Study of NiGa2O4 microneedles grown by a thermal-evaporation method

NiGa2O4 microneedles with variable morphology and dimensions were synthesized by an autocatalytic Vapor-Liquid-Solid process using Ga2O3, metallic Ga and Ni precursor powders. The resulting structures exhibit {100} crystallographic facets and different inversion degrees of the spinel structure owing to the diverse temperatures employed during the synthesis. Advantage was taken of the high crystallinity and preferred orientation of the structures to study and assign the Raman vibrational modes. Photoluminescence measurements reveals defect-related and near-bandgap emissions in the probed microstructures. The growth process and the physical mechanisms involved were also discussed.