Optimized Parameters for Identifying the Layer Number of Few Layer Chromium Tri-iodide from a Theoretical Perspective: Implications for Two-Dimensional Spintronics

Chromium tri-iodide (CrI3), a recently discovered two-dimensional ferromagnetic material for spintronics, has attracted great attention because of its intriguing physical properties, such as insulating character, layer-dependent magnetism, and out-of-plane magnetic easy axis. However, the instability of few layer CrI3 under ambient conditions hinders layer-number characterization by atomic force microscopy, which prevents the exploration of layer-dependent properties and applications. Here, we theoretically propose that the layer number of few layer CrI3 can be identified by optical-contrast and Raman-intensity ratio methods. In the optical contrast method, by using an appropriate monochromatic incident light, the contrast of few layer CrI3 on an SiO2/Si substrate can be maximized. Thicknesses of 75-90, 230-270, and 385-450 nm of SiO2 are suitable for obtaining optimized optical contrast. The Raman intensity ratio between few layer CrI3 and an SiO2/Si substrate is sensitive to the variation in thickness of the flakes and can be used for CrI3 layer number characterization. This work provides two accurate, nondestructive, and efficient methods to identify the layer number of few layer CrI3 and the corresponding optimized parameters, such as SiO2 thickness and light wavelength, for two-dimensional spintronic applications.