Large Scale Growth And Property Engineering Of 2D Transition Metal Dichalogenides

Damage-free and rapid transfer of chemical vapor deposition（CVD）grown two-dimensional transitional metal dichalcogenides（2D TMDs）is an important premise for the industrial research and application of 2D TMDs.Developing such a transfer method is necessary for the promotion of the development for 2D TMDs.The properties of 2D TMDs,especially their electronic and optical properties,are closely correlated with layer numbers due to the interlayer interaction.Tuning the interlayer interaction is an appealing way to bring new properties in 2D TMDs,which enriches the potential applications for 2D TMDs.In this work,we proposed new methods to mainly address above two issues.For the damage-free and rapid transfer of CVD grown 2D TMDs,we realized this by growing 2D TMDs on water soluble layers,which was introduced between growth substrate and the synthesized 2D TMDs during the growth process.Here,we used MoS₂and Na Cl as representatives for 2D TMD and water soluble layer,respectively,to demonstrate this concept.The optical and electrical measurements for the grown and transferred MoS₂indicated that the high quality of MoS₂ was kept after transfer.Furthermore,the developed transfer method was proved to be a general strategy and can be used to transfer other 2D TMDs with different sizes grown on different substratesby by using various water soluble salts.Tuning properties of 2D TMDs by interlayer interaction is one of the most important subjects in the study of 2D materials.However,tuning interlayer interaction in weakly coupled 2D TMDs is limted due to the absence of effective strategies.Here,we proposed a new strategy for enhancing interlayer interaction in weakly coupled bilayer MoS₂ by doping with vanadium atoms.Through doping with appropriate concentration of V atoms,the electrical conductance of doped bilayer MoS₂ was enhanced by several magnitudes than monolayer case.Through scanning transmission electron microscopy（STEM）characterization and first-principle calculation,we found the origin for this was that the effect of vanadium doping on electronic structures of monolayer and bilayer MoS₂ was very different.In monolayer MoS₂,vanadium doping introduces highly localized states in the band gap of MoS₂,which do not contribute to electrical conduction nearly.However,in doped bilayer MoS₂,the vanadium doping changes the full occupied states of S-3p_z orbitals in pristine bilayer MoS₂ into partially occupied states in doped bilayer MoS₂ and the enhanced hybridization between these S-3p_z states from adjacent MoS₂layers leading to the formation of additional conduction paths,which enhances the interlayer interaction and the electrical conductance of doped bilayer MoS₂.Monolayer MoS₂ shows attracting photoluminescence（PL）properties because of its direct band gap.However,we found that the PL was quenched when the doped V concentration exceeded a critical point,which is abnormal to other doped MoS₂ systems.We proposed a few possible mechanisms for this PL quenching phenomenon and it is very reasonable to explanine this by Auger recombination induced by vanadium doping.Interlayer interaction not only tunes the properties of layer-structured materials effectively,but also palys a key role in tuning the properties of nonlayered materials.Theoretical calculation showed that the band gap of lead sulphide（PbS）presents oscillation with the layer number（odd number layer or even number layer）and becomes topological insulator when its thickness thin down to several cell units.In order to verify it in experiment,we tried to synthesize thin PbS flakes by CVD and carried out some characterizations.