CVD Controllable Preparation And Growth Mechanism Of 2H-WS₂ And 1T-VS₂ Nanosheets

Because of the peculiar properties and potential applications of graphene,transition metal dichalcogenides(TMDs)with special structures and properties are one of the most representative members of the two-dimensional layered materials family.Among many TMDs materials,tungsten disulfide(WS₂)and vanadium disulfide(VS₂)are favored by researchers.2H-WS₂ has the characteristics of adjustable band gap and has great development prospects in the field of electricity.Different from WS₂ structure,the electronic structure of 1T-VS₂ has no band gap and partially filled band at Fermi level.These excellent metal properties make VS₂ receive wide attention in the field of electronic devices.However,there are still many challenges in the preparation and growth of WS₂ and VS₂.In recent years,chemical vapor deposition(CVD)is considered to be the most effective method for the growth of TMDs materials.At present,the traditional CVD has been able to prepare WS₂ single crystals with the size of several hundred microns,but there are still some problems,such as poor crystallinity,lack of large-scale preparation,unclear growth mechanism and so on.In addition,for VS₂ materials,most researchers tend to explore their physical and chemical properties,but there are few studies on the preparation methods of VS₂ single crystal materials.Combined with the existing problems,this paper will use an improved CVD method to prepare WS₂ single crystals with different morphologies and stacking structures under different growth conditions,and explore its growth mechanism.In addition,VS₂nanosheets with good morphology can be grown by adjusting different growth parameters.1.Through atmospheric CVD(APCVD)method,an improved semi-closed double tube combined quartz tube structure was used to prepare 2H-WS₂ nanosheets with diverse morphology and different stacking structures.First of all,by exploring the effects of various growth parameters on 2H-WS₂growth,the optimal growth conditions for preparing high-quality 2H-WS₂ nanosheets were obtained as temperature 850?,Ar=50 sccm and reaction time 15 min.Secondly,OM and AFM analysis showed that2H-WS₂ nanosheets has regular shape,uniform thickness and a size of about 100?m.XRD and Raman confirmed that WS₂ was mainly a 2H phase structure.XPS and TEM confirmed that there were only two elements W and S in the samples,which were uniformly distributed and had good crystallinity.Finally,the growth mechanism of 2H-WS₂ nanosheets with different shapes and stacked structures was discussed,and it was pointed out that 2H-WS₂ nanosheets with terrace structure and spiral structure followed LBL and SDD growth mechanism respectively.2.Molten salt-assisted CVD method was used to grow 1T-VS₂ nanosheets.By growing 1T-VS₂ nanosheets on different substrates,the best substrate for 1T-VS₂material growth is mica substrate.By studying the effects of growth temperature and carrier gas rate on the growth of 1T-VS₂,the optimal growth conditions of 1T-VS₂nanosheets were determined as reaction temperature 750?and H₂ flow rate 4 sccm.OM,AFM and TEM tests show that the sample has good morphology and uniformity.XRD and Raman analysis show that the sample is mainly 1T phase structure.XPS confirmed that the composition elements of the sample are V and S,and the atomic ratio is close to 1:2,indicating that 1T-VS₂ nanosheets have high crystallinity.