Study Of Layers Identification Of 2D Materials Based On Optical Contrast

With the advancement of instrument science as well as the development of experimental technology,two-dimensional nanomaterials gradually move from theory to reality.The two-dimensional materials possess excellent performance and potential application in various fields such as mechanics,optics,electricity,and magnetism.Since studies have demonstrated that the number of layers of two-dimensional materials has a significant influence on its properties,it is particularly important to carry out the identification of 2D materials layers number.Traditional characterization methods are able to perform the layer identification work by using confocal raman spectroscopy and atomic force microscopy.However,the samples suffer from some irreversible damage during the characterization process.As an alternative,optical contrast achieves the efficient identification of the number of layers of a two-dimensional material.This method is fast,simple,and does not cause damage to the sample.This paper focuses on the discussion of optical contrast,and studies the reliability and practicability of the optical contrast values of different materials,including graphene,InSe,MoS₂ and GaSe.The main contents of this paper include the following two aspects:First,based on Fresnel formula,we analyze the derivation process and calculation formula of single-layer membrane and two-layer membrane.The above theory is applied to the calculation model of the current study.We analyze the derivation process and calculation formula of the average theoretical optical contrast value of the samples.We introduce the relevant processes and crucial points of simulation calculation.On the basis of the traditional mechanical peeling,we propose two methods of mechanical peeling and adapt them to the current study.Meanwhile,the equipment and method for the actual layer number characterization of the sample are also briefly summarized.The actual optical contrast value of the samples are derived and calculated.The selection principle and approach of the band interval value are also presented.Second,we describe the four kinds of materials,including graphene,InSe,MoS₂and GaSe.On the one hand,we calculate and plot the average theoretical optical contrast value and theoretical waveform of the three bands of the above four two-dimensional materials on the platform of MATLAB.On the other hand,we prepare one to four layers of the above four two-dimensional materials by using mechanical peeling,and confirm the corresponding layer number of them by confocal Raman spectroscopy and atomic force microscopy.We further select the suitable channel for comparing the average theoretical optical contrast with the actual value of the four materials by MATLAB.Finally,we calculate the deviation between the actual optical contrast and the theoretical value of the four two-dimensional materials with layer numbers ranging from 1 to 4,and fit the calculation formulas of the actual optical contrast for the above materials.