Investigation On The Anisotropic Structual And Electrical Stabilities Of Two-dimensional Tin Selenide

Due to their excellent physicochemical properties such as tunable energy band,high carrier mobility,high photogenerated carrier collection rate,and high mechanical strength,two-dimensional materials are widely used in optoelectronics,photonics,biosensing,energy conversion and storage fields,which has broad application prospects.As an indirect bandgap semiconductor,two-dimensional tin selenide（SnSe）has been reported to have a ZT value as high as 2.6（a dimensionless figure of merit that describes the efficiency in thermoelectric materials）,and has become a research hotspot in the field of thermoelectrics.Due to its excellent flexibility and planar properties,SnSe can be used in flexible devices and wearable devices.In addition to strain engineering,as an in-plane anisotropic 2D material,the crystal structure of SnSe also provides a new dimension for the regulation of its physical properties.In addition,due to its advantages of nontoxicity,low cost,and abundant reserves,SnSe can also be used in lithium-ion batteries and catalysis.Since SnSe is inevitably affected by external forces and chemical environment in the process of material preparation,device processing and application,studying the mechanical and chemical stability of the material and revealing the regulation effect of structure on device performance will be very important for device design,preparation and application.Performance evaluation has important guiding significance.This paper mainly takes SnSe with low lattice symmetry as the research object,and studies its mechanical properties,structural stability and electromechanical properties:（1）The in-plane anisotropy it has can make it have a good application prospect in new electronic devices.Realizing the determination of its in-plane crystallographic orientation is the basis for the design and fabrication of related devices.By characterizing the morphology and structure of SnSe nanosheets prepared by mechanical exfoliation,we revealed the cleavage trend:SnSe tends to cleavage along{011}plane to form long and straight nanosheets.Combined with first-principles calculations,we further revealed the anisotropic mechanical behavior of SnSe,which shows a cleavage trend due to the fact that the[011]direction has lower fracture strain and stress than[001]and[010].The research in this aspect provides an experimental basis for the rapid determination of SnSe crystal orientation.（2）Since SnSe is exposed to an alkaline environment in electrochemical applications,and the transfer and fabrication of 2D material electronic devices usually involve chemical etching,it is crucial to study its structural stability in an alkaline environment.We analyzed the structural stability of SnSe in an alkaline environment.In an alkaline environment,single-crystal SnSe nanosheets exhibit anisotropic etching process,and their single-crystal structure will gradually transform into polycrystals composed of SnSe₂,Sn,and Se grains.This research will provide ideas for the design,fabrication and performance optimization of SnSe devices.（3）Strain engineering is one of the effective methods to present the physical properties of two-dimensional materials.The excellent mechanical properties of 2D SnSe make it promising for application in flexible electronic devices.Here,we discovered the crystallographic orientation-dependent piezoresistive effect present in SnSe:the electrical conductivity of SnSe nanosheets gradually decreases（increases）with increasing tensile（compressive）strain.Its electromechanical response factor is as high as 460,which is significantly better than other common two-dimensional materials such as MoS₂,ReSe₂,and BP.The anisotropic piezoresistive effect of 2D SnSe provides experimental support for its applications in wearable electronic devices,strain sensors and other fields.