Structural SPR Tunability of Metal@Graphene Core–Shell Nano-Needle and Nano-Disk

Abstract

In present paper, a design of the graphene-coated metal (Ag/Au/Cu) nano-disk (2D) and nano-needle (1D) has been studied within the quasi-static approximation. The core@shell nano-geometries display dual dipolar plasmonic resonances which can be influenced by the resonance coupling between the plasmonic modes of the core and shell. These results indicate two different types of plasmon coupling and their wide range of SPR tunabilty: one is symmetric (1100~1600 nm) and other is anti-symmetric coupling (700~1120 nm). The resonance tunability in the symmetric and the anti-symmetric modes are strongly dependent on the sizes of the metallic core (semi major axes of the core 16~24 nm), graphene mono layer (GML) shell thickness (0.01~0.05 nm), and the ASR (0.06~0.12) of the core@shell nano-structure. Metal@GML nano-geometries are embedded in organic environment of the two different polymer matrices PCDTBT:PC71BM (em=3.36) and PTB7:PC71BM (em=3.47) that show an appropriate SPR tunability instead of non-coated metallic nano-disk and nano-needle. We have analyzed optical properties of coated and non-coated nano-geometries in terms of SPR tunability and extinction efficiency (Qext). For a fixed ASR, the symmetric modes of nano-disks have a wide range of SPR tunability in the IR range, while for nano-needles, both the modes having wide range of tunability in visible to IR region. Similarly for a fix TGML, the symmetric modes of nano-needles have a high tunability in the IR region. Hence, both the nano-geometries having a great potential for light trapping in the desirable range of wavelength of solar spectrum.