The high-yield and scalable production of single-layer ternary transition metal dichalcogenide nanosheets with ≈66% of metallic 1T phase, including MoS(2x)Se2(1-x) and Mo(x)W(1-x)S2 is achieved via electrochemical Li-intercalation and the exfoliation method. Thin film MoS(2x)Se2(1- x) nanosheets drop-cast on a fluorine-doped tin oxide substrate are used as an efficient electrocatalyst on the counter electrode for the tri-iodide reduction in a dye-sensitized solar cell.

2D black phosphorus (BP) and rhenium dichalcogenides (ReX , X = S, Se) possess intrinsic in-plane anisotropic physical properties arising from their low crystal lattice symmetry, which has inspired their novel applications in electronics, photonics, and optoelectronics. Different from BP with poor environmental stability, ReX has low-symmetry distorted 1T structures with excellent stability. In ReX , the electronic structure is weakly dependent on layer numbers, which restricts their property tunability and device applications. Here, the properties are tuned, such as optical bandgap, Raman anisotropy, and electrical transport, by alloying 2D ReS and ReSe . Photoluminescence emission energy of ReS Se monolayers (x from 0 to 1 with a step of 0.1) can be continuously tuned ranging from 1.62 to 1.31 eV. Polarization behavior of Raman modes, such as ReS -like peak at 212 cm , shifts as the composition changes. Anisotropic electrical property is maintained in ReS Se with high electron mobility along b-axis for all compositions of ReS Se .

In this study, we correlated the angular dependence of the Raman response of black phosphorus to its crystallographic orientation by using transmission electron microscopy and Raman spectroscopy. It was found that the intensity of the 2 mode reached a maximum when the polarization direction of the incident light was parallel to the zigzag crystallographic orientation. Notably, it was further confirmed that the zigzag crystallographic direction exhibited superior conductance and carrier mobility. Because of the lattice extension along the armchair direction, an intensification of the anisotropic Raman response was observed. This work provides direct evidence of the correlation between anisotropic properties and crystallographic direction and represents a turning point in the discussion of the angular-dependent electronic properties of black phosphorus.♯ These authors contributed equally to this work

Herein we report the successful doping of tellurium (Te) into molybdenum disulfide (MoS) monolayers to form MoS Te alloy with variable compositions via a hydrogen-assisted post-growth chemical vapor deposition process. It is confirmed that H plays an indispensable role in the Te substitution into as-grown MoS monolayers. Atomic-resolution transmission electron microscopy allows us to determine the lattice sites and the concentration of introduced Te atoms. At a relatively low concentration, tellurium is only substituted in the sulfur sublattice to form monolayer MoSTe alloy, while with increasing Te concentration (up to ∼27.6% achieved in this study), local regions with enriched tellurium, large structural distortions, and obvious sulfur deficiency are observed. Statistical analysis of the Te distribution indicates the random substitution. Density functional theory calculations are used to investigate the stability of the alloy structures and their electronic properties. Comparison with experimental results indicate that the samples are unstrained and the Te atoms are predominantly substituted in the top S sublattice. Importantly, such ultimately thin Janus structure of MoSTe exhibits properties that are distinct from their constituents. We believe our results will inspire further exploration of the versatile properties of asymmetric 2D TMD alloys.

In the current extensive studies of layered two-dimensional (2D) materials, compared to the hexagonal ones, like graphene, hBN and MoS2, low symmetry 2D materials have shown great potential for applications in anisotropic devices. Rhenium diselenide (ReSe2) has the bulk space group P1 � and belongs to triclinic crystal system with a deformed cadmium iodide type structure. Here we propose an electron diffraction based method to distinguish monolayer ReSe2 membrane from multilayer ReSe2, and its two different vertical orientations, our method could also be applicable to other low symmetry crystal systems, including both triclinic and monoclinic lattices, as long as their third unit-cell basis vectors are not perpendicular to their basal planes. Our experimental results are well explained by kinematical electron diffraction theory and corresponding simulations. The generalization of our method to other 2D materials, like graphene, is also discussed.Address correspondence to Chuanhong Jin, chhjin@zju.edu.cn Moreover, ReS2 and ReSe2 share similar crystal structures, they both have a distorted octahedral 1T structure and belong to triclinic crystal system, and Re atoms form zigzag chains in the basal plane, arising from the Peierls distortion. Therefore, ReSe2 and ReS2 flakes have both in-plane and out-of-plane anisotropy, and recently there have been numbers of applications based on their anisotropic properties [12][13][14][15][16][17].When materials are thinned down to atomically thin membranes, thickness begins to play an important role in tailoring their properties, and vice versa, there are a variety of techniques to determine their thicknesses, ranging from image contrast of reflected light microscopy [18][19][20][21][22][23][24], second harmonic microscopy [25][26][27][28], intuitive atomic force microscopy and cross-sectional imaging to Raman and photoluminescence spectroscopy [29][30][31][32]. In the field of electron microscopy, there are miscellaneous methods to identify thickness as well, which include peak shift in plasmon spectroscopy [33,34], direct high-resolution transmission electron microscopy (HRTEM) imaging combined with simulations [35] and linearity in annular dark field scanning transmission electron microscope (ADF-STEM) signals [36,37]. Apart from the above methods, electron diffraction analysis [34,[38][39][40][41][42][43] has also been demonstrated as an efficient tool to determine thickness in 2D materials, since it could be conducted on any commercial uncorrected TEM conveniently with negligible beam damages on a large area of pristine crystalline samples. Furthermore, diffraction based methods usually involve a series of sample tilting or use the relative ratio of the chosen diffraction spots, and some researchers noticed the intensity mismatch in a pair of crystallographically equivalent diffraction spots (Friedel pair) [41,44,45], here we demonstrate a method of identifying monolayer ReSe2 by the centrosymmetry with a single diffraction pattern.

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