University of Chicago Team Finds Way to Make Previously Impossible Metal Nitride Nanocrystals

University of Chicago chemists have cracked a long-standing materials problem: how to make nanocrystals from metal nitrides, a class of materials so chemically stable that they had resisted every conventional synthesis method. The breakthrough, published in Nature, opens the door to printable electronics, flexible LEDs, and new biomedical coatings.

Metal nitrides are already everywhere. Gallium nitride makes the blue LEDs in your screen and light bulbs. Titanium nitride appears in medical implants because it is biocompatible and wear-resistant. Niobium nitride is used in superconducting circuits. Molybdenum nitride serves as an industrial catalyst. Turning these materials into nanocrystals could let engineers mix them into polymers, print them with inkjet techniques, or embed them in fabrics and flexible substrates.

The obstacle was chemistry, not equipment. The bonds between metal and nitrogen atoms in nitrides are exceptionally strong. During crystal growth, ions need to rearrange before settling into their final positions. In most materials this happens naturally. In metal nitrides, the bonds are so tight that ions get stuck in wrong positions, producing defective crystals that do not function properly.

Lead author Ruiming Lin, a graduate student at UChicago, and senior author Dmitri Talapin tackled the problem by rethinking the growth medium. Their method uses molten salts as a liquid medium, combined with a precise temperature and ammonia pressure window. Under those conditions, the metal-nitrogen bonds can break and reform more easily, letting the crystal lattice organize correctly. The process produces nanocrystals from nearly a dozen nitride materials, including titanium nitride and niobium nitride, at sizes small enough for advanced applications.

The practical implications span several industries. Gallium nitride nanocrystals can be formulated into quantum dot inks for next-generation displays. Titanium nitride nanocrystals could coat implants with antimicrobial surfaces or improve wear resistance. Niobium nitride versions may make superconducting circuits cheaper to produce. The materials are also relatively inexpensive, which matters for commercial adoption.

The research used facilities at UChicago and Argonne National Laboratory. Funding came from the U.S. Department of Energy, Samsung, the National Science Foundation, and the Air Force Office of Scientific Research. Lin said the first electron microscope images of the crystals were a visceral payoff: billions of them fit on a fingernail, and they were structurally perfect. The team is now working with partners to explore device applications.