Controllable Preparation And Physical Property Study Of Low Dimensional Layered W/Mo-based Transition Metal Dichalcogenides

Two-dimensional layered transition metal dichalcogenides?2D TMDCs?have rich crystal structures and novel properties,and 2D TMDCs have good application prospects in photocatalysis,electronic devices,photoelectric detection and others.Among the physical properties of semiconductor TMDCs,photoluminescence?PL?is one of the most representative,which represents the bandgap structure of TMDCs.However,there are some inconsistencies in previous studies on the PL of TMDCs single crystal.In addition,the controllable preparation of large area,high quality TMDCs containing Te element is still insufficient.Therefore,this paper studies the controllable preparation process and physical properties of MoS₂,MoTe₂ and WTe₂,and makes up the blank of electrochemical catalysis of WTe₂.Firstly,the growth of MoS₂ single crystal is regulated by the mole ratio of MnO₂ to MoO₃.We found that MnO₂ can effectively reduce the nucleation rate of MoS₂ and promote the lateral growth.The MoS₂ with different morphologies can be obtained at different positions of the growth substrate.Finally,Raman,TEM and theoretical calculation were used to analyze the phenomenon that the PL strength of MoS₂ crystal gradually decreased from the middle to the edge of MoS₂ single crystal.Secondly,large area WTe₂ films were prepared by tellurization of the precursor films of tungsten oxide.We systematically studied the influence of various parameters on the quality of WTe₂ thin films by XRD and Raman tests,and studied the optical and electrical properties of WTe₂ thin films.Finally,we found that in the magnetoresistance test of thin WTe₂ film,the samples with different thickness have weak anti-localization effect,and the magnetoresistance presents an unsaturated state.Thirdly,we studied the influence of the thickness on the phase transition of MoTe₂during the preparation process,and found that the larger the thickness,the easier the formation of 2H phase.Meanwhile,we studied the transition process from 1T'to 2H phase by successive tellurization of 1T'MoTe₂ thin films.Instead of converting 1T'phase directly to 2H phase,1T'MoTe₂ firstly convert to a intermediate phase?1T'@2H?and then convert it to 2H phase.Fourthly,The preparation of large area WTe₂ thin films was made by chemical vapor deposition under 500?with WCl₆ and Te as source materials.Spin relaxation of WTe₂and MoTe₂ films was studied combining with magneto-optic Kerr at room temperature.We found that spin relaxation time of WTe₂ and MoTe₂ can reach to nanosecond at room temperature.Besides,applied external magnetic field has no big influence on WTe₂ and MoTe₂ spin relaxation.Fifthly,Large-scale WTe₂ with high quality can be prepared with a two-step method.And different morphology of WTe₂ can be obtained by controlling the morphology of the first step.By comparing hydrogen evolution performance of WTe₂ with WS?Se?₂ samples prepared with the same method,we found that WTe₂ electrode material displays larger catalytic current,smaller overpotential and Tafel slope due to good conductivity and larger active surface area.