Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level

Single-molecule surface-enhanced Raman scattering (SERS) has been extensively studied over the past decade. In this paper, we propose a novel method to obtain ultrahigh enhancement of local electric fields by using a silver nanoshell with a gain core above a silver substrate. Numerical results show that an ultrahigh enhancement factor of the local electric field on the order of 10⁵-10⁶ and a SERS enhancement factor on the order of 10²⁰-10²⁵ can be obtained with the present system. The SERS enhancement factor is five orders of magnitude greater than the highest theoretical value reported for SERS applications at the single-molecule level. In addition, we use the finite-element method to analyze in detail the influences of the gain coefficient of the gain core and the other structure parameters on the enhancement factor.