Microstructural Simulation And Electrical Properties Study Of Silicon Nanotubes

Silicon nanotubes are a kind of semiconductor material with rich structure and excellent properties.The microstructure of silicon nanotubes will determine their macroscopic properties.Understanding the stability law of silicon nanotubes in the heating process is of great theoretical and practical significance for controlling the growth of materials according to demand and deeply understanding the relationship between macroscopic properties and microstructure of materials.In this paper,molecular dynamics method was used to systematically explore the evolution of microstructure of single-walled and double-walled silicon nanotubes during heating.In order to further explain the deformation mechanism,the density functional theory is used to analyze and calculate the deformation mechanism.This paper provides sufficient theoretical support for the design and development of high performance silicon nanotubes.Firstly,the thermal stability of silicon nanotubes was studied by molecular dynamics.The results show that the melting points of single-wall/double-wall armchair type and zigzag type silicon nanotubes are only related to their diameters,and have nothing to do with the types of nanotubes.When the diameter is larger than20 (?),the structure size has little effect on the melting point of the double-walled serrated and handrail silicon nanotubes.For the double-walled armchair(n,n)@(n+m,n+m)silicon nanotubes,there is a special quadrilateral structure;For the double-walled serrated silicon nanotubes(n,0)@(n+m,0),there are three special structures: triangle,quadrilateral and pentagon.The results show that the structure of silicon nanotubes has the degeneracy of melting point,and the special structure of silicon nanotubes is the result of the interaction of the spacing of silicon nanotubes and the arrangement of atoms.Secondly,the electrical properties of single and double-walled armchair silicon nanotubes were studied by density functional theory.The results show that the structure of both double-wall and single-wall armchair type silicon nanotubes changes from indirect bandgap semiconductor to direct bandgap semiconductor with the increase of tube diameter.When the chirality index n is a multiple of 3,the band gap of single-walled and double-walled zigzag silicon nanotubes suddenly decreases,and the structure becomes nearly metallic.Finally,the roughness of the tube wall of the special shape silicon nanotubes is explained by the density of states diagram because of the mixing of sp2 and sp3.The smooth pipe wall is the result of the increasing proportion of sp2 hybridization,which confirms the structure rule found.