Self‐Rolling SiO₂/Au Based Epsilon‐Near‐Zero Metamaterials

Abstract

effective media with prescribed dispersion and values of the electric permittivity (ε) and magnetic permeability (μ). The advancements in dispersion engineering provide the desired material response at different frequency ranges as well as additional functionalities such as loss control or photonic doping. [3] One class of metamaterials that have highly anisotropic and hyperbolic (or indefinite) dispersion are known as hyperbolic metamaterials (HMMs), where one of the principal components of the ε tensor is opposite in sign to the other two principal components. [4] The effective material dispersion of such metamaterials can be controlled by changing the amount of metal and dielectric materials forming the structure. [5] Some of the promising applications of HMM include optical hyperlenses which demonstrate far-field optical imaging beyond the diffraction limit, [6] near-perfect absorption, [7] abnormal scattering, [8] high-sensitivity sensors, [9] and long-range energy transfer. [10] Additionally, HMMs provide an epsilon-near-zero (ENZ) feature where the real permittivity approaches zero at a certain wavelength range. The HMMs composed of alternating metal and dielectric thin layers have been demonstrated to exhibit ENZ behaviour in the designed wavelength region from visible to near-infrared [11][12][13] with the potential of ultrafast tuning of the permittivity. [14] This flexibility has extended the applications exhibited only by the naturally occurring ENZ materials to a broader range from plasmon-phonon coupling [15] and optical switching, [16] to non-resonant optical sensing [17] and the control of the localized surface plasmon resonances of nanoantennas. [18] Another way of realizing certain effective electromagnetic responses, by all means, analogous to the metamaterials, is provided by the structural dispersion properties especially by the utilization of the waveguides. Engineering of the structural dispersion -where the optical properties depend on the geometry of the structure -has been studied in various waveguide designs. [19,20] One may define an effective relative permittivity for a guided mode in a waveguide. In other words, the dispersion of propagation inside a waveguide, for the fundamental mode, is equivalent to that of propagation in a medium with effective permittivity. Both rectangular waveguides and cylindrical waveguides have been identified to exhibit different fundamental waveguide modes with a cutoff frequency where the permittivity of the media is defined as approximately zero. This Wave propagation in epsilon-near-zero (ENZ) media offers exciting possibilities in the field of nanophotonics. Here, a thin film self-rolling technique to fabricate SiO 2 /Au based 3D multilayer structures is implemented. These cylindrical multilayer metamaterials are utilized to take advantage of the material dispersion as well as the structural dispersion to obtain self-rolling ENZ metamaterials at the visible to near-infrared wavelength range. The ENZ features are investigated initially by modelling th...