Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS 2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm-1) as well as high selectivity towards H 2 S relative to CO, NH 3 , H 2 , and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm-1 , respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS 2 alone are not sufficient to explain the observed high sensitivity towards H 2 S. A major role in this behavior is also played by O doping in the S sites of the WS 2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.

Their fascinating properties are the result of the layered structure held together by weak van der Waals forces similarly to graphene, however, in TMDCs one layer is much more complex; consisting of a hexagonal plane of transition metals (typically metals of group IV-VII) sandwiched between two planes of chalcogens (S, Se, and Te) by strong covalent bonds (Figure 1). In 2004, the pioneering isolation of graphene sheets [1] gave a tremendous boost to the scientific community scrutinizing similar layered materials which can be separated relatively easily to single-layers or so-called monolayers. Based on their unique electronic transport properties and advantageous band structure these materials are suggested to have a great number of applications in transistors, [2][3][4] solar cells, [5][6][7] optoelectronic devices, [8,9] catalysts, [10] and sensors. [11] As might be anticipated their properties at atomic scale, greatly differ from their bulk counterpart. Recently, monolayers of MoS 2 and WS 2 have been found to exhibit direct semiconducting band gap in the visible spectrum rather than an indirect one that is well-known for their bulk phase. [12] In addition to material thickness, the band gap can be further fine-tuned, implying also beneficial changes in material properties, by doping TMDCs with different chalcogen atoms. As an example, when the thickness of MoS 2 is reduced from bulk to monolayer a significant increase in the band gap can be observed, from ≈1.2 to ≈1.8 eV, [12] accompanied with an indirectto-direct transition, and as expected, single layers also exhibit Layered transition metal chalcogenides possess properties that not only open up broad fundamental scientific enquiries but also indicate that a myriad of applications can be developed by using these materials. This is also true for tungsten-based chalcogenides which can provide an assortment of structural forms with different electronic flairs as well as chemical activity. Such emergence of tungsten based chalcogenides as advanced forms of materials lead several investigators to believe that a tremendous opportunity lies in understanding their fundamental properties, and by utilizing that knowledge the authors may create function specific materials through structural tailoring, defect engineering, chemical modifications as well as by combining them with other layered materials with complementary functionalities. Indeed several current scientific endeavors have indicated that an incredible potential for developing these materials for future applications development in key technology sectors such as energy, electronics, sensors, and catalysis are perhaps viable. This review article is an attempt to capture this essence by providing a summary of key scientific investigations related to various aspects of synthesis, characterization, modifications, and high value applications.Finally, some open questions and a discussion on imminent research needs and directions in developing tungsten based chalcogenide materials for future applications are present...

In this work, WS2 nanowire-nanoflake hybrids are synthesized by the sulfurization of hydrothermally grown WO3 nanowires. The influence of temperature on the formation of products is optimized to grow WS2 nanowires covered with nanoflakes. Current-voltage and resistance-temperature measurements carried out on random networks of the nanostructures show nonlinear characteristics and negative temperature coefficient of resistance indicating that the hybrids are of semiconducting nature. Bottom gated field effect transistor structures based on random networks of the hybrids show only minor modulation of the channel conductance upon applied gate voltage, which indicates poor electrical transport between the nanowires in the random films. On the other hand, the photo response of channel current holds promise for cost-efficient solution process fabrication of photodetector devices working in the visible spectral range.

MoS2/Janus TMDC heterostructure stacking patterns with different stacking orientations.

van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS 2 nanowirenanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to $0.4 AW À1 are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices.