# Fileset

[Ultrathin Freestanding Photonic Nanomembrane Enabling Atomic-Level Control of Light Coupling.docx](https://mdr.nims.go.jp/filesets/ca60c8b1-def5-4849-a76c-d5a2c6bb2433/download)

## Creator

[Ya-Lun Ho](https://orcid.org/0000-0001-8274-5978)

## Rights

[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Ultrathin Freestanding Photonic Nanomembrane Enabling Atomic-Level Control of Light Coupling](https://mdr.nims.go.jp/datasets/12d3ded8-240e-425f-b0e0-5b897108fa13)

## Fulltext

Ultrathin Freestanding Photonic Nanomembrane Enabling Atomic-Level Control of Light CouplingPresentation Number: EL07.02.02Ya-Lun Ho*11National Institute for Materials Science, Ibaraki, JapanAbstract BodyAs promising candidates for next-generation quantum and semiconductor technologies, atomic-layer and two-dimensional (2D) materials offer unique opportunities for manipulating light–matter interactions at the atomic level. However, their ultrathin nature confines the available interaction volume, posing inherent limitations to efficient optical coupling and integration with nanophotonic architectures. Realizing their full potential requires photonic platforms capable of concentrating light into atomic-scale regions while minimizing radiative dissipation.To achieve atomic-level control over light coupling, an ultrathin freestanding photonic nanomembrane is developed, serving as a versatile platform for integrating atomic-layer and 2D materials. Freestanding nanomembranes, characterized by their extreme thinness and absence of substrates, exhibit excellent optical transparency, high-Q resonance capability, and broad material compatibility. By completely removing the substrate, the nanomembrane restores out-of-plane symmetry and suppresses radiative leakage, thereby enabling strong optical field confinement. This suspended configuration maximizes light–matter interactions through localized surface fields and ensures dimensional compatibility with atomic-layer materials. Through atomic-layer deposition (ALD) of dielectric material, we demonstrate atomic-scale thickness modulation, where a single ALD cycle induces a Å-level redshift of the high-Q resonance. High-resolution spatial mapping further reveals excellent uniformity and reproducibility across the entire nanomembrane.Building on this atomically controllable nanomembrane platform, we integrate transition metal dichalcogenide (TMD) monolayers such as WS2, WSe2, and MoS2, which possess strong excitonic resonances, direct bandgaps, and pronounced nonlinear optical responses. The freestanding photonic nanomembrane supports quasi-bound states in the continuum (quasi-BICs) that suppress radiative losses while confining light tightly within the monolayer region, leading to enhanced light–matter interactions. This strong coupling gives rise to quasi-BIC–mediated exciton–polariton formation, accompanied by pronounced enhancement in photoluminescence (PL) and second-harmonic generation (SHG) with excellent spatial uniformity across a large area. Noted that the enhanced SHG response not only evidences efficient nonlinear coupling but also enables polarization-resolved mapping that reveals crystal orientation and grain boundaries, providing a practical means for large-area structural characterization of 2D materials. Furthermore, femtosecond-pumped SHG spectroscopy uncovers multiple narrowband peaks associated with distinct quasi-BIC modes, serving as direct spectral evidence of resonantly enhanced nonlinear interactions. The predominantly in-plane excitonic dipole orientation in TMD monolayers further contributes to mode-selective enhancement under TE and TM quasi-BIC resonances.In summary, this work establishes freestanding nanomembranes as a robust and scalable nanophotonic platform that combines atomic-scale dimensional control, strong exciton–photon coupling, and Å-level precision in high-Q resonance engineering. This architecture opens new opportunities for realizing exciton–polariton devices and advancing quantum and nonlinear photonics.