Central OC Times

Researchers at the University of California, Irvine have developed a novel method to produce ultra-thin bismuth crystals, potentially advancing the manufacturing of flexible electronics. The study, published in Nature Materials, details how this new technique could make cost-effective flexible technologies more feasible.

"Bismuth has fascinated scientists for over a hundred years due to its low melting point and unique electronic properties," said Javier Sanchez-Yamagishi, assistant professor of physics & astronomy at UC Irvine and co-author of the study. "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."

The team produced bismuth sheets only a few nanometers thick. According to Sanchez-Yamagishi, theorists have predicted that bismuth contains special electronic states allowing it to become magnetic when electricity flows through it—an essential property for quantum electronic devices based on the magnetic spin of electrons.

One significant discovery by the researchers is quantum oscillations originating from the surfaces of these crystals. "Quantum oscillations arise from the motion of an electron in a magnetic field," explained Laisi Chen, a Ph.D. candidate in physics & astronomy at UC Irvine and one of the lead authors. "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."

Amy Wu, another Ph.D. candidate in Sanchez-Yamagishi’s lab, compared their new method to using a tortilla press. To create ultra-thin sheets of bismuth, they compressed it between two hot plates with molding plates smooth at an atomic level. "We then made a kind of quesadilla or panini where the bismuth is the cheesy filling and the tortillas are the atomically flat surfaces," Wu 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," Sanchez-Yamagishi added. "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."

Sanchez-Yamagishi believes their method could generalize to other materials like tin, selenium, tellurium and related alloys with low melting points. This approach might be interesting for future flexible electronic circuits.

The research team plans to explore additional ways compression and injection molding methods can be used for making next-generation computer chips for phones or tablets. "Our new team members bring exciting ideas to this project," said Chen. "We’re working on new techniques to gain further control over the shape and thickness of grown bismuth crystals. This will simplify how we fabricate devices and take it one step closer for mass production."

Collaborators included researchers from UC Irvine, Los Alamos National Laboratory and Japan's National Institute for Materials Science. The Air Force Office of Scientific Research primarily funded this research with partial support from UC Irvine's Center for Complex and Active Materials Seed Program under NSF's Materials Research Science and Engineering Center.

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