Semiconductor-Metal-Semiconductor Core-Multishell Nanowires as Negative-Index Metamaterial in Visible Domain

Abstract

Negative-index metamaterials (NIMs) exhibiting both negative refraction as well as phase reversal, particularly in the visible range, have drawn considerable attention in the past decade due to their potential applications in cloaking, sensing and sub-diffraction-limit imaging. NIM are often realized by arraying sub-wavelength nanostructures (meta-atoms) exhibiting spectrally overlapped magnetic and electric resonances. Most designs so far use scaling down of the resonant elements and employ materials with the right optical constants to obtain NIM in the visible range. However, large losses due to absorption in most metals and semiconductors as well as reduced coupling with light due to scaling pose a challenge to achieving low-loss NIM. Here, we employ plasmon hybridization in semiconductor-metal-semiconductor core-multishell (CMS) nanowires as a unique approach to design low loss, isotropic and polarization dependant NIM in the visible range. Based on numerical simulations, we demonstrate an effective refractive index of 21 and a figure of merit (FOM) of 17 at 650 nm for a representative Si-Ag-Si CMS nanowire NIM and a refractive index of 21, FOM of 25 at 590 nm for a GaP-Ag-GaP CMS nanowire NIM.I n the past decade many breakthroughs have been made towards realizing isotropic, bulk negative-index metamaterial (NIM) in various spectral regimes 1,2 . Specifically, in the visible range, negative refraction has been demonstrated using metallic nanowires embedded in a dielectric matrix 3,4 , fishnet structures 5-7 , metaldielectric stacks/sandwiches 8-10 , planar waveguides 11 and metal-insulator-metal coaxial waveguides 12,13 . Despite the tremendous progress in the design and fabrication of NIM, developing high performance NIM without active loss compensation in the optical domain remains a challenge. This is due to large losses arising from both the NIM designs as well as the materials. The best experimental value for the figure of merit FOM~R e n eff À Á Im n eff À Á reported so far are 3.34 in the visible and 3.5 in near-infrared range obtained from fishnet NIM 7,14 . More recently, theoretical designs have been reported for low loss plasmonic NIM utilizing the geometry dependant Mie excitations in Ag-GaP hybrid rods 15 , Ag-Si core-shell (CS) nanospheres 16 and nanowires 17 . Specifically, in the CS structures the core diameter and the shell thickness are chosen so that the magnetic dipole resonance arising from the dielectric shell and the electric dipole resonance (localized surface plasmon resonance -LSPR) in the metal core spectrally overlap. Around this double resonance, both the electric and magnetic dipole moments in the nanosphere/wire are strongly negative. These sub-wavelength CS structures demonstrating such double resonance feature satisfy the requirements of a NIM meta-atom, therefore CS structures can be engineered into a NIM with simultaneously negative permittivity and permeability. Since the natural magnetic resonance occurring in the dielectric shell is coupled to the LSPR within the same CS...

Tailoring Optical and Plasmon Resonances in Core-shell and Core-multishell Nanowires for Visible Range Negative Refraction and Plasmonic Light Harvesting: A Review

“…Using full numerical simulations performed with COMSOL and S parameter retrieval method [62,63] , the real part of the effective refractive index and FOM was found to be about À1 and 17, Reprinted from Ref. [30] . respectively, around 660 nm ( Fig.…”

“…The use of an intermediate lowpermittivity layer between the metal and semiconductor has been explored in order to shift the double resonance into the visible range [29] . Alternatively, plasmon hybridization in semiconductormetal-semiconductor CMS NWs has been shown as a simple and effective route towards achieving high FOM in the visible range [30] .…”

“…The magnetic and electric polarizability per unit length can be obtained from the magnetic and electric moment, respectively, and the magnitude of the incident field (H 0 and ε 0 E 0 ) [30] . The magnetic polarizability normalized to the area of cross section (A) is as follows:…”

“…Here we highlight the results of our recent theoretical studies focusing on two very diverse applications, namely, visible range NIM (Ref. [30] ) and scalable plasmonic photoelectrodes (Ref. [33] © 2014 ACS, Ref.…”

Analysis of surface plasmon resonance in the composite core(Au)/interlayer/shell(Ag) nanoparticles

“…Recently, core/shell nanostructures based on Au and Ag have been found especially versatile to adjust their properties by combining with such materials as other metals [13,14], semiconductors [15][16][17][18][19], magnetic materials, [10,20], etc. Many novel phenomena appear due to the property difference and interaction between the core and shell.…”