Growth of core-shell Ga-GaN nanostructures via a conventional reflux method and the formation of hollow GaN spheres

We report the growth of core-shell Ga-GaN nanostructures by simple refluxing of a mixture of GaCl3 and lithium bis(trimethylsilyl)amide (LiHMDS) in trioctylamine at 380 °C for 24 h under nitrogen flow. The resulting spherical Ga-GaN nanostructures had diameters of ~550 nm. By immersing the nanostructures in aqua regia, the gallium cores could be removed, and hollow GaN spheres with thicknesses of 15-25 nm were produced. The shells consisted of connected GaN nanocrystals of both cubic and hexagonal phases. Infrared spectroscopy confirmed the presence of silica or silicate in the GaN shells. The silicon source likely comes from the pyrolysis of LiHMDS. The growth process was studied by examining the intermediate products formed. Gallium metal cores appeared below 380 °C, followed by the slow formation of GaN nanocrystals on the core surfaces. The slow growth of the GaN shells is related to the gradual supply of the nitrogen source from the thermal decomposition of LiHMDS. Thinner shells with a thickness of ~10 nm were prepared at a reaction temperature of 340 °C, but the spheres were more prone to breakage. The hollow GaN spheresexhibited a broad emission band centered at ~550 nm.