Research Of Graphene Based On Nonlinear Optical Microscopy

Graphene has many magical physical,chemical and biological properties due to its unique structure.Many researches have shown that graphene has the strong mechanical,good electrical,excellent electrical and unique optical properties.It is also a kind of typical 2d and3 d material so that is widely used for solar cells,transistors,etc.In addition,Graphene is expected to be used in production of gene sequencing and super computer.So the quality of graphene characterization is becoming stricter.Firstly,Speaking from the overview of nonlinear optics,then on The principle of the two-photon fluorescence,second harmonic and coherent anti stokes Raman scattering were analyzed theoretically.At the same time,the structure characteristics,preparation methods and the transfer method of the graphene and foam material were studied in detail.In this paper,Graphene grown on polished copper foils and unpolished copper foils was imaged using a five-channel multiphoton microscope using two-photon excitation fluorescence(TPEF),second harmonic generation(SHG),and coherent anti-Stokes Raman scattering(CARS).The morphology and film quality of the graphene can be analyzed from these three images.Because of unique vibration advantage,CARS is much better resolution than TPEF and SHG.TPEF reflects defects of the graphene,and the weak signal of SHG can prove the central symmetry of graphene.TPEF and SHG signal both can provide multilayer graphene layers and then use them to analyze the graphene layers and defect.Graphene Raman spectroscopy analysis and TPEF,SHG and CARS image analysis of graphene and unpolished copper foil grown on polished copper foils and the ratio of the intensity of the 2D peak and the G peak using the Raman spectrum demonstrate that the graphene grown on polished copper foil is a monolayer grapheme but graphene grown on unpolished copper foil is multilayer graphene.It can be seen clearly in the CARS images that graphene grown on unpolished copper foil has obvious stratification.The TPEF and SHG signals of the graphene grown on the unpolished copper foil are significantly weaker than those of the graphene grown on the polished copper foil,a clear contrast can be seen in the composite images of TPEF,SHG and CARS.At the same time,the graphene grown on the unpolished copper foil was characterized by CARS and TPEF,and it was found that it retained the structural characteristics of the original copper film.Using this property,we can make more complex devices by changing the structure of the copper thin film.In addition,three-dimensional scanning imaging of foamed porous graphene was performed using theCARS microscope for the first time,the spatial structure of porous graphene was observed by the CARS microscope,and the distribution of graphene on the surface was analyzed.The scanning depth can be up to 2.5 microns,so that CARS microscope can be used to analyze multi-layer porous graphene and lay a foundation for its application in other fields in the future.