scholarly journals Metallic phase transition metal dichalcogenide quantum dots showing different optical charge excitation and decay pathways

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Bo-Hyun Kim ◽  
Min-Ho Jang ◽  
Hyewon Yoon ◽  
Hyun Jun Kim ◽  
Yong-Hoon Cho ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Transition Metal ◽  
Photophysical Properties ◽  
Quantum Confinement Effect ◽  
Stokes Shift ◽  
Transition Metal Dichalcogenides ◽  
Metallic Phase ◽  
Excitation Wavelength ◽  
Transition Metal Dichalcogenide ◽  
Defect States

AbstractThe charge excitation and decay pathways of two-dimensional heteroatomic quantum dots (QDs) are affected by the quantum confinement effect, bandgap structure and strong exciton binding energy. Recently, semiconducting transition metal dichalcogenides (TMDs) have been intensively studied; however, the charge dynamics of metallic phase QDs (mQDs) of TMDs remain relatively unknown. Herein, we investigate the photophysical properties of TMD-mQDs of two sizes, where the TMD-mQDs show different charge excitation and decay pathways that are mainly ascribed to the defect states and valence band splitting, resulting in a large Stokes shift and two excitation bands for maximum photoluminescence (PL). Interestingly, the dominant excitation band redshifts as the size increases, and the time-resolved PL peak redshifts at an excitation wavelength of 266 nm in the smaller QDs. Additionally, the lifetime is shortened in the larger QDs. From the structural and theoretical analysis, we discuss that the charge decay pathway in the smaller QDs is predominantly affected by edge oxidation, whereas the vacancies play an important role in the larger QDs.

Observation of quantum-confined exciton states in monolayer WS2 quantum dots by ultrafast spectroscopy

Nanoscale ◽  
2021 ◽  
Author(s):  
Shuwen Zheng ◽  
Lei Wang ◽  
Hai-yu Wang ◽  
chenyu Xu ◽  
Yang Luo ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Transition Metal ◽  
Edge Effect ◽  
Quantum Confinement ◽  
Ultrafast Spectroscopy ◽  
Photophysical Properties ◽  
Quantum Confinement Effect ◽  
Confinement Effect ◽  
Transition Metal Dichalcogenide ◽  
Fundamental Study

Monolayer transition metal dichalcogenide quantum dots (TMDC QDs) could exhibit unique photophysical properties, because of both lateral quantum confinement effect and edge effect. However, there is little fundamental study on...

scholarly journals Second-harmonic generation enhancement in monolayer transition-metal dichalcogenides by using an epsilon-near-zero substrate

2021 ◽  
Vol 3 (1) ◽  
pp. 272-278
Author(s):  
Pilar G. Vianna ◽  
Aline dos S. Almeida ◽  
Rodrigo M. Gerosa ◽  
Dario A. Bahamon ◽  
Christiano J. S. de Matos
Keyword(s):  
Dielectric Constant ◽  
Transition Metal ◽  
Harmonic Generation ◽  
Nonlinear Effect ◽  
Second Harmonic ◽  
2D Materials ◽  
Transition Metal Dichalcogenides ◽  
Transition Metal Dichalcogenide ◽  
Metal Dichalcogenides ◽  
Epsilon Near Zero

The scheme illustrates a monolayer transition-metal dichalcogenide on an epsilon-near-zero substrate. The substrate near-zero dielectric constant is used as the enhancement mechanism to maximize the SHG nonlinear effect on monolayer 2D materials.

scholarly journals Reactive plasma cleaning and restoration of transition metal dichalcogenide monolayers

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Daniil Marinov ◽  
Jean-François de Marneffe ◽  
Quentin Smets ◽  
Goutham Arutchelvan ◽  
Kristof M. Bal ◽  
...  
Keyword(s):  
High Temperature ◽  
Transition Metal ◽  
Field Effect Transistors ◽  
Removal Rate ◽  
2D Materials ◽  
Scale Up ◽  
Transition Metal Dichalcogenides ◽  
Chemical Properties ◽  
Plasma Cleaning ◽  
Transition Metal Dichalcogenide

AbstractThe cleaning of two-dimensional (2D) materials is an essential step in the fabrication of future devices, leveraging their unique physical, optical, and chemical properties. Part of these emerging 2D materials are transition metal dichalcogenides (TMDs). So far there is limited understanding of the cleaning of “monolayer” TMD materials. In this study, we report on the use of downstream H2 plasma to clean the surface of monolayer WS2 grown by MOCVD. We demonstrate that high-temperature processing is essential, allowing to maximize the removal rate of polymers and to mitigate damage caused to the WS2 in the form of sulfur vacancies. We show that low temperature in situ carbonyl sulfide (OCS) soak is an efficient way to resulfurize the material, besides high-temperature H2S annealing. The cleaning processes and mechanisms elucidated in this work are tested on back-gated field-effect transistors, confirming that transport properties of WS2 devices can be maintained by the combination of H2 plasma cleaning and OCS restoration. The low-damage plasma cleaning based on H2 and OCS is very reproducible, fast (completed in a few minutes) and uses a 300 mm industrial plasma etch system qualified for standard semiconductor pilot production. This process is, therefore, expected to enable the industrial scale-up of 2D-based devices, co-integrated with silicon technology.

Size-dependent phase stability in transition metal dichalcogenide nanoparticles controlled by metal substrates

Nanoscale ◽  
2021 ◽  
Author(s):  
Albert Bruix ◽  
Jeppe Vang Lauritsen ◽  
Bjork Hammer
Keyword(s):  
Transition Metal ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Phase Stability ◽  
Transition Metal Dichalcogenides ◽  
Transition Metal Dichalcogenide ◽  
Metal Substrates ◽  
Size Dependent ◽  
Metal Dichalcogenides

Nanomaterials based on MoS2 and related transition metal dichalcogenides are remarkably versatile; MoS2 nanoparticles are proven catalysts for processes such as hydrodesulphurization and the hydrogen evolution reaction, and transition metal...

scholarly journals Realization of Lasing Emission from One Step Fabricated WSe2 Quantum Dots

Nanomaterials ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 538
Author(s):  
Pengpeng Ren ◽  
Wenfei Zhang ◽  
Yiqun Ni ◽  
Di Xiao ◽  
Honghao Wan ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Transition Metal Dichalcogenides ◽  
Laser Cavity ◽  
Threshold Value ◽  
Gain Medium ◽  
Excitation Wavelength ◽  
Excitation Threshold ◽  
Ultrasonic Probe ◽  
Metal Dichalcogenides ◽  
One Step

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) quantum dots (QDs) are the vanguard due to their unique properties. In this work, WSe2 QDs were fabricated via one step ultrasonic probe sonication. Excitation wavelength dependent photoluminescence (PL) is observed from WSe2 QDs. Room-temperature lasing emission which benefits from 3.7 times enhancement of PL intensity by thermal treatment at ~470 nm was achieved with an excitation threshold value of ~3.5 kW/cm2 in a Fabry–Perot laser cavity. To the best of our knowledge, this is the first demonstration of lasing emission from TMDCs QDs. This indicates that TMDCs QDs are a superior candidate as a new type of laser gain medium.

scholarly journals Exciton g-factors in monolayer and bilayer WSe2 from experiment and theory

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jonathan Förste ◽  
Nikita V. Tepliakov ◽  
Stanislav Yu. Kruchinin ◽  
Jessica Lindlau ◽  
Victor Funk ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metal Dichalcogenides ◽  
Transition Metal Dichalcogenide ◽  
Layer Transition ◽  
General Terms ◽  
Indirect Excitons ◽  
Metal Dichalcogenides ◽  
Experimental Findings ◽  
Experimental And Theoretical Studies

Abstract The optical properties of monolayer and bilayer transition metal dichalcogenide semiconductors are governed by excitons in different spin and valley configurations, providing versatile aspects for van der Waals heterostructures and devices. Here, we present experimental and theoretical studies of exciton energy splittings in external magnetic field in neutral and charged WSe2 monolayer and bilayer crystals embedded in a field effect device for active doping control. We develop theoretical methods to calculate the exciton g-factors from first principles for all possible spin-valley configurations of excitons in monolayer and bilayer WSe2 including valley-indirect excitons. Our theoretical and experimental findings shed light on some of the characteristic photoluminescence peaks observed for monolayer and bilayer WSe2. In more general terms, the theoretical aspects of our work provide additional means for the characterization of single and few-layer transition metal dichalcogenides, as well as their heterostructures, in the presence of external magnetic fields.

scholarly journals Exfoliated transition metal dichalcogenide nanosheets for supercapacitor and sodium ion battery applications

2019 ◽  
Vol 6 (8) ◽  
pp. 190437 ◽  
Author(s):  
Santanu Mukherjee ◽  
Jonathan Turnley ◽  
Elisabeth Mansfield ◽  
Jason Holm ◽  
Davi Soares ◽  
...  
Keyword(s):  
Transition Metal ◽  
Metal Ion ◽  
Coulombic Efficiency ◽  
Transition Metal Dichalcogenides ◽  
Sodium Ion ◽  
Transition Metal Dichalcogenide ◽  
Composite Electrodes ◽  
Metal Dichalcogenides ◽  
Storage Technologies ◽  
Supercapacitor Applications

Growing concerns regarding the safety, flammability and hazards posed by Li-ion systems have led to research on alternative rechargeable metal-ion electrochemical storage technologies. Among the most notable of these are Na-ion supercapacitors and batteries, motivated, in part, by the similar electrochemistry of Li and Na ions. However, sodium ion batteries (SIBs) come with their own set of issues, especially the large size of the Na + ion, its relatively sluggish kinetics and low energy densities. This makes the development of novel materials and appropriate electrode architecture of absolute significance. Transition metal dichalcogenides (TMDs) have attracted a lot of attention in this regard due to their relative ease of exfoliation, diverse morphologies and architectures with superior electronic properties. Here, we study the electrochemical performance of Mo-based two-dimensional (2D) layered TMDs (e.g. MoS 2 , MoSe 2 and MoTe 2 ), exfoliated in a superacid, for battery and supercapacitor applications. The exfoliated TMD flakes were interfaced with reduced graphene oxide (rGO) to be used as composite electrodes. Electron microscopy, elemental mapping and Raman spectra were used to analyse the exfoliated material and confirm the formation of 2D TMD/rGO layer morphology. For supercapacitor applications in aqueous electrolyte, the sulfide-based TMD (MoS 2 ) exhibited the best performance, providing an areal capacitance of 60.25 mF cm −2 . For SIB applications, TMD electrodes exhibited significantly higher charge capacities than the neat rGO electrode. The initial desodiation capacities for the composite electrodes are 468.84 mAh g −1 (1687.82 C g −1 ), 399.10 mAh g −1 (1436.76 C g −1 ) and 387.36 mAh g −1 (1394.49 C g −1 ) for MoS 2 , MoSe 2 and MoTe 2 , respectively. Also, the MoS 2 and MoSe 2 composite electrodes provided a coulombic efficiency of near 100 % after a few initial cycles.

scholarly journals Transition Metal Dichalcogenides as Strategy for High Temperature Electron-Hole Superfluidity

2020 ◽  
Vol 5 (1) ◽  
pp. 22
Author(s):  
Sara Conti ◽  
David Neilson ◽  
François M. Peeters ◽  
Andrea Perali
Keyword(s):  
Transition Metal ◽  
Double Layer ◽  
Transition Metal Dichalcogenides ◽  
Mean Field ◽  
Transition Metal Dichalcogenide ◽  
Transition Temperatures ◽  
Electron Hole ◽  
Interesting Phenomenon ◽  
Wide Range ◽  
High Transition

Condensation of spatially indirect excitons, with the electrons and holes confined in two separate layers, has recently been observed in two different double layer heterostructures. High transition temperatures were reported in a double Transition Metal Dichalcogenide (TMD) monolayer system. We briefly review electron-hole double layer systems that have been proposed as candidates for this interesting phenomenon. We investigate the double TMD system WSe 2 /hBN/MoSe 2 , using a mean-field approach that includes multiband effects due to the spin-orbit coupling and self-consistent screening of the electron-hole Coulomb interaction. We demonstrate that the transition temperature observed in the double TMD monolayers, which is remarkably high relative to the other systems, is the result of (i) the large electron and hole effective masses in TMDs, (ii) the large TMD band gaps, and (iii) the presence of multiple superfluid condensates in the TMD system. The net effect is that the superfluidity is strong across a wide range of densities, which leads to high transition temperatures that extend as high as T B K T = 150 K.

scholarly journals Squeezed metallic droplet with tunable Kubo gap and charge injection in transition metal dichalcogenides

2020 ◽  
Vol 117 (12) ◽  
pp. 6362-6369 ◽  
Author(s):  
Jiaren Yuan ◽  
Yuanping Chen ◽  
Yuee Xie ◽  
Xiaoyu Zhang ◽  
Dewei Rao ◽  
...  
Keyword(s):  
Transition Metal ◽  
Electron Tunneling ◽  
Energy Levels ◽  
Photon Emission ◽  
Transition Metal Dichalcogenides ◽  
Three Dimensional ◽  
Electronic Energy ◽  
Transition Metal Dichalcogenide ◽  
Metallic Droplet ◽  
Electronic Energy Levels

Shrinking the size of a bulk metal into nanoscale leads to the discreteness of electronic energy levels, the so-called Kubo gap δ. Renormalization of the electronic properties with a tunable and size-dependent δ renders fascinating photon emission and electron tunneling. In contrast with usual three-dimensional (3D) metal clusters, here we demonstrate that Kubo gap δ can be achieved with a two-dimensional (2D) metallic transition metal dichalcogenide (i.e., 1T′-phase MoTe2) nanocluster embedded in a semiconducting polymorph (i.e., 1H-phase MoTe2). Such a 1T′/1H MoTe2nanodomain resembles a 3D metallic droplet squeezed in a 2D space which shows a strong polarization catastrophe while simultaneously maintaining its bond integrity, which is absent in traditional δ-gapped 3D clusters. The weak screening of the host 2D MoTe2leads to photon emission of such pseudometallic systems and a ballistic injection of carriers in the 1T′/1H/1T′ homojunctions which may find applications in sensors and 2D reconfigurable devices.

Sign in / Sign up

Export Citation Format

Share Document