Enhancement of Raman scattering using silica microparticles

Currently, enhancement of Raman scattering for nanoscale characterization is mostly based on tip- or surface-enhanced methods. However, both approaches have some dilemmas which impede their wide applications. In this study, we investigated a novel approach to enhance Raman scattering using closely-packed micro and submicro silica spherical particles. The enhancement phenomena haven been demonstrated by the silicon phonon mode of crystalline silicon (c-Si) substrates as well as the vibration modes of single-walled carbon nanotubes (SWCNTs) covered with microparticles. The studies show that the enhancement effects strongly depend on the particle size. Specifically, when the particle size is close to the beam waist of the incident laser, the strongest enhancement occurs. Numerical simulations are performed to calculate electric field distribution inside and outside the dielectric particles using the Optiwave™ software which is based on the finite difference time domain (FDTD) algorithm under the perfectly matched layer (PML) boundary conditions. The simulated results reveal the existence of photonic nanojects in the vicinity outside the particles along with the light traveling direction. The nanojets outside of the particles with a length of 100 nm and a waist of 120 nm are believed to be the base for Raman scattering enhancement. This technique has potential applications in many areas such as surface science, biology, and microelectronics.