Influence of swift heavy ion irradiation on bimetallic gold-silver nanoparticles in dielectric matrices and their optical properties

Abstract

Nanosized gold-silver (AuAg) alloy nanoparticles (NPs) of sizes, 2 nm -25 nm embedded in fused quartz are synthesized using sequential implantation and post annealing at 900℃ for 1 h in Argon environment. The post annealed film is irradiated using swift heavy ions (SHI), 120 MeV Ag ions to investigate the effect of electronic energy deposition, (Se×ϕ), on size, shape and composition of the alloy NPs. Transmission electron microscopy (TEM) analysis of the as- implanted AuAg film reveals the formation of small sized, 1.8 nm-3.5 nm, bimetallic AuAg NPs. Rutherford backscattering spectroscopy (RBS) spectra along with its fitted graph convey the annealing induced out diffusion, mixing and formation of larger sized, 2 nm -25 nm, alloy NPs through Ostwald ripening. SHI irradiation results in deformation in shape from spherical to ellipsoidal alloy NPs with major axis align along the beam direction and the average aspect ratio is about 1.20. RBS analysis results convey the formation of Ag enriched alloy NPs after irradiation. The smaller nanoparticles are found dissolved while larger ones grow and elongate along the ion beam direction. SPR properties are modified by SHI induced processes of melting, sputtering and re-precipitation in the ion tracks.The un-irradiated film exhibits a single intense SPR peak at 536 nm, while the irradiated film gives rise two SPR peaks: Ist, a blue shifted SPR peak from 536 nm to 515 nm with significantly reduced intensity and much wider FWHM; and, IInd, a small SPR peak around 460 nm. SHI induced modifications on the NPs are understood in terms of thermal spike model. The detailed analysis shows that SHI can be used as a tool to tailor size, shape and composition of the bimetallic AuAg alloy NPs and their SPR properties.