Freestanding Resist Metasurface Supporting Higher-Order BICs for Efficient Field Enhancement in TMD Monolayers

TL;DR

This paper demonstrates that freestanding metasurfaces supporting higher-order quasi-BICs can significantly enhance light-matter interactions in 2D semiconductors, enabling stronger field enhancement and PL emission.

Contribution

It introduces higher-order BICs in freestanding metasurfaces as a novel method to improve light-matter coupling in 2D materials, with experimental validation.

Findings

First-order quasi-BICs show 127-fold PL enhancement.

Higher-order BICs outperform zeroth-order modes in field enhancement.

Experimental results confirm strong coupling in WS2 monolayers.

Abstract

Enhancing light-matter coupling in two-dimensional (2D) semiconductors such as transition metal dichalcogenide monolayers remains a central challenge in nanophotonics due to their atomic thickness, which limits their interaction volume with light. Here, we demonstrate that first-order quasi-bound states in the continuum (quasi-BICs) supported by a freestanding metasurface provide exceptionally strong surface field enhancement, enabling efficient coupling with a tungsten disulfide (WS2) monolayer. Triangular-lattice polymer patterns on silicon nitride membranes are fabricated to realize these higher-order modes. Simulations reveal that first-order quasi-BICs exhibit much stronger field enhancement than zeroth-order modes at the top surface where the WS2 monolayer is placed. Photoluminescence (PL) measurements confirm a remarkable PL enhancement factor of 127 for first-order quasi-BICs, over six times larger than that of zeroth-order quasi-BICs. These results establish higher-order BICs in freestanding metasurfaces as a powerful route to engineer light-matter interactions in 2D semiconductors for advanced nanophotonic and quantum photonic applications.