Tunable localized surface plasmon resonance absorption in silver-based nanoplasmonics
摘要
Nanoplasmonic surfaces built up from silver nanoparticles (NPs) and core–shell Ag@Ag2O NPs with highly tunable optical properties are synthesized along two different reaction channels. Their structural properties are studied in detail and new in-depth physical insights into their tunable localized surface plasmon resonant absorption (LSPR) are provided. Classical electrodynamics model with size-modified complex dielectric constant data for Ag predicts narrow symmetrical LSPR band in monodisperse population of small (5–20 nm) Ag NPs with a red shift of the band maximum position (λm) of 5 nm upon particle size increase from 5 to 20 nm. Compared to our experimental data, the predicted λm is too low by 54 nm (356 vs. 410 nm). In line with our experiments, the LSPR band undergoes inhomogeneous broadening when NPs size dispersion is included, accompanied with a shift of λm from 356 to 371 nm (still 40 nm below the experimental value). Excellent agreement with our experiments (λm shift to 410 nm and inhomogeneous broadening with high-wavelength side asymmetry) is achieved applying the effective medium approach with experimentally determined size dispersion, which accounts for the influence of the glass substrate and interparticle coupling in the close-packed Ag NPs on the LSPR absorption. When the synthesis is carried out along sonochemically induced reaction channel, Ag2O shell is formed around the Ag core, leading to the most prominent LSPR band shift (~ 90 nm), which we attribute to a change in effective refraction index from 1.5 to 2.2.