Structure, optical property, and refractive index sensitivity of SiO2 wafer sequentially implanted with dual metal ions: Two case studies

Using 0.5-mm-thick SiO2 wafers as substrates, Au3+Ag3 sample was prepared by sequentially implanting 45 keV Au ions and 30 keV Ag ions to the same fluence of 3.0 × 1016 ions/cm2, and Zn2+Au4.5 sample was fabricated by first implanting 40 keV Zn ions to a fluence of 2.0 × 1016 ions/cm2 and then 30 keV Au ions to a fluence of 4.5 × 1016 ions/cm2. The structural and optical properties of the two samples as well as their refractive index sensitivities were systematically investigated. The results revealed that although Au3+Ag3 sample did not possess a single nanocomposite surface layer due to the formation of approximately double-layer Au–Ag alloy nanoparticles with minor difference in composition, it still had a chance to become a refractive index sensor since its characteristic reflection signal associated with the shallower-layer Au–Ag alloy nanoparticles linearly depended on the refractive index of the monitored medium in terms of intensity. In Zn2+Au4.5 sample, a single nanocomposite surface layer containing Au nanoparticles was formed. Owing to the presence of Zn2SiO4, the dielectric environment of Au nanoparticles was slightly improved. As a result, the Zn2+Au4.5 sample, compared to that implanted with Au ions alone, increased by ∼32% in refractive index sensitivity.