The stretching of metals at the atomic level allows researchers to create materials important for quantum, electronic, and spintronic applications

May 22, 2023

(Nanowerk News) A team led by the University of Minnesota Twin Cities has developed a groundbreaking, first-of-its-kind method that makes it easy to manufacture high-quality metal oxide thin films from “stubborn” metals that have historically been difficult to synthesize in an atomically precise manner. This research paves the way for scientists to develop better materials for a wide range of next-generation applications including quantum computing, microelectronics, sensors and energy catalysis.

The researchers’ paper was published in Natural Nanotechnology (“Metal Oxidation Engineering Using Epitaxial Strains”).

“This is truly a remarkable discovery, as it uncovers an unparalleled and simple way to navigate material synthesis at the atomic scale by harnessing the forces of epitaxial strain,” said Bharat Jalan, senior author of the paper and a Shell Professor and Chair at the University. Minnesota Department of Chemical Engineering and Materials Science. “This breakthrough is a significant advance with broad implications in various fields. Not only does it provide a means to achieve atomically precise synthesis of quantum materials, but it also has great potential for controlling oxidation-reduction pathways in a wide range of applications, including catalysis and chemical reactions occurring in batteries or fuel cells.”

“Stubborn” metal oxides, such as those based on ruthenium or iridium, play an important role in a wide range of applications in information science and quantum electronics. However, turning them into thin films has been a challenge for researchers due to the inherent difficulty of oxidizing metals using high vacuum processes.

The manufacture of these materials has puzzled materials scientists for decades. While some researchers have achieved successful oxidation, the methods used so far are expensive, unsafe, or produce poor quality materials.

University of Minnesota researchers’ solution? Stretch.

While trying to synthesize metal oxides using conventional molecular beam epitaxy, a low-energy technique that produces a single layer of material in an ultra-high vacuum, the researchers made a groundbreaking discovery. They found that incorporating a concept called “epitaxial strain”—effectively stretching the metal at the atomic level—significantly simplifies the oxidation process of this stubborn metal.

“This allows the creation of technologically important metal oxides from stubborn metals in ultra-high vacuum atmospheres, which has been a longstanding problem,” said Sreejith Nair, first author of the paper and Ph.D. chemical engineering University of Minnesota. student. “Current approaches to synthesis have limitations, and we needed to find new ways to push those boundaries further so that we could make better quality materials. Our new method for stretching materials at the atomic scale is one way to improve the performance of current technologies.”

Although the University of Minnesota team used iridium and ruthenium as examples in this paper, their method has the potential to produce oxides with atomic precision from metals that are difficult to oxidize. With this groundbreaking discovery, the researchers aim to empower scientists around the world to synthesize these new materials.

The researchers teamed up with collaborators at Auburn University, University of Delaware, Brookhaven National Laboratory, Argonne National Laboratory, and fellow University of Minnesota Chemical Engineering and Materials Science lab Professor Andre Mkhoyan to verify their method.

“When we looked at these metal oxide films very closely using a very powerful electron microscope, we captured the arrangement of the atoms and determined their type,” explains Mkhoyan. “Sure enough, they are well timed and timely as they should be in this crystal film.”

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