Multilayered Nanostructure for Inducing a Large and Tunable Optical Field

Objective: The localized surface plasmon resonance (LSPR) and field enhancement of multilayered nanostructure over single and dimer configuration is studied using finite difference time domain (FDTD) method. Experimental: In multilayered nanostructure, there exist concentric nanoshells and metallic core which are separated by a dielectric layer. Strong couplings between the core and nanoshell plasmon resonance modes show a shift in LSPR and enhancement in field around nanostructure. The calculation of the electric field enhancement shows a sharp increase in the electric field on the surface of inner core i.e., inside the dielectric layer of Metal-Dielectric-Metal (MDM) structure whereas smaller enhancement on the outer layer of MDM structure is observed. Results: The Au-Air-Au mono MDM nanostructure shows strong near-field enhancement as compared to bare nanosphere in the infrared region, which have potential applications in surfaceenhanced spectroscopy, whereas Al-Air-Al and Ag-Air-Ag shows potential towards lower wavelength region. On coupling the MDM nanostructure forming a dimer configuration the field enhancement factor increases to 10^8. Conclusion: As compared to other nanostructures, MDM nanostructure provides both strong field enhancement and wide wavelength tunability therefore promising for surface enhanced Raman spectroscopy (SERS) applications.