Coupling between plasmonic nanohole array and nanorod array: the emerging of a new extraordinary optical transmission mode and epsilon-near-zero property

Abstract

The compound Ag nanohole structures with an Ag nanorod in the middle of an Ag nanohole are investigated by finite-difference-time-domain calculations. The structure shows strong polarization-dependent optical properties. A new extraordinary optical transmission (EOT) mode is observed when the polarization direction is aligned with the long axis of the nanorods, and its resonance wavelength red-shifts exponentially with the nanorod length. Around this resonance wavelength, the real part of the effective permittivity also becomes zero, demonstrating the epsilon-near-zero (ENZ) property. The new EOT mode is found to be the result of the enhanced local radiation of the nanorods as well as the electromagnetic coupling to the nanoholes to produce the enhanced transmission. The tunable resonance wavelength, EOT, strong near-field enhancement, and ENZ properties make the structure ideal for many potential applications, such as ultrathin optical filter, polarizers, surface-enhanced spectroscopies, etc.

Large-Area Fabrication of Complex Nanohole Arrays with Highly Tunable Plasmonic Properties

“…To better understand the origin of the spectral features, Figure d,e plots the local E z -field distributions at the Ag–glass interface at λ D 5 0° . Based on discussions of similar structures in ref and other references, ,, the new EOT peak P 3 was induced by the coupling of the LSPR of the NR and an in-phase resonance of the rim of the NH, which is consistent with what is shown in Figure d: a strong dipole resonance of the NR and the high local electric field (the maximum | E / E 0 | 2 = 1077 and the average | E / E 0 | 2 = 3.7 over a unit cell) are demonstrated. In part, this also explains why the F at λ P 3 exceeds unity for the NRinNH structure.…”

“…Furthermore, according to finite difference time domain (FDTD) calculations, , planar NR in NH (NRinNH) structures also possess strong polarization-dependent optical properties and a new tunable EOT mode but with higher transmission when compared to that of tilted NRs grown on NH structures in ref . In addition, an epsilon-near-zero (ENZ) property was also presented at the new EOT resonance wavelength with the same tunability . The local E -fields around the NRs are greatly enhanced at the new EOT wavelength, rendering these structures potentially useful for surface-enhanced spectroscopies, such as surface-enhanced Raman scattering and surface-enhanced infrared absorption. , Experimentally, these structures have been realized with E-beam lithography and focused ion beam lithography.…”

“…In particular, nanohole (NH) arrays with asymmetric hole structures, , or combined with other asymmetric nanostructures, , have been widely reported due to their improved structural design freedom and novel optical properties. Among these asymmetric hole arrays, periodic nanorod (NR) and nanohole asymmetric compound structures are of interest. − NH array structures possess both localized surface plasmon resonance (LSPR) and surface plasmon polaritons (SPPs), while NR arrays exhibit two LSPR modes, i.e ., the transverse and longitudinal modes. A combined NR and NH compound asymmetric structure should demonstrate novel optical properties.…”

Performance of Transparent Metallic Thin Films

“…The thickness of the metal film or the spacing and width of the NW determine the intrinsic transmission and extinction property of the structure. However, many structures used in TMFs are also composed of subwavelength holes or even hole arrays, such as the NH array fabricated by nanosphere lithography (NSL), with a strong plasmonic effect; in particular, the extraordinary optical transmission (EOT) effect will occur. , In this case, both the Beer–Lambert law and effective medium theory are not valid, rather the surface plasmonic waves and the localized surface plasmon resonance (SPR) dominate the transmission property. In addition, the quality of the film or NW has a significant effect on the optical property of the structure since the skin depth δ is proportional to .…”

Highly Conductive Nanograting–Nanohole Structures with Tunable and Dual-Band Spectral Transparency

“…For example, multilayer transparent conductive oxide (TCO) and metal NH (TCO/metal NH/TCO) structures have been investigated to simultaneously improve the optical transparency and electrical properties. , However, the fabrication strategy is rather complicated, but the performance is not significantly improved. Recent studies have shown that when NH changes to compound nanostructures, such as nanoparticle in NHs, − nanodisk in NHs, − and nanorods in NHs, the EOT-related property can be tuned significantly due to the plasmonic coupling effect or hybridization. − We have hypothesized that if the nanostructure is selected appropriately, the conductance of the compound structure (i.e., NH + another nanostructure) could also be improved along with the tuned optical properties.…”