Researchers at Soochow University, University of Science and Technology of China, Peking University, ShanghaiTech University, Beijing Graphene Institute and additional collaborators have developed a copper-based growth process that produces large-area trilayer graphene films with uniform thickness and improved mechanical strength.
Schematic representation illustrating the synchronous growth process catalyzed by the heterogeneous Cu–Cu2O substrate. Inset: schematic of the graphene edge–Cu–Cu2O three-phase interfaces. Image from: Nature Communications
The team stated that much of graphene's functional promise - especially in electronics and optoelectronics - relies not on the single-layer form that dominates laboratory work, but on precise multilayer structures. Adding layers enables electronic band structures to be tuned and improves properties such as stiffness and thermal transport. Despite this, the controlled synthesis of multilayer graphene films with consistent thickness across large areas has remained quite elusive.
The core difficulty seems to stem from the mismatch between existing thin-film growth theories and the chemistry of two-dimensional materials. Traditional epitaxy mechanisms, designed for materials with uniform surface bonding, do not translate well to systems like graphene, where strong in-plane bonds coexist with weak out-of-plane interactions. As a result, initial single-layer growth is relatively straightforward, but nucleating and expanding additional layers without sacrificing uniformity is far more difficult. Competing methods, such as top-feeding or bottom-feeding growth, have attempted to address this but have struggled with film consistency and scale.
The recent study proposes a fundamentally different strategy. In their paper, the team introduces edge-feeding synchronous epitaxy, a growth approach that enables all layers of graphene to expand together during synthesis. This eliminates irregular stacking and allows for uniform multilayer films across wafer-scale dimensions.
The scientists set out to solve the challenge of layer non-uniformity by shifting the growth mechanism itself - from sequential layer formation to synchronized lateral growth from the edges. At the center of the method is a heterogeneous copper–copper oxide (Cu–Cu₂O) catalyst, formed by controlled in situ oxidation of copper foil. The resulting Cu₂O layer forms around the periphery of growing graphene islands and serves a critical three-part role. It helps break down methane gas molecules (the carbon source), facilitates directional diffusion of atomic carbon to the graphene edge, and reduces the energetic cost of adding new atoms to that edge. This combination stabilizes multilayer island growth and prevents the unwanted nucleation of misaligned layers.
The team explained that the Cu₂O performs three functions simultaneously - it dissociates the precursor, delivers carbon atoms efficiently to the edge, and lowers the edge energy to keep all layers growing together.
The team validated the synchronized growth mechanism using isotopic labeling and depth-resolved mass spectrometry. Carbon-13 and oxygen-18 isotopes were used to track where atoms accumulated during synthesis. Data showed that carbon atoms entered through Cu₂O and attached directly to the edges of graphene islands, rather than forming separate layers beneath existing ones. Raman spectroscopy confirmed that isotopic rings formed in parallel across all three layers, reinforcing the conclusion that growth proceeded synchronously.
Density functional theory calculations supported these findings. They showed that the Cu₂O interface lowered the activation energy required to break methane into carbon atoms, and that atomic carbon could diffuse through Cu₂O with extremely low energy barriers - down to 0.02 electronvolts along certain directions. These theoretical values matched experimental observations of fast carbon delivery to the growth front.
A key advantage of the method is the ability to tune the number of graphene layers by adjusting the Cu₂O thickness and the carbon precursor concentration. Films with between two and seven layers were synthesized by varying the gas composition and oxidation duration. Trilayer graphene with ABA stacking - a configuration valued for its distinct electronic properties - was a particular focus.
The researchers demonstrated that their method could be scaled to produce A3-sized films (42 × 30 cm) with over 98.7% trilayer coverage. These films were analyzed using high-resolution Raman mapping and photoemission spectroscopy, confirming both uniform stacking and the expected electronic band structure.
Mechanical characterization further highlighted the robustness of the trilayer films. Compared to monolayer and bilayer graphene, the trilayer variant showed greater resistance to tearing and deformation during transfer. Nanoindentation experiments revealed a two-dimensional Young’s modulus of around 1000 N/m and a breaking strength of 170 N/m—nearly three times that of monolayer films.
In addition to its immediate application in graphene synthesis, the team sees broader implications for the new method. The edge-feeding concept could be generalized to other two-dimensional materials that share similar growth challenges. By coupling catalytic design with precise control over precursor diffusion and interface energy, the researchers suggest that new classes of uniform multilayer films could be realized using related strategies.
By demonstrating a self-limiting, scalable, and uniform growth method for few-layer graphene, this study offers both a working solution to a major manufacturing bottleneck and a conceptual advance in epitaxy for 2D systems. Rather than attempting to refine older growth regimes, the researchers designed a new one from the ground up, built around the unique physical constraints of layered materials.
