Preparation Of Transition Metal Sulphur Compounds And Research On Photoelectric Properties

The properties of two dimensional materials have been widely paid attention by the researchers of physics and materials science.The properties of two-dimensional materials are closely related to the components,structures and layer numbers of materials.The controllable preparation of two dimensional materials is the prerequisite and foundation for their applications,and it is a hot research topic at present.The energy band structure of transitional metal dichalcogenides?TMDs?,such as WS₂,MoS₂,and so on,when thinned from the bulk to monolayer,changes from the indirect band gap to the direct band gap,showing excellent photoelectronic properties.TMDs are expected to be used in many fields,such as solar cells,photodetectors,photocatalysis,lithium-ion batteries,sensors and so on.As a typical representative,WS₂ has rich physical properties,such as valley polarization,energy band structure tunability,and so on.It has wide applications in many fields.This paper explores the preparation methods and photoelectric performance of WS₂ from the following three aspects.The main contents of this paper are as follows:?1?The effects of various factors on the growth of WS₂ were discussed in seven aspects,such as the precursor,pressure,growth temperature,growth time,amount of sulfur powder,gas flow rate and the location of the substrate.Finally,the optimum preparation conditions of the WS₂ were obtained:WS_2.9 as the tungsten source,atmospheric pressure,growth temperature 900?,and the holding time 10 min,the amount of sulfur powder 0.7g,and the flow rate of Ar 160 sccm.Under this condition,WS₂ triangular flakes with single-domain size of about 400?m were prepared with high crystalline quality.?2?The transferring methods of WS₂ flakes with three different polymers were studied.The different polymers are PMMA?Polymethyl methacrylate?,PS?Polystyrene?and PVP?Polyvinylpyrrolidone?/PVA?Polyvinyl alcohol?Using PMMA as a transferring medium can achieve large-area transfer,but the removal of PMMA is not complete,and acetone could cause WS₂ film to be destroyed.Polymer PS has stronger adhesion than PMMA,so it can almost transfer all WS₂ flakes from orginal substrate to target substrage.But PS has to be rinsed by toluene and PS is not easy to be cleaned out.The water-soluble PVP/PVA transfer method can realize the complete transfer of WS₂ flakes,and also ensure that PVP/PVA can be completely removed by only deionized water.Based on our results,PVP/PVA method proves to be the best.?3?The liquid exfoliation of WS₂ powder with different chemical reagents was explored.The stable,uniform WS₂ suspensions with high concentration were achieved.WS₂ flexible thin films were prepared by vaccum filtration and the corresponding photoelectric device were designed.The effects of centrifugal speeds and graphene doping dose on the photoelectric properties of WS₂ films were studied.