Rapid Layer-Number Identification of MoS₂ Nanosheet in MoS₂/MoO₂ Conformal Heterostructures by Color: Implications for the Fabrication of 2D/3D Heterostructures

The conformal integration of two-dimensional (2D) materials and conventional bulk (3D) materials has triggered great investigation because of the new physical couplings arising at 2D/3D interfaces. The electronic structures of 2D materials are layer dependent, which suggests that the physical properties of 2D/3D heterostructures can be effectively modulated by controlling the layer numbers of 2D materials. However, the precise thickness identification of 2D materials in conformal epitaxial 2D/3D heterostructures is still challenging. We proposed a rapid and nondestructive optical approach to determine the layer number of the MoS2 nanosheet in a MoS2/MoO2 conformal heterostructure synthesized by chemical vapor deposition. By developing a four-layer reflection model based on Fresnel laws, the optical color charts of MoS2/MoO2 heterostructures with different layer numbers of the MoS2 nanosheet were theoretically calculated. The present derived color charts fit well with the optical microscopy images of MoS2/MoO2 heterostructures, with the layer number of the MoS2 nanosheet further verified by Raman and photoluminescence spectroscopy and annular dark-field scanning transmission electron microscopy characterizations. In particular, the contrast of MoS2/MoO2 heterostructures can be efficiently regulated by the wavelength of incident light, which is validated by the presented theoretical model and experimental observation. Our results provide a rapid way to identify the layer number of 2D material in 2D/3D heterostructures, which will benefit the fabrication and application of 2D/3D conformal heterostructures.