1,721,059 research outputs found
Hot electron effects and electric field scaling near the metal-insulator transition in multilayer MoS2
Full text linkThe layered transition metal dichalcogenides have emerged as valuable platforms to study the challenging problem of metal-insulator transition in two dimensions. It was demonstrated that multilayer MoS2 exhibits clearly distinctive metallic and insulating behaviors in conductivity in response to both temperature and the electric field. Here, we report on the scaling analyses of conductivity for the electric field in addition to the temperature, which is performed with the consideration of electron-electron interactions for multilayer MoS2. Based on the analysis of hot electron effects in the electric field, we find that scaling for the electric field is relevant for the metallic phase in the high-field regime, enabling one to extract the dynamical critical exponent z close to 1. This result supports that the metal-insulator transition in multilayer MoS2 is a true quantum critical phenomenon, in which strong interactions induce the transition. ©2020 American Physical Society11sciescopu
Load-Dependent Friction Hysteresis on Graphene
No full textNanoscale friction often exhibits hysteresis when load is increased (loading) and then decreased (unloading) and is manifested as larger friction measured during unloading compared to loading for a given load. In this work, the origins of load-dependent friction hysteresis were explored through atomic force microscopy (AFM) experiments of a silicon tip sliding on chemical vapor deposited graphene in air, and molecular dynamics simulations of a model AFM tip on graphene, mimicking both vacuum and humid air environmental conditions. It was found that only simulations with water at the tip graphene contact reproduced the experimentally observed hysteresis. The mechanisms underlying this friction hysteresis were then investigated in the simulations by varying the graphene water interaction strength. The size of the water graphene interface exhibited hysteresis trends consistent with the friction, while measures of other previously proposed mechanisms, such as out-of-plane deformation of the graphene film and irreversible reorganization of the water molecules at the shearing interface, were less correlated to the friction hysteresis. The relationship between the size of the sliding interface and friction observed in the simulations was explained in terms of the varying contact angles in front of and behind the sliding tip, which were larger during loading than unloading. © 2016 American Chemical Society11sciescopu
van der Waals Metallic Transition Metal Dichalcogenides
No full textTransition 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, pressures, and strains. Some representative band structures of metallic transition metal dichalcogenides and their strong layer-dependence are reviewed and updated, both in theoretical calculations and experiments. In addition, we discuss the physical properties of metallic transition metal dichalcogenides such as periodic lattice distortion, magnetoresistance, superconductivity, topological insulator, and Weyl semimetal. Approaches to overcome current challenges related to these materials are also propose
Recent Development of Two-Dimensional Transition Metal Dichalcogenides and Their Applications
Full text linkThis article reviews the recent progress in 2D materials beyond graphene and includes mainly transition metal dichalcogenides
Efficient Exciton-Plasmon Conversion in Ag Nanowire/Monolayer MoS2 Hybrids: Direct Imaging and Quantitative Estimation of Plasmon Coupling and Propagation
No full text[No abstract available123261sciescopu
Influence of residual promoter to photoluminescence of CVD grown MoS2
No full textMonolayer MoS2 has attracted extensive attention owing to its promising applications in optoelectronic devices. Recently, uniform and highly crystalline monolayer MoS2 was grown through chemical vapor deposition (CVD) using seed materials as a growth promoter. However, residual seed materials can remain on the surface of a monolayer MoS2 flake on a SiO2/Si substrate after growth. Here, we observe drastically increased photoluminescence (PL) intensity at the edge of MoS2 flake where residual particles are attached after repeated laser irradiation. On the other hand, the PL intensity of pure MoS2 remained almost the same. We attribute this to the effect of p-doping of the edge MoS2 by the adsorbed H2O and O2 molecules in the residual particles. The p-doping effect of MoS2 is confirmed by the confocal PL and Raman spectroscopy analysis. © 2016 Elsevier B.V111sciescopuskc
Two-dimensional membrane as elastic shell with proof on the folds revealed by three-dimensional atomic mapping
Full text linkThe great application potential for two-dimensional (2D) membranes (MoS 2, WSe 2, graphene and so on) aroused much effort to understand their fundamental mechanical properties. The out-of-plane bending rigidity is the key factor that controls the membrane morphology under external fields. Herein we provide an easy method to reconstruct the 3D structures of the folded edges of these 2D membranes on the atomic scale, using high-resolution (S)TEM images. After quantitative comparison with continuum mechanics shell model, it is verified that the bending behaviour of the studied 2D materials can be well explained by the linear elastic shell model. And the bending rigidities can thus be derived by fitting with our experimental results. Recall almost only theoretical approaches can access the bending properties of these 2D membranes before, now a new experimental method to measure the bending rigidity of such flexible and atomic thick 2D membranes is proposed. © 2015 Macmillan Publishers Limited. All rights reserved8911sciescopu
Vertically Conductive MoS2 Spiral Pyramid
No full textMoS2 spirals grown by the chemical vapor deposition method, driven by a threading dislocation, has a peculiar rhombohedral-like structure. This threading dislocation can carry helical current in the vertical direction and greatly enhances the vertical conductance in the MoS2 multilayer samples.
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim112131sciescopu
Characterization of the structural defects in CVD-grown monolayered MoS2 using near-field photoluminescence imaging
No full textStructural defects can critically influence the electrical and optical properties of monolayered molybdenum disulfide (MoS2) grown by chemical vapor deposition (CVD); thus, convenient optical methods that can visualize grain boundaries (GBs) and other structural defects are in great demand. Although photoluminescence (PL) imaging can identify the presence of relatively large defects, the limited spatial resolution of PL imaging prevents the identification of nanosized structural defects in the monolayered MoS2. Additionally, the origin of the PL signal contrast observed at certain types of structural defects, such as GBs, is not yet understood. Here, we present near-field PL images of CVD-grown monolayered MoS2, collected to identify nanosized line defects and adlayer defects in the monolayered MoS2. Our results of correlated scanning electron microscopy imaging and the inspection of near-field PL profiles of line defects and GBs suggest that decreased PL on GBs is due to the local physical damage of the MoS2 film rather than due to the presence of localized states. This journal is © The Royal Society of Chemistry139381sciescopu
Selective Amplification of the Primary Exciton in a MoS2 Monolayer
Full text linkOptoelectronics applications for transition-metal dichalcogenides are still limited by weak light absorption and their complex exciton modes are easily perturbed by varying excitation conditions because they are inherent in atomically thin layers. Here, we propose a method of selectively amplifying the primary exciton (A(0)) among the exciton complexes in monolayer MoS2 via cyclic reexcitation of cavity-free exciton-coupled plasmon propagation. This was implemented by partially overlapping a Ag nanowire on a MoS2 monolayer separated by a thin SiO2 spacer. Exciton-coupled plasmons in the nanowire enhance the A(0) radiation in MoS2. The cumulative amplification of emission enhancement by cyclic plasmon traveling reaches approximately twentyfold selectively for the A(0), while excluding other B exciton and multiexciton by significantly reduced band filling, without oscillatory spectra implying plasmonic cavity effects. © 2015 American Physical Society119171sciescopu
- …
