Researchers engineer metal oxidation using epitaxial strain

A University of Minnesota Twin Cities-led team has developed a method that makes it easier to create high-quality metal oxide thin films out of ‘stubborn’ metals that have been difficult to synthesise in an atomically precise manner. This research paves the way for scientists to develop better materials for various next-generation applications including quantum computing, microelectronics, sensors and energy catalysis. The research findings were published in Nature Nanotechnology.

Bharat Jalan, senior author of the paper, said the development unveils an unparalleled and simple way to navigate material synthesis at the atomic scale by harnessing the power of epitaxial strain. “This breakthrough represents a significant advancement with far-reaching implications in a broad range of fields. Not only does it provide a means to achieve atomically precise synthesis of quantum materials, but it also holds immense potential for controlling oxidation-reduction pathways in various applications, including catalysis and chemical reactions occurring in batteries or fuel cells,” Jalan said.

‘Stubborn’ metal oxides, such as those based on ruthenium or iridium, play a crucial role in numerous applications in quantum information sciences and electronics. However, converting them into thin films has been challenging for researchers due to the inherent difficulties in oxidising metals using high-vacuum processes. While some researchers have successfully achieved oxidation, the methods used thus far have been costly, unsafe or have resulted in poor material quality.

While attempting to synthesise metal oxides using conventional molecular beam epitaxy, a low-energy technique that generates single layers of material in an ultra-high vacuum changer, the researchers found that incorporating a concept called ‘epitaxial strain’ — effectively stretching the materials at the atomic level — simplifies the oxidation process of these stubborn metals. Sreejith Nair, first author of the paper, said epitaxial strain enables the creation of technologically important metal oxides out of stubborn metals in ultra-high vacuum atmospheres. “The current synthesis approaches have limits, and we need to find new ways to push those limits further so that we can make better-quality materials. Our new method of stretching the material at the atomic scale is one way to improve the performance of the current technology,” Nair said.

Although the University of Minnesota team used iridium and ruthenium as examples in the research paper, their method has the potential to generate atomically precise oxides of any hard-to-oxidise metal. With this discovery, the researchers aim to empower scientists to synthesise these novel materials. The researchers worked closely with fellow University of Minnesota Materials Science Professor Andre Mkhoyan’s lab to verify their method.

“When we looked at these metal oxide films very closely using very powerful electron microscopes, we captured the arrangements of the atoms and determined their types. Sure enough, they were nicely and periodically arranged as they should be in these crystalline films,” Mkhoyan said.

Image credit: iStock.com/Ladislav Kubeš