The conventional synthesis of two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures is low yielding and lack the heterojunction interface quality. The chemical vapor deposition (CVD) techniques have achieved highquality heterostructure interfaces but require a high synthesis temperature (>600 °C) and have a low yield of heterostructures. Therefore, the large scale and high interface quality of TMDC heterojunctions using low-temperature synthesis methods are in demand. Here, high-quality, wafer-scale MoS 2 and WS 2 heterostructures with 2D interfaces were prepared by a one-step sulfurization of the molybdenum (Mo) and tungsten (W) precursors via plasma-enhanced CVD at a relatively low temperature (150 °C). The 4 inch wafer-scale synthesis of the MoS 2 −WS 2 heterostructures was validated using various spectroscopic and microscopic techniques. Further, the photocurrent generation and photoswitching phenomenon of the so-obtained MoS 2 −WS 2 heterostructures were studied. The photodevice prepared by the MoS 2 −WS 2 heterostructures at 150 °C showed a photoresponsivity of 83.75 mA/W. The excellent photoresponse and faster photoswitching highlight the advantage of MoS 2 −WS 2 heterostructures toward advanced photodetectors.

The tunneling effect is an additional factor. [3] For example, TMD-TMD heterostructures can improve electron-hole separation because of the desired bandgap alignment and can form a natural p-n junction. [4] The advancement in nanofabrication techniques has drawn attention to 2D materials and heterostructures. [5] Graphene-based heterostructures are well known, and many research attempts have been devoted toward using the superior properties of graphene, such as high conductivity, broadband absorption, and better current modulation with a high on/off current ratio. [6] However, despite substantial interest in graphenebased heterostructure, intensive research has not been conducted because of the limitation of fabrication method. Reliably providing samples with a high uniform quality and sufficient size has been impossible. The following two types of heterostructure fabrication have been reported: physical transfer (e.g., wet transfer supported by PMMA or PDMS) [7] or hydrothermal methods such as nanosheet heterostructure (a few micrometer size). [8] Physical transfer makes guaranteeing the reproducibility of quality difficult because it is processed manually. The hydrothermal method is unsuitable for research that requires a Makersof point-of-care devices and wearable diagnostics prefer flexible electrodes over conventional electrodes. In this study, a flexible electrode platform is introduced with a WS 2 /graphene heterostructure on polyimide (WGP) for the concurrent and selective determination of dopamine and serotonin. The WGP is fabricated directly via plasma-enhanced chemical vapor deposition (PECVD) at 150 °C on a flexible polyimide substrate. Owing to the limitations of existing fabrication methods from physical transfer or hydrothermal methods, many studies are not conducted despite excellent graphene-based heterostructures. The PECVD synthesis method can provide an innovative WS 2 /graphene heterostructure of uniform quality and sufficient size (4 in.). This unique heterostructure affords excellent electrical conductivity in graphene and numerous electrochemically active sites in WS 2 . A large number of uniform qualities of WGP electrodes show reproducible and highly sensitive electrochemical results. The synergistic effect enabled well-separated voltammetric signals for dopamine and serotonin with a potential gap of 188 mV. Moreover, the practical application of the flexible sensor is successfully evaluated by using artificial cerebrospinal fluid.

Herein, a layer of molybdenum oxide (MoOx), a transition metal oxide (TMO), which has outstanding catalytic properties in combination with a carbon‐based thin film, is modified to improve the hydrogen production performance and protect the MoOx in acidic media. A thin film of graphene is transferred onto the MoOx layer, after which the graphene structure is doped with N and S atoms at room temperature using a plasma doping method to modify the electronic structure and intrinsic properties of the material. The oxygen functional groups in graphene increase the interfacial interactions and electrical contacts between graphene and MoOx. The appearance of surface defects such as oxygen vacancies can result in vacancies in MoOx. This improves the electrical conductivity and electrochemically accessible surface area. Increasing the number of defects in graphene by adding dopants can significantly affect the chemical reaction at the interfaces and improve the electrochemical performance. These defects in graphene play a crucial role in the adsorption of H+ ions on the graphene surface and their transport to the MoOx layer underneath. This enables MoOx to participate in the reaction with the doped graphene. N‐ and S‐doped graphene (NSGr) on MoOx is active in acidic media and performs well in terms of hydrogen production. The initial overpotential value of 359 mV for the current density of −10 mA/cm2 is lowered to 228 mV after activation.

Herein, the tribological behavior of layered few nanometer‐thick MoS2 thin films is evaluated to identify their applicability to an oil‐free solid‐lubrication coating layer. The MoS2 thin films are synthesized using a plasma sulfurization process with optimized steps and conditions derived from a previous study. MoS2 thin films with different thicknesses are heat treated at 400 °C to investigate the effect on their tribological properties. The ball‐on‐disk method is used to observe the friction and wear behavior of the MoS2 thin films, and this test is carried out under an applied load of 0.5 N in an ambient atmosphere (≈23 °C). The coefficient of friction of the unheated MoS2 layers increases rapidly at 32–36 cycles regardless of the thickness. However, the heat‐treated MoS2 films maintain a lower coefficient of friction for more cycles (60–86 cycles). The heat treatment effect effectively increases the wear life of the MoS2 thin film. Based on this result, it is believed that the heat‐treated MoS2 thin films can be potential solid lubricant candidate for micro‐ and nanoelectromechanical systems.

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