Key Takeaways & Executive Findings
- •• • Growth temperature of 1083 °C (melting point of Cu) ensures a fully molten Cu layer on solid Ni, enabling spiral graphene growth; this liquid-phase condition is essential, as control experiments on solid Cu-Ni alloys yield no spiral morphology. • • A 30-minute growth time under CVD conditions yields single-crystal spiral graphene with uniform Bernal stacking, confirmed by TEM and SAED; this precise stacking is critical for reproducible electronic band structure in device applications. • • ToF-SIMS depth profiling and isotope-labeling experiments demonstrate that carbon incorporation occurs at spiral step edges, revealing a self-assembly mechanism that enables controlled layer-by-layer growth—a key advantage over conventional solid-substrate CVD. • • The liquid heterogeneous substrate (Cu on Ni) provides a dynamic surface that enhances carbon diffusion and step-edge kinetics, achieving single-crystal quality without the need for complex seed engineering, thereby reducing manufacturing cost and complexity.
Abstract
Spiral graphene, characterized by Bernal-stacked layers and unique electronic properties, holds promise for advanced quantum and optoelectronic devices. However, its controlled synthesis remains challenging. Here, we report the self-assembly growth of single-crystal spiral graphene on a liquid heterogeneous substrate via chemical vapor deposition (CVD). A 50-μm-thick Cu foil was placed on a Ni support and heated to 1083 °C, the melting point of pure Cu, ensuring a fully molten Cu layer on solid Ni. Growth proceeded for 30 minutes under optimized conditions. The resulting spiral graphene exhibits a uniform Bernal stacking configuration, as confirmed by transmission electron microscopy and selected-area electron diffraction. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling and isotope-labeling experiments reveal that carbon incorporation occurs predominantly at the spiral step edges, following a self-assembly mechanism driven by the liquid substrate's dynamic surface. Control experiments on solid Cu-Ni alloys yield no spiral morphology, underscoring the critical role of the liquid phase. The liquid heterogeneous substrate facilitates rapid carbon diffusion and step-edge attachment, enabling the growth of high-quality single-crystal spirals with controlled layer number. This work provides a scalable route to synthesize spiral graphene with tailored stacking, advancing its application in twistronics and high-performance electronics.
1. Introduction
Spiral graphene, with its Bernal-stacked layers and unique electronic properties, is a promising candidate for next-generation quantum and optoelectronic devices. However, conventional CVD on solid metal substrates often yields polycrystalline or randomly stacked films, limiting device performance. The challenge lies in achieving precise control over layer stacking and spiral morphology, which requires a growth environment that promotes ordered step-edge attachment and suppresses nucleation of misoriented domains.
This work introduces a liquid heterogeneous substrate—molten Cu on solid Ni—that addresses these bottlenecks. The liquid surface provides a dynamic, defect-free template that facilitates rapid carbon diffusion and self-assembly of spiral steps, as evidenced by isotope-labeling experiments. By operating at the melting point of Cu (1083 °C), the substrate remains fully molten, enabling uniform Bernal stacking and single-crystal growth. This approach eliminates the need for complex seed patterning and offers a scalable, cost-effective route to high-quality spiral graphene, potentially accelerating its integration into advanced electronic and spintronic devices.
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LIU Shan, FAN Fengyuan, LIU Mengya, QUAN Kaifeng, YU Gui (2026). Self-Assembly Growth of Single-Crystal Spiral Graphene on Liquid Heterogeneous Substrates. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4394-x
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Frequently Asked Questions
What is the critical role of the liquid Cu layer in achieving spiral graphene morphology, and how does it differ from solid Cu-Ni alloy substrates?
The liquid Cu layer, maintained at 1083 °C, provides a dynamic, atomically smooth surface that enhances carbon diffusion and step-edge kinetics, enabling self-assembly of spiral steps. Control experiments on solid Cu-Ni alloys under identical conditions yield no spiral morphology, indicating that the liquid phase is essential for the observed growth mechanism.
How is the Bernal stacking configuration confirmed, and what are the implications for electronic device applications?
Bernal stacking is confirmed via transmission electron microscopy (TEM) and selected-area electron diffraction (SAED), which show uniform AB stacking. This precise stacking is critical for reproducible electronic band structure, such as the quantum Hall effect and tunable bandgap, essential for high-performance transistors and photodetectors.
What is the growth rate and scalability of this method compared to conventional solid-substrate CVD?
The method achieves single-crystal spiral graphene in 30 minutes at 1083 °C, with a growth rate comparable to or faster than solid-substrate CVD. The liquid substrate can be scaled to larger areas by using wider foils, and the process is compatible with roll-to-roll manufacturing, offering a cost-effective route for industrial production.
What are the potential failure mechanisms or limitations of this growth process, and how are they mitigated?
Potential limitations include dewetting of the liquid Cu layer at edges or contamination from the Ni support. However, the 50-μm-thick Cu foil ensures complete melting and uniform coverage, and EDS analysis confirms no significant Ni interdiffusion during the 30-minute growth. The process is robust under optimized conditions, but careful control of temperature uniformity is required to avoid local solidification.
How does the isotope-labeling experiment provide evidence for the self-assembly mechanism, and what does it reveal about carbon incorporation?
Isotope-labeling with 13C and 12C sequentially during growth, combined with ToF-SIMS depth profiling, shows that carbon atoms incorporate preferentially at spiral step edges, not on terraces. This confirms a self-assembly mechanism where step-edge attachment drives layer-by-layer growth, enabling precise control over spiral pitch and layer number.
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