Multiband Plasmonic Sierpinski Carpet Fractal Antennas

Abstract

Deterministic fractal antennas are employed to realize multimodal plasmonic devices. Such structures show strongly enhanced localized electromagnetic fields typically in the infrared range with a hierarchical spatial distribution. Realization of engineered fractal antennas operating in the optical regime would enable nanoplasmonic platforms for applications, such as energy harvesting, light sensing, and bio/chemical detection. Here, we introduce a novel plasmonic multiband metamaterial based on the Sierpinski carpet (SC) space-filling fractal, having a tunable and polarizationindependent optical response, which exhibits multiple resonances from the visible to midinfrared range. We investigate gold SCs fabricated by electron-beam lithography on CaF 2 and Si/SiO 2 substrates.Furthermore, we demonstrate that such resonances originate from diffraction-mediated localized surface plasmons, which can be tailored in deterministic fashion by tuning the shape, size, and position of the fractal elements. Moreover, our findings illustrate that SCs with high order of complexity present a strong and hierarchically distributed electromagnetic near-field of the plasmonic modes. Therefore, engineered plasmonic SCs provide an efficient strategy for the realization of compact active devices with a strong and broadband spectral response in the visible/mid-infrared range. We take advantage of such a technology by carrying out surface enhanced Raman spectroscopy (SERS) on Brilliant Cresyl Blue molecules deposited onto plasmonic SCs. We achieve a broadband SERS enhancement factor up to 10 4 , thereby providing a proof-of-concept application for chemical diagnostics.

Graphene Plasmonic Fractal Metamaterials for Broadband Photodetectors

“…Deterministic fractals 35 are self-similar objects generated by geometrical rules, having a non-integer (Hausdorff-Besicovitch) dimension. Sierpinski carpets can be generated by a recursive geometrical algorithm employing a Lindenmayer system implementation 34 . We designed Au/G SCs starting from a graphene unit cell of side L 0 = 10 μm that is divided into a 3 × 3 array of sub-cells of lateral size L 1 = L 0 3 −1 , with an Au square placed in the central sub-cell.…”

“…We designed Au/G SCs starting from a graphene unit cell of side L 0 = 10 μm that is divided into a 3 × 3 array of sub-cells of lateral size L 1 = L 0 3 −1 , with an Au square placed in the central sub-cell. By iteratively applying the same rule to the generated sub-cells of size = = − L L L 3 t t t 0 0  , it is possible to obtain fractals for higher orders t of complexity 34 . In this way, we indirectly patterned graphene, thereby realizing an Au/G fractal metamaterial that can be thought as a discrete Au SC and a complementary continuous graphene SC.…”

“…log /log 189 H 1 34 . By employing electron-beam lithography, reactive-ion etching, metal evaporation, and lift-off techniques (see Methods), we fabricated the first five orders of an Au/G SC on a Si/SiO 2 substrate (see Supplementary Information 1).…”

“…As we have previously reported in ref. 34 , the Au SC can be regarded as a metallo-dielectric photonic quasi-crystal. In Fig.…”

Atomistic simulations of phonon behaviors in isotopically doped graphene with Sierpinski carpet fractal structure

“…The Sierpinski Carpet (SC) fractal structure is one of the self-similar sets, which is fabricated by the technique of dividing a square into some smaller squares, removing one square, and continuing recursively [19]. It is reported that the bandgap in phononic crystals dominating the elastic wave propagation can be changed by conducting the SC fractal structures, which is widely used in the fractal antennas design [20][21][22][23]. Furthermore, the effect of SC fractal structure on the k of the Si/Ge nanocomposites is evaluated by using MD method [24].…”