Ohio University (Athens, OH) Chemistry Professor Paul Gregory Van Patten and Ph.D. student Guiquan Pan disclose a rapid, room temperature method for the synthesis of gallium nitride nanopowder in U.S. Patent 7,641,880. According to Van Patten and Pan, in the direct production of GaN by the metathesis of Li3N and GaCl3 or GaBr3 or GaI3, the reaction rate and yields can be greatly enhanced by including diethyl ether in the reaction system.
A metal nitride product, such as GaN, is synthesized by the metathesis of a metal nitride reactant, such as Li.sub.3N, and a salt of a monovalent anion and the metal forming the metal nitride product, such as GaCl3, GaBr3, or GaI3, in a liquid reaction medium which contains an ether as an accelerating agent. The researchers found “surprisingly” that the addition of the ether greatly accelerates the reaction whereby complete reaction can be achieved within hours at room temperature.
The inventive metathesis reaction provides a new route to GaN nanocrystals which is a significant improvement over the previously reported similar metathesis reactions. While earlier metathesis reactions have been previously studied by others, the catalytic nature of diethyl ether reported here represents a significant advance in the production of GaN powders.
The ether bath regulates the reaction temperature so that product decomposition is avoided, yet unlike other solvents and additives the ether does not completely quench the reaction or compromise yield. This method appears to be the most practical yet reported for synthesis of nanocrystalline GaN. It should permit easy scale-up and may eventually be adapted for production of colloidal GaN quantum dots.
Ohio University research data showed strong electronic quantum confinement in the as-prepared particles, which was unexpected since no surface capping ligand was added to restrict particle growth. According to Van Patten and Pan, the most likely explanation for the observed quantum confinement is that the simultaneous formation of LiCl and GaN bonds in close proximity at the surface results in the formation of nanodomains of GaN that are entirely surrounded by LiCl, thus giving rise to the quantum-confined PL emission in the as-prepared product. Absent any capping ligand in the mixture, the most likely protective cap on the GaN particles is LiCl.
