For the past two decades, researchers have been diligently working to refine tetradymite films made from ternary tetradymite—a mineral composed of bismuth, tellurium, and sulfur. These materials are intriguing due to their potential as topological insulators, where electrical current flows along the surface, while the interior remains insulated, thus minimizing energy dissipation. The surface conduction of these materials also exhibits spin properties, which could significantly benefit the development of spintronic devices that operate on minimal power. Scientists have now made huge advancements which suggest that these materials might soon play a crucial role in the field of wearable electronics and other miniature devices.

In collaborative research involving scientists from The Ohio State University (Columbus, OH, USA), the team successfully created thin films, ranging from 90 to 150 nanometers in thickness, which are advanced versions of ternary tetradymite. Their findings indicate that these films exhibit superior electron mobility compared to similar materials, making them highly conducive to electrical currents. The low defect density within these films ensures minimal interference with the movement of electrons on the surface, simialar to a clear, open freeway for electrons. These optimal conditions were achieved using molecular beam epitaxy (MBE), a process that starts with the same crystal structure as tetradymite but introduces substitutions of other elements to create compositions with unique conduction properties. This method has effectively reduced the concentration of charge carriers that typically populate the interior of natural tetradymites, thereby enhancing electron mobility.

This research has moved beyond merely constructing these films to comprehensively testing their properties in the laboratory—a significant progression since previously, materials studied were considerably larger. The meticulous testing of these materials led to the identification of elusive oscillations, which confirmed that the films were nearly scatter-free, a marked improvement over natural variants. Further investigations into the films’ thermoelectric properties were conducted through sensitive thermal tests. Inspired by these findings, published in Materials Today Physics, the team is already developing new film versions. While practical applications may still be a few years away, the potential of these energy-efficient films is vast. They could be integrated into ultra-thin chips used in miniature electronics, potentially laying the groundwork for powering robots or wearable technologies designed to regulate body temperature.

“These materials, naturally speaking, just aren’t the best quality in terms of thin film growth, but we need thin films to make devices,” said co-lead author Brandi Wooten, a recent PhD graduate in materials science and engineering at Ohio State. “This is a nice paper showing we can make these materials good enough in thin film form to be put into devices. This is a stepping stone to getting these materials to do more.” 

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