Finite difference time domain (FDTD) method is adapted to investigate near-field enhancement effects on plasmonic structures (patterned in gold film) such as concentric rings with small separation, square, and rectangle. The near-fields effect on surface enhanced Raman scattering (SERS) is typically studied on square and rectangular structures. These metal structures are fabricated by laser interference lithography. Raman active molecules (Rhodamine 6G in PMMA (polymethyl methacrylate)) are spread onto patterned structure by spin coating, and Renishaw inVia Raman spectrometer was used to study SERS. Typical SERS enhancement of the order of 105 is seen for square and rectangular structures. It is observed that the corner points and edges of square and rectangular structures are most sensitive to concentrate near fields. In the case of concentric rings, huge near fields are seen to exist at the gap between the metal rings. Concentric rings are proposed to be very effective structure for SERS sensing applications such as molecular identification and biological mapping.
Accessing the Hotspots of Cavity Plasmon Modes in Vertical Metal–Insulator–Metal Structures for Surface Enhanced Raman Scattering
