Metasurface engineering of transition metal dichalcogenides by anisotropic etching

A major objective within two-dimensional materials research is to tailor the electronic and photonic properties via nanopatterning. Electron beam lithography is a flexible technique that is widely used to pattern large areas with regular nanostructures. However, nanometer-scale edge roughness and resolution variability typically compromise the pattern quality.

We combine electron beam lithography with anisotropic reactive ion etching to realize nanoscale hexagonal patterns in multilayer transition metal dichalcogenides (TMDs) [1]. Anisotropic etching, where the etch rate varies with in-plane crystal orientation, is achieved using a sulphur hexafluoride plasma with low power and high pressure. The etched patterns have ultrasharp corners, near atomic edge smoothness. Of the studied TMDs, WS₂ exhibits the largest degree of etching anisotropy [1].

Anisotropic etching is a promising tool for making TMD-based metasurfaces [2,3], that take advantage of the high refractive indices and non-lossy nature of TMDs for dielectric light confinement. We will present our recent efforts in realizing optical resonances in TMDs structured by anisotropic etching. Such devices may find applications within sensing, integrated photonics, and optical communication technology.

[1] D. Danielsen et al., ACS Appl. Mater. Interfaces, 13, 41886-41894, (2021).

[2] P. Zotev, et al., ACS Nano 16, 6493-6505 (2022).

[3] B. Munkhbat, et al., Nat. Com. 11, 4604 (2020).