Organic Anisotropic Excitonic Optical Nanoantennas

Abstract

Optical nanoantennas provide control of light at the nanoscale, which makes them important for diverse areas ranging from photocatalysis and flat metaoptics to sensors and biomolecular tweezing. They have traditionally been limited to metallic and dielectric nanostructures that sustain plasmonic and Mie resonances, respectively. More recently, nanostructures of organic J‐aggregate excitonic materials have been proposed capable of also supporting nanooptical resonances, although their advance has been hampered from difficulty in nanostructuring. Here, the authors present the realization of organic J‐aggregate excitonic nanostructures, using nanocylinder arrays as model system. Extinction spectra show that they can sustain both plasmon‐like resonances and dielectric resonances, owing to the material providing negative and large positive permittivity regions at the different sides of its exciton resonance. Furthermore, it is found that the material is highly anisotropic, leading to hyperbolic and elliptic permittivity regions. Nearfield analysis using optical simulation reveals that the nanostructures therefore support hyperbolic localized surface exciton resonances and elliptic Mie resonances, neither of which has been previously demonstrated for this type of material. The anisotropic nanostructures form a new type of optical nanoantennas, which combined with the presented fabrication process opens up for applications such as fully organic excitonic metasurfaces.

Multipole Mie Resonances in MXene-Antenna Arrays

“…This is because the excitations of MXene resonances have a surface nature, and the field penetration is not strong enough to induce magnetic resonances, resulting in relatively weak magnetic resonances in analytical calculations and numerical simulations of the field profiles. Unlike low-loss high-refractive-index antennas where Mie resonances are primarily confined within the antenna, in the case of MXene and plasmonic antennas, the field distribution is mainly localized outside the antenna, ,, and the surrounding medium’s refractive index plays an important role in controlling resonance strength and spectral positions. In fact, the surrounding index has a higher degree of resonance control than antenna size and shape.…”

Electromagnetic Resonance in Organic Conductive Polymers

“…Namely, one type of nanostructure only supports one type of resonance, either all-dielectric electromagnetic resonance or plasmon resonance. The coexistence of these two types of resonance in one type of nanostructure has been observed in organic J-aggregate excitonic materials . The organic J-aggregate excitonic materials possess negative and largely positive permittivity (real part) regions at the two sides of their excitonic resonance.…”

“…The coexistence of these two types of resonance in one type of nanostructure has been observed in organic J-aggregate excitonic materials. 56 The organic J-aggregate excitonic materials possess negative and largely positive permittivity (real part) regions at the two sides of their excitonic resonance. Organic conductive polymers might also sustain the two types of resonance in one nanostructure in two different spectral regions simultaneously.…”

Magnetic Mode Coupling in Hyperbolic Bowtie Meta-Antennas

“…Mode (ii), on the other hand, is linked to closed loops in the current densities and a confined magnetic field inside each triangular element of the meta-antenna (Figure f,g), clearly corresponding to the excitation of magnetic dipoles in elements of the meta-antenna. Although this magnetic mode has been previously observed in cylindrical metaparticles, , it is important to consider the shape effect on the magnetic resonance of a single element of the bowtie. The triangular geometry considered here clearly supports the magnetic resonance at a wavelength of 1406 nm, with the spectral position of the mode independent of the incident light polarization (Figure S3a, Supporting Information).…”