Mid-infrared plasmonic tuning via nanogap control in periodic multilayer graphene nanoribbons

• Resonance peak is redshifted with decreasing the gap of multilayer graphene nanoribbon (GN).
• Resonance shift is reduced with increasing the number of graphene layer or EF of GN.
• Inter-GN interaction and localized plasmon effect were considered to explain the results.
• Nanogap control in GNs provides an insight in designing effective plasmonic devices.

Plasmonic tuning at mid-infrared wavelength by regulating the nanogap between the adjacent multilayer graphene nanoribbons (GNs) is investigated with Finite-Difference Time-Domain (FDTD) method. The 100-nm-wide multilayer GNs formed on a SiO2/p-Si show that plasmon resonance moves to longer wavelength by decreasing the nanogap from 100 nm to 5 nm, due to the inter-nanoribbon attractive interaction. Also, the resonance wavelength shifts are 7.0, 4.8 and 3.9–3.3 μm in this nanogap range for 1-, 2-, 3- and 4-layer GNs, respectively, at Fermi energy (EF) of 0.2 eV, implying enhanced confinement in plasmonic oscillation as the number of graphene layer increases. Meanwhile, by shifting the EF from 0.2 eV to 0.4 eV, the resonance peaks for each multilayer GN move to shorter wavelengths, and the peak shifts in the same nanogap range are further decreased resulting from the increased charge carriers involved in the localized plasmonic oscillation. These observed results can provide an insight in designing mid-infrared plasmonic devices for advanced nano-photonic systems.