The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Hanan Dery - One of the best experts on this subject based on the ideXlab platform.
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Exciton valley depolarization in monolayer Transition-Metal Dichalcogenides
Physical Review B, 2020Co-Authors: Min Yang, Dinh Van Tuan, Cédric Robert, Dmitry Smirnov, Xavier Marie, Hanan DeryAbstract:The valley degree of freedom is a sought-after quantum number in monolayer Transition-Metal Dichalcogenides. Similar to optical spin orientation in semiconductors, the helicity of absorbed photons can be relayed to the valley (pseudospin) quantum number of photoexcited electrons and holes. Also similar to the quantum-mechanical spin, the valley quantum number is not a conserved quantity. Valley depolarization of excitons in monolayer Transition-Metal Dichalcogenides due to long-range electron-hole exchange typically takes a few ps at low temperatures. Exceptions to this behavior are monolayers ${\mathrm{MoSe}}_{2}$ and ${\mathrm{MoTe}}_{2}$ wherein the depolarization is much faster. We elucidate the enigmatic anomaly of these materials, finding that it originates from Rashba-induced coupling of the dark and bright exciton branches next to their degeneracy point. When photoexcited excitons scatter during their energy relaxation between states next to the degeneracy region, they reach the light cone after losing the initial helicity. The valley depolarization is not as fast in monolayers ${\mathrm{WSe}}_{2}$, ${\mathrm{WS}}_{2}$, and ${\mathrm{MoS}}_{2}$, wherein the degeneracy is absent resulting in negligible Rashba-induced coupling between bright and dark excitons.
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Exciton valley depolarization in monolayer Transition-Metal Dichalcogenides
Physical Review B, 2020Co-Authors: Min Yang, Dinh Van Tuan, Cédric Robert, Dmitry Smirnov, Xavier Marie, Hanan DeryAbstract:The valley degree of freedom is a sought-after quantum number in monolayer Transition-Metal Dichalcogenides. Similar to optical spin orientation in semiconductors, the helicity of absorbed photons can be relayed to the valley (pseudospin) quantum number of photoexcited electrons and holes. Also similar to the quantum-mechanical spin, the valley quantum number is not a conserved quantity. Valley depolarization of excitons in monolayer Transition-Metal Dichalcogenides due to long-range electron-hole exchange typically takes a few ps at low temperatures. Exceptions to this behavior are monolayers MoSe2 and MoTe2 wherein the depolarization is much faster. We elucidate the enigmatic anomaly of these materials, finding that it originates from Rashba-induced coupling of the dark and bright exciton branches next to their degeneracy point. When photoexcited excitons scatter during their energy relaxation between states next to the degeneracy region, they reach the light cone after losing the initial helicity. The valley depolarization is not as fast in monolayers WSe2, WS2 and likely MoS2 wherein the Rashba-induced coupling is negligible.
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Coulomb interaction in monolayer Transition-Metal Dichalcogenides
Physical Review B, 2018Co-Authors: Dinh Van Tuan, Min Yang, Hanan DeryAbstract:Recently, the celebrated Rytova-Keldysh potential has been widely used to describe the Coulomb interaction of few-body complexes in monolayer Transition-Metal Dichalcogenides. Using this potential to model charged excitons (trions), one finds a strong dependence of the binding energy on whether the monolayer is suspended in air, supported on ${\mathrm{SiO}}_{2}$, or encapsulated in hexagonal boron-nitride. However, empirical values of the trion binding energies show weak dependence on the monolayer configuration. This deficiency indicates that the description of the Coulomb potential is still lacking in this important class of materials. We address this problem and derive a new potential form, which takes into account the three atomic sheets that compose a monolayer of Transition-Metal Dichalcogenides. The new potential self-consistently supports (i) the nonhydrogenic Rydberg series of neutral excitons and (ii) the weak dependence of the trion binding energy on the environment. Furthermore, we identify an important trion-lattice coupling due to the phonon cloud in the vicinity of charged complexes. Neutral excitons in their ground state, on the other hand, have weaker coupling to the lattice due to the confluence of their charge neutrality and small Bohr radius.
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polarization analysis of excitons in monolayer and bilayer Transition Metal Dichalcogenides
Physical Review B, 2015Co-Authors: Hanan Dery, Yang SongAbstract:The authors theoretically study optical Transitions in Transition-Metal Dichalcogenides. In particular, they explain the difference between the excitonic properties of monolayer MoSe${}_{2}$ and WSe${}_{2}$. Excitons in WSe${}_{2}$ are thought to be bound to impurities. An alternative theory presented in this paper suggests that these excitons correspond to low-energy optical Transitions. The authors also put forward an alternative explanation as to why the excitons in MoSe${}_{2}$ have vanishing polarization. They attribute this phenomenon to polaron-induced Rabi oscillations between dark and bright excitons.
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transport theory of monolayer Transition Metal Dichalcogenides through symmetry
Physical Review Letters, 2013Co-Authors: Yang Song, Hanan DeryAbstract:We present a theory that elucidates the major momentum and spin relaxation processes for electrons, holes, and hot excitons in monolayer Transition-Metal Dichalcogenides. We expand on spin flips induced by flexural phonons and show that the spin relaxation is ultrafast for electrons in free-standing membranes while being mitigated in supported membranes. This behavior due to interaction with flexural phonons is universal in two-dimensional membranes that respect mirror symmetry, and it leads to a counterintuitive inverse relation between mobility and spin relaxation.
Young Hee Lee - One of the best experts on this subject based on the ideXlab platform.
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van der Waals Metallic Transition Metal Dichalcogenides
Chemical reviews, 2018Co-Authors: Gang Hee Han, Dinh Loc Duong, Dong Hoon Keum, Seok Joon Yun, Young Hee LeeAbstract:Transition Metal Dichalcogenides are layered materials which are composed of Transition Metals and chalcogens of the group VIA in a 1:2 ratio. These layered materials have been extensively investigated over synthesis and optical and electrical properties for several decades. It can be insulators, semiconductors, or Metals revealing all types of condensed matter properties from a magnetic lattice distorted to superconducting characteristics. Some of these also feature the topological manner. Instead of covering the semiconducting properties of Transition Metal Dichalcogenides, which have been extensively revisited and reviewed elsewhere, here we present the structures of Metallic Transition Metal Dichalcogenides and their synthetic approaches for not only high-quality wafer-scale samples using conventional methods (e.g., chemical vapor transport, chemical vapor deposition) but also local small areas by a modification of the materials using Li intercalation, electron beam irradiation, light illumination, pr...
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Recent development of two-dimensional Transition Metal Dichalcogenides and their applications
Materials Today, 2017Co-Authors: Wonbong Choi, Gang Hee Han, Juhong Park, Nitin Choudhary, Deji Akinwande, Young Hee LeeAbstract:Recent advances in atomically thin two-dimensional Transition Metal Dichalcogenides (2D TMDs) have led to a variety of promising technologies for nanoelectronics, photonics, sensing, energy storage, and opto-electronics, to name a few. This article reviews the recent progress in 2D materials beyond graphene and includes mainly Transition Metal Dichalcogenides (TMDs) (e.g. MoS 2 , WS 2 , MoSe 2 , and WSe 2 ). These materials are finding niche applications for next-generation electronics and optoelectronics devices relying on ultimate atomic thicknesses. Albeit several challenges in developing scalable and defect-free TMDs on desired substrates, new growth techniques compatible with traditional and unconventional substrates have been developed to meet the ever-increasing demand of high quality and controllability for practical applications. The fabrication of novel 2D TMDs that exhibit exotic functionalities and fundamentally new chemistry is highlighted. And finally, in parallel with the electronics, the considerable effort devoted to using these materials for energy and sensing applications is discussed in detail.
Martin Pumera - One of the best experts on this subject based on the ideXlab platform.
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Universal Method for Large-Scale Synthesis of Layered Transition Metal Dichalcogenides.
Chemistry (Weinheim an der Bergstrasse Germany), 2017Co-Authors: Zdeněk Sofer, David Sedmidubský, Jan Luxa, Daniel Bouša, Štěpán Huber, Petr Lazar, Martin Veselý, Martin PumeraAbstract:The layered Transition Metal Dichalcogenides are currently amongst the most intensively investigated materials. These compounds constitute a broad family of materials, with characteristic layered structures, covering both semiconductors and Metallic materials. The great attention arises from the possibility to exfoliate these materials down to single layers with many unique properties, such as thickness dependent band-gap energy, and the possibility of tuning transport properties by phase Transitions. The research in the field of Transition Metal Dichalcogenides is also motivated by their high electrocatalytic activity towards several industrially important reactions, such as the hydrogen evolution reaction, as well as many other applications in nano- and optoelectronics. Although these materials are studied intensively, their availability is extremely limited and only disulfides of molybdenum and tungsten are broadly commercially available. Here an optimized procedure for simple direct synthesis of Transition Metal Dichalcogenides using powder Metals and elemental chalcogens is reported. The optimized thermal treatment allowed the synthesis scaling of the sulfides, selenides and tellurides of 4th, 5th, 6th, and 7th group of layered-structure Dichalcogenides. The synthesized Transition Metal Dichalcogenides were single phase. The phase purity, structure, and morphology were investigated in detail by electron microscopy and EDS, X-ray diffraction, and Raman spectroscopy.
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two dimensional Transition Metal Dichalcogenides in biosystems
Advanced Functional Materials, 2015Co-Authors: Kourosh Kalantarzadeh, Martin Pumera, Torben Daeneke, Michael S Strano, Sally L GrasAbstract:The intriguing properties of two-dimensional Transition Metal Dichalcogenides (2D TMDCs) have led to a significant body of fundamental research and rapid uptake of these materials in many applications. Specifically, 2D TMDCs have shown great potential in biological systems due to their tunable electronic characteristics, unique optical properties, stability in aqueous environments, large surface area that can be manipulated and functionalized as well as an intercalatable layered structure, and low levels of toxicity. Here, the characteristics and use of 2D TMDCs for biological applications are reviewed and future possibilities for these materials in biological systems are outlined.
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Exfoliated Transition Metal Dichalcogenides (MoS2, MoSe2, WS2, WSe2): An electrochemical impedance spectroscopic investigation
Electrochemistry Communications, 2015Co-Authors: Adeline Huiling Loo, Alessandra Bonanni, Zdenek Sofer, Martin PumeraAbstract:Abstract Owing to the enthralling properties which Transition Metal Dichalcogenides present, they are facing immense scientific interest from researchers. Till date, these two-dimensional materials have been assessed for a wide array of different applications and there are various synthetic methods of attaining them in their respective bulk and exfoliated forms. Herein, we explore the effects of lithium ion intercalation exfoliation process on the charge transfer resistance of Transition Metal dichalcogenide materials (MoS 2 , MoSe 2 , WS 2 and WSe 2 ). We also show that electrochemical activation of the Transition Metal Dichalcogenides results in decreased resistance towards charge transfer, as demonstrated by electrochemical impedance spectroscopy.
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layered Transition Metal Dichalcogenides mos2 and ws2 for sensing and biosensing
Trends in Analytical Chemistry, 2014Co-Authors: Martin Pumera, Adeline Huiling LooAbstract:Abstract Layered Transition-Metal Dichalcogenides comprise a category of two-dimensional materials that offer exciting properties, including Metallic and semi-conducting electrical capabilities, fluorescence and fast heterogeneous electron transfer. To date, these materials have mostly been employed in energy-storage and generation devices. However, in very recent times, there was a significant emerging trend in their utilization in analytical chemistry. Hence, this review aims to provide an introduction to this new trend for the analytical community.
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layered Transition Metal Dichalcogenides for electrochemical energy generation and storage
Journal of Materials Chemistry, 2014Co-Authors: Martin Pumera, Zdeněk Sofer, Adriano AmbrosiAbstract:Layered Transition Metal Dichalcogenides (TMDs) (MoS2, MoSe2, WS2, WSe2, etc.) are a chemically diverse class of compounds having band gaps from 0 to ∼2 eV and remarkable electrochemical properties. The band gaps and electrochemical properties of TMDs can be tuned by exchanging the Transition Metal or chalcogenide elements. After a brief description of the most commonly followed synthetic routes to prepare TMDs, we wish to highlight in this review the diverse electrochemical applications of MoS2, a representative and well-studied TMD, which range from its use as catalysts in hydrogen evolution reactions to its adoption in supercapacitors, batteries, solar cells, and hydrogen storage.
Gang Hee Han - One of the best experts on this subject based on the ideXlab platform.
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van der Waals Metallic Transition Metal Dichalcogenides
Chemical reviews, 2018Co-Authors: Gang Hee Han, Dinh Loc Duong, Dong Hoon Keum, Seok Joon Yun, Young Hee LeeAbstract:Transition Metal Dichalcogenides are layered materials which are composed of Transition Metals and chalcogens of the group VIA in a 1:2 ratio. These layered materials have been extensively investigated over synthesis and optical and electrical properties for several decades. It can be insulators, semiconductors, or Metals revealing all types of condensed matter properties from a magnetic lattice distorted to superconducting characteristics. Some of these also feature the topological manner. Instead of covering the semiconducting properties of Transition Metal Dichalcogenides, which have been extensively revisited and reviewed elsewhere, here we present the structures of Metallic Transition Metal Dichalcogenides and their synthetic approaches for not only high-quality wafer-scale samples using conventional methods (e.g., chemical vapor transport, chemical vapor deposition) but also local small areas by a modification of the materials using Li intercalation, electron beam irradiation, light illumination, pr...
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Recent development of two-dimensional Transition Metal Dichalcogenides and their applications
Materials Today, 2017Co-Authors: Wonbong Choi, Gang Hee Han, Juhong Park, Nitin Choudhary, Deji Akinwande, Young Hee LeeAbstract:Recent advances in atomically thin two-dimensional Transition Metal Dichalcogenides (2D TMDs) have led to a variety of promising technologies for nanoelectronics, photonics, sensing, energy storage, and opto-electronics, to name a few. This article reviews the recent progress in 2D materials beyond graphene and includes mainly Transition Metal Dichalcogenides (TMDs) (e.g. MoS 2 , WS 2 , MoSe 2 , and WSe 2 ). These materials are finding niche applications for next-generation electronics and optoelectronics devices relying on ultimate atomic thicknesses. Albeit several challenges in developing scalable and defect-free TMDs on desired substrates, new growth techniques compatible with traditional and unconventional substrates have been developed to meet the ever-increasing demand of high quality and controllability for practical applications. The fabrication of novel 2D TMDs that exhibit exotic functionalities and fundamentally new chemistry is highlighted. And finally, in parallel with the electronics, the considerable effort devoted to using these materials for energy and sensing applications is discussed in detail.
Praveen Mishra - One of the best experts on this subject based on the ideXlab platform.
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Interaction of Fluorescent Gold Nanoclusters with Transition Metal Dichalcogenides Nanosheets: A Spectroscopic Study
Journal of Luminescence, 2020Co-Authors: Arun Singh Patel, Anirban Chakraborti, Praveen MishraAbstract:Abstract In this paper, the interaction of few tens of atoms containing gold nanoclusters with two dimensional nanosheets of Transition Metal Dichalcogenides nanosheets has been explored. The gold nanoclusters have been synthesized using chemical reduction method in presence of protein molecules as stabilizing agent. The Transition Metal Dichalcogenides nanosheets of molybdenum disulfide (MoS 2 ) has been chemically exfoliated. Different microscopic and optical spectroscopic tools have been used for characterizing the physical properties of the gold nanoclusters and the two dimensional nanosheets of MoS 2 . The gold nanoclusters exhibit fluorescence emission at 690 nm. However, the interaction with Transition Metal Dichalcogenides diminishes drastically the fluorescence intensity of the nanoclusters. The time resolved fluorescence study shows that the fluorescence lifetime of fluorescent materials can be altered in presence of MoS 2 nanosheets, and the energy transfer phenomena can be observed.