| Two dimensional(2D)Monolayers of group IV-VI compounds have a folded honeycomb structure,high carrier mobility,moderately wide indirect band gap and inplane anisotropy,which have attracted much attention in the field of 2D materials research in recent years.These advantages make it a great potential for applications in the field of optoelectronic devices.The materials are prone to atomic deletion,doping or deformation during preparation and processing,and defects will inevitably appear.These defects can lead to the disruption of the periodicity of the material lattice and the formation of scattering centers or complex carrier centers,which in turn affect the electronic structure and physical properties of the material.In addition,one dimensional(1D)nanotubes have unique size and chirality related energy band characteristics,and the study of material properties with structural changes through energy band engineering can provide a reasonable basis for the design of new functional optoelectronic devices.In this paper,the properties of 2D IV-VI compound monolayers and their defect structures,as well as the curled and folded IV-VI singlewalled nanotube structures along different directions,are thoroughly investigated by using a first-principles calculation method combining density functional theory(DFT)and Non-equilibrium green’s function(NEGF).The main studies are as follows:1.Two-dimensional Sn S armchair and zigzag structures were constructed in the periodic system,and the two-probe device system was created on the basis of the optimized periodic structure.The photocurrent is calculated for the energy range of incident polarized light from 1.4 e V to 3.4 e V.The results show that the variation curve of the photocurrent with the incident light polarization angle θ is cos(2θ);the photocurrent has a large intensity in the energy range of incident photons from 2.2 e V to 3.4 e V,and there are two peaks of photocurrent near 2.4 e V and 3.2 e V;at the same photon energy,the photocurrent increases with the increase of bias voltage and finally reaches the saturation value;the photocurrent results have obvious extinction ratio characteristics and strong in-plane anisotropy.The rich photocurrent results of 2D Sn S materials in the visible energy range indicate that they can be widely used in optoelectronic devices.2.Two-dimensional Sn S structures containing single-vacancy defects of sulfur or tin atoms were investigated.The defect formation energy,transition energy level,band structure,and density of states of the single-vacancy sulfur atom defect and singlevacancy tin atom defect structures were calculated,and the adsorption characteristics of the stable defect structures for NO and SO2 were further investigated.The results show that the defect sites in the material are the main adsorption points for gas molecules,that there is charge transfer between the gas molecules and the defect system,and that the Sn atomic vacancy defects introduce magnetic properties into the system.And the calculated results of transmission spectra further confirm that the defect Sn S monolayers can be used as sensors for NO and SO2 gases.3.Armchair and zigzag single-walled Ge S nanotube structures were established,and stable structures of Ge S nanotubes with different tube diameters were obtained after optimization by atomic relaxation.The band structure and density of states of different tube diameters were calculated based on the stable structures.The Young’s modulus of armchair(11,11),(13,13)and(15,15)nanotubes were calculated by fitting deformation and binding energy curves.The results show that Ge S nanotubes are semiconducting materials,and their band gap values increase with the increase of nanotube diameter;Ge S nanotubes are stress-sensitive materials,especially the structures of zigzag Ge S nanotubes are more affected by the stress change;the Young’s modulus of armchair(11,11),(13,13)and(15,15)nanotubes are 227.488,211.888 and 213.920 Gpa,respectively,which are greater hardness than silicon nanotubes and black phosphorus nanotubes. |
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