Ultrathin crystals open up new possibilities in electronics and quantum computing

UC Irvine researchers have developed an ultrathin bismuth material designed for use in flexible technologies.

In a study published in Natural materialsscientists at the University of California, Irvine, describe a new method for making very fine crystals of the element bismuth—a process that could make it easier to make cheap, flexible electronic components an everyday reality.

“Bismuth has fascinated scientists for more than a hundred years because of its low melting point and unique electronic properties,” said Javier Sanchez-Yamagishi, assistant professor of physics and astronomy at UC Irvine and co-author of the study. “We have developed a new method for making very fine crystals of materials such as bismuth and, in doing so, revealing the hidden electronic behaviors of metal surfaces. »

The bismuth sheets made by the team are only a few nanometers thick. Sanchez-Yamagishi explained how theorists predicted that bismuth would contain special electronic states that allow it to become magnetic when electricity passes through it – an essential element for quantum electronic devices based on the magnetic spin of electrons.

One of the hidden behaviors observed by the team are so-called quantum oscillations that originate from the surface of the crystal. “Quantum oscillations arise from the movement of electrons in a magnetic field,” said Laisi Chen, Ph.D. candidate in physics and astronomy at UC Irvine and one of the paper’s lead authors. “If an electron can complete a complete orbit around a magnetic field, this can have important effects on the performance of electronics. Quantum oscillations were first discovered in bismuth in the 1930s, but had never been observed in nanometer-thick bismuth crystals.

Innovative production techniques

Amy Wu, a PhD candidate in physics in Sanchez-Yamagishi’s lab, compared the team’s new method to a tortilla press. To make the ultrathin sheets of bismuth, Wu explained, they had to crush the bismuth between two hot plates. To get the sheets as flat as they are, they had to use casting plates that were perfectly atomically smooth, meaning there are no microscopic dents or other imperfections on the surface. “Then we made a kind of quesadilla or panini where the bismuth is the cheese filling and the tortillas are atomically flat surfaces,” Wu said.

“There was this nervous moment when we spent more than a year making these beautiful thin crystals, but we didn’t know if their electrical properties would be extraordinary,” Sanchez-Yamagishi said. “But when we cooled the device in our laboratory, we were astonished to observe quantum oscillations, never seen before in thin films of bismuth. »

“Compression is a very common manufacturing technique used to make common household materials like aluminum foil, but it’s not typically used to make electronic materials like the ones in your computers,” Sanchez-Yamagishi added. “We believe that our method will generalize to other materials, such as tin, selenium, tellurium and related alloys with low melting points, and could be interesting for research into future flexible electronic circuits. »

Next, the team wants to explore other ways of using compression and injection molding methods to make the next computer chips for phones or tablets.

“Our new team members bring exciting ideas to this project, and we are working on new techniques to better control the shape and thickness of the developed bismuth crystals,” said Chen. “This will simplify the way we manufacture devices and bring us one step closer to mass production. »

The research team included collaborators from UC Irvine, Los Alamos National Laboratory and the National Materials Science Institute in Japan. The research was primarily funded by the Air Force Office of Scientific Research, with partial support from UC Irvine’s Center for Seed Complexes and Active Materials, a National Science Foundation-sponsored Materials Science and Engineering Research Center.