Formation of metallic vanadium nanoparticles in SiO2 by ion implantation and of vanadium oxide nanoparticles by additional thermal oxidation

Metallic V nanoparticles (NPs) were formed in silica glass by implantation with V+ ions of 60 keV to a fluence of 1.0 × 1017 ions/cm2. Annealing in oxygen gas at 800 °C transformed the metallic NPs to oxide NPs. While the mean diameter of the metal V NPs was 8.4 nm in the as-implanted state, the diameters steeply increased during oxidation, with some exceeding 100 nm. Since at least 15 different composition phases, such as V2O3, V3O7, V6O13, V9O17, etc., are known for vanadium oxides, identification of the oxide phase of the NPs was not easy. X-ray diffraction (XRD) was not a powerful tool for phase identification of the NPs, because the diffraction peaks were broad due to the nanometric sizes of the particles and readily shift due to stress effects. The temperature dependence of the optical absorption spectrum was measured. The observed spectra were almost unchanged between 3.3 and 370 K. Combining the spectral result and the XRD results, the candidates were narrowed down to three phases, V2O5, V4O9, and V7O13, from the 15 candidates. Among the three, the V2O5 phase is the most probable because the absorption spectrum and the oxygen partial pressure for its formation were both consistent.

► Vanadium nanoparticles of 8.4 nm in mean diameter are formed by ion implantation.
► V2O5 nanoparticles are formed by thermal oxidation of metallic vanadium NPs in SiO2.
► V2O5 phase is determined from 15 candidate phases.
► Phase identification is made by optical spectroscopy and X-ray diffraction.
► Temperature dependent spectroscopy is used for identification of multiple oxide phases.