Plasmonic disordered array of hemispherical AgNPs on SiO2@c-Si: Their optical and SERS properties

The study of optical and plasmonic properties of structures is an important step in the development of substrates for surface-enhanced Raman scattering (SERS) applications. In this work, structures based on a disordered array of hemispherical silver nanoparticles (AgNPs) on a single-crystal silicon (c-Si) substrate are studied. A simple and reproducible method is proposed in which an Ag island film obtained by chemical reduction of AgNO3 is transformed after annealing at 350 degrees C into an array of hemispherical AgNPs on a thin SiO2 layer. The average radii of AgNPs range from 30 to 130 nm, which can be varied due to the concentration of AgNO3 in the initial deposition solution. Numerical calculations of the scattering, absorption, and extinction cross-sections are used to determine the positions of the localized surface plasmon resonance (LSPR) multipoles depending on the hemispherical AgNP size. The splitting of the LSPR dipole is found in the reflection spectra at oblique angles of incidence for p-polarization of light, which indicates the prolate shape of the hemispherical AgNPs. Finally, SERS shows reliable detection of 10-7 M (crystal violet) with the enhanced factor similar to 6.2 x 105 and the relative standard deviation of signal similar to 10%. These studies suggest that hemispherical AgNPs on a SiO2@c-Si are promising candidates for detecting triphenylmethane dyes.