Uniformity Control Of MoS₂ Crystal Distribution And The Study Of The Preparation Method

Since the discovery of graphene,two-dimensional materials have aroused wide interest due to their excelent mechanical,optical and electrical properties.As a classical transition metal sulfide（TMDs）,2D MoS₂ has shown great potential in catalysis,sensing,photoelectric detection and other fields.The continuous development of application promotes the investigation of MoS₂ preparation.However,there are still many problems and chalenges in the preparation techniques and growth control methods of 2D MoS₂.In this article,the non-uniform distribution character of MoS₂,which is universal in many cases,on the growing substrate is studied,and the growth process of MoS₂,especially the chemical vapor deposition（CVD）method is studied.With the aid of finite element software,the influence mechanism of distribution uniformity is explored and analyzed,and the distribution uniformity of MoS₂ on the substrate is improved.The main research contents are as follows:Firstly,2D MoS₂ were prepared on Si/SiO₂ substrates by CVD,and characterized by optical microscopy,atomic force microscopy and Raman spectroscopy.The results show that the growth condition of MoS₂ in the side region and the middle region of the substrate is quite different,in the side region,there are a few crystals,but with large size and good quality;in the middle region,there are quite a few crystals,but the size is small,and some crystals overlap one another.The size difference reaches 14μm,and the effective growth area size is 1.2 cm²The simulation model of CVD growth process was established by the introduction of the finite element method,and its validity and accuracy were verified.We extracted the factors that may affect the uniformity of MoS₂ distribution on the substrate,including pressure,temperature and carrier gas velocity on the substrate surface.It is concluded that the velocity of gas on the substrate is the key factor that affect the uniformity of MoS₂ distribution.The distribution of carrier gas velocity on the substrate surface was further studied.The distance between velocity contour and substrate have the similar side-middle difference,and the thickness of low velocity area in the side region is thicker than that in the middle region.Combined with the boundary layer theory,the movement of gaseous precursor in the boundary layer during CVD process is analyzed from the perspective of nucleation.The substrate placement method with the growth face up was proposed calculated by finite element simulation.The simulation results show that,in the face up method,the velocity distribution on the substrate is uniform,and the distance from the velocity contour to the substrate is almost the same,showing no side-middle difference.It is predicted that the face up method can improve the uniformity of MoS₂ distribution on the substrate.The validity and accuracy of the simulation prediction were further verified by experiments.The experiments results show that MoS₂ is evenly distributed on the substrate,with good quality and small size difference of about 3μm,and the growth area covers the whole substrate,about 3 cm².This work studies the morphology distribution on the substrate and its potential influence factors with the aid of the finite element method.This work provides a new way for improving the distribution uniformity of MoS₂ and designing new preparation methods,which should facilitate subsequent design and development of new devices.