Van der Waals Materials for Applications in Nanophotonics

Abstract

Numerous optical phenomena and applications have been enabled by nanophotonic structures. Their current fabrication from high refractive index dielectrics, such as silicon (Si) or gallium phosphide (GaP), pose restricting fabrication challenges while metals, relying on plasmons and thus exhibiting high ohmic losses, limit the achievable applications. An emerging class of layered, so‐called van der Waals (vdW), crystals is presented as a viable nanophotonics platform in this work. The dielectric response of 11 mechanically exfoliated thin‐film (20–200 nm) vdW crystals is extracted, revealing high refractive indices up to n = 5, pronounced birefringence up to Δn = 3, sharp absorption resonances, and a range of transparency windows from ultraviolet to near‐infrared. Nanoantennas are subsequently fabricated on silicon dioxide (SiO2) and gold, utilizing the compatibility of vdW thin films with a variety of substrates. Pronounced Mie resonances are observed due to the high refractive index contrast on SiO2, leading to a strong exciton‐photon coupling regime as well as largely unexplored high‐quality‐factor, hybrid Mie‐plasmon modes on gold. Additional vdW‐material‐specific degrees of freedom in fabrication are further demonstrated by realizing nanoantennas from stacked twisted crystalline thin‐films, enabling control of nonlinear optical properties, and post‐fabrication nanostructure transfer, important for nano‐optics with sensitive materials.

High Q Hybrid Mie–Plasmonic Resonances in van der Waals Nanoantennas on Gold Substrate

“…2 As the height is increased to 78 nm (Figure 2b,e), we introduce the HOAP and an additional MP mode, and we denote these MP 1 and MP 2 . We extracted the quality factor of the ED and MP modes in experiment for WS 2 nanoantennas 24 Left and central columns show data corresponding to single pillars (monomers), while right column corresponds to double pillars (dimers) with a separation of 475 nm. ED corresponds to the ED mode, and AP and HOAP correspond to the anapole and higher-order anapole states, respectively.…”

“…23 Use of TMDs thus opens exciting additional possibilities in the design and fabrication of hybrid dielectric−metallic structures of a variety of thicknesses, enabling the advanced control of photonic and plasmonic resonances on the nanoscale. 24 In this work, we provide detailed insights into the physics of hybrid dielectric−metallic nanophotonic systems that can host high-quality factor modes not seen in purely dielectric Mie resonators. To do this, we first simulate a WS 2 nanoantenna suspended in a vacuum using the finite-difference time-domain (FDTD) method.…”

“…This avoids difficulties with material bonding as well as lattice matching requirements and growth in molecular beam epitaxy chambers, which are associated with fabricating nanostructures from other conventional dielectrics such as GaAs and GaP . Use of TMDs thus opens exciting additional possibilities in the design and fabrication of hybrid dielectric–metallic structures of a variety of thicknesses, enabling the advanced control of photonic and plasmonic resonances on the nanoscale …”

Revealing Mie Resonances with Enhanced and Suppressed Second‐Order Nonlinear Optical Responses in a Hexagonal‐Prism‐Like MoS2 Nanoparticle

“…In comparison, the real part of the out‐of‐plane permittivity is much smaller. [ 35 ] For wavelengths longer than 750 nm, the imaginary part of the plane permittivity (Im ε xx, ε yy ) approaches zero. It implies MoS 2 becomes a lossless dielectric material with a high refractive index.…”

Leaky Waves in Flatland

“…Over the past decade, optoelectronics and photonics have witnessed the advent of 2D materials, either occurring in natural forms, such as in the case of layered van der Waals materials [ 1–3 ] (e.g., graphene, transition‐metal dichalcogenides, and hexagonal boron nitride), or as artificially engineered in the form of “metasurfaces.” [ 4 ] This trend has catalyzed the development of “flatland” platforms that enable the nanoscale control of the light flow and extreme light‐matter interactions in the form of “polaritons,” that is, hybrid excitations of matter oscillations and photons. [ 5,6 ] In turn, these phenomena promise disruptive advances in a variety of application scenarios, ranging from sensing and nanoscale‐imaging, to communications and safety.…”