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Researchers have shown it is possible to expand the field of twistronics—literally. They have demonstrated a technique that allows them to fabricate oxide twistronic materials at much larger scales while also controlling the twist angles between materials that dictate their structural and electronic properties.
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The field of twistronics examines how the angle between layers of two-dimensional (2D) materials affects their electronic properties. The paper, "Deterministic Fabrication of Large-Area, High-Crystallinity Oxide Moiré Superlattices," is published in the journal ACS Nano.
From weak forces to oxides
"The field of twistronics was developed using 2D materials that are bonded by weak van der Waals forces," says Ruijuan Xu, corresponding author of a paper on the work and an assistant professor of materials science and engineering at North Carolina State University. "Our work here demonstrates it is possible to use layers of oxide materials that are connected by strong chemical bonds—while precisely controlling the twist angle between crystalline oxide membranes.
"The strong interlayer bonding we found between oxide layers suggests there may be entirely new interfacial phenomena to explore," adds Xu. "We've demonstrated the ability to control many of the materials' characteristics—including phase structure and domain configuration—in ways that offer new routes for designing materials and devices tailored to specific applications."
Building large-area twisted membranes
For this work, the researchers synthesized crystalline sodium niobate (NaNbO3) membranes and used photolithography to create a set of visual markers along the perimeter of each membrane. One NaNbO3 membrane was then lifted and placed on top of another NaNbO3 membrane. The researchers monitored the alignment of the visual markers during assembly to precisely control the relative twist angle between the two layers. Once they established the desired angle, they performed a material-specific annealing process to establish strong chemical bonding between the layers.
"Scale matters for devices," says Xu. "Because these crystalline membranes can be fabricated over large areas and transferred onto different supports, this approach provides a practical path toward twist-engineered oxide electronics."
Atomic distortions at the interface
The researchers also used synchrotron X-ray diffraction techniques to capture what is happening at the interface between the two layers.
"We found that the bonds between the two layers are so strong that they are distorting the atomic structure of the material—creating a gradual rotation of the atomic lattice at the interface between the layers," says Xu. "We also found changes to the phase structure of the material. It remains to be seen how this will affect material properties, but that's something we are exploring."
Extending the method beyond sodium niobate
The researchers note that while this work was done using NaNbO3 as a model, the technique could be extended to other complex oxides.
"Our work demonstrates a technique for creating large-area oxide twistronic materials with controlled twist angles and a strong chemical bond between layers," says Xu. "It's an exciting time for oxide twistronics, with new opportunities to engineer complex oxide functionalities through twist."
More information: Reza Ghanbari et al, Deterministic Fabrication of Large-Area, High-Crystallinity Oxide Moiré Superlattices, ACS Nano (2026). DOI: 10.1021/acsnano.6c04794
Provided by North Carolina State University
This story was originally published on Phys.org.
