utilizing the metal vapor released at high temperatures to catalyze the decomposition of the carbon source; activating the carbon source using plasma to reduce the growth temperature, suitable for substrates with low thermal tolerance (e.g., GaN); introducing oxygen or water (H₂O) vapor and other oxygen-containing compounds to etch amorphous carbon and reduce the growth barrier at the edge of graphene; and using transition-metal nanoparticles (e.g., Fe) to epitaxially grow graphene nanoribbons on insulating substrates (e.g., h-BN). While extensive research has been conducted on the low catalytic activity and high surface migration energy of non-metal substrates, relatively few studies have investigated how graphene growth behavior and structural characteristics vary across different crystal planes of these materials.

Wang et al. developed a catalyst-free ultrafast quenching technology based on scanning electromagnetic induction (SEMI) to direct synthesize graphene on AlN crystal planes. An electromagnetic induction field generated by a planar coil was used to rapidly graphitize dopamine-derived carbon precursors in an oxygen-free environment within seconds, leveraging efficient, contactless, and localized heating capabilities. The grown graphene shows a certain substrate crystallographic dependence: Raman spectroscopy analysis indicates that the stress state at the interface between graphene and AlN is influenced by the AlN crystal plane (e.g., the c-plane or the m-plane) it contacts. Specifically, the 2D peak of graphene grown on the c-plane (0 0 0 1) of polycrystalline AlN shows an obvious redshift (the 2D peak is located at approximately 2684 cm⁻¹), while on the m-plane (1 0 ī 0), the coupling is weaker, and the 2D peak is located at the intrinsic position of approximately 2700 cm⁻¹. This stress difference and the resulting Raman peak shift phenomenon are very likely due to the strong coupling effect existing at the graphene‒AlN interface. The strong interfacial coupling effect between the c-plane of graphene and the AlN substrate helps to reduce the surface resistance of the graphene‒AlN heterostructure. Therefore, to fabricate devices with low interface resistance, an AlN (c-plane) substrate is a good choice. This work was reported by Frontiers of Materials Science recently.