The effect of size-asymmetry of plasmonic heterodimers in surface-enhanced Raman scattering

Assembling metal nanoparticles to provide strong electric field hot spots in their gap spaces for surface-enhanced Raman scattering (SERS) is a great challenge. Therefore, the optimization of assembly parameters is at the heart of design and fabrication of SERS substrates. Herein, we experimentally demonstrate the SERS activity of hierarchical assembled size-asymmetric heterodimers (HDs) of silver nanoparticles (AgNPs) to unveil the effect of size-asymmetry in SERS enhancement factors (EFs). The HDs show an optimum configuration in which maximum EF is achieved. To study the underlying physics of the plasmonic coupling in HDs, we use the discrete dipole approximation method. The theoretical results confirm that the effects of AgNPs on each other through their electric near-fields can be considere as the key point to generate strong hot spots in HDs for SERS.