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Collective strong light-matter coupling in hierarchical microcavity-plasmon-exciton systems
摘要： Polaritons are compositional light-matter quasiparticles that arise as a result of strong coupling between the vacuum field of a resonant optical cavity and electronic excitations in quantum emitters. Reaching such a regime is often hard, as it requires materials possessing high oscillator strengths to interact with the relevant optical mode. Two-dimensional transition metal dichalcogenides (TMDCs) have recently emerged as promising candidates for realization of strong coupling regime at room temperature. However, these materials typically provide coupling strengths in the range of 10-40 meV, which may be insufficient for reaching strong coupling with low quality factor resonators. Here, we demonstrate a universal scheme that allows a straightforward realization of strong coupling with 2D materials and beyond. By intermixing plasmonic excitations in nanoparticle arrays with excitons in a WS2 monolayer inside a resonant metallic microcavity, we fabricate a hierarchical system with the collective microcavity-plasmon-exciton Rabi splitting exceeding ~500 meV at room temperature. Photoluminescence measurements of the coupled systems show dominant emission from the lower polariton branch, indicating the participation of excitons in the coupling process. Strong coupling has been recently suggested to affect numerous optical- and material-related properties including chemical reactivity, exciton transport and optical nonlinearities. With the universal scheme presented here, strong coupling across a wide spectral range is within easy reach and therefore exploring these exciting phenomena can be further pursued in a much broader class of materials.
关键词： TMDC,Strong plasmon-exciton coupling,collective Rabi splitting,monolayer WS2
更新于2025-09-23 15:21:21
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Multi-electron anisotropic quantum dots/TMDCs/CNT families under magnetic field: analytical treatment to first Brillouin zone by Fermi liquid model
摘要： Acute Coulomb interaction of the two-dimensional systems has drawn special attention due to its unusual logarithmic Green function expansion. As the number of electrons (N) increases, Pauli Exclusion principle emerges inevitably with rapidly growing electronic correlations. Quantum dot, Transition metal dichalcogenides (TMDC) and Carbon nanotube (CNT) families of 2-D anisotropic mesoscopic systems are rich habitats of electrons. Schr?dinger equations of such electrons in electrical confinement and transverse magnetic field can be recast in self-adjoint Whittaker-M functions facilitating each Coulomb interaction to terminable, exact and single summed Lauricella function via Chu-Vandermonde identity. For N = 3, 4, 5, 6, . . . 20, multipoles of Green function expansion also succumb to terminable, single-summed, analytical integrals by inserting discretised closure relations. Thus, multi-configuration Slater determinantal states are employed for strong correlation of Fermi liquid model of first Brillouin zone (FBZ) within giga-units of reciprocal lattices (mesoscopic scale). Chemical potential, addition energies of WS2, GaAs and model systems of dielectric constant = 1.0 have set benchmark at low and high confinement potentials, as a function of magnetic field and density of electrons. Because of sharp falls in surface integrals of both Newman and Dirichlet forms of Green function, Coulomb interaction takes to (or leads to) multipole expansion of generic coordinates. Formation of composite-fermions may be anticipated. At the most, octupole is sufficient for the convergence.
关键词： Lauricella Functions,multi-configuration slater determinant,Fermi liquid model,strong Coulomb interaction,quantum dots/TMDC
更新于2025-09-23 15:21:01
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - 2D materials for optoelectronic devices
摘要： There is currently interest in 2D transition metal dichalcogenide (TMDC) materials, MX2 (M=Mo,W, X=S,Se,Te), for optoelectronic devices. These materials, when thinned down to a single layer, are an example of atomically thin truly two dimensional direct gap semiconductors. The reduction of dimensionality is a reason for strongly enhanced electron - electron interactions, which result in optical properties at room temperature dominated by neutral and charged excitons with binding energies orders of magnitude larger than room temperature and those found in standard compound semiconductors, e.g., GaAs quantum wells.
关键词： Bethe-Salpeter equation,optoelectronic devices,excitons,TMDC,2D materials
更新于2025-09-19 17:13:59
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Simulation analysis of functional MoSe <sub/>2</sub> layer for ultra-thin Cu(In,Ga)Se <sub/>2</sub> solar cells architecture
摘要： The influence of Molybdenum diselenide transition metal dichalcogenide material (p-type MoSe2 TMDC) as an interfacial layer between the ultra-thin Cu(In,Ga)Se2 (CIGS) absorber layer, with thickness less than 500 nm, and molybdenum back contact was studied using SCAPS-1D simulation package. The possible effects of the p-MoSe2 layer on the electrical properties and the photovoltaic parameters of the CIGS thin-film solar cells have been investigated. Band gap energy, carrier concentration, and the layer thickness of the p-MoSe2 were varied in this study. The optimum band gap is found to be of 1.3 eV. Interfacial layers of thicknesses less than 200 nm have been found to cause deterioration for the overall cell performance. This might be attributed to the increase in the back-contact recombination current and the reduction of the built-in potential at p-MoSe2/CIGS junction. Furthermore, the MoSe2 layer would form the so-called back surface field (BSF), due to the associated wider band gap with respect to that of CIGS absorber layer. Additionally, the simulation of the I–V characteristic showed a higher slope which implies that MoSe2 layer at the CIGS/Mo interface acts in a beneficial way on the CIGS/Mo hetero-contact adapting it from Schottky type contact to quasi-ohmic contact. The conversion efficiency has increased significantly from 14.61% to 22.08%, without and with the MoSe2 layer, respectively. These findings are very promising for future high performance and cost-effective solar cell devices.
关键词： SCAPS,thin film solar cell,CIGS,TMDC
更新于2025-09-16 10:30:52
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Quantum-enhanced tunable spin-valley dependent excitonic second harmonic generation in molybdenum disulfide quantum dots
摘要： Developing a robust system with a strong tunable nonlinear second harmonic generation (SHG) is desirable. In this work, we calculate SHG arising from the excitonic states of monolayer molybdenum disulfide quantum dots (MoS2 QDs) with a parabolic confinement potential within massive Dirac fermion model using the density matrix formalism. We theoretically demonstrate that MoS2 QDs can exhibit a giant and tunable Spin-Valley dependent excitonic SHG, which can be tuned from 0 to ～107 pm/V and realized by biasing nanostructured gates or by position-dependent doping. Remarkably, the strength of SHG response is more than two orders of magnitude higher than that in monolayer MoS2. Furthermore, robust excitonic effects together with strong spin-valley coupling in monolayer transition metal dichalcogenides quantum dots (TMDC QDs), which are tunable depending on the strength of the quantum confinement, make them as a promising candidate for ultrathin nonlinear optical materials with large nonlinearities. We believe that this study could spark interest in the nonlinear optical properties of TMDC QDs and open up a variety of new avenues for versatile novel 2D nonlinear photonics and optoelectronic nanodevices.
关键词： second harmonic generation,spin-valley coupling,TMDC QDs,excitonic nonlinear optical properties
更新于2025-09-12 10:27:22
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Ruthenium decorated tungsten disulfide quantum dots for CO2 gas sensor
摘要： In this work, a selective chemi-resistive gas sensor for carbon dioxide gas detection at room temperature (~ 25 °C) was successfully fabricated, where ruthenium decorated tungsten disulfide (Ru@WS2) quantum dots (QDs) have been used as the sensing material. A mixed solvent of lithium hydroxide (LiOH·H2O) and N-Methyl-2-pyrrolidone (NMP) were used to obtain the Ru decorated WS2 QD from the exfoliated WS2 nanoflakes. Then the prepared WS2 QD and Ru@WS2 QD were confirmed using different material characterisation techniques. The gas sensors were then exposed to various concentration of CO2 gas in dry air condition. Also, the effect of humidity of both the sensors in 5000 ppm CO2 gas has been studied. The Ru@WS2 QDs based sensor showed superior sensitivity and good selectivity to CO2 gas in comparison with isopropanol, acetone, ethanol, methanol and benzene at room temperature than WS2 QD. The sensor showed an increase in resistance when exposed to CO2 gas ranging from 500 to 5000 ppm, indicating p-type characteristics. Ru@WS2 QD shows less effect at different humid condition compares to WS2 QD as a CO2 gas sensor.
关键词： Ruthenium decorated tungsten disulfide (Ru@WS2),Transition metal dichalcogenides (TMDC),Quantum Dot (QD),Sensitivity,Selectivity,Gas sensor
更新于2025-09-11 14:15:04
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Bi-layer high-<i>k</i> dielectrics of Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> to reduce damage to MoS<sub>2</sub> channel layers during atomic layer deposition
摘要： To implement Two-dimensional (2D) transition metal dichalcogenides (TMDCs) in electric devices, a top-gated device structure is desired. However, there has been possibility of the channel layer being damaged during the upper dielectric deposition process. Because several layers of 2D TMDCs are atomically thin, the damage may significantly degrade the overall electrical performance. In this study, we investigated the damage to molybdenum disulfide (MoS2) during the atomic layer deposition (ALD) of single dielectrics of Al2O3 and ZrO2. We observed the MoS2 layers were damaged, depending on the ALD process conditions; the kind of oxidant and the growth temperature. To reduce the damage, we formed a bi-layered Al2O3/ZrO2 dielectric structure by developing a two-step ALD process. It is notable that the electrical performance of the device was significantly improved compared to those using the single dielectrics, indicating this two-step process is a promising candidate to satisfy the requirements of future 2D TMDCs-based electronics.
关键词： 2D TMDC,high-k dielectric,Atomic layer deposition,MoS2
更新于2025-09-10 09:29:36
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Dynamic theory of nanophotonic control of two-dimensional semiconductor nonlinearities
摘要： We introduce a Maxwell-Bloch simulation approach which self-consistently combines a microscopic description of the carrier and polarization dynamics of a transition-metal-dichalcogenide (TMDC) monolayer with a spatiotemporal full-wave time-domain simulation of Maxwell’s equations on the basis of a ?nite-difference time-domain (FDTD) method beyond the slowly varying amplitude or paraxial approximations. This offers a platform to realistically model, in particular, the typical ultrafast optical excitation experiments in micro- and nanocavities. Our simulations con?rm that the weak screening of the Coulomb interaction in TMDC monolayers yields pronounced exciton lines in the linear spectrum and we uncover the second-order nonlinearity represented in the semiconductor Maxwell-Bloch equations by an intraband dipole moment. This allows us to calculate the spectral shape of the exceptionally strong second-harmonic generation around the exciton lines of TMDC monolayers. We demonstrate that the second-harmonic signal can remarkably be further enhanced by several orders of magnitude through a suitably designed (one-dimensional) photonic microcavity. Due to its self-consistency, ?exibility, explicit spatio-temporal resolution on the nanoscale and the ready access to light ?eld and electron dynamics, our theory and computational approach is an ideal platform to design and explore spatiotemporal nonlinear and quantum dynamics in complex photonic or plasmonic micro- and nanostructures for optoelectronic, nanophotonic and quantum applications of TMDC monolayers.
关键词： second-harmonic generation,nonlinear optical response,TMDC monolayer,Maxwell-Bloch simulation,photonic microcavity
更新于2025-09-09 09:28:46
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Exfoliated $$\hbox {WS}_{2}$$WS2 nanosheets: optical, photocatalytic and nitrogen-adsorption/desorption characteristics
摘要： In this work, we report on structural, optical, photocatalytic and nitrogen adsorption–desorption characteristics of WS2 nanosheets developed via a hydrothermal route. X-ray diffraction (XRD) studies have revealed a hexagonal crystal structure, whereas nanodimensional sheets are apparently observed in scanning and transmission electron microscopy (SEM and TEM) micrographs. As compared to the bulk counterpart, the WS2 nanosheets exhibited a clear blue shift. Through Brunauer–Emmett–Teller (BET) surface area analysis, average surface area, pore volume and pore size of the NSs were calculated as 211.5 m2 g?1, 0.433 cc g?1 and 3.8 nm, respectively. The photocatalytic activity of the WS2 nanosheets was also examined with malachite green (MG) as the target dye under both UV and day light (visible) illumination conditions. Accordingly, a degradation ef?ciency as high as 67.4 and 86.6% were witnessed for an irradiation time duration of 60 min. The nano-WS2 systems have immense potential in optoelectronics, solid-lubrication and other next generation elements.
关键词： sorption process,photocatalysis,TMDC,Nanosheets
更新于2025-09-04 15:30:14