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Polarized THz Emission from In-Plane Dipoles in Monolayer Tungsten Disulfide by Linear and Circular Optical Rectification
摘要： Recent advances in the development of polarized terahertz (THz) emission from nanomaterials have not only opened up a new “TeraNano” interdiscipline but also provided a new tool for nonlinear optical process research. Herein, THz radiation mechanism of monolayer tungsten disulfide (WS2) is first investigated by both linear and circular polarization laser excitations at room temperature. The results reveal that polarized THz emission is dominated by the optical rectification based on in-plane nonlinear dipoles, which is totally different from that of bulk WS2. The mechanism is verified by the azimuthal angle and pump polarization angle dependence of THz emission in both experiment and theory. Furthermore, controllably elliptically polarized THz emission is observed with the maximum ellipticity of ≈0.52 based on nonresonant nonlinear process under the circularly polarized excitation. A clear understanding of THz radiation mechanism of 2D materials will facilitate further design, optimization, and polarization control of integrable 2D THz optoelectronics.
关键词： THz radiation,monolayer WS2,in-plane nonlinear dipoles,optical rectification,elliptically polarized THz emission
更新于2025-09-23 15:23:52
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Screening Effect of Ultrathin Gold Films on Excitons in Monolayer WS2
摘要： Screening plays an important role in determining the energy levels and binding energies of excitons in two-dimensional (2D) semiconductors. However, the photoelectric properties of 2D materials deposited upon metal films are often assumed to remain unaffected by the screening effect. Herein, we derive the reflectance contrast spectra of monolayer WS2 on different thicknesses of ultrathin gold films by using the transfer matrix method, and investigate the screening effect of ultrathin gold films on excitons in monolayer WS2. We show that the exciton binding energy of the ground state gradually decreases as the gold film thickness increases due to the enhanced screening effect. Nevertheless, it may be due to the impact of free-electron scattering on the permittivities of gold films: exciton resonance energies of the ground state and the first excited state gradually increase as the gold film thickness increases, which are different from previously reported variation trend of exciton energy levels with the thickness of screening media of 2D materials. As a consequence, the electronic bandgap of the exciton only presents a small variation range of less than 4 meV with thickening of the gold film from 0.0 to 40 nm. These findings shed light on understanding to what extent the screening effect of gold films affects the excitons in 2D materials.
关键词： Ultrathin gold film,Transfer matrix method,Excitonic properties,Monolayer WS2,Dielectric screening effect
更新于2025-09-23 15:22:29
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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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Atypical Defect-Mediated Photoluminescence and Resonance Raman Spectroscopy of Monolayer WS2
摘要： Defects play an indispensable role in tuning the optical properties of two-dimensional(2D) materials. Herein, we study the influence of defects on the photoluminescence (PL) and resonance Raman spectra of as-grown monolayer(1L) WS2. Increasing the density of defects significantly lowers the excitonic binding energy by up to 110 meV. These defect-modified excitonic binding energies in1L-WS2 strongly mediate the Raman resonance condition, resulting in unexpected Raman intensity variations in the LA(M), 2LA(M) and phonon modes. The sample with the highest density of defects exhibits an almost temperature independent resonance in different Raman modes at low temperature, while the samples with low densities of defects exhibit clear resonance with decreasing temperature. This study will further increase our understanding of the role of defects in resonance Raman spectroscopy and of the phonon-exciton interaction in 1L-WS2.
关键词： photoluminescence,defects,excitonic binding energy,resonance Raman spectroscopy,monolayer WS2
更新于2025-09-19 17:15:36
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Controlled Synthesis of Large Scale Continuous monolayer WS2 Film by Atmospheric Pressure Chemical Vapor Deposition
摘要： Synthesis of monolayer transition metal dichalcogenides (TMDs) in large-size is crucial to their practical applications in electronics and optoelectronics. Here, large scale continuous monolayer WS2 film has been successfully grown by atmospheric pressure chemical vapor deposition (APCVD) method. By modulating three growth parameters, Ar gas flow rate, the temperature of WO3 precursor and the distance between substrate and WO3 precursor, WS2 film with different grain size can be obtained. At optimal processing condition, large-scale monolayer WS2 with lateral dimension can reach 1 millimeter above. This would pave the way for scale production of continuous monolayer TMDs film.
关键词： large scale,monolayer WS2,atmospheric pressure chemical vapor deposition,continuous film
更新于2025-09-16 10:30:52
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CVD controlled growth of large-scale WS <sub/>2</sub> monolayers
摘要： Monolayer tungsten disulfide (WS2) with a direct band gap of ca. 2.0 eV and stable properties has been a hotspot in two-dimensional (2D) nanoelectronics and optoelectronics. However, it remains challenging to successfully prepare monolayer WS2. In this paper, we report the chemical vapor deposition (CVD) growth behavior of hexagonal WS2 monolayers by using WS2 powders and sodium triosulfate (Na2S2O3) as precursors. We observed the Na2S2O3 has a significant effect on the WS2 triangular and leaf-like shapes. In addition, based on proposed S-termination and W-termination theory, the growth mechanisms for different shapes of WS2 were discussed.
关键词： monolayer,WS2,CVD,growth mechanism,Na2S2O3
更新于2025-09-16 10:30:52
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Enhancing Nonradiative Energy Transfer between Nitridized Carbon Quantum Dots and Monolayer WS2
摘要： Two-dimensional (2D) monolayer (1L) transition metal dichalcogenides (TMDs) suffer from a low absorption in the visible light region. Nonradiative energy transfer (NRET) is an effective method to enhance such absorption, which, as shown in this study, can be accomplished by using surface nitridized carbon quantum dots (CQDs). The optical absorption and photoluminescence (PL) of CQDs in the visible light region can be greatly enhanced by increasing the level of nitridization. The nitridized CQDs exhibit weak p-type doping but strong PL quenching in contact with vapor transport (VT)-deposited 1L-WS2. Owing to the good overlap between the fluorescence and absorption spectra for CQDs and 1L-WS2, an interactive NRET process reduces the PL lifetimes of both CQDs and 1L-WS2. The NRET efficiency can be greatly enhanced by up to 73% for samples coated with CQDs of increasing surface nitridization.
关键词： Nonradiative energy transfer,Nitridized carbon quantum dots,Optical absorption,Monolayer WS2,Photoluminescence
更新于2025-09-11 14:15:04