- Improving the efficiency of moving electrons through a material will help empower the next generation of technologies.
- Scientists at MIT improved electron mobility, which measures how quickly electricity travels through a material, by creating a thin film atom by atom using molecular beam epitaxy to lower the material’s number of impurities and defects.
- Producing the highest electron mobility yet measured, this material—and others like it—could be a game-changer for thermoelectric devices and spintronic applications.
When it comes to making advanced technologies, moving electrons as efficiently as possible is basically the whole ballgame—after all, it’s why room temperature superconductors, with their promise of zero electrical resistance, remain the “holy grail” of materials science.
However, plunging materials toward absolute zero isn’t the only way to make technology more efficient, as scientists can also improve a material’s electron mobility, or how quickly electrons move through a material.
To improve this electron mobility, measured in the oh-so-memorable unit of centimeters squared per volt-second (cm^2/V-s), scientists at MIT leveraged a process known as molecular beam epitaxy to build a thin film, one atom at a time. The result was a ternary tetradymite only 100 nanometers thick, but far exceeding any other materials’ electron mobility. The results of this study were published in the journal Materials Today Physics.
“Before, what people had achieved in terms of electron mobility in these systems was like traffic on a road under construction—you’re backed up, you can’t drive, it’s dusty, and it’s a mess,” MIT’s Jagadeesh Moodera, a co-author of the study, said in a press statement. “In this newly optimized material, it’s like driving on the Mass Pike with no traffic.”
Ternary tetradymite is a mineral naturally found in gold and quartz deposits near hydrothermal vents and composed of various combinations of bismuth, antimony tellurium, sulfur, and selenium. Putting aside the logistics required to source such a material at scale, the elements found in these minerals naturally often interchange positions, especially bismuth tellurium, which introduces defects and impurities, leading to a lower electron mobility.
Instead, the MIT scientists essentially took matters into their own hands and built a crystalline structure one atom at a time. Using molecular beam epitaxy, atoms are fired onto a substrate in a vacuum under controlled temperatures. This process essentially creates a ternary tetradymite film with little to no impurities.
Building these films is one thing—figuring out if they have a high electron mobility is another challenge entirely. Luckily, the researchers have a technique that measures (Shubnikov-de Haas) quantum oscillations by lowering the material to ultracold temperatures, introducing a strong magnetic field, and then running a current through the film.
“It turns out, to our great joy and excitement, that the material’s electrical resistance oscillates,” University of Ottawa’s Hang Chi, who worked on the study as a research scientist at MIT, said in a press statement. “Immediately, that tells you that this has very high electron mobility.”
The team discovered that the film exhibited 10,000 cm2/V-s, the highest of any ternary tetradymite film yet known. This result likely circles back to the material’s lack of impurities, which allowed the electrons to pass more freely, just like a car speeding along an uncongested highway.
The scientists say these kinds of breakthroughs can be game-changers for thermoelectric devices that convert waste heat into energy or spintronic applications, which process information using an electron’s spin.
“To keep uncovering new things, we have to master the material growth,” Chi said. “By studying this delicate quantum dance of electrons, scientists can start to understand and identify new materials for the next generation of technologies that will power our world.”
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.
