Growth Mechanism Of 2D WS₂ By The Influence Of Liquid Au And Carrier Gas And The Deviations Of Evaporation Modes

In recent years,two-dimensional layered materials have attracted worldwide attention due to their unique properties.Unlike zero band gap graphene,most single-layer transition metal chalcogenides?TMDs?are direct band gap semiconductors.Among TMDs materials,high electrical conductivity and high carrier mobility endows WS₂ a large application prospect in optoelectronic devices.The synthesis method affects the parameters such as the morphology and properties of the film,so it is particularly important to choose a suitable synthesis method.As an extension of the CVD method,films grown by the control of liquid metal exhibit a very novel phenomenon.However,the controllably of films by this method still have many challenges.In this paper,2D WS₂films were synthesized by the control of liquid metal,the effects of growth parameters on growth of 2 D structure and morphology were analyzed.Besides,the deviations of evaporation modes in two different morphologies of 2D WS₂ film were studied.The main research are as follows:Firstly,the WS₂ film was successfully grown on SiO₂?300 nm?/Si substrates by the influence of liquid Au.Four growth parameters:the state of Au foil,the melting time of Au foil,growth temperature,the precusors of W were explicitly explored.The result shows that liquid Au has a strong adsorption effect on the precusors of W.Therefore,at the stage of preparing substrates with W precursors adsorbed,liquid Au will adsorb and dissolve a large number of W atoms,and these atoms will be evaporated again during the growth stage to provide raw materials for the growth of WS₂ films.The longer the melting time of the Au foil,that is,the longer the W adsorption time,or the lower the melting point of the W precursor,the more W precursors adsorbed and dissolved by the liquid Au,and the higher the density of the WS₂ film growing on the substrate surface.In addition,we also found that the growth temperature has little effect on the adsorption and dissolution of W atoms and the growth of the film.Secondly,the WS₂ film was successfully grown on SiO₂?300 nm?/Si by the influence of liquid Au and carrier gas.There is a breakthrough in the film size by an order of magnitude by using this method.The influence of positions on the substrates and growth temperature on the morphologies of film was analyzed.Then the variations in the layer numbers and the size of WS₂film were further studied.It is found that the growth process was mainly influenced by the variation of"the concentration of local W atom"under the combined action of liquid Au and carrier gas.The size of WS₂film increases first and then decreases far from the center of liquid Au.The layers number of WS₂in the affected regions of liquid Au is obvious larger than that of the unaffected region.Besides,when the growth temperature gradually increases,the size of WS₂ film increases first and then decreases.Finally,we investigated the deviations of evaporation modes in two different morphologies of 2 D WS₂ film?films of uniform thickness and films with a center stack?.The result shows that these parameters mainly affect the"local S-W concentration"on the substrate surface and the free energy of the S and W atoms,and further affect the evaporation rate of the film:the evaporation rate is directly proportional to the free energy of the S and W atoms,and inversely proportional to the"local S-W concentration".In addition,there are significant differences in the evaporation modes between these two kinds of films:films with a center stack only peel from the boundaries and defects,films of uniform thickness not only peel from the boundaries and defects,but also peel off layer by layer from the surface.This shows that there may be a"pinning effect"at the center of the film with the center stack,which causes the interlayer force of the film to be greater than the film of uniform thickness.The deviations in evaporation modes implies that the growth modes of the two films may be completely different.