Comparison of Surface-Enhanced Raman Spectroscopy on Absorbing and Nonabsorbing Nanostructured Substrates

Comparison between surface-enhanced Raman scattering (SERS) on optically absorbing and nonabsorbing nanostructured substrates has been conducted. Nanostructured Si and Si₃N₄ substrates covered with silver nanoparticles (AgNPs) were prepared by identical fabrication process based on metal thin film thermal dewetting technique. Images of scanning electron microscopy (SEM) show similar morphology between both devices. According to finite difference time domain (FDTD) simulation, electric field enhancement from localized surface plasmon resonance (LSPR) is stronger in nonabsorbing Si₃N₄ substrate in comparison to that of the optically absorbing Si with the same structures. The results of Raman measurements agree with FDTD simulated results and consistently show that the enhancement factor (EF) of nanostructured Si₃N₄ SERS device is higher than that of Si by around 4 times for various targeted analytes and excitation wavelengths. This suggests that optically nonabsorbing material is more appropriate as SERS substrate as compared to absorbing material