Controllable CVD Preparation And Characterization Of Large-Area And High-Quality Transition-Metal Dichalcogenides

Two-dimensional(2D)transition-metal dichalcogenides(TMDCs,MX₂)have attracted tremendous research attention in recent ten years due to their remarkable electronic and optical properties,including the presence of direct-bandgap for monolayer TMDCs,the quantum spin Hall effect,the valleytronics,as well as the 2D superconductivity,implying extensive potential applications.Among them,chemical vapor deposition(CVD)has been widely demonstrated to be an effective technique to synthesize high-quality TMDCs as well as their in-plane and vertical heterostructures by using different precursors.At present,a quantitative control of the precursor with high precision and good repeatability is still challenging.Moreover,the process to synthesize a designed pattern of TMDCs is complicated.Here,by using an industrial inkjet-printer,an in situ aqueous precursor with robust usage control at the picogram(10^-12 g)level is achieved,and by precisely tuning the inkjetprinting parameters,followed by a rapid heating process,large-area patterned TMDCs films with centimeter size and good thickness controllability,as well as heterostructures of the TMDCs,are achieved facilely,and high-quality single-domain monolayer TMDCs with millimeter-size can be easily synthesized within 30 seconds(corresponding to a growth rate up to 36.4?ms^-1).The resulting monolayer Mo S₂ and Mo Se₂ exhibits excellent electronic properties with carrier mobility up to 21 and 54 cm²V^-1s^-1,respectively.The study paves a simple and robust way for the in situ ultrafast and patterned growth of high-quality TMDCs and heterostructures with promising industrialization prospects.Moreover,this ultrafast and green method can be easily used for synthesis of other 2D materials with slight modification.The specific research content is as follows:Firstly,the water solution of ammonium molybdate tetrahydrate has been chosen as the aqueous precursors due to its high solubility in water,low cost,high stability,and safety in ambient,as well as wide availability in industry.The rheology of inkjet inks has been firstly studied to obtain the printable aqueous precursors.Pure deionized(DI)water is not inkjet-printable since the surface tension?(m N·m^-1),the viscosity?(m Pa·s),the density?as well as the diameter d of the printer nozzle should be within certain ranges for a printable ink.the inverse Ohnesorge number Z,can be used to determine if an ink is printable to form stable drops.If 1<Z<20,the ink is expected to be printable.the printing parameters are carefully optimized as follows:DPI=1440*1440 or 1440*720 and C=0.1 mg/ml to obtain monolayer TMDCs.Secondly,during the CVD growth process,Si O₂ and soda lime glass are selected as the substrate.First,by adjusting the parameters,the growth temperature is 750°C,the Ar is 5sccm,and the growth time is 5min,large-area patterned TMDC film in centimeter size with good controllability of the thickness,as well as vertical and in-plane heterostructures of TMDC could be achieved on Si O₂/Si by a simple growth process.Second,the growth temperature was further risen to 1050°C,due to isotropic and homogeneous glass surface,it can effectively reduce the nucleation center,high-quality monolayer TMDCs in millimeter-size,including Mo Se₂and Mo S₂ can be synthesized on the isotropic molten glass substrate within 30 s(corresponding to a growth rate up to 36.4?m/s).Then through optical microscope(OM),atomic force microscope(AFM),Raman spectroscopy(Raman),photoluminescence spectroscopy(PL),scanning electron microscope(SEM)and transmission electron microscope(TEM)characterization methods,the prepared samples were analyzed characterization.They reveal the high quality of the TMDC films from the ultrafast growth strategy with inkjet-printed aqueous precursors.Finally,to evaluate the electrical performance of the synthesized TMDCs,their field effect carrier mobilities have been measured.The FET devices were fabricated by using a maskless UV lithography.Both Mo Se₂ and Mo S₂ FET devices demonstrated the typical characteristics of n-type semiconductors,the mobility measurements obtained with good ohmic contact showed 54 and 21 cm²V^-1s^-1for Mo Se₂ and Mo S₂,respectively.Mo Se₂ and Mo Se₂-Graphene photoelectric devices were also prepared,and it was found through testing that the devices had good light response performance.Lay the foundation for the subsequent practical application of TMDCs.