Abstract:Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics.… Show more
“…The crystal structure and the corresponding electric dipole moments of monolayer Janus MoSSe are illustrated in figure 1. The relaxed lattice parameter is a=b=3.25 Å in conjunction with a 2.43 Å S-Mo bond length and a 2.54 Å Se-Mo bond length, which agree well with the results in [10]. Owing to the different electronegativity, the electrons locating around S and Se atoms are less than Mo atoms, and thus the dipole moments direction is from S and Se atoms to Mo atoms.…”
Section: Resultssupporting
confidence: 84%
“…Besides, different MoS 2 based morphologies have been successfully synthesized, such as MoS 2 nanorods [6], nanopetals [7], nanopowder [8] and nanotubes [9]. Recently, a new monolayer 2D TMDs Janus MoSSe, with out-of-plane asymmetry, has been successfully fabricated [10,11]. The out-of-plane asymmetry introduce a intrinsic vertical electric field which is absent in symmetry MX 2 .…”
Electron-phonon (e-ph) interaction in monolayer Janus MoSSe has been investigated using ab initio approach. We find that the asymmetric structure induced net dipole moment in MoSSe introduce an enhanced e-ph interaction compared to the symmetric MoS 2 . Through the mode resolved scattering analysis, we demonstrate that the out-of-plane optical mode in MoSSe contributing to the total eph scattering rates are much more than MoS 2 . Around the band edges, the maximum mean free paths (MFPs) of both electrons and holes along zigzag (ZZ) direction are found to be 4 nm in MoSSe, while the MFPs along armchair directions are significantly shorter than along ZZ direction, meaning the highly anisotropic transport properties in MoSSe.
“…The crystal structure and the corresponding electric dipole moments of monolayer Janus MoSSe are illustrated in figure 1. The relaxed lattice parameter is a=b=3.25 Å in conjunction with a 2.43 Å S-Mo bond length and a 2.54 Å Se-Mo bond length, which agree well with the results in [10]. Owing to the different electronegativity, the electrons locating around S and Se atoms are less than Mo atoms, and thus the dipole moments direction is from S and Se atoms to Mo atoms.…”
Section: Resultssupporting
confidence: 84%
“…Besides, different MoS 2 based morphologies have been successfully synthesized, such as MoS 2 nanorods [6], nanopetals [7], nanopowder [8] and nanotubes [9]. Recently, a new monolayer 2D TMDs Janus MoSSe, with out-of-plane asymmetry, has been successfully fabricated [10,11]. The out-of-plane asymmetry introduce a intrinsic vertical electric field which is absent in symmetry MX 2 .…”
Electron-phonon (e-ph) interaction in monolayer Janus MoSSe has been investigated using ab initio approach. We find that the asymmetric structure induced net dipole moment in MoSSe introduce an enhanced e-ph interaction compared to the symmetric MoS 2 . Through the mode resolved scattering analysis, we demonstrate that the out-of-plane optical mode in MoSSe contributing to the total eph scattering rates are much more than MoS 2 . Around the band edges, the maximum mean free paths (MFPs) of both electrons and holes along zigzag (ZZ) direction are found to be 4 nm in MoSSe, while the MFPs along armchair directions are significantly shorter than along ZZ direction, meaning the highly anisotropic transport properties in MoSSe.
“…Due to the progress in experimental equipment and techniques, the Janus structure (a sandwich structure with the central metallic layer and two marginal layers of different chalcogen atoms) can be fabricated using the modified Chemical Vapor Deposition (CVD) method. As shown in figure 2(a), Zhang and co-workers synthesized Janus SeMoS using the following steps: the top-layer S atoms of the synthesized MoS 2 SL is firstly replaced by H atoms with a remote hydrogen plasma (Janus HMoS SL formed); then, the H atoms of HMoS SL are replaced by Se atoms with a thermal selenization (Janus SeMoS SL formed) [19]. Soon after, as displayed in figure 2(b), Lou and co-workers also independently fabricated the SMoSe SL using the sulfurization method.…”
Section: Experimental Synthesis Of Janus Tmdcsmentioning
confidence: 99%
“…Based on the experimental progress, novel electronic properties of Janus SLs have been found, such as a huge piezoelectric effect, robust Rashba spin splitting, a second-harmonic generation (SHG) response [19], and high basal plane HER catalytic activity [20]. They can result in the interesting applications in gas sensors, piezoelectric devices, thermal electric devices, solar cells, ion batteries, and so on.…”
Section: Experimental Synthesis Of Janus Tmdcsmentioning
Janus two-dimensional (2D) materials, referring to the layers with different surfaces, have attracted intensive research interest due to the unique properties induced by symmetry breaking, and promising applications in energy conversion. Based on the successful experimental synthesis of Janus transition metal dichalcogenides (TMDC), here we present a review on their potential application in photocatalytic overall water splitting, from the perspectives of the latest theoretical and experimental progress. Four aspects which are related to photocatalytic reaction, including the adsorption of water molecules, utilization of sunlight, charge separation and transport, and surface chemical reactions have been discussed, and it is concluded that the Janus structures have better performances than symmetric TMDCs. At the end of this review, we raise further challenges and possible future research directions for Janus 2D materials as water-splitting photocatalysts.
Two‐dimensional material (2D) that possesses atomic thin geometry and remarkable properties is a star material for the fundamental researches and advanced applications. Defects in 2D materials are critical and fundamental to understand the chemical, physical, and optical properties. Photoluminescence arises in 2D materials owing to various physical phenomena including activator/dopant‐induced luminescence and defect‐related emissions, and so forth. With the advanced transmission electron microscopy (TEM) technologies, such as aberration correction and low voltage technologies, the morphology, chemical compositions and electronic structures of defects in 2D material could be directly characterized at the atomic scale. In this review, we introduce the applications of state‐of‐the‐art TEM technologies on the studies of the role of atomic defects in the photoluminescence characteristics in 2D material. The challenges in spatial and time resolution are also discussed. It is proved that TEM is a powerful tool to pinpoint the relationship between the defects and the photoluminescence characteristics.
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