Gap‐Plasmon Induced One‐Order Enhancement of Optical Anisotropy of 2D Black Phosphorus

Abstract

Anisotropic 2D materials with unique thermoelectric, electrical, and optical characteristics offer prospects for various angle-dependent devices. Yet, few anisotropic 2D materials are exploited. Black phosphorus (BP) is a newly rediscovered 2D material with striking in-plane anisotropy. However, experimental illustrations of the optical anisotropy of 2D BP are very limited presumably due to the ultrathin thickness of the few-layered BP which weakens the lightmatter interaction. To solve this problem, herein a hybrid nanostructure is fabricated using a one-step self-assembly deposition of gold (Au) nanoparticle (NP) clusters onto the few-layered BP residing on a silica (SiO 2) substrate. Such a hybrid nanostructure can squeeze the light into AuNPs-SiO 2 gap through the gap plasmon resonance, enabling the confined light to interact efficiently with the ultrathin BP film. Angle-resolved polarized Raman spectra measurement is carried out to study the influence of the AuNPs on the in-plane optical anisotropy of the BP. About 20 times enhancement of Raman intensity anisotropy is experimentally achieved using AuNPs. The AuNPs-BP system is not only useful for high-performance polarization-dependent photonic devices but also a universal methodology for exploring the in-plane anisotropy of low-symmetry 2D materials. Furthermore, the high-throughput self-assembly fabrication shows its potential for industrial-scale manufacturability.

Review of Anisotropic 2D Materials: Controlled Growth, Optical Anisotropy Modulation, and Photonic Applications

“…Au nanoparticles can excide gap‐mode plasmon on BP surface, resulting in 20 orders increase in optical anisotropy. [ 205 ] Such enhancement can be explained by the selective distribution of plasmon‐induced hot carriers along the armchair direction. Interestingly, the LSP excited by Au nanoparticle is layer dependent: the light–matter interaction is isotropic in multilayer HfSe 2 and ZrSe 2 , while it is suppressed in the perpendicular direction on monolayers.…”

Hyperspectral Molecular Orientation Mapping in Metamaterials

“…By placing nanodiscs of different diameters over nanothin polymer film, the weak absorbance can be quantified. This also implies, that by creating anisotropic patterns of top-layer nanostructures in MIM metasurfaces, a strongly anisotropic response is expected as observed by using nanoparticles [30]. Enhancement of E-field component perpendicular to the surface (aligned with direction of propagation) is a feature which can probe not only lateral in-plane field enhancements [31].…”

Photonics Empowered Passive Radiative Cooling

“…Metasurfaces [ 37,76–82 ] show unparalleled capabilities on controlling light–mater interaction at the subwavelength scale by a simple array of meta‐atoms, greatly easing the fabrication complexity compared with their counterpart metamaterials. Structures, such as plasmonic perfect absorbers [ 83–91 ] and all‐dielectric absorbers, [ 92 ] can be optimized for achieving selective emitters by machine learning methods. In typical metal–insulator–metal plasmonic absorber structures, complete absorption occurs at specific wavelength.…”