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

In this work, we demonstrate the application of differential reflectance spectroscopy (DRS) to monitor the growth of molybdenum disulfide (MoS) using chemical vapor deposition (CVD). The growth process, optical properties, and structure evolution of MoS 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 MoS 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.