An optimal substrate design for SERS: dual-scale diamond-shaped gold nano-structures fabricated via interference lithography.

Dual-scale diamond-shaped gold nanostructures (d-DGNs) with larger scale diamond-shaped gold nanoposts (DGNs) coupled to smaller scale gold nanoparticles have been fabricated via interference lithography as a highly reliable and efficient substrate for surface enhanced Raman scattering (SERS). The inter- and intra-particle plasmonic fields of d-DGNs are varied by changing the periodicity of the DGNs and the density of gold nanoparticles. Because of the two different length scales in the nanostructures, d-DGNs show multipole plasmonic peaks as well as dipolar plasmonic peaks, leading to a SERS enhancement factor of greater than 10(9). Simulations are carried out by finite-difference time-domain (FDTD) methods to evaluate the dependence of the inter- and intra-particle plasmonic field and the results are in good agreement with the experimentally obtained data. Our studies reveal that the combination of two different length scales is a straightforward approach for achieving reproducible and great SERS enhancement by light trapping in the diamond-shaped larger scale structures as well as efficient collective plasmon oscillation in the small size particles.