Nanostructured transition metal dichalcogenide multilayers for advanced nanophotonics

Abstract

Transition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indexes and optical anisotropy. Here, we extend this vision to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes, as well as proof-ofconcept waveguides and resonators. We specifically focus on various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods. The specific materials studied here include semiconducting WS 2 , in-plane anisotropic ReS 2 , and metallic TaSe 2 , TaS 2 and NbSe 2 . The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high-index nanophotonics, plasmonics and on-chip optical circuits. The knowledge of TMD material-dependent nanofabrication parameters developed here will help broaden the scope of future applications of these materials in all-TMD nanophotonics.

Optical Constants of Several Multilayer Transition Metal Dichalcogenides Measured by Spectroscopic Ellipsometry in the 300–1700 nm Range: High Index, Anisotropy, and Hyperbolicity

“…This opens a possibility of using multilayer TMDs for low-loss nanophotonics, including waveguides and high quality factor resonators. 31,45 In the visible spectral range, the imaginary parts of permittivities exhibit pronounced resonances corresponding to A-, B-, and C-excitons (Figure 3). For instance, in Figure 3, the in-plane imaginary parts of permittivities show clear A-exciton resonances at ∼676 nm (1.835 eV in MoS 2 ), ∼803 nm (1.544 eV in MoSe 2 ), ∼1167 nm (1.062 eV in MoTe 2 ), ∼629 nm (1.972 eV in WS 2 ), and ∼764 nm (1.624 eV in WSe 2 ), respectively.…”

“…This opens a possibility of using multilayer TMDs for low-loss nanophotonics, including waveguides and high quality factor resonators. 31,45 In the visible spectral range, the imaginary parts of permittivities exhibit pronounced resonances corresponding to A-, B-, and C-excitons (Figure 3). For instance, in Figure 3, the 11,39,40,46,47 An important feature of all studied multilayer TMDs is their large birefringence Δn.…”

Multifunctional and Transformative Metaphotonics with Emerging Materials

“…154 However, potential applications go way beyond the field of nonlinear optics, as high refractive index by itself empowers metasurfaces for structural color generation, waveguides, photonic crystal slabs, etc. 155 Unique lattice structure of TMDCs also facilitates advanced fabrication routines with fine control over the lateral etching process. Munkhbat et al found that anisotropic wet etching using hydrogen peroxide applied to TMDs induces a self-terminating process, resulting in the formation of hexagonal structures of predefined order and complexity.…”

“…The combination of high refractive index and strong nonlinear response driven by the excitonic nature of TMDCs already inspired several realizations of metasurfaces and nanoantennas for harmonic generation . However, potential applications go way beyond the field of nonlinear optics, as high refractive index by itself empowers metasurfaces for structural color generation, waveguides, photonic crystal slabs, etc . Unique lattice structure of TMDCs also facilitates advanced fabrication routines with fine control over the lateral etching process.…”

Optical constants of several multilayer transition metal dichalcogenides measured by spectroscopic ellipsometry in the 300-1700 nm range: high-index, anisotropy, and hyperbolicity

“…This property opens a possibility of using multilayer TMDs for low-loss nanophotonics applications. 33,40 Another interesting optical feature in multilayer TMDs is their anisotropic properties due to vdW stacking nature, which results in large birefringence. Fig.…”