The Investigation On Synthesis And Properties Of Graphene/transition Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides（TMDCs）with a structure analogous to graphene have attracted intense attention due to their unique electronic characteristics,tunable bandgap,and optical properties.These advantages could be beneficial for a wide range of applications,such as in electronic devices,flexible film transistors,and optoelectronic devices.Reducing the thickness of TMDCs to their ultimate dimension of single layer affects their physical and chemical properties,for example,the transition from indirect to direct bandgap has a large impact on the functionality.Monolayer TMDCs are complementary to the zero-bandgap graphene due to their direct bandgaps and are a promising candidate for the realizing various semiconductor devices.Thus,the development of large-scale and high-quality monolayer TMDCs is of great importance.Tuning the bandgap of thin-layered TMDCs nanocrystals by controlling their composition or structure is considered to be an important method of tailoring light absorption,electron transition,and carrier mobility.However,the large-scale synthesis of TMDCs with a tunable bandgap on graphene remains challenging owing to the difficulty in controlling uniformity of the layer thickness.Herein,we report on the large-area synthesis of a uniform monolayer MoS_2（1-x）Se_2x film on a monolayer graphene using chemical vapor deposition to realize a 2D heterostructure.A phototransistor with the MoS_2（1-x）Se_2x/graphene heterostructure exhibits a high responsivity of 40.64 mA/W with good stability,which can be developed and integrated into advanced optoelectronic devices.Optimizing the crystal structure and large-scale uniformity of monolayer TMDCs is of significant importance for achieving high carrier mobility and strong photo-luminescence efficiency.A large-area uniform of single-crystal TMDCs is important for advanced optoelectronics based on 2D atomic crystals.However,difficulies in controlling the growth parameters restrict its development in devices.Monolayer WS₂ has great potential to be applied in semiconducting electronics owing to its moderate band gap,excellent theoretical phonon-limited electron mobility,and photoluminescence quantum yield.Although the quality of large-scale WS₂ film by CVD method is not desirable.Thus large-area high-quality monolayer WS₂ remains a great challenge.Herein,we present the synthesis of triangular single-crystal monolayer WS₂ flakes with good uniformity by adjusting the introduction time of the S precursor and the distances between the precursors and substrate.Investigation indicates that a series of triangular（side length of 233μm）monolayer WS₂ flakes shows high-quality structure and homogenous crystallinity.Field effect transistors based on the fabricated triangular monolayer WS₂demonstrate environmentally stable charge transport with a field effect mobility of50.5 cm²/Vs and current modulation I_on/I_offff of～10⁷ at 10 K.The results of this study pave the way for the application of monolayer WS₂ in a multitude of 2D-material-based devices.