Gallium nitride (GaN), a key material for LEDs and electronics, can now be obtained in the form of nanocrystals. The study was published on July 15 in Nature.
A nanocrystal is a crystal whose dimensions are measured in billionths of a meter. At this scale, its optical and electronic properties can differ from those of the bulk material. These particles can also be dispersed in a liquid. They then become easier to deposit as an ink or to mix with other materials.
Example of GaN high electron mobility transistors (manufactured by the Ferdinand-Braun Institute).
Image Wikimedia
Gallium nitride, or GaN, is already used in LED lighting and in electronic components designed to operate at high power. Its chemical and thermal stability is an asset in these applications. Yet, this same stability made it difficult to manufacture colloidal nanocrystals, that is, those suspended in a controlled manner in a solution.
The difficulty comes from the very strong bonds between the metal and nitrogen. To form small, regular crystals, the atoms must be able to reorganize during synthesis. Conventional processes then require high temperatures, incompatible with the solvents used to manufacture many nanocrystals.
The team circumvented this problem with a bath of molten inorganic salts. In this medium, they reacted metal halides with ammonia under pressure. The researchers identified temperature and pressure conditions in which the metal-nitrogen bonds can break and then reform easily enough to allow the growth of nanocrystals.
The method is not limited to GaN. The authors also report the synthesis of nanocrystals of titanium, vanadium, niobium, molybdenum, tantalum, and tungsten nitride. Some of these materials are already used in resistant coatings, catalysts, superconductors, or medical implants.
These nanocrystals could expand the ways in which nitrides are used. The researchers specifically mention printed electronics, flexible devices, and integration into polymers or fabrics. These applications remain to be developed, however.
The next steps will depend on the ability to produce these particles on a larger scale and to integrate them into functional components. This result provides laboratories with a new family of nanomaterials, previously very difficult to obtain in this form.