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Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their synergetic effects with other 2D materials, such as graphene and hexagonal boron nitride, in TMD-based heterostructures. Therefore, it is important to understand the physical properties of TMD-TMD vertical heterostructures for their applications in next-generation electronic devices. However, the conventional synthesis process of TMD-TMD heterostructures has some critical limitations, such as nonreproducibility and low yield. In this paper, we synthesize wafer-scale MoS2-WS2 vertical heterostructures (MWVHs) using plasma-enhanced chemical vapor deposition (PE-CVD) via penetrative single-step sulfurization discovered by time-dependent analysis. This method is available for fabricating uniform large-area vertical heterostructures (4 in.) at a low temperature (300 °C). MWVHs were characterized using various spectroscopic and microscopic techniques, which revealed their uniform nanoscale polycrystallinity and the presence of vertical layers of MoS2 and WS2. In addition, wafer-scale MWVHs diodes were fabricated and demonstrated uniform performance by current mapping. Furthermore, mode I fracture tests were performed using large double cantilever beam specimens to confirm the separation of the MWVHs from the SiO2/Si substrate. Therefore, this study proposes a synthesis mechanism for TMD-TMD heterostructures and provides a fundamental understanding of the interfacial properties of TMD-TMD vertical heterostructures.

In this study, we successfully demonstrate the fabrication of a MoS2-graphene heterostructure (MGH) on a 4 inch wafer at 300 °C by depositing a thin Mo film seed layer on graphene followed by sulfurization using H2S plasma. By utilizing Raman spectroscopy and high-resolution transmission electron microscopy, we have confirmed that 5–6 MoS2 layers with a large density of sulfur vacancies are grown uniformly on the entire substrate. The chemical composition of MoS2 on graphene was evaluated by X-ray photoelectron spectroscopy, which confirmed the atomic ratio of Mo to S to be 1:1.78, which is much lower than the stoichiometric value of 2 from standard MoS2. To exploit the properties of the nanocrystalline and defective MGH film obtained in our process, we have utilized it as a catalyst for hydrodesulfurization and as an electrocatalyst for the hydrogen evolution reaction. Compared to MoS2 grown on an amorphous SiO2 substrate, the MGH has smaller onset potential and Tafel slope, indicating its enhanced catalytic performance. Our practical growth approach can be applied to other two-dimensional crystals, which are potentially used in a wide range of applications such as electronic devices and catalysis.

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 high-quality 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 MoS2 and WS2 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 MoS2-WS2 heterostructures was validated using various spectroscopic and microscopic techniques. Further, the photocurrent generation and photoswitching phenomenon of the so-obtained MoS2-WS2 heterostructures were studied. The photodevice prepared by the MoS2-WS2 heterostructures at 150 °C showed a photoresponsivity of 83.75 mA/W. The excellent photoresponse and faster photoswitching highlight the advantage of MoS2-WS2 heterostructures toward advanced photodetectors.

This paper reports an increase in the optical reflectivity of two kinds of copolymers used in contact lenses, with different proportions of silicon and fluorine derivatives, when irradiated with 4.1 MeV alpha particles from an 241Am source. The fiber-optic reflectance technique showed that the lens with a higher proportion of silicon and fluorine content and a lower proportion of methyl-methacrylate is more susceptible to alpha radiation. X-Ray photoelectron spectroscopy and Raman spectroscopy have revealed the formation of silicon oxide and carbide species as a result of chain scission and recombination in the 20 μm thick irradiated regions of lens materials. It is presumed that the high (260 eV/nm) linear energy transfer of alpha particles in polymers creates trapped gas “Bubbles”, and the observed increase in the optical reflectivity with increased irradiation time is explained on the basis of diffuse reflectance caused by the scattering of light from the hard surfaces of these “Bubbles”.

The metallic 1T phase of WS2 (1T-WS2 ), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER). As the semiconductor 2H phase of WS2 (2H-WS2 ) is inherently stable, methods for synthesizing 1T-WS2 are limited and complicated. Herein, a uniform wafer-scale 1T-WS2 film is prepared using a plasma-enhanced chemical vapor deposition (PE-CVD) system. The growth temperature is maintained at 150 °C enabling the direct synthesis of 1T-WS2 films on both rigid dielectric and flexible polymer substrates. Both the crystallinity and number of layers of the as-grown 1T-WS2 are verified by various spectroscopic and microscopic analyses. A distorted 1T structure with a 2a0 × a0 superlattice is observed using scanning transmission electron microscopy. An electrochemical analysis of the 1T-WS2 film demonstrates its similar catalytic activity and high durability as compared to those of previously reported untreated and planar 1T-WS2 films synthesized with CVD and hydrothermal methods. The 1T-WS2 does not transform to stable 2H-WS2 , even after a 700 h exposure to harsh catalytic conditions and 1000 cycles of HERs. This synthetic strategy can provide a facile method to synthesize uniform 1T-phase 2D materials for electrocatalysis applications.

DNA extracted from salmon has recently attracted the attention of researchers, resulting in applications of DNA in photonic and electronic devices. Porphyra-334, a type of mycosporine-like amino acids (MAAs), also plays an important role in photoprotection for a variety of marine organisms including bacteria and algae. Although MAA and DNA molecules have been intensively studied, fabrication methodology and applicability of MAA-embedded DNA complexes for physical applications have been seldom discussed due to incompatibility between biological samples and physical platform. Here, Porphyra-334 embedded DNA was investigated to understand its electrical transport property with the aid of silicon nanowire/nanoribbon field effect transistors (NW/NR FETs). Its chemical stability was determined by cyclic voltammetry upon illumination of UV light. The current of DNA-SiNW FET was enhanced by the addition of Porphyra-334 and upon illumination of UV light. Conductivities of PDNA-SiNW FET compared to SiNW FET were increased up to ∼70% at dark and ∼40% under UV light due to the presence of Porphyra-334 and excess injection of charge carriers in Porphyra-334 embedded DNA generated by absorbing UV light, respectively. The addition of Porphyra-334 in DNA-SiNR FET lowered its energy level and resulted in large threshold voltage shift towards the negative scale. In addition, its electrochemical property was studied by cyclic voltammetry and impedance spectroscopy. Porphyra-334 in DNA solution which inhibited oxidation of DNA showed relatively lower current indicating high electrochemical stability and decrease of resistance compared to pristine DNA solution based on results of impedance spectroscopy.