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[Chih‐Zong Deng](https://orcid.org/0009-0005-2398-5353), [Chun‐Hao Chiang](https://orcid.org/0000-0002-9066-4657), Sunhao Shi, Jui‐Han Fu, [Yen‐Ju Wu](https://orcid.org/0000-0003-2647-3407), [Kuniaki Konishi](https://orcid.org/0000-0003-2389-9787), [Vincent Tung](https://orcid.org/0000-0003-3230-0932), [Chun‐Wei Chen](https://orcid.org/0000-0003-3096-249X), [Ya‐Lun Ho](https://orcid.org/0000-0001-8274-5978)

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[Atomic‐Scale Light Coupling Control in Ultrathin Photonic Membranes](https://mdr.nims.go.jp/datasets/f2871619-0482-4e64-9113-f2c78187b6fb)

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Atomic‐Scale Light Coupling Control in Ultrathin Photonic MembranesAdvanced Functional Materialswww.afm-journal.deRESEARCH ARTICLEAtomic-Scale Light Coupling Control in Ultrathin PhotonicMembranesChih-Zong Deng1 Chun-Hao Chiang1 Sunhao Shi2 Jui-Han Fu2 Yen-Ju Wu3 Kuniaki Konishi4Vincent Tung2 Chun-Wei Chen5 Ya-Lun Ho11Research Center For Electronic and Optical Materials, National Institute for Materials Science (NIMS), Ibaraki, Japan 2Department of Chemical SystemEngineering, School of Engineering, The University of Tokyo, Tokyo, Japan 3Center for Basic Research on Materials, National Institute for Materials Science(NIMS), Ibaraki, Japan 4Institute for Photon Science and Technology, School of Science, The University of Tokyo, Tokyo, Japan 5Department of MaterialsScience and Engineering, Center of Atomic Initiative For New Materials, National Taiwan University, Taipei, TaiwanCorrespondence: Jui-Han Fu (fuj@g.ecc.u-tokyo.ac.jp) Ya-Lun Ho (HO.Ya-Lun@nims.go.jp)Received: 12 September 2025 Revised: 3 October 2025 Accepted: 23 March 2026Keywords: atomic layers | bound states in the continuum | light-matter interaction | nanomembranes | ultrathinABSTRACTAtomic-layer and 2D materials have emerged as essential building blocks for next-generation quantum and semiconductortechnologies, where atomic-scale control over light-matter interactions is critical. However, their inherently small interactionvolume poses fundamental challenges for efficient integration into quantum and nanophotonic devices. Addressing thislimitation requires the development of photonic platforms that can effectively enhance atomic-scale optical coupling. To thisend, freestanding nanomembranes with extreme thinness and minimal radiative loss offer an ideal framework for integratingthese materials into photonic systems. Here, we demonstrate an ultrathin photonic nanomembrane enabling atomic-scalecontrol of light coupling. This architecture supports strong field confinement at the surface and significantly enhances light-matter interaction. Through the integration of atomic-layer dielectrics, we achieve Å-level thickness modulation, where eachdeposition cycle leads to an ultrafine shift of the high-Q resonance. High-resolution spatial mapping further confirms uniformand deterministic resonance tuning across the nanomembrane surface. Furthermore, by integrating a WS2 monolayer withthe photonic nanomembrane, strong field localization within the monolayer and a significant emission enhancement areachieved. This approach offers a scalable and versatile route for atomic-scale light coupling, helping to overcome the limitationsof conventional photonics and opening opportunities in quantum photonics, optoelectronics, and advanced semiconductortechnologies.1Ac(eiasTc©AhIntroductiontomic-layer materials, including 2D materials and atomi-ally precise dielectric films grown by atomic layer depositionALD), with thicknesses ranging from a few angstroms to sev-ral nanometers, have emerged as foundational componentsn nanophotonics, optoelectronics, quantum technology, anddvanced semiconductor research [1–15]. Their extreme dimen-ional confinement enables significant light-matter interactionshis is an open access article under the terms of the Creative Commons Attribution License, which permited.2026 The Author(s). Advanced Functional Materials published by Wiley-VCH GmbHdvanced Functional Materials, 2026; 36:e24286ttps://doi.org/10.1002/adfm.202524286and offers unique opportunities for manipulating light at theatomic scale. However, the inherently small optical interactionvolume of these materials imposes critical challenges on theirintegration into photonic systems, as their extreme thinnesslimits their ability to confine optical fields or effectively modulateresonant optical modes. To fully exploit their potential, it isessential to design nanophotonic platforms that not only providefield confinement at the interface with the atomic-layer materialsbut also exhibit dimensional compatibility with these atomicallyits use, distribution and reproduction in any medium, provided the original work is properly1 of 13http://www.afm-journal.dehttps://doi.org/10.1002/adfm.202524286https://orcid.org/0009-0005-2398-5353https://orcid.org/0000-0002-9066-4657https://orcid.org/0000-0003-2647-3407https://orcid.org/0000-0003-2389-9787https://orcid.org/0000-0003-3230-0932https://orcid.org/0000-0003-3096-249Xhttps://orcid.org/0000-0001-8274-5978mailto:fuj@g.ecc.u-tokyo.ac.jpmailto:HO.Ya-Lun@nims.go.jphttp://creativecommons.org/licenses/by/4.0/https://doi.org/10.1002/adfm.202524286http://crossmark.crossref.org/dialog/?doi=10.1002%2Fadfm.202524286&domain=pdf&date_stamp=2026-04-03tiHotFbamamlshItntopNsatroiwmAttafefnomilclreNepspssatclMsFIGURE 1 (a) Schematic illustration of the ultrathin freestandingphotonic nanomembrane designed for atomic-scale manipulation oflight coupling and ultrasensitive optical characterization. Tailoring ofmode resonances at the nanomembrane surface is realized through Å-level controlled dielectric deposition leveraging quasi-bound states inthe continuum (quasi-BICs). (b) Cross-sectional scanning transmissionelectron microscopy (STEM) image and (c) top-view scanning electronmicroscopy (SEM) image depicting the structural morphology of the pho-tonic nanomembrane with a Si-supported boundary. (d) High-resolutionspectral mapping and (e) PL spectra demonstrating emission wavelengthvariations induced by a single ALD cycle of a dielectric layer. The whitebox marks the position of the photonic nanomembrane. The scale barrepresents 6 µm. (f) Spatially resolved spectral shift profile extracted alongthe x-axis through the center of thewhite box, illustrating high uniformityand deterministic resonance tuning.2 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creathin materials to ensure efficient coupling and strong near-fieldnteraction.owever, conventional nanophotonic architectures are typicallyrders of magnitude thicker than atomic-layer materials, leadingo substantial mode mismatch and inefficient coupling [16–20].urthermore, many nanophotonic platforms rely on substrate-ased structures, which suffer from inherent limitations suchs substrate-induced optical loss, constrained modal confine-ent, and resonance rigidity with minimal spectral tunability,ll of which hinder effective interaction with atomically thinaterials. This challenge is particularly pronounced for atomic-ayer materials, where extreme thickness constraints imposetringent requirements on photonic designs capable of sustainingigh-Q optical modes while preserving near-field enhancement.n addition to integration challenges, characterizing atomicallyhin materials remains difficult due to their minimal thick-ess and the limitations of conventional techniques [21]. Whileransmission electron microscopy (TEM) offers atomic-scale res-lution, it requires high-vacuum conditions and extensive samplereparation, and it can potentially damage fragile structures.on-destructive methods such as X-ray reflectometry (XRR) andpectroscopic ellipsometry (SE) demand large, uniform areas andre sensitive to interface roughness, reducing accuracy for ultra-hin films. Atomic force microscopy (AFM) provides high spatialesolution but only probes localized regions and lacks directptical sensitivity. These constraints highlight the need for non-nvasive, high-sensitivity optical methods that are compatibleith ambient conditions and suitable for probing atomic-layeraterials.mong various nanophotonic approaches, platforms engineeredo support high-Q modes–particularly bound states in the con-inuum (BICs)–offer unique advantages for light confinementnd interaction enhancement. BICs arise from destructive inter-erence between radiative channels, enabling optical modes toxhibit minimal radiative losses and achieve extreme field con-inement with theoretically infinite Q-factors [22, 23]. Like manyanophotonic structures, many BIC-based implementations relyn substrate-supported configurations composed of high-indexaterials on low-index backgrounds [24–32]. This geometrynherently breaks vertical symmetry and introduces radiativeeakage through the substrate, degrading Q-factors and fieldonfinement [33–35]. To suppress these losses, index-matchingayers or polymer coatings are often applied [36, 37], but theyeduce surface accessibility and limit the near-field couplingssential for atomic-scale integration.anomembranes [18–20, 38], as thin and freestanding structures,xhibit excellent optical transparency, strong integration com-atibility, and the ability to sustain high-Q resonances withoutubstrate-induced losses. These attributes make them an ideallatform for overcoming the intrinsic limitations of substrate-upported BIC photonic structures. By entirely removing the sub-trate, these membrane structures restore out-of-plane symmetrynd eliminate radiative leakage pathways, thereby preservinghe non-radiative nature of BICs and enabling strong fieldonfinement [39–47]. This suspended configuration maximizesight-matter interactions by supporting localized surface fields.ore importantly, efficient optical interaction at the atomiccale requires photonic structures with thicknesses comparableof 13to that of atomic-layer materials. Freestanding nanomembranesuniquely fulfill this requirement by enabling ultrathin archi-tectures, ensuring dimensional compatibility, and enhancedcoupling efficiency.In this work, we present an ultrathin and freestanding pho-tonic nanomembrane that enables control of light coupling viaatomic layer dielectric tuning with Å-level thickness precision(Figure 1a), and further demonstrate its capacity for 2D materialintegration by facilitating light–matter interactions in transitionmetal dichalcogenide (TMD) monolayers. By combining extremethinness with substrate-free operation, it provides a versatileplatform for integrating atomic-layer materials into advancednanophotonic and quantum systems. Notably, sustaining high-Q resonances within such an ultrathin configuration representsAdvanced Functional Materials, 2026ive Commons Licenseastbfbh1resraBbs(nc(abploaipsan2PTpdwarau(a0acQbiacDhctaDmA 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatkey advance for nanophotonic device performance. To under-tand the underlying mechanisms, we systematically investigatehe influence of nanomembrane thickness on optical resonanceehavior and identify substrate-induced field leakage as a primaryactor degrading Q-factors. Freestanding photonic nanomem-ranes, by eliminating this loss pathway, maintain exceptionallyigh Q-values across a wide spectral range, with Q = 9632 at63 nm, Q = 3074 at 42 nm, and Q = 1480 at 29 nm. Theseesults demonstrate that resonance quality can be preservedven when the membrane thickness is reduced into the deepubwavelength regime [29]. These findings underscore the criticalole of freestanding architectures in overcoming optical lossesnd achieving robust high-Q resonances at extreme thicknesses.eyond sustaining high-Q resonances, the ultrathin nanomem-rane enables deterministic control of light coupling at the atomiccale. High-resolution spatial mapping of photoluminescencePL) spectroscopy confirms that a single ALD cycle of siliconitride (SiN, the dielectric material same as the nanomembrane),orresponding to 0.65 Å in thickness, induces a 0.09 nm redshiftFigure 1d,e), and further reveals excellent spatial uniformitycross the membrane. Furthermore, we extend the platformeyond dielectric tuning by integrating aWS2 monolayer with thehotonic nanomembrane. This integration results in strong fieldocalizationwithin themonolayer and a significant enhancementf emission, showing that ultrathin nanomembranes providen effective route for controlling and enhancing light–matternteractions with 2D materials. This work establishes a versatilehotonic platform for atomic-scale light-matter control, enablingtrong field confinement, Å-level resonance tuning, and directccess to atomic-layer dielectrics and 2D materials for advancedanophotonic and quantum applications.Design and Optical Characteristics of thehotonic Nanomembranehe proposed SiN hole-array photonic nanomembrane is com-osed of a triangular lattice of airholes with lattice period P,iameter D in a SiN nanomembrane of thickness T (Figure 2a),here the coordinate system used throughout the manuscript islso indicated. Figure 2b presents the simulated angle-dependenteflectance spectra for the structurewithP= 600 nm,D= 300 nm,nd T = 150 nm under x-polarized illumination. Numerical sim-lations were performed using rigorous coupled-wave analysisRCWA) to characterize the structure. The incident light is tiltedlong the y-direction (θy ). The incident angle θy is kept between◦ and 5◦ in order to focus on the symmetry-protected BICs thatre expected to arise at the Γ point. At normal incidence, the opti-al spectrum reveals modes exhibiting the theoretically infinite-factor characteristic of BICs, allowing for a clear distinctionetween guided modes (GMs) and BICs (Figure S1). However,n practical implementations, perfect BIC conditions are rarelychieved, resulting in quasi-BICs—modes that remain highlyonfined but still couple weakly to the radiative continuum.espite this residual coupling, quasi-BICs retain exceptionallyigh Q-factors, making them particularly advantageous for appli-ations that require strong light confinement while maintainingunable interactions with the surrounding environment. Ournalysis identifies two GMs and four BICs at normal incidence.ue to the nature of the triangular lattice, the observable opticalodes differ depending on whether the incident angle is alongdvanced Functional Materials, 2026the x- or y-direction. Additional simulations of the reflectancespectrum with light incident along the x-direction (Figure S2)reveal three more BICs (BICTM1, BICTM2, and BICTE2).The distributions of electric energy densities Eden for the reso-nances at 2◦ incident angle for GMs and quasi-BICs are presentedin Figure 2c. Analysis of the electric field component distributions(|Ex|, |Ey|, |Ez|) enables the classification of transverse-electric(TE) and transverse-magnetic (TM) modes (Figure S3). The TMmodes predominantly exhibit out-of-plane resonance character-istics, while TE modes demonstrate in-plane resonance behavior.Seven quasi-BICs were observed: three TM modes in the shorterwavelength range (∼550–670nm) and four TEmodes in the longerwavelength range (∼710–810 nm). The longer resonance wave-lengths of the TE modes result from their stronger confinementwithin high-index regions, leading to a higher effective refractiveindex. Compared to GMs, which typically experience radiativelosses and thus have finite Q-factors, quasi-BICs remain largelydecoupled from free-space radiation near normal incidence.This weak radiative coupling enables them to sustain ultrahighQ-factors and significantly enhanced field intensities. Notably,BICTE4 exhibits an electric energy density approaching the orderof 106, whereas GMTE only reaches approximately 101. AmongTE quasi-BICs, BICTE4 is the only mode that exhibits resonancecharacteristics along both the primary lattice directions, whileBICTE3 and BICTE2 (Figure S2) show electric energy densities onthe order of 104 and 103, predominantly confined along the x- andy-directions, respectively.3 Thickness-Dependent Mode Behaviors inUltrathin Photonic NanomembranesTo realize an ultrathin photonic nanomembrane, we next inves-tigated the influence of nanomembrane thickness variation andthe effect of substrate presence on the opticalmodes. Our analysisfocused on how changes in the photonic slab thickness impactmode characteristics, including Q-factor, field enhancement, andfield distribution. Figure 3a,e presents simulated reflection spec-tra for two configurations: a SiN photonic slab on a SiO2 substrateand a freestanding SiN photonic nanomembrane, respectively.Both configurations were analyzed across varying thicknessesunder x-polarized light incidence at a 2◦ angle along they-direction. In both configurations, all modes exhibited ablueshift with decreasing thickness, attributable to reducedeffective optical path length. For the SiO2-substrate configu-ration (Figure 3a), all resonances undergo attenuation, andthe reflection peaks progressively lose contrast as the photonicslab thickness decreases. TM modes exhibit an even earliersuppression, with the BICTM3 becoming negligibly weak in thesimulated response for thicknesses below 150 nm. The Q-factorvariations with thickness for GMs and quasi-BICs are presentedin Figure 3b.While the BICTE4 maintained a high Q-factor (∼104),its resonance diminished to anundetectable level in the simulatedresponse at approximately 100nm thickness. TheGMTM exhibiteda relatively low Q-factor (∼102). The extinction of both GMs andquasi-BICs at reduced thicknesses was attributed to strong fieldleakage into substrate radiation channels, preventing sustainedresonance. In contrast, the freestanding nanomembrane config-uration (Figure 3e) preserved notably high Q-factors and strongresonance even at thicknesses below 100 nm.3 of 13ive Commons LicenseFIGURE 2 (a) Schematic representation of the SiN photonic nanomembrane, comprising triangular-lattice air-hole array defined by lattice periodP = 600 nm, hole diameter D = 300 nm, and nanomembrane thickness T = 150 nm. (b) Simulated angle-dependent reflection spectra under x-polarizedillumination as the incident angle varies along the y-direction, revealing distinct optical resonances including GMs and quasi-BICs. (c) Electric energydensity (Eden) distributions of the corresponding resonant modes identified in panel (b), with field intensities presented on a logarithmic scale, highlightmode confinement and near-field enhancement characteristics.FIGURE 3 Simulated reflection spectra as a function of structural thickness for (a) SiN hole-array photonic slabs supported on a SiO2 substrate,and (e) freestanding photonic nanomembranes. The incident light is x-polarized with an incident angle of 2◦ along the y-direction. Correspondingsimulated Q-factor variations for GMs and quasi-BICs in (b) substrate-supported photonic slabs and (f) photonic nanomembranes. Electric energydensity Eden distributions in the xz-plane for the BICTE4 and BICTM3 in (c) the substrate-supported photonic slabs and (g) photonic nanomembranes atselected thicknesses. The xz-plane distributions are presented at the center and a position y= 0.257 µmoffset from the center for the BICTE4 and BICTM3,respectively, corresponding to their maximum field intensities. Maximum Eden values at the top membrane surface (xy-plane) of (d) the substrate-supported photonic slabs and (h) the photonic nanomembranes, highlighting significantly enhanced field confinement achievable in the ultrathinfreestanding configuration.UiiBi4 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Cnlike the substrate-based configuration, where the reflectionntensity decreases with reducing thickness due to field leakagento the substrate, the reflection peaks of both GMs and quasi-ICs in the nanomembrane configuration remain high, indicat-ng strong optical mode confinement and resonance. Notably,of 13all TE modes remain observable even when the nanomembranethickness is reduced below 10 nm. In contrast, for the two TMmodes (GMTM and BICTM3), reflection peaks become difficultto resolve below a thickness of approximately 75 nm. How-ever, these modes exhibit progressively narrower linewidths andAdvanced Functional Materials, 2026reative Commons Licenseiwpwwtt(srsaAsaStcFb2ctiatFnGnniinncbtrNtmAsamae4NTBsptdaA 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatncreasing Q-factors as the nanomembrane thickness decreases,hile their resonance remains strong. The inability to resolve theeaks arises from simulation limitations, specifically the finiteavelength resolution, which fails to accurately capture modesith extremely narrow bandwidths. This effect is distinct fromhe mode extinction observed in the substrate-based configura-ion near the cutoff thickness, where field leakage dominatesFigure 3a). The nanomembrane configuration provides a moretable optical environment for both GMs and quasi-BICs undereduced thickness conditions, in contrast to the substrate-basedtructure, where substrate-induced radiation losses significantlyffect mode confinement.dditionally, the nanomembrane configuration exhibits superiorpectral tunability compared to the substrate-based structure,s evidenced by the more pronounced blueshift of resonances.pecifically, when the thickness is reduced from 200 to 100 nm,he BICTE4 exhibits a blueshift of 112 nm in the nanomembraneonfiguration, compared to 72 nm in the substrate configuration.urther reducing the thickness to 25 nm results in a totallueshift of approximately 270 nm from its original position at00 nm thickness, demonstrating the significant spectral tuningapability of the nanomembrane structure. This superior spectralunability primarily arises from two factors: the higher refractivendex contrast between the photonic nanomembrane and air,nd the absence of substrate coupling, which allows the modeo undergo greater changes in its dispersion characteristics.igure 3f illustrates the simulated Q-factor variations with thick-ess for the nanomembrane configuration. For TM modes, bothMTM and BICTM3 exhibited an increase in Q-factor as the thick-ess decreased. Since the electric field along the z-direction domi-ates the resonance, TM-polarizedmodes exhibit greater sensitiv-ty to thickness variations compared to TE modes. Furthermore,n a freestanding nanomembrane configuration, which elimi-ates substrate-induced radiation losses, TM modes achieve sig-ificantly higher Q-factors compared to their substrate-supportedounterparts, especially for the thinner (< 100 nm) structure. Thisehavior corresponds to the stronger enhancement of the elec-romagnetic field at the photonic nanomembrane-air interface,ather than being confined within the photonic nanomembrane.otably, the highest Q-factor observed for TM-quasi-BICs inhe nanomembrane configuration reached 105, two orders ofagnitude higher than that of substrate-supported structures.mong the TE modes, the BICTE4 exhibited relatively hightability in its Q-factor, decreasing by only one order ofmagnitudes the thickness was reduced to 25 nm from 200 nm, while stillaintaining a high value on the order of 103. This higher Q-factorrises from its efficient resonance characteristics and high fieldnhancement as discussed in Figure 2b,c.Field Confinement in Ultrathin Photonicanomembraneshe field confinement and enhancement characteristics of quasi-ICs and GMs were further investigated as a function of thelab and nanomembrane thicknesses. Figure 3c,d focuses on thehotonic slab atop a SiO2 substrate, while Figure 3g,h examineshe nanomembrane case. Figure 3c displays the electric energyensity distribution in the xz-plane of two modes: the BICTE4t the thicknesses of 150 and 100 nm, and the BICTM3 at thedvanced Functional Materials, 2026thicknesses of 175 and 150 nm. As the thickness approaches100 nm for the BICTE4 and 150 nm for BICTM3, significant fieldleakage into the substrate weakens field confinement, making itdifficult to sustain the modes. Figure 3d illustrates the maximumelectric energy density Eden, surface at the top surface of the slab.Consistent with previously discussed Q-factor trends, quasi-BICs demonstrate stronger surface fields compared to GMs. TheBICTE4 field intensity decreases with reduced thickness due todiminished confinement from reduced material volume. BICTM3experiences even greater field leakage into the substrate due tothe vertical resonance of the TM mode, resulting in weak fieldenhancement and barely sustaining at a relatively large thicknessof 150 nm.Figure 3g illustrates the electric energy density distributions inthe xz-plane of the BICTM3 and BICTE4 for thicknesses of 150 and100 nm for the nanomembrane case. Compared to the substrate-based configuration in Figure 3c, both modes retain strong fieldenhancement near the surface as the nanomembrane thicknessdecreases, benefiting from the absence of substrate-inducedfield leakage. The Eden, surface for the photonic nanomembrane isplotted in Figure 3h. Due to their significantly higher Q-factorsand lower radiative losses compared to GMs, the quasi-BICsexhibit higher surface field enhancements compared to GMs.The BICTE4 benefits from superior out-of-plane confinementand is consequently less sensitive to thickness variations; itssurface field enhancement remains on the order of 104 whenthickness decreases from 200 to 75 nm, only declining to 103 whenfurther reduced to 25 nm. For the BICTM3, stronger surface fieldenhancement occurs with reduced thickness because its fieldis predominantly localized at the photonic nanomembrane-airinterface rather than being strongly confined within the photonicnanomembrane. The surface field enhancement reaches a highvalue of approximately 105 at a thickness of 50 nm. As previouslynoted, obtaining simulation results for structures thinner thanthis becomes increasingly challenging due to spectral resolutionlimitations in the simulation.In summary, the proposed photonic nanomembrane maintainsstrong surface fields even with very small thicknesses. At50 nm thickness, the BICTE4 and BICTM3 maintain impressivefield enhancements of approximately 104 and 105, respectively.Notably, the BICTE4 demonstrates remarkable stability, decreas-ing by less than one order of magnitude when the thickness isreduced from 200 to 25 nm. In contrast, the presence of a substratesignificantly disrupts and attenuates these modes due to fieldleakage, causing the optical mode resonance to become too weakto observe in thinner structures (< 100 nm). Furthermore, quasi-BICs consistently outperform GMs by approximately two ordersof magnitude in surface field enhancement, underscoring theirexceptional potential for applications in sensing applicationsand light-matter interactions within photonic structures andatomically thin 2D materials.5 High-QMode Resonances Tailoring inUltrathin Photonic NanomembranesTo experimentally validate the theoretical predictions of theoptical properties, optical characterization was first performedon a 200 nm-thick SiN photonic nanomembrane, serving as5 of 13ive Commons LicenseFIGURE 4 (a) Reflectance spectra of the photonic nanomembranewith a thickness of 200 nm under varying incident angles. PL emissionspectra from the SiN photonic nanomembrane, presented for (b) the fullspectral region of interest at lower spectral resolution and (c) the BICTE4region at higher spectral resolution, clearly resolving its high-Q resonancecharacteristics.aTlfl3smsyBsecaqtmenqBrpBTabmasSRT6 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatn initial demonstration before exploring thinner structures.he reflectance spectra were measured using a supercontinuumaser source (ROCK 480, LEUKOS, France). The light wasocused using a 20× objective lens (NA = 0.25). The reflectedight was collected and analyzed using a spectrometer (Kymera28i Spectrograph, Oxford Instruments Group, UK) to obtainpectral measurements. Comprehensive details of the opticaleasurements are provided in the Methods section. Figure 4ahows the angle-resolved reflectance spectra measured along the-direction. At normal incidence (θy = 0◦), symmetry-protectedICs remain uncoupled from far-field radiation due to theirymmetric mode profiles. The spectrum at normal incidencexhibits two main features, with a narrow peak at 661.9 nmorresponding to the GMTM and a broader peak at 689.5 nmssociated with the GMTE. As the incident angle increases,uasi-BICs gradually couple to the far field, and at θ = 1.52◦wo modes (BICTE1 and BICTE3) become clearly observable. Theeasured reflection spectra of the SiN photonic nanomembranexhibit consistency with the simulated reflectance spectrum atear-normal incidence, confirming the presence of GMs anduasi-BICs as predicted by the simulations.ecause the SiN membrane used in this work exhibits defect-elated states, a broad-band PL emission is observed under opticalumping (Figure S4), allowing the investigated GMs and quasi-ICs to couple to this PL band and exhibit high-Q resonances.his approach enables the probing of high-Q quasi-BICs throughPL emission peak, which improves the signal-to-noise ratioy reducing contributions from reflection and scattering. Such aethod is advantageous for demonstrating light coupling controlt the atomic-layer scale. Figure 4b,c presents the emissionpectra of the SiN photonic nanomembrane. The PL spectra of theiN photonic nanomembranes were obtained utilizing a confocalaman/PL microscope system (alpha300 R, WITec, Germany).he samples were excited with a CW laser at 488 nm. Theof 13excitation light was focused by objective lenses with a magnifica-tion of 10× (NA= 0.25). The excited emission was collected by thesame objective lenses. The emission intensity distributions wereobtained using a motorized x-y-sample scanning stage for con-focal emission imaging. The nanomembrane was excited usinga 488 nm continuous wave laser, and the resulting broadbandPL emission was observed at approximately 500–800 nm (FigureS4). This emission is associated with defect-related states in SiN.The PL spectra of the SiN photonic nanomembrane exhibit highconsistency with reflectance measurements at near-normal inci-dence, further confirming the presence of GMs and quasi-BICsas predicted by the theoretical analysis. For the GMs, the GMTMmanifests as a well-defined peak, while the GMTE overlaps withadjacent quasi-BICs. Although this overlap complicates the directidentification of the GMTE, its presence is confirmed throughcorrelation with the reflectance measurements in Figure 4a. Thethree TM-quasi-BICs exhibit distinct spectral characteristics, withBICTM3 displaying the narrowest emission peak. This observationaligns well with the simulation results. However, due to theoverlap of emission peaks, accurately resolving its Q-factorremains challenging. For the TE-quasi-BICs, although the spec-tral position of BICTE1 is shifted from the SiN PL band, it exhibitsa high emission intensity comparable to that of the GMTM, whichresonates near 650 nm. The significant enhancement of emission(up to ∼100-fold compared to a plain nanomembrane, as shownin Figure S5) demonstrates the potential of these structuresfor photonic applications in surface-emitting lasing, nonlinearoptics, and quantum light generation. Notably, while BICTE4exhibits relativelyweak emission due to its wavelength being nearthe edge of the SiN PL band, it demonstrates an exceptionallyhigh Q-factor of approximately 8065, as shown in Figure 4c. Thismeasurement was obtained using a spectrometer grating with1800 lines/mm, which provides significantly higher resolutioncompared to the 150 lines/mm grating used in Figure 4b, wherethe BICTE4 is difficult to resolve.To extend the investigation to ultrathin nanomembranes, pho-tonic nanomembranes with controlled thicknesses were devel-oped. Building upon the initial study of a 200 nm-thicknanomembrane, the nanomembrane thickness was graduallyreduced using a low-damage reactive ion etching (RIE) processwith highly precise thickness modulation. This approach ensuresexceptional structural preservation while enabling systematicexploration of optical properties in the ultrathin regime. The PLspectra of photonic nanomembranes with different thicknesses,measured using spectrometer gratings with 150 lines/mm and1800 lines/mm, are presented in Figure 5a,b, respectively. Theexperimentally measured resonance wavelengths show strongagreement with our simulations, as demonstrated in Figure 5c,d.All modes exhibit the expected blueshift toward shorter wave-lengths as the thickness decreases. In Figure 5b, the BICTE4manifests as a remarkably sharp peak with an exceptional Q-factor of 9632 at a thickness of 163 nm. The Q-factor graduallydecreases with reducing thickness but remains impressively highat 2037 and 1480 for thicknesses of 36 and 29 nm, respectively(Figure S6). The BICTE4 shift from 806.49 to 590.87 nm isdemonstrated experimentally, spanning a substantial portionof the visible spectrum, exhibiting the great tunability of res-onances by controlling the thickness. For TM modes, as thethickness decreases, their wavelengths shift further from the SiNPL emission band, making their observation more challengingAdvanced Functional Materials, 2026ive Commons LicenseFIGURE 5 PL spectra of the photonic nanomembrane as a function of nanomembrane thickness, illustrating (a) GMs and quasi-BICs, and (b)specifically highlighting the high-Q BICTE4 region at higher spectral resolution. (c) Simulated and (d) experimentally measured resonance wavelengthsof GMs and quasi-BICs as a function of nanomembrane thickness. Corresponding (e) simulated and (f) experimentally measured Q-factors for the GMsand quasi-BICs, demonstrating sustained high-Q resonances achievable in the ultrathin nanomembrane regime.iafattaGNmaaWBhtTfOtarssnticfhnwA 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatn ultrathin structures. The BICTM3 remains observable onlyt a 163 nm-thick photonic nanomembrane, exhibiting a Q-actor of 3809 (Figure S7). Figure 5e,f presents the simulatednd measured Q-factors as a function of thickness, respec-ively. The TE quasi-BICs exhibit consistently higher Q-factorshan TE GMs across all thicknesses, with BICTE4 displayingQ-factor more than two orders of magnitude higher thanMTE, as confirmed by both experimental and simulated results.otably, the experimental results demonstrate that all BICTE4aintain high Q-factors within the same order of magnitudes the thickness decreases, sustaining strong resonance event 29 nm.hile numerous photonic structures exhibiting high-Q quasi-ICs have been reported, the majority of these demonstrationsave been conducted in the near-infrared region, with rela-ively few studies achieving high Q-factors in the visible range.able S1 presents a comparison of experimentally obtained Q-actors in nanophotonic structures operating in the visible range.ur freestanding structure demonstrates Q-factors of 103 inhe visible wavelength range while maintaining an exception-lly thin layer of just 29 nm. In this wavelength range, mosteported approaches to achieving high Q-factors in photonictructures supporting quasi-BICs have relied on either thickuspended photonic nanomembranes [42, 44] or substrate-basedanoarrays [27–31, 36]. While the former requires substantialhickness to ensure sufficient field confinement, the latter typ-cally suffers from reduced Q-factors due to additional leakyhannels introduced by out-of-plane asymmetry. The presentedreestanding photonic nanomembrane achieves and sustainsigh-Q resonances in the visible region at an ultrathin thick-ess, representing a significant advancement in miniaturizationithout compromising performance. Furthermore, the finite-sizedvanced Functional Materials, 2026effect generally leads to Q-factor degradation [47, 48], with high-Q modes often observed in larger sample sizes. Despite theselimitations, our structure maintains strong optical confinementeven within a compact footprint of just 25 µm × 25 µm. Notably,most measurements of quasi-BICs reported in the visible spec-tral regime have been characterized through transmission orreflection measurements [27, 29, 31, 44] or via lasing signalsunder high-power excitation in conjunction with optical gainmedia [28, 30, 31]. In contrast, our approach demonstrates high-Q quasi-BICs through a spontaneous emission peak excitedwith low pump power. This method provides an improvedsignal-to-noise ratio and enhanced detection limits while min-imizing the risk of sample damage associated with high-powerexcitation, making it well-suited for applications that rely onhigh-Q resonances.6 Atomic Layer Controlled Light Coupling inUltrathin Photonic NanomembranesTo achieve such atomic-level control over light coupling at thenanomembrane surface, atomically thin dielectrics are integratedvia ALD, ensuring atomic-scale precision in thickness controland interface quality (Figure 6). ALD was performed on thenanomembrane using a plasma-enhanced ALD system (AD-230LP, SAMCO Inc., Japan), with SiN selected as the depositedmaterial at a deposition rate of 0.65 Å per cycle. (see Meth-ods) Figure 6a presents the PL spectra of the 48 nm-thicknanomembrane before ALD deposition and after undergoing 8ALD cycles, followed by an additional 2 cycles (totaling 10 cycles),corresponding to the BICTE4. This measurement was obtainedusing a spectrometer grating with 1800 lines/mm. The initialPL emission peak was observed at 596.94 nm. After 8 ALD7 of 13ive Commons LicenseFIGURE 6 (a) PL spectra demonstrating spectral shifts of the BICTE4 in the 48-nm-thick photonic nanomembrane induced by atomic-scaledielectric depositions through ALD. The inset compares simulated and experimentally measured BICTE4 emission shifts due to ALD, where TALDrepresents the estimated ALD thickness used in the simulation. (b) Spatially resolvedmapping of the BICTE4 emission peak wavelengths before and afteratomic-layer depositions, demonstrating uniform and deterministic wavelength shifts across the nanomembrane surface. The scale bar represents 6 µm.(c) Emission peak wavelengths of the BICTE4 for eachmapped pixel, extracted from the emission regionmarked with dashed boxes in (b). Comparativeanalysis of field enhancement using normalized Eden distributions along the z-direction for (d) 48-nm and (f) 200-nm thick photonic nanomembranes,before ALD deposition (black) and after a 1.30-Å dielectric layer deposition (red). The right panels provide detailed views of the nanomembrane surfacefacing the incident light. The xy-plane field distribution variations before and after ALD for (e) 48-nm and (g) 200-nm thick nanomembranes at thesame z-position indicated in (d) and (f). The field distributions illustrate enhanced near-field interactions attainable in the ultrathin nanomembraneconfiguration.caosusBcfTw1PsviAtFpsnotaprmt8 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creaycles, the BICTE4 red-shifted to 598.01 nm, corresponding toshift of 1.07 nm for an estimated deposited layer thicknessf 5.2 Å. With an additional 2 cycles, the mode further red-hifted to 598.31 nm, exhibiting an incremental shift of 0.30 nmpon the deposition of an extra 1.3 Å. Figure 6b presents thepatial mapping of the PL emission peak wavelengths of theICTE4 across the nanomembrane, while Figure 6c shows theorresponding peakwavelengths for eachmapped pixel, extractedrom the emission regionmarked with dashed boxes in Figure 6b.his measurement was obtained using a spectrometer gratingith 600 lines/mm. An 8 × 8-pixel region (corresponding to6 µm × 16 µm) exhibits high uniformity, confirming that theL peak shifts induced by the ALD process are robust and con-istent across the photonic nanomembrane. The emission peakariation induced by a single-cycle ALD is further demonstratedn Figure 1e. A redshift of 0.09 nm was confirmed for a singleLD cycle, attributed to the high Q-factor of 2992, correspondingo an estimated atomic-layer thickness of 0.65 Å (see Methods).urthermore, high-resolution spatial mapping of the emissioneak wavelength exhibits excellent uniformity, verifying thatub-Å atomic-level control over light coupling at the ultrathinanomembrane surface has been successfully achieved. The insetf Figure 6a presents the simulated and measured shift (Δλ) ofhe BICTE4 induced by the deposition of a dielectric layer on48 nm-thick nanomembrane surface. Numerical simulationsredict (inset of Figure 6a) a redshift consistentwith experimentalesults, confirming the strong agreement between theory andeasurement. It is noted that TALD represents the estimated ALDhickness used in the simulation.of 13tIn Figure 6d–g, we further analyze the near-field enhancementin both thin (T = 48 nm) and thick (T = 200 nm) photonicnanomembranes, with and without the deposition of a 2-cycleALD layer (1.30 Å). The normalized field enhancement distri-butions along the z-direction at the midpoint between two airholes in the x-direction are compared for both cases. The 48 nm-thick nanomembrane exhibits a significantly larger variationin surface field enhancement compared to the 200 nm-thickstructure. Additionally, for the ultrathin nanomembrane, thesurface field density exhibits a greater relative change upondeposition, highlighting its enhanced sensitivity to atomic-scalemodifications. This amplified field response in the ultrathinnanomembrane is primarily attributed to the larger ratio ofthe deposited dielectric layer thickness relative to the overallnanomembrane thickness. This demonstrates the advantage ofultrathin photonic nanomembranes for achieving enhanced lightcoupling with atomic-layer dielectrics and monolayer 2D mate-rials, where precise control over surface optical interactions iscritical.It is noted that atomic-layer dielectrics pose challenges foratomic-level light coupling due to their low refractive index andminimal extinction coefficient, leading to weak optical contrast.In contrast, 2D semiconductors, such as TMDmonolayers, owingto their high refractive indices and strong extinction coefficients,show pronounced resonance variations under atomic-scale mod-ifications, as discussed in the introduction and demonstrated inFigure 7. Our demonstration highlights the capability of the ultra-thin photonic nanomembrane system to resolve subtle opticalAdvanced Functional Materials, 2026ive Commons LicenseFIGURE 7 (a) Simulated reflectance spectra of a 58-nm-thick photonic nanomembrane before and after 8 cycles of ALD of SiN, together with thesimulated absorptance of the samemembrane with aWS2 monolayer on top. (b) Spatial distribution of the electric field energy density in xz-plane for thequasi-BICs with a WS2 monolayer integrated onto the photonic nanomembrane. (c) PL spectra of a WS2 monolayer on an unstructured nanomembranecompared with that on the photonic nanomembrane. Inset: Optical microscope image of the photonic nanomembrane with the transferred WS2monolayer. (d) Enhancement factor, defined as the PL intensity ratio between the WS2 monolayer on the photonic nanomembrane and that on theunstructured membrane, together with the PL spectrum of the bare 58-nm-thick nanomembrane prior to WS2 transfer.vsnllsa7EMBAmemTibtFt(Ws[A 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatariations within atomic-layer dielectrics at the nanomembraneurface. This ensures that the proposed ultrathin photonicanomembrane can achieve significantly enhanced atomic-scaleight coupling when integrated with other 2D materials orow-dimensional material systems, providing a robust and ver-atile platform for next-generation nanophotonic and quantumpplications.Ultrathin Photonic Nanomembrane fornhanced Light–Matter Interaction in TMDonolayersuilding on the atomic-level light-coupling control enabled byLD-based dielectric tuning, the platform with integrated 2Daterial is subsequently investigated. Figure 7 illustrates thenhanced light-matter interaction achieved by integrating a 2Daterial (WS2 monolayer) with the photonic nanomembrane.he details of the synthesis of the WS2 monolayer are providedn the Methods section. Here, the resonance variations inducedy atomic-layer SiN and by integration of a WS2 monolayer onhe photonic nanomembrane are first investigated and compared.igure 7a presents the simulated spectra of a 58-nm-thick pho-onic nanomembrane, the samemembrane with 8-cycle SiN ALD0.52 nm thick), and the same membrane with integration of aS2 monolayer (0.6 nm thick). It should be noted that, due to thetrong extinction coefficient of WS2 near its excitonic transition49], reflection spectra do not clearly reveal the resonances;dvanced Functional Materials, 2026therefore, we instead simulated the absorptance spectrum ofthe WS2-integrated photonic nanomembrane. The resonancewavelengths of the bare photonic nanomembrane are identifiedat 579.87 nm (GMTE), 580.90 nm (BICTE1), 617.72 nm (BICTE3),and 642.52 nm (BICTE4). Deposition of 8 SiN-ALD cycles redshiftsthese resonances by 1.03, 1.22, 1.26, and 1.25 nm, respectively.In contrast, integration of the WS2 monolayer induces muchlarger redshifts of 5.99 nm for GMTE, 12.10 nm for BICTE3, and10.58 nm for BICTE4. Notably, the BICTE1 resonance exhibits modesplitting in the absorption spectrum (Figure S8), a clear signatureof strong coupling between the TMD exciton and the quasi-BICs[33, 41, 44]. This difference highlights that integration with a2D material such as a WS2 monolayer leads to more significantresonance variations. More importantly, the coupling betweenthe quasi-BIC modes and the excitonic response of WS2 givesrise to enhanced light–matter interaction and the onset of strongexciton–photon coupling, as evidenced by the observed modesplitting. Figure 7b shows the spatial distribution of the electricfield energy density at the two polariton branches resulting fromRabi splitting of the exciton resonance coupled to BICTE1 (605.53and 620.09 nm) and at BICTE3 (629.82 nm). The field is stronglyamplified and tightly confined within the WS2 monolayer nearthe top surface instead of the photonic nanomembrane. This con-firms the strong exciton–photon coupling arising from the largespatial overlap between the quasi-BIC resonance field and theWS2 monolayer. The resulting enhanced light–matter interactionleads to a pronounced increase in emission. In Figure 7c, the9 of 13ive Commons LicenseentaepwwuBpeagiF8Tncthon4iattfcatmcbamdselnttoptt99TpmT1 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatmission spectrum from aWS2 monolayer placed on the photonicanomembrane is substantially enhanced compared to that ofhe same monolayer placed on the unstructured nanomembranerea. Figure 7d quantifies the emission enhancement using thenhancement factor, defined as the ratio of PL from WS2 on thehotonic nanomembrane to that on unstructured membranes,hich reaches a maximum of 113-fold at the coupled resonanceavelength. The observed strong enhancement suggests thepper and lower polariton branches resulting from exciton–IC hybridization. These results demonstrate that ultrathinhotonic nanomembranes provide an effective platform fornhancing light–matter interactions in the 2D material at thetomic scale. It is noted that through appropriate photoniceometry design, the ultrathin photonic nanomembrane can bentegrated with a wide range of 2D materials, as discussed inigure S9.Conclusionhis work demonstrates an ultrathin freestanding photonicanomembrane that enables atomic-level control over lightoupling between light incidence and the quasi-BIC modes ofhe photonic nanomembrane, achieving Å-scale modulation ofigh-Q optical resonances. Through a systematic investigationf both GMs and quasi-BICs, we reveal that these ultrathinanomembranes sustain high-Q factors, maintaining 3074 at2 nm and 1480 even at 29 nm. By eliminating substrate-nduced losses, this design preserves strong optical confinementnd near-field enhancement, overcoming the inherent limita-ions of conventional nanophotonic structures. Furthermore,he integration of atomically thin dielectrics via ALD con-irms the sub-Å precision of light coupling and atomic-layerharacterization, with a single ALD cycle (0.65 Å) inducing0.09 nm redshift. High-resolution spatial mapping verifieshe uniformity of this shift, demonstrating robust and deter-inistic control over atomic-scale light-matter interactions. Inontrast to thicker photonic structures, ultrathin nanomem-ranes exhibit pronounced sensitivity of their resonant modesnd field distributions to surface modifications at the Å scale,aking them promising platforms for coupling with atomic-layerielectrics, 2D materials, and other low-dimensional quantumystems. The pronounced PL enhancement together with thexciton–polariton mode splitting further demonstrates the strongight–matter interaction achieved in the 2D material–photonicanomembrane platform. By establishing a scalable and highlyunable photonic platform, thiswork not only advances nanopho-onic technologies, including quantum photonics, nonlinearptics, and ultrasensitive optical sensing, but also provides aowerful approach for sub-Å precision material characteriza-ion, which is critical for the most advanced semiconductorechnologies.Methods.1 Simulation Detailshe far-field reflectance spectra and dispersion diagram of thehotonic nanomembrane, as well as the near-field electric andagnetic field distributions of the resonance modes, were com-0 of 13puted using the rigorous coupled-wave analysis (DiffractMOD,RSoft Design Group, USA). All simulations were performedunder periodic boundary conditions in the x- and y-axes andperfectly matched-layer conditions in the z-axis, with plane-wavelight incidence and the incident angle along the z-axis. Theelectric field E is normalized by the electric field amplitude ofthe incident light. The electric energy density is defined as UE =½∫Re[ε(r′)] |E|2 dV, where E is the electric field, ε is the spatiallydependent permittivity, and V is the volume of the simulationgrid. The simulation results were normalized by the input power.The refractive index of SiN was modeled according to literaturevalues [50].9.2 Optical MeasurementThe reflection spectra of the SiN photonic nanomembraneswere measured using a supercontinuum laser source (ROCK480, LEUKOS, France). The SiN nanomembranes were providedby Ted-Pella Inc. and further nanofabricated for the ultrathinnanomembrane samples utilized in this work. The light wasfocused using a 20× objective lens. The reflected light wascollected and analyzed using a spectrometer (Kymera 328i Spec-trograph Oxford Instruments Group, UK) to obtain the spectralmeasurements. The PL spectra of the SiN photonic nanomem-braneswere obtained utilizing a confocal lasermicroscope system(alpha300 R, WITec, Germany). The samples were excited witha CW laser at 488 nm. The excitation light was focused byobjective lenses with a magnification of 10× (NA = 0.25). Theexcited emission was collected and analyzed with a spectrom-eter. The emission intensity distributions were obtained usinga motorized x-y-sample scanning stage for confocal emissionimaging.9.3 Characterization of FreestandingNanomembraneThe freestanding ultrathin SiN nanomembraneswere first treatedwith carbon deposition, with a thickness of 450 nm on thesurface and 225 nm on the backside, to enhance the mechanicalstability of the nanomembrane and suppress charge buildup.A room-temperature curing epoxy resin was then prepared bymixing the base and curing agents in a 3:1 ratio, followed bythorough stirring and degassing before being injected into thebackside of the nanomembrane to provide structural supportfor the freestanding film. The resin was cured at 60◦C for 5h to ensure structural stability. Focused ion beam scanningelectron microscopy (FIB-SEM) (Ethos NX5000, Hitachi High-ech, Japan) was then used to identify the interface between theSiN nanomembrane and the Si support frame, enabling preciseextraction of the nanomembrane for scanning transmissionelectron microscopy (STEM) (Talos F200X G2, Thermo FisherScientific, USA) cross-sectional analysis. The sample for theobservation was carefully separated from the support frame andmounted onto a TEM grid. The sample was thinned to below100 nm, after which the final film thickness was verified usingTEM imaging. The SEM images of etched photonic nanomem-branes confirm that the thinning process does not compromisethe fidelity of the original photonic nanomembrane design(Figure S10).Advanced Functional Materials, 2026ive Commons License9SbncpcTdf0Ear19WdfwzwSsahtegptTw(niPt1p1PnATJIt(NNtUA 16163028, 2026, 44, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202524286 by National Institute For, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creat.4 Atomic Layer DepositioniN thin films were deposited using an ALD process withis(diethylamino)silane (BDEAS) as the silicon precursor anditrogen plasma (N2 plasma) as the reactant. The deposition wasarried out at a substrate temperature of 350◦C under a chamberressure of 8.8 Pa. In this work, a small number of ALD cycles (1–8ycles) were performed to achieve atomic-scale dielectric control.o estimate the atomic-layer thickness per ALD cycle, calibrationata from 2400 ALD cycles were referenced. The total depositedilm thickness of 145.76 nm yielded a growth per cycle (GPC) of.65 Å/cycle, consistent with previous ALD calibration studies.ach cycle consisted of precursor exposure, plasma activation,nd purge steps, with a total duration of 25 s per cycle. Theefractive index of the deposited SiN film was characterized to be.934..5 Preparation for WS2 MonolayerS2 films were synthesized by conventional chemical vaporeposition (CVD) in a one-zone horizontal 2-inch quartz tubeurnace. Tungsten trioxide (WO3, Sigma–Aldrich, 99.9%, 100mg)as used as the tungsten precursor and placed at the centerone together with c-plane sapphire substrates. The center zoneas heated to 960◦C and maintained for 15min for film growth.ulfur powders (S, Sigma–Aldrich, 99.99%, 3 g), which were pre-olidified before use, were placed upstream in a quartz boatnd heated by an external heating belt to 145◦C. The sulfureatingwas initiated 10min prior to the central zone reaching thearget growth temperature. Before growth, the furnace tube wasvacuated to base pressure and then purged with a mixed carrieras consisting of Ar (200 sccm) and H2 (40 sccm) at a constantressure of 20 torr. After growth, the system was naturally cooledo room temperature under the Ar/H2 flow.he transfer of WS2 films was carried out using a PDMS-assistedet etching approach. A home-fabricated polydimethylsiloxanePDMS) stamp was laminated onto the WS2 film surface byatural adhesion. The sapphire substrate was then etched awayn KOH solution, releasing the WS2 film onto the PDMS. TheDMS/WS2 stack was subsequently brought into contact withhe photonic nanomembrane and placed under vacuum forh to enhance the adhesion between the WS2 film and thehotonic nanomembrane. Afterward, mild heating at 60◦C for0min was applied to facilitate the detachment of WS2 from theDMS, leaving the film successfully transferred onto the photonicanomembrane.cknowledgementshis workwas supported by JSPS KAKENHIGrant Numbers JP23K26155,P21H04660. A part of this work was supported by Advanced Researchnfrastructure for Materials and Nanotechnology in Japan (ARIM) ofhe Ministry of Education, Culture, Sports, Science and TechnologyMEXT) (Proposal No. JPMXP1225NM5090). Financial support by theational Science and Technology Council (NSTC), Taiwan Grant Nos.STC-114-2112-605-M-002-032-MY3, NSTC-113-2124-M-002-007 and Cen-er of Atomic Initiative for New Materials (AI-Mat), National Taiwanniversity, from the Featured Areas Research Center Program withindvanced Functional Materials, 2026the framework of the Higher Education Sprout Project by the Ministryof Education in Taiwan (Grant No. 111L900801), is also acknowledged.The authors would like to extend our grateful appreciation to Dr. TakuroNagai, Dr. Noriyuki Okada, Dr. Makoto Oishi, and Dr. Rika Mizuta fromthe Electron Microscopy Unit, Research Network and Facility ServicesDivision, National Institute for Materials Science NIMS, for importanttechnical support on TEM.FundingJSPS KAKENHI Grant Nos. JP23K26155 and JP21H04660; AdvancedResearch Infrastructure For Materials and Nanotechnology in Japan(ARIM) of the Ministry of Education, Culture, Sports, Science and Tech-nology (MEXT), Japan (Proposal No. JPMXP1225NM5090); National Sci-ence and Technology Council (NSTC), Taiwan Grant Nos. NSTC-114-2112-605-M-002-032-MY3 and NSTC-113-2124-M-002-007-; Areas ResearchCenter Program, Higher Education Sprout Project by the Ministry ofEducation in Taiwan (Grant No. 111L900801).Conflicts of InterestThe authors declare no conflicts of interest.Data Availability StatementThe data that support the findings of this study are available from thecorresponding author upon reasonable request.References1. L. Loh, J. Wang, M. Grzeszczyk, M. Koperski, and G. Eda, “TowardsQuantum Light-Emitting Devices Based on van der Waals Materials,”Nature Reviews Electrical Engineering 1 (2024): 815–829, https://doi.org/10.1038/s44287-024-00108-8.2. S. Song, M. Rahaman, and D. 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See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttps://doi.org/10.1038/nature20799https://doi.org/10.1038/s41467-021-24502-0https://doi.org/10.1002/adma.202405978https://doi.org/10.1002/adom.201900239https://doi.org/10.1016/j.tsf.2022.139568 Atomic-Scale Light Coupling Control in Ultrathin Photonic Membranes 1 | Introduction 2 | Design and Optical Characteristics of the Photonic Nanomembrane 3 | Thickness-Dependent Mode Behaviors in Ultrathin Photonic Nanomembranes 4 | Field Confinement in Ultrathin Photonic Nanomembranes 5 | High-Q Mode Resonances Tailoring in Ultrathin Photonic Nanomembranes 6 | Atomic Layer Controlled Light Coupling in Ultrathin Photonic Nanomembranes 7 | Ultrathin Photonic Nanomembrane for Enhanced Light-Matter Interaction in TMD Monolayers 8 | Conclusion 9 | Methods 9.1 | Simulation Details 9.2 | Optical Measurement 9.3 | Characterization of Freestanding Nanomembrane 9.4 | Atomic Layer Deposition 9.5 | Preparation for WS2 Monolayer Acknowledgements Funding Conflicts of Interest Data Availability Statement References Supporting Information