Self-Assembling Strain-Driven Domains in Epitaxial Graphene: A Path to Scalable Quantum Devices

Graphene, often heralded as the material of the future, is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice. Its unique combination of exceptional electronic, mechanical, and thermal properties has made it a cornerstone in the exploration of advanced materials. However, many of the groundbreaking phenomena in graphene—such as unconventional superconductivity, quantum Hall effects, and correlated electronic states—rely on precise manipulation of its stacking arrangements. Specifically, twisting or aligning graphene layers at specific angles can induce these emergent properties. Yet, the methods to achieve such control remain technically challenging, labor-intensive, and far from scalable. The production of twisted bilayer and trilayer graphene, often through exfoliation followed by mechanical alignment, is a delicate and demanding process. It requires highly skilled techniques to stack graphene sheets with atomic precision at specific angles, such as the so-called “magic angle.” This approach, while effective in laboratory settings, is impractical for large-scale applications. Additionally, these methods produce limited and inconsistent results, making it difficult to integrate graphene’s extraordinary capabilities into commercial technologies like quantum computing or high-performance electronic devices.

Another significant challenge lies in the inherent instability and defect susceptibility of twisted graphene systems. Misalignments, contamination during fabrication, and a lack of reproducibility can disrupt the electronic properties these systems are supposed to exhibit. Furthermore, the triangular patterns of stacking domains typically formed in twisted graphene are not always well-suited for device fabrication, as their geometries often complicate electrode placement and current flow. To address these challenges, the researchers in this study turned their attention to epitaxial graphene—a type of graphene grown directly on silicon carbide (SiC) substrates. Epitaxial graphene offers an attractive alternative because its growth process is both scalable and repeatable. However, until now, epitaxial graphene has been largely overlooked for producing stacking domain patterns like those seen in twisted graphene.

The motivation for this study was to explore whether epitaxial graphene could bypass the technical hurdles of manual twisting and alignment while achieving comparable emergent electronic properties. By leveraging strain-induced phenomena during the growth process, new research paper published in Proceedings of the National Academy of Sciences conducted by Dr. Martin Rejhon, Dr  Nitika Parashar, Dr  Lorenzo Schellack, Dr  Mykhailo Shestopalov, Professor Jan Kunc, and led by Professor Elisa Riedo from the New York University Tandon School of Engineering, the researchers uncovered new self-organizing patterns of stacking domains. Their findings have revealed the spontaneous emergence of striped ABA and ABC stacking domains, paving the way for more robust, reproducible, and scalable graphene-based quantum and electronic devices. This work represents a critical step toward integrating graphene into real-world applications by simplifying its production without sacrificing its remarkable properties.

The researchers investigated the potential for spontaneous formation of stacking domains in three-layer epitaxial graphene grown on silicon carbide (SiC). Their aim was to circumvent the complex and non-scalable processes typically required for twisted graphene systems. Using thermal sublimation, they grew graphene layers directly on the Si-face of SiC, a method that allows precise control over the number of graphene layers by manipulating temperature, gas pressure, and sublimation rates. This setup provided a structured environment to observe how natural strain during growth could influence the material’s structural and electronic properties. A critical part of the study involved conductive atomic force microscopy (c-AFM), a technique that probes the local electrical conductance of materials at nanometer resolution. By focusing on two- and three-layer regions of epitaxial graphene, the researchers found striking differences. In two-layer regions, no discernible conductance patterns emerged, indicating that stacking domains were absent. However, in the three-layer regions, a remarkable discovery was made: alternating stripes of high and low conductance, directly corresponding to ABA and ABC stacking domains. These stripes, approximately 30–70 nanometers wide, extended over micrometer-scale areas, demonstrating a spontaneous self-organization that had not been observed before in epitaxial graphene. Further experiments revealed that these stripes were robust and highly uniform. The researchers varied the bias voltage applied during c-AFM imaging and observed that the difference in conductance between ABA and ABC domains was consistent and predictable, with the high-conductance domains exhibiting approximately 1.7 times the conductance of the lower ones. This ratio closely matched theoretical predictions and earlier observations in twisted exfoliated graphene, validating the presence of distinct stacking orders. Notably, the conductance patterns were unaffected by mechanical forces, such as shearing or scanning at different angles, underscoring the stability of these domains—a critical attribute for potential device applications.

Kelvin probe force microscopy (KPFM) was also employed to map the surface potential of the graphene layers. However, unlike c-AFM, KPFM did not detect the stripes due to its lower spatial resolution, highlighting the nanoscale precision required to observe these phenomena. This finding emphasized the importance of advanced characterization techniques to uncover subtle structural and electronic features. The interplay between strain and geometry during the growth process emerged as the driving factor behind these results. The researchers noted that the striped patterns aligned along the longer axis of the three-layer regions, suggesting that the strain energy was minimized by forming elongated domains rather than triangular ones. This behavior deviated from the triangular stacking domains typically observed in twisted graphene, offering a new perspective on how geometry and strain can dictate stacking configurations. In addition to mapping conductance, the team conducted mechanical stress tests to examine the resilience of the stacking domains. Even under increased load from the AFM tip, the stripes maintained their structural integrity and conductance characteristics, demonstrating their durability. The researchers also explored whether similar patterns could form in quasi-free-standing graphene produced by hydrogen intercalation. Interestingly, no such patterns were observed, further confirming that the striped domains were unique to the epitaxial growth process and the strain it introduces.

In conclusion, Professor Elisa Riedo and her colleagues created stacking domains without the need for the labor-intensive and inherently limited process of twisting layers. The discovery that three-layer epitaxial graphene can spontaneously form ordered ABA and ABC stacking domains is significant because it challenges the long-held assumption that mechanical manipulation is necessary to achieve such configurations. By leveraging natural strain induced during the growth process on  SiC, the researchers have provided a scalable, reproducible, and robust alternative that could revolutionize the production of graphene for quantum and electronic technologies. The implications of this research extend beyond the confines of graphene itself. The self-organizing domains, with their nanoscale uniformity and stability, create opportunities for manufacturing devices that rely on high precision and performance, such as field-effect transistors, quantum Hall effect devices, and charge density wave systems. Importantly, the study demonstrates how the interplay between strain and geometry during growth can be harnessed to influence material properties, providing a framework that could be applied to other two-dimensional materials. From a technological perspective, the scalability of the epitaxial method could significantly lower the barrier for integrating graphene into commercial applications. The stripe-shaped domains are particularly suited for electronic devices since their geometry naturally facilitates current flow along well-defined paths. Unlike triangular stacking domains observed in twisted graphene, these stripes simplify electrode placement, making fabrication more straightforward and reducing the risk of performance variability.

Another critical implication lies in the robustness of the domains. Their stability under mechanical stress, varying voltages, and scanning conditions ensures that they can endure the demanding environments of practical devices. This resilience not only enhances their utility but also underscores the reliability of the epitaxial growth method as a platform for developing advanced materials. The study also opens new avenues for exploring fundamental physics. The unique electronic properties of ABA and ABC domains, coupled with their scalability, provide a fertile ground for investigating exotic quantum phenomena. For instance, the potential for topological edge states in the ABC domains could pave the way for innovations in Floquet engineering, where periodic external driving is used to manipulate quantum systems. Furthermore, the ability to control stacking domains through pregrowth patterning of the SiC substrate suggests an exciting opportunity for custom-designed quantum materials tailored to specific applications. By offering a practical, cost-effective, and scalable solution to a longstanding challenge, this research bridges the gap between experimental breakthroughs and real-world applications. It lays the foundation for integrating graphene into next-generation technologies, advancing the material from a laboratory curiosity to a cornerstone of quantum and electronic innovation.