By Steve Koppes
Photo courtesy of George Joch, Argonne National Laboratory

Crystals are the key materials for a huge list of applications. We rely on crystals in our computers, in our watches, in cars, on streets, everywhere. What new opportunities can quasicrystals bring to”
—Dmitri Talapin
Assistant Professor in Chemistry

The miniscule structures that Elena Shevchenko and Dmitri Talapin study and create are entrancingly complex, made of nanocrystals that interlock in a strict order that never repeats itself.

Their work on the tiny lattices, called quasicrystals, has placed the young husband-wife team at the frontier of the search for new nanomaterials, with potential uses ranging from information storage to improved solar cells. They bring complementary interests to their scientific collaboration. Shevchenko, 33, a nanoscientist at Argonne National Laboratory’s Center for Nanoscale Materials, constantly experiments with crystalline structures; Talapin, 35, an Assistant Professor in Chemistry at the University of Chicago, explores the physical principles and mathematical rules underlying their experiments.

When an experiment produces novel results, Talapin wants to find out why. But when Shevchenko sees that something has gone awry, she says, “I will just try something new.”

Finding Fundamental Rules for Nanocrystals

Their collaboration broke new ground last fall with a paper in the journal Nature, showing for the first time a method of creating quasicrystals using self-assembling nanoparticles. It was one of about 30 papers that the scientists have co-authored since they met as undergraduates in Minsk at Belorussian State University. For the Nature study, they worked closely with Christopher Murray and his nanomaterials research group at the University of Pennsylvania.

“We figured out the fundamental rules of what governs the self-assembly of quasicrystals,” Talapin says. “Nature forces these random spheres to pack together into really complex, three-dimensional patterns.”

Such work earned Shevchenko a place last year in Technology Review’s list of 35 top innovators under the age of 35. The magazine quoted nanotechnology pioneer and UChicago alumnus Paul Alivisatos, SB’81, director of Lawrence Berkeley National Laboratory, who called Shevchenko “the best grower of nanocrystals in the world today.”

Because quasicrystals are rare, scientists have not yet fully explored their potential applications. However, studies point to the possibility of using the crystals to make materials with unprecedented mechanical, optical, and electronic properties.

Those efforts would greatly benefit from a better understanding of fundamental rules governing the formation of quasicrystals, Talapin says. Their study continues to give scientists a new appreciation for the complexity and beauty of solids, which form the basis of modern life and technology.

“Crystals are the key materials for a huge list of applications,” Talapin says. “We rely on crystals in our computers, in our watches, in cars, on streets, everywhere. What new opportunities can quasicrystals bring to us?”

Work Reveals a Nanoscale “Golden Ratio”

Shevchenko, who is part of Argonne’s NanoBio Interfaces Group, experimentally synthesized the first quasicrystals in their collaboration with Murray. “I noticed that they were quite unusual,” she says, but she did not know she had produced quasicrystals until Talapin identified them as such based on their formal geometric properties. Then Murray determined that a certain size ratio of large and small particles was needed to make the quasicrystals.

This golden ratio of 0.43 held true even for different types of nanocrystals. It applied to Shevchenko’s iron oxide and gold quasicrystals, to the lead sulfide and palladium quasicrystals that postdoctoral scientist Maryna Bodnarchuk synthesized in Talapin’s laboratory, and to the differently sized iron oxide and gold quasicrystals produced in Murray’s lab.

At that point, Shevchenko says, “we became confident that this is actually a general phenomenon” and not some random occurrence.

The trio’s collaborative efforts stretch back to 2004, where Shevchenko and Talapin served as postdoctoral fellows at the IBM T.J. Watson Research Center in Yorktown Heights, N.Y., and Murray managed the center’s nanoscale materials and devices department.

Shevchenko first encountered Murray’s work after joining Horst Weller’s group as a PhD student at the University of Hamburg in Germany. At the time, working with him, or with Paul Alivisatos at the University of California, Berkeley, sounded more like dream than reality.

“They were so far away from us, I didn’t even think about working with them,” Shevchenko says.

On the Staff of the Molecular Foundry

But Talapin and Shevchenko, who both received their PhDs at Hamburg, would soon be working with Alivisatos after they secured research positions at the Molecular Foundry of Lawrence Berkeley National Laboratory. Shevchenko sometimes finds that when she begins working in what she thinks is a new area, a literature search reveals that Alivisatos had published on the topic years earlier.

Murray is now the Richard Perry University Professor of Chemistry and Materials Science and Engineering at the University of Pennsylvania. Shevchenko finds it useful to share Murray’s papers with young new associates as an example worthy of emulation. “He has very high standards,” she says.

Shevchenko and Talapin do as well. With similar backgrounds and interests, says Talapin, laughing, “very often we come to the same idea at the same time.”