Researchers from the University of California, Irvine, have developed a novel technique for producing ultra-thin bismuth crystals. This discovery could help make the production of low-cost, flexible electronics more commonplace. The study has been published in Nature Materials.
Squeezing bismuth between atomically smooth molding plates made of a material called hexagonal boron nitride results in extremely thin and flat crystals with unique quantum electronic properties. Image Credit: Eli Krantz / Krantz NanoArt
Bismuth has fascinated scientists for over a hundred years due to its low melting point and unique electronic properties. We developed a new method to make very thin crystals of materials such as bismuth, and in the process reveal hidden electronic behaviors of the metal’s surfaces.
Javier Sanchez-Yamagishi, Assistant Professor and Study Co-Author, Department of Physics & Astronomy, University of California Irvine
The team created sheets of bismuth that are merely a few nanometers thick. Sanchez-Yamagishi outlined theorists' predictions that bismuth has unique electronic states that enable it to turn magnetic when electricity passes through it. This property is crucial for quantum electronic devices that rely on the electron's magnetic spin.
The group has discovered that so-called quantum oscillations coming from the crystal surfaces are one of the hidden behaviors.
Quantum oscillations arise from the motion of an electron in a magnetic field. If the electron can complete a full orbit around a magnetic field, it can exhibit effects that are important for the performance of electronics. Quantum oscillations were first discovered in bismuth in the 1930s, but have never been seen in nanometer-thin bismuth crystals.
Laisi Chen, Ph.D. Candidate and Study Lead Author, Department of Physics & Astronomy, University of California Irvine
A physics Ph.D. candidate in Sanchez-Yamagishi's lab named Amy Wu compared the team's new technique to a tortilla press. Wu clarified that the process involved squishing bismuth between two hot plates to create incredibly thin sheets. They had to use molding plates that are atomically smooth, meaning their surface is free of microscopic divots and other flaws, to achieve the desired level of flatness in the sheets.
We then made a kind of quesadilla or panini where the bismuth is the cheesy filling and the tortillas are the atomically flat surfaces.
Amy Wu, Ph.D. Candidate, Department of Physics, University of California Irvine
Sanchez-Yamagishi said, “There was this nervous moment where we had spent over a year making these beautiful thin crystals, but we had no idea whether its electrical properties would be something extraordinary. But when we cooled down the device in our lab, we were amazed to observe quantum oscillations, which have not been previously seen in thin bismuth films.”
“Compression is a very common manufacturing technique used for making common household materials such as aluminum foil but is not commonly used for making electronic materials like those in your computers. We believe our method will generalize to other materials, such as tin, selenium, tellurium, and related alloys with low melting points, and it could be interesting to explore for future flexible electronic circuits,” said Sanchez-Yamagishi.
The group's next goal is to investigate additional applications for compression and injection molding techniques in producing computer chips for smartphones and tablets.
Chen added, “Our new team members bring exciting ideas to this project, and we’re working on new techniques to gain further control over the shape and thickness of the grown bismuth crystals. This will simplify how we fabricate devices, and take it one step closer for mass production.”
The National Institute for Materials Science in Japan, Los Alamos National Laboratory, and UC Irvine were among the research team's partners. The study was partially supported by the UC Irvine Center for Complex and Active Materials Seed Program, a Materials Research Science and Engineering Center under the National Science Foundation. It was primarily funded by the Air Force Office of Scientific Research.
Journal Reference:
Chen, L., et al. (2024) Exceptional electronic transport and quantum oscillations in thin bismuth crystals grown inside van der Waals materials. Nature Materials. doi.org/10.1038/s41563-024-01894-0.