In this work, we used a finite-difference time-domain (FDTD) characterization to demonstrate that the e-field near metal nanoparticles (NPs) can be enhanced by dielectric grating structure. An array of Au NPs ($\phi$ = 60~nm) with 4~nm gaps is set as a plasmonic system. The Au NP arrays on a flat polydimethylsiloxane (PDMS) substrate and a thin Au film-coated substrate are considered as control samples. Coupling with a PDMS line grating (5~$\mu$m $\times$ 3~$\mu$m $\times$ 1~$\mu$m = width $\times$ gap $\times$ height) is carried out by placing the Au NP array on the PDMS grating and by putting the PDMS grating on the Au NP array on a thin Au-film-coated substrate. The dependences of the Wavelength and the angle of incidence of a plane-wave source on the e-field intensity are investigated. For the sample systems in the result, the maximum e-field of the PDMS-grating-coupled samples is enhanced by more than a factor of two compared to that in the control samples. This finding will be helpful to develop e-field-enhancing templates for surface-enhanced raman spectroscopy (SERS) applications.

Keywords: Finite-difference time-domain simulation, Localized surface plasmon resonance, Grating