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arXiv:2607.11768

Spacer-Mediated Gold Nanocube Arrays for Edge-Localized Excitonic Enhancement in Monolayer MoS2

Abdullah Efe Yildiz, Emre Ozan Polat

physics.opticsphysics.app-phphysics.comp-phquant-phSubmitted Jul 13, 2026• Announced Jul 14, 2026
arXivHTMLPDF

Abstract

Plasmonic nanostructures offer an effective route for enhancing light-matter interaction in atomically thin semiconductors, whose optical response is intrinsically limited by their sub-nanometer active thickness. Here, we numerically investigate excitonic enhancement in monolayer (ML) Molybdenum Disulfide (MoS2) coupled to size-tuned gold (Au) nanocube arrays separated by thin aluminum oxide (Al2O3) and hexagonal boron nitride (h-BN) spacer layers. By varying the nanocube side length, the localized surface plasmon resonance is tuned across the visible spectral range to modulate the A- and B-excitonic transitions of monolayer MoS2. We show that the nanocube-size-dependent spectral redshift can be further controlled through the spacer material and thickness, enabling systematic tuning of the near-field distribution, carrier generation rate, quantum yield, and radiative decay enhancement. Localized plasmonic confinement yields excitation-rate enhancements of up to 4.35 at B-excitonic transition (605 nm) and 3.66 at A-excitonic transition (650 nm), while the radiative decay-rate enhancement exceeds 80, leading to 350-fold photoluminescence enhancement. Although both A- and B-excitonic channels are enhanced simultaneously, their relative contributions depend on nanocube size, spacer material, and spacer thickness, indicating wavelength-dependent excitonic modulation rather than strict exciton-selective switching. These findings establish Au nanocube arrays as a simple, scalable, and tunable plasmonic platform for enhancing excitonic carrier generation and emission in ML MoS2.

Comments
21 Pages, 5 Figures, 2 Tables

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Geometry-Controlled Exciton Selectivity in Monolayer MoS2 Using Plasmonic Hollow Nanocavities

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Spectral control of closely spaced excitonic transitions is central to valleytronic photonics, nanoscale light sources, and wavelength-encoded sensing. In monolayer molybdenum disulfide (MoS2), the A and B excitons are separated by only tens of meV, making selective excitonic emission control both fundamentally important and technologically challenging. Here, we numerically investigate plasmon-enhanced excitonic emission from monolayer MoS2 coupled to vertically oriented hollow gold nanocylindrical cavities through a dielectric spacer. Finite-difference time-domain simulations combined with a photoluminescence-rate framework enable separate evaluation of excitation enhancement, radiative decay modification, nonradiative quenching, and excitonic charge generation. By tuning the cavity aspect ratio, the localized surface plasmon resonance is selectively aligned with either the A- or B-exciton transition, while the spacer thickness and refractive index regulate near-field coupling and the local density of optical states. Under optimized conditions, the excitation rate is enhanced by up to 4.34-fold and the radiative decay rate by more than 40-fold, yielding photoluminescence enhancements of 143.85 and 87.27 for the A and B excitons, respectively. The cavity also redistributes the relative excitonic peak intensities, producing exciton-selective peak ratios up to 2.4 times higher than those of bare MoS2. These results establish hollow plasmonic nanocavities as geometry-tunable platforms for exciton-selective emission and charge-generation control in atomically thin semiconductors.

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We study how to obtain the channel-tunable bistable states in a coupled system consisting of a monolayer MoS 2 nanomechanical resonator (NR) and a metallic nanoshell (MNS) beyond the dipole approximation. The MNS is constructed by a metallic core and a dielectric shell. The calculated results show that the linear absorption spectrum exhibits some new features, such as three-phonon resonance, Rayleigh resonance, and ac-Stark resonance. In a strong exciton-plasmon coupling regime, the absorption peak and amplification peak in the absorption spectrum can be greatly enhanced by adjusting the exciton-phonon coupling strength. Especially, we plot the bistability phase diagrams in the system’s parameter space and highlight the strong dependency of the lower (upper) bistable threshold on the pumping intensity, the MNS-NR distance, and the dielectric shell thickness. The ratio of linear absorption in the upper and lower stable states can reach 42. For a given MNS with a fixed shell thickness, it is easy to achieve single-channel or dual-channel bistable states by only adjusting the exciton-phonon coupling strength via modulation of the length of the MoS 2 nanosheet along the NR axis. The findings obtained here are very useful for extensive applications such as optical memory cells and channel-tunable bistable switches.

Optics Express•May 7, 2025•2 citations
Plasmonic nanostructures offer an effective route for enhancing light-matter interaction in atomically thin semiconductors, whose optical response is intrinsically limited by their sub-nanometer active thickness. Here, we numerically investigate excitonic enhancement in monolayer (ML) Molybdenum Disulfide (MoS2) coupled to size-tuned gold (Au) nanocube arrays separated by thin aluminum oxide (Al2O3) and hexagonal boron nitride (h-BN) spacer layers. By varying the nanocube side length, the localized surface plasmon resonance is tuned across the visible spectral range to modulate the A- and B-excitonic transitions of monolayer MoS2. We show that the nanocube-size-dependent spectral redshift can be further controlled through the spacer material and thickness, enabling systematic tuning of the near-field distribution, carrier generation rate, quantum yield, and radiative decay enhancement. Localized plasmonic confinement yields excitation-rate enhancements of up to 4.35 at B-excitonic transition (605 nm) and 3.66 at A-excitonic transition (650 nm), while the radiative decay-rate enhancement exceeds 80, leading to 350-fold photoluminescence enhancement. Although both A- and B-excitonic channels are enhanced simultaneously, their relative contributions depend on nanocube size, spacer material, and spacer thickness, indicating wavelength-dependent excitonic modulation rather than strict exciton-selective switching. These findings establish Au nanocube arrays as a simple, scalable, and tunable plasmonic platform for enhancing excitonic carrier generation and emission in ML MoS2.
Spectral control of closely spaced excitonic transitions is central to valleytronic photonics, nanoscale light sources, and wavelength-encoded sensing. In monolayer molybdenum disulfide (MoS2), the A and B excitons are separated by only tens of meV, making selective excitonic emission control both fundamentally important and technologically challenging. Here, we numerically investigate plasmon-enhanced excitonic emission from monolayer MoS2 coupled to vertically oriented hollow gold nanocylindrical cavities through a dielectric spacer. Finite-difference time-domain simulations combined with a photoluminescence-rate framework enable separate evaluation of excitation enhancement, radiative decay modification, nonradiative quenching, and excitonic charge generation. By tuning the cavity aspect ratio, the localized surface plasmon resonance is selectively aligned with either the A- or B-exciton transition, while the spacer thickness and refractive index regulate near-field coupling and the local density of optical states. Under optimized conditions, the excitation rate is enhanced by up to 4.34-fold and the radiative decay rate by more than 40-fold, yielding photoluminescence enhancements of 143.85 and 87.27 for the A and B excitons, respectively. The cavity also redistributes the relative excitonic peak intensities, producing exciton-selective peak ratios up to 2.4 times higher than those of bare MoS2. These results establish hollow plasmonic nanocavities as geometry-tunable platforms for exciton-selective emission and charge-generation control in atomically thin semiconductors.
Near-infrared (NIR) emitters operating in the 650-900 nm range are highly attractive for imaging and sensing in turbid media; however, cadmium-free InP-based quantum dots (QDs) often suffer from limited brightness due to nonradiative pathways and inefficient photon outcoupling. In particular, heterostructured InP QDs can exhibit band alignments that induce partial spatial separation of charge carriers, leading to reduced electron-hole wavefunction overlap. This modifies intrinsic recombination dynamics and enhances the sensitivity of their emission to the surrounding photonic environment. Here, we investigate silver toroidal plasmonic nanoantenna dimers (Ag TPNDs) through finite-difference-time-domain (FDTD) simulations as a geometry-tunable platform for enhancing NIR emission of heterostructured InP-based QDs. The coupled toroidal geometry supports strongly confined bonding modes that generate intense nanogap hotspots, while its resonance can be systematically tuned through the toroid aspect ratio. By spectrally aligning the antenna response with QD emission bands (675-845 nm), we achieve large Purcell enhancements together with high quantum efficiencies, demonstrating efficient conversion of enhanced decay rates into radiative emission. We further show that nanometer-scale variations in emitter-antenna separation strongly modulate the radiative rates and spectral response. These results establish toroidal plasmonic nanodimers as a topology-driven platform for controlling emission in NIR quantum emitters and for advancing NIR nanophotonic applications.
Conventional approaches to light-matter interactions rely on engineering photonic density of states. More recently, tailoring the spatial geometry of atoms or emitters themselves has emerged as a powerful and complementary route to control collective radiative properties. Here we experimentally realize a geometry-engineered ensemble of rare-earth ions by fabricating a periodic array of subwavelength gold nanoholes on lithium niobate implanted with thulium ions, forming a semi-two-dimensional array of quantum emitters embedded in a high-index crystalline thin film. The hybrid structure can simultaneously support localized and lattice plasmon resonances from the metallic array and collective atomic resonances from the ion ensemble. Using time-resolved photoluminescence and temperature-dependent measurements, we observe enhanced radiative emission attributed to collective atomic effects mediated by the nanohole lattice, distinct from single-emitter Purcell enhancement. Our results demonstrate a new regime of light-matter interaction opening a pathway toward broadband and scalable, geometry-controlled quantum optical interfaces in solid-state platforms.
We deposited niobium nitride (NbN) thin film by radio-frequency (RF) magnetron sputtering on MgO substrate at 800 ºC (with Tc ~15 K). To increase the photodetectivity, we design an Ag nanocube nanoresonator with a strong gap-plasmon resonance in the visible range to further enhance the photoresponsivity by engineering the optical response for the NbN superconducting devices. This is due to the superconducting states are broken down by a localizing strong electromagnetic field. To design the plasmonic nanostructures, we calculated the electromagnetic field distribution of Ag nanocube/Al2O3/NbN structure by finite-difference time-domain (FDTD). We observed a strong plasmonic resonance field which tightly confined in the Al2O3 layer between the Ag nanocube and NbN film at a resonant wavelength of 532 nm. In the end, we will also discuss the detailed working mechanism and the potential application of plasmon-enhanced photodetection in NbN superconducting photodetectors.
Inspired by the remarkable ability of plasmons to boost radiative emission rates, we propose leveraging acoustic graphene plasmons (AGPs) to realize tunable, giant Purcell enhancements for single-photon, entangled-photon, and multipolar quantum emitters. These AGPs are localized inside a cavity defined by a graphene sheet and a metallic nanocube and filled with a dielectric of thickness of a few nanometers and consisting of stacked layers of 2D materials, containing impurities or defects that act as quantum light emitters. Through finite-difference time domain (FDTD) calculations, we show that this geometry can achieve giant Purcell enhancement factors over a large portion of the infrared (IR) spectrum, up to 6 orders of magnitude in the mid-IR and up to 4 orders of magnitude at telecommunications wavelengths, reaching quantum efficiencies of 95\% and 89\%, respectively, with high-mobility graphene. We obtain Purcell enhancement factors for single-photon electric dipole (E1), electric quadrupole (E2), and electric octupole (E3) transitions and two-photon spontaneous emission (2PSE) transitions, of the orders of 10410^{4}104, 10710^{7}107, 10910^{9}109, and 10910^9109, respectively, and a quantum efficiency of 79\% for entangled-photon emission with high-mobility graphene at a wavelength of λ=1.55λ=1.55λ=1.55 μμμm. Importantly, AGP mode frequencies depend on the graphene Fermi energy, which can be tuned via electrostatic gating to modulate fluorescence enhancement in real time. As an example, we consider the Purcell enhancement of spontaneous single- and two-photon emissions from an erbium atom inside single-layer (SL) WS2_22​. Our results could be useful for electrically tunable quantum emitter devices with applications in quantum communication and quantum information processing.
We study how to obtain the channel-tunable bistable states in a coupled system consisting of a monolayer MoS 2 nanomechanical resonator (NR) and a metallic nanoshell (MNS) beyond the dipole approximation. The MNS is constructed by a metallic core and a dielectric shell. The calculated results show that the linear absorption spectrum exhibits some new features, such as three-phonon resonance, Rayleigh resonance, and ac-Stark resonance. In a strong exciton-plasmon coupling regime, the absorption peak and amplification peak in the absorption spectrum can be greatly enhanced by adjusting the exciton-phonon coupling strength. Especially, we plot the bistability phase diagrams in the system’s parameter space and highlight the strong dependency of the lower (upper) bistable threshold on the pumping intensity, the MNS-NR distance, and the dielectric shell thickness. The ratio of linear absorption in the upper and lower stable states can reach 42. For a given MNS with a fixed shell thickness, it is easy to achieve single-channel or dual-channel bistable states by only adjusting the exciton-phonon coupling strength via modulation of the length of the MoS 2 nanosheet along the NR axis. The findings obtained here are very useful for extensive applications such as optical memory cells and channel-tunable bistable switches.