Research On Optical And Electronic Properties Of Two Dimensional Materials

This article mainly studies the optical and electrical properties of two-dimensional materials.By analyzing the properties of electrical transport and optical second harmonics of two-dimensional materials,we can further understand the research methods and research status of two-dimensional materials,and achieve a better understanding of two-dimensional materials.The article not only has an overall grasp,but also has the purpose of doing a focused and in-depth research.The first chapter of this article summarizes two-dimensional materials and reviews the related developments in this research field,and shows the examples of graphene and layered transition metal disulfides.Then,the energy band properties,the valley polarization of two-dimensional materials and external field on the research on the effect of two-dimensional materials are summarized.In Chapter 2,this article introduces the optical research content of two-dimensional materials,briefly introduces nonlinear optics,second harmonic generation and their principles,and introduces popular optical research methods in two-dimensional materials,such as magneto-optical Kerr effect(MOKE)technology experiment,ultrafast spectroscopy,Raman spectroscopy,etc.Chapter 3 presents the theoretical research methods of the electrical transport properties of two-dimensional materials,and briefly summarizes the non-equilibrium Green's function(NEGF)and density functional theory(DFT).Next,in Chapter 4,this article focuses on the microscopic second-harmonic generation(SHG)technology experiment,describes the built-up microscopic SHG experimental optical path,and uses the built-up optical path to perform SHG testing on the BaTiO₃ thin film samples grown on SrTiO₃.The advantage of the microscopic SHG optical path is that it can have relatively high spatial resolution.It is able to observe and detect micron-level small samples in real time.What's more,the microscopic objective lens can focus the fundamental frequency light to a small extent and the required sampling range is smaller.It has higher SHG excitation efficiency than ordinary spherical lens.In this paper,the symmetry break of the BaTiO₃ film is confirmed through experiments,and the SHG signal of the sample under different incident light power is explored.Finally,a simple and effective method is used to judge whether the source of SHG signal is pure,and it is pointed out that the influence of the substrate on the SHG signal intensity may appear during the SHG experiment.In Chapter 5,we use Matlab to calculate the energy band and transport conductance of silicene.We introduce the silicene nano band model and calculation method,and use the tight-binding model and non-equilibrium Green's function method to study different geometric structures.The electrical control method of the transport properties of silicene narrowed nanoribbons,the band structure and transport properties under the influence of external electric field and potential energy are discussed.In addition,we have studied the influence of the position and width of the central scattering zone on the conductivity of the system,and found that the position and width can affect the conductivity to a large extent.Interestingly,the symmetrical structure of the central region can cause resonance effects and significantly increase the conductivity of the silicene heterojunction.Therefore,this is an effective method to adjust the transport properties of the silicene heterojunction.As a result,we propose a novel dual-channel structure.Compared with the single-channel structure of the same width,the conductance of this structure is almost twice that of the single-channel structure.