Engineering 'hot spots' for surface-enhanced Raman scattering

Abstract

Strong Raman signals have been observed in various molecules attached to rough metal film surfaces or nano silver/gold particles. This phenomenon is denoted as surface enhanced Raman scattering (SERS). Recent experiments have shown that the effective cross sections of Raman scattering can reach the same level that of fluorescence of good laser dyes, making SERS a promising single-molecular detection tool. The commonly used substrates for SERS consist of colloidal Ag/Au particle aggregates, where SERS active sites, called "hot spots", are only found by chance and not controllable. The poor repeatability and controllability of these SERS substrates have prevented SERS from viable industrial applications, therefore it is imperative to design and fabricate optimized "hot spots" with desired plasmon resonance frequency in a controllable fashion. In this paper, we present a new class of composite nano particles, which is consisted of stacked alternative metal/dielectric layers, called nanoburger. We study optical properties of these nanoburger particles by using discrete dipole approximation method. The numerical results show that nanoburger particles possess many advantages over single layered particles, including high brightness or scattering intensity, high local field enhancements, and more freedom of tuning plasmon resonance wavelength. Another important merit of the nanoburger particles is that they can be fabricated with traditional micro/nano lithography techniques, and thus are integrable with techniques such as lab-in-a-chip.