Metal nitrides are everywhere in modern industry: gallium nitride in phone-screen backlights, titanium nitride coatings on orthopedic implants, niobium nitride in superconducting circuits, molybdenum nitride in refining catalysts. They are hard, heat-resistant, and corrosion-proof — yet for decades the field could not make them as colloidal nanocrystals.
That changed at the end of August, when the Talapin group at the University of Chicago, together with Argonne National Laboratory, published a Nature paper synthesizing about a dozen of them at once. The paper's keywords are honest: ammonia pressure, molten salt.
Why it never worked before
Crystal growth can be pictured as a square dance: ions hold hands, the music shifts, partners swap positions, and the lattice locks in a new layer. The problem with metal nitrides is that the metal–nitrogen bond is so strong that partners refuse to let go — once a wrong bond forms, the crystal's order is ruined on the spot.
Talapin put it bluntly: "If bonds cannot break as bonds form, that's a death sentence for nanocrystals." He added that the approach "goes against all conventional wisdom in this field."
Nanoscale makes the problem worse: the smaller the crystal, the larger its surface-to-volume ratio, so a single wrong bond claims a proportionally bigger share. Bulk crystals can be forced by high-temperature physical vapor deposition — but that yields hard films, not colloidal particles that can be dispersed, printed, or coated from solution.
The recipe: heat the dance floor, let go of the partner
The solution has two halves, each doing one job:
- Molten salt as the medium — it "supports" freshly nucleated crystal faces, protecting them from solvent damage.
- The temperature × ammonia-pressure combination — tuned to a sweet spot, metal–nitrogen bonds become breakable and re-formable. Bonds can reconnect, partners can swap, and wrong bonds get a second chance to correct themselves.
- Flexible lighting — GaN as printable luminescent ink on plastic
- Inkjet-printed electronics
- Polymer composites
- Textile electronics
- Implantable devices — titanium nitride coatings that flexibly conform to biological tissue
First author Ruiming Lin, a UChicago PhD student, summarized: "We demonstrated a route to nearly a dozen materials that traditional methods simply could not synthesize."
From hard films to inks — the real news
The synthesis itself is a means. The valuable part is the change of form: for the first time these nitrides exist as colloids — dispersible in solution, usable as inks. Potential applications (currently a roadmap, not demonstrated device data) include:
The funding list reveals industrial intent: the US Department of Energy, NSF, Air Force Office of Scientific Research, plus a quantum-dot cluster collaboration with Samsung — clearly interested in next-generation display and semiconductor materials, not spoons.
The next milestone is on the device side: whoever first prints a lit device from GaN nanocrystal ink turns this pot of molten salt from a Nature paper into a production line. On the chemistry side, the door is open.