Ann Arbor Times

Scientists from the University of Michigan and Harvard University have developed a new sample holder for electron microscopes that allows specimens to be cooled near absolute zero for over 10 hours. This innovation enables atomic-level imaging of materials while they exhibit quantum properties.

The team’s work, funded by the Department of Energy and National Science Foundation, addresses limitations in current cryogenic microscopy. Conventional systems using liquid helium can only maintain extreme cold—about -423 degrees Fahrenheit (20 Kelvin)—for a few minutes or up to a few hours. However, many advanced materials require longer observation at such low temperatures to study their quantum behaviors.

Robert Hovden, associate professor at the University of Michigan and corresponding author of the study published in the Proceedings of the National Academy of Sciences, explained, “When the atoms get that cold, they don’t move much, and that radically changes the behavior of the material.” He added, “A lot of really cool things happen. Metals can become insulators or superconductors, and we can design qubits and new computer memories around them. If we want to understand how these properties emerge, we need to observe the materials at those low temperatures for the entire duration of an experiment.”

Imaging at even colder temperatures than previous ultracold microscopy is necessary for studying certain quantum effects and achieving higher resolutions. While liquid helium could bring samples closer to absolute zero compared to liquid nitrogen, its tendency to boil rapidly has previously made it impractical for long-duration imaging due to vibrations that blur images.

“It’s like pouring water on hot lava,” Hovden said. “Not only do you get all these vibrations from the boiling liquid, but the temperature swings all over the place, so the rod contracts and you can’t hold the exact temperature you need.”

The new system uses a heat exchanger attached to the sample holder. As helium evaporates through this exchanger before exiting via an exhaust vent, it cools the specimen with minimal vibration—thanks in part to flexible pipes and rubber insulators limiting movement caused by boiling helium. The device achieves temperature stability within 0.004 degrees Fahrenheit (0.002 Kelvin), which is ten times better than existing instruments.

Ismail El Baggari from Harvard’s Rowland Institute noted, “Being able to see the atomic arrangement as the material changes could be the key to understanding and harnessing the atomic and nanoscale processes that give quantum materials their amazing properties.”

Building such a precise instrument presented engineering challenges. Emily Rennich, first author on the study who constructed much of the device during her undergraduate studies at Michigan, described overcoming hurdles through trial-and-error manufacturing: “Figuring out how to fabricate this thing and test it inside the microscope were huge hurdles to overcome... I didn’t actually have very many manufacturing or design skills before I started. Only through a lot of trial and error, and talking to other machinists, were we able to make something that worked.”

The technology is already being used at Michigan Center for Materials Characterization by researchers nationwide for experiments not previously possible.

Miaofang Chi from Oakridge National Laboratory commented on its significance: “I’m excited about this breakthrough, something I’ve anticipated for nearly a decade. The team’s achievement will have a lasting impact.”

The University of Michigan startup h-Bar Instruments LLC has licensed this technology; both Hovden and U-M have financial interests in h-Bar Instruments.

Additional support came from Harvard’s Rowland Institute. The device was built at several facilities including Michigan Center for Materials Characterization and university machine shops.