Study On Microscopic Reflectance Difference Spectroscopy And Applications In Two-dimensional Materials

Since monolayer black phosphorus(also known as phosphorene,BP)was successfully exfoliated,anisotropic two-dimensional(2D)materials have attracted extensive attentions.Various anisotropic two-dimensional materials with different structures and properties have been reported,showing great application prospects in electronics,optoelectronics,new energy,advanced manufacturing,and other fields.Until now,the methods to characterize anisotropic 2D materials are still in the initial stage and facing severe hurdles,such as accurate measurement of optical anisotropy,identification of crystalline orientation and so on.In this paper,the imaging approach of reflectance difference spectroscopy for 2D materials is studied.A microscopic reflection difference spectrometer(micro-RDS)and an azimuth-dependent reflectance difference microscopy(ADRDM)was developed to solve the key characterization problems in the field of anisotropic 2D materials,including the accurate measurement of optical anisotropy,crystalline orientation,film thickness,and the characterization of heterostructures and modulations of anisotropic 2D materials.In the order of the research sequence,the work in the thesis can be listed as the following:1.The depolarization effect of high numerical aperture objective lens was systematically studied,which provides a theoretical basis for the design of microscopic difference spectrometer suitable for two-dimensional materials.Based on the three-phase model,the physical mechanism of reflectance difference spectroscopy was discussed,and the scattering matrix method was proposed for the direct calculation of reflectance difference spectroscopy of multilayer heterostructures.2.A micro-reflectance difference spectrometer based on liquid crystal variable retardation(LCVR)was developed and an innovative method of compensating component's installation error through online calibration of LCVR was proposed to suppress pseudo-RDS signal introduced by depolarization effect of the objective lens.The system error is better than?0.002 when a 100x objective is integrated.An azimuth-dependence reflectance difference microscopy with wavelength adjustable function was developed.The optical system,hardware control system,data acquisition and processing,and software design were discussed.We proposed an online calibration method to overcome temperature dependent phase retardation of LCVR.3.The imaging reflectance difference spectroscopy was proposed to directly resolve optical anisotropy and unambiguously determine the crystalline orientation of anisotropic 2D materials.Using the optical anisotropy as a highly sensitive probe,the fundamental properties and modulations of the 2D materials,such as BP and Re S₂,were studied,which establishes a route to characterize 2D using RDS technology and promote the study of anisotropic 2D materials.4.For the first time,anisotropic dielectric screening effect was utilized to modify in-plan isotropy into in-plane anisotropy of isotropic 2D materials.As a demonstration,the surface anisotropy of Mo S₂ monolayer was induced by anisotropic Al₂O₃(1120).The different dielectric environments of air,_on and _en of Al₂O₃(1120)dramatically changed the binding energies of excitons in Mo S₂ monolayer from 0.1 to dozens me V.5.We proposed the design of nano-polarizer based on anisotropic 2D materials and a resonant cavity for the first time.The BP nano-polarizer composed of BP crystal as the birefringence crystal and transparent silica on a silicon substrate as the resonant cavity was systematically studied.Finally,the experimental result was presented.