Defect-Enhanced Exciton–Exciton Annihilation in Monolayer Transition Metal Dichalcogenides at High Exciton Densities
About: This article is published in ACS Photonics.The article was published on 2021-09-15. It has received 18 citations till now. The article focuses on the topics: Exciton & Monolayer.
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TL;DR: In this article, the existence of efficient exciton-exciton annihilation, a four-body interaction, in monolayer MoS2 was identified experimentally in ultrafast transient absorption measurements through the emergence of a decay channel varying quadratically with exciton density.
Abstract: Monolayer MoS2 is a direct-gap two-dimensional semiconductor that exhibits strong electron-hole interactions, leading to the formation of stable excitons and trions. Here we report the existence of efficient exciton-exciton annihilation, a four-body interaction, in this material. Exciton-exciton annihilation was identified experimentally in ultrafast transient absorption measurements through the emergence of a decay channel varying quadratically with exciton density. The rate of exciton-exciton annihilation was determined to be (4.3 ± 1.1) × 10(-2) cm(2)/s at room temperature.
292 citations
TL;DR: In this study, optical nonlinear activators for ONNs are prepared by combining Ti3C2Tx MXene with microfibers and their principles are verified and Activation functions obtained from experimental measurements are used to simulate multiclassification and super‐resolution reconstruction tasks with performance comparable to that of activation functions commonly used in computers.
Abstract: Optical neural networks (ONNs) are particularly advantageous owing to their inherent parallelism and low energy consumption. However, one of the obstacles to the implementation of ONNs is the lack of optical nonlinearity. In this study, optical nonlinear activators for ONNs are prepared by combining Ti3C2Tx MXene with microfibers and their principles are verified. Activation functions obtained from experimental measurements are used to simulate multiclassification and super‐resolution reconstruction tasks with performance comparable to that of activation functions commonly used in computers. Four necessary criteria are proposed and validated for evaluating the performance of the nonlinear activator: recovery time, deviation from linearity, the activation function close to identity mapping, and reconfigurability of the configuration. Theoretically, the nonlinear activator can compute 100 times faster than commonly used electronic computers and can be used as a nonlinear activation unit for ONNs to help the integration of ONNs with artificial intelligence.
8 citations
01 Jan 2022-Journal of Materials Chemistry C. Materials for Optical, Magnetic and Electronic Devices
TL;DR: The PL emission and carrier relaxation of CuInP 2 S 6 vary greatly with temperature under phase transition, while the two-photon absorption changes slightly with temperature as discussed by the authors , and the PL emission was shown to be stable with temperature.
Abstract: The PL emission and carrier relaxation of CuInP 2 S 6 vary greatly with temperature under phase transition, while the two-photon absorption changes slightly with temperature.
7 citations
TL;DR: In this paper , the excited-state dynamics of few-layer molybdenum disulfide (FL-MoS2) are studied in conditions of strong light-matter coupling to plasmon polaritons.
Abstract: The excited-state dynamics of few-layer molybdenum disulfide (FL-MoS2) are studied in conditions of strong light–matter coupling to plasmon polaritons. Hot carrier extraction in these systems has been proposed due to the observation of slow cooling of the high-energy C exciton relative to the bandgap A exciton. Here, we show that in conditions of ultrastrong coupling to plasmon polaritons, the lifetimes of the two slowest C exciton decay processes are extended by factors of 1.5 and 5.8 in FL-MoS2. We hypothesize that strong coupling delocalization suppresses multiple decay mechanisms throughout the visible spectrum in MoS2 such as defect scattering, intervalley scattering of band-nested excitations to the Κ-valley band edges, and exciton–exciton annihilation. We also find that decay from the upper to the lower hybrid mode is not ultrafast as seen in organic systems but in fact introduces an additional delay of ∼20 ps. Our observations show that strong coupling can be used to extend the lifetimes of hot excitons in FL-MoS2 and potentially in other two-dimensional transition-metal dichalcogenides, with potential for above-bandgap photophysics and photochemistry applications such as hot carrier extraction, which could lead to more efficient solar energy conversion.
5 citations
TL;DR: In this article , a comprehensive study of the charge carrier dynamics of a monolayer MoS2 flake has been studied using transient transmission technique near A-exciton under high excitation densities well above the Mott density.
Abstract: Due to the growing interest in monolayer (ML) molybdenum disulfide (MoS2) in several optoelectronic applications like lasers, detectors, sensors, it is important to understand the ultrafast behavior of the excited carriers in this material. In this article, a comprehensive study of the charge carrier dynamics of a monolayer MoS2 flake has been studied using transient transmission technique near A-exciton under high excitation densities well above the Mott density. Fluence dependent studies has been carried out to understand the origin of the processes which modifies its optical response under excitation. The dissociation of excitons leads to an observed fast bandgap renormalization. At later times when large number of carriers relax the remaining carriers forms excitons leading to a bleaching effect.
5 citations
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TL;DR: Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors, and could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.
Abstract: Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.
12,477 citations
TL;DR: This observation shows that quantum confinement in layered d-electron materials like MoS(2), a prototypical metal dichalcogenide, provides new opportunities for engineering the electronic structure of matter at the nanoscale.
Abstract: Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.
7,886 citations
TL;DR: Ultraensitive monolayer MoS2 phototransistors with improved device mobility and ON current are demonstrated, showing important potential for applications in MoS 2-based integrated optoelectronic circuits, light sensing, biomedical imaging, video recording and spectroscopy.
Abstract: A very sensitive photodector based on molybdenum disulphide with potential for integrated optoelectronic circuits, light sensing, biomedical imaging, video recording or spectroscopy is now demonstrated.
4,212 citations
TL;DR: In this paper, it was shown that only the Raman frequencies of E 1 and A 1g peaks vary monotonously with the layer number of ultrathin Molybdenum disulfi de (MoS 2 ).
Abstract: Molybdenum disulfi de (MoS 2 ) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of E 1 and A1g peaks vary monotonously with the layer number of ultrathin MoS 2 fl akes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS 2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS 2 . The asymmetric Raman peak at 454 cm − 1 , which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS 2 , is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ( A2u ). Our fi ndings suggest a clear evolution of the coupling between electronic transition and phonon when MoS 2 is scaled down from three- to two-dimensional geometry.
3,375 citations
TL;DR: In this paper, the electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties are reviewed.
Abstract: The electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties are reviewed. Recent advances in the development of atomically thin layers of van der Waals bonded solids have opened up new possibilities for the exploration of 2D physics as well as for materials for applications. Among them, semiconductor transition metal dichalcogenides, MX2 (M = Mo, W; X = S, Se), have bandgaps in the near-infrared to the visible region, in contrast to the zero bandgap of graphene. In the monolayer limit, these materials have been shown to possess direct bandgaps, a property well suited for photonics and optoelectronics applications. Here, we review the electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties.
2,612 citations