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.