An In Situ Reflectance Spectroscopic Investigation to Monitor Two-Dimensional MoS₂ Flakes on a Sapphire Substrate

In this work, we demonstrate the application of differential reflectance spectroscopy (DRS) to monitor the growth of molybdenum disulfide (MoS₂) using chemical vapor deposition (CVD). The growth process, optical properties, and structure evolution of MoS₂ were recorded by in-situ DRS. Indeed, blue shifts of the characteristic peak B were discussed with the decrease of temperature. We also obtained the imaginary part of the MoS₂ dielectric constant according to reflectance spectra. This method provides an approach for studying the change of two-dimensional (2D) materials' dielectric constant with temperature. More importantly, our work emphasizes that the DRS technique is a non-destructive and effective method for in-situ monitoring the growth of 2D materials, which is helpful in guiding the preparation of 2D materials.