Enhanced Raman scattering by self-assembled silica spherical microparticles

A technique was developed to achieve enhanced Raman scattering of the silicon photon modes using closely packed micro- and submicron silica spherical particles. Investigation on the particle-size dependence of Raman enhancement revealed that the strongest enhancement occurs when the particle diameter is equal to the spot size of the incident laser beam. Calculations using the OPTIWAVE (TM) software based on the finite difference time domain algorithm under the perfectly matched layer boundary conditions were carried out. The results showed that photonic nanojets are formed in the vicinity outside the particles along the propagation direction of incident light. It was found that the nanojets are confined to a length of 100 nm with a waist of 120 nm. The presence of the strongly localized electromagnetic fields within the nanojets accounts for the enhanced Raman scattering. This technique has potential applications both in modern and traditional areas of surface science such as surface oxidation, adhesion, corrosion, and catalytic processes, and many other areas in biology, chemistry, materials science, and microelectronics. (c) 2007 American Institute of Physics.