Nanocrystals are so important that they were the basis of the 2023 Nobel Prize in Chemistry. However, scientists have so far only been able to make them from a limited number of materials. A team of chemists from the University of Chicago and Argonne National Laboratory has now published a method for making nanocrystals from metal nitrides, a class of materials for which this was previously virtually impossible.
The study was published July 15 in the journal Nature and could open new doors for electronics, flexible lighting and medical implants. According to Ruiming Lin, a doctoral student at the University of Chicago and first author of the paper, the team showed how nearly a dozen materials could be made that could not be synthesized by traditional methods.
Metal nitrides are already widely used in technology and industry. The most famous example is gallium nitride, the material used in almost all modern LED lighting, from LED bulbs to laptop screens. If such materials are transformed into nanocrystals, their applications may extend far beyond rigid thin films.
Gallium nitride in the form of nanocrystals opens the way to flexible lighting, implants and new electronics
In the future, nanocrystals of gallium nitride and similar materials could be mixed with polymers, printed with an inkjet method, or integrated into fabrics and other flexible devices. Dmitri Talapin, a professor of chemistry and molecular engineering at the University of Chicago, says this expands the boundaries of the field and lays the foundation for the use of nitrides as nanomaterials.
Nanocrystals are very small crystals, so tiny that millions or billions of them could fit on the surface of a nail. On that scale, materials often exhibit unusual and useful properties, such as intense light emission or enhanced chemical reactions.
The problem with metal nitrides lies precisely in their durability. They are tough, biocompatible, resistant to heat and corrosion, making them suitable for consumer electronics and medicine. However, the same stability hinders the formation of nanocrystals, because during crystal growth, ions must be moved and reconnected into a proper structure.
In metal nitrides, the bonds between metal and nitrogen are extremely strong, so they are difficult to break and re-form. Talapin explains that this is a serious problem for nanocrystals, because one wrong connection can spoil the entire growth process.
The solution came in two steps. The team first relied on the earlier discovery that molten salts can stabilize the formation of nanocrystals. They then found the right combination of ammonia temperature and pressure, at which the bonds between the metal and nitrogen can more easily break and re-establish.
Scientists have shown that the method is not only valid for gallium nitride, but also for other important nitrides. These include titanium nitride, used in medical implants, niobium nitride, an industrially important superconductor, and molybdenum nitride, a common catalyst.
These materials are not only useful, but also relatively cheap. Therefore, the researchers expect that the possibility of making them in the form of nanocrystals could significantly expand their application. Lin says he still remembers the moment he first saw those crystals through an electron microscope, with the hope that the discovery will end up in practical technologies, reports MSN.