Substrate optimization for advanced optical characterization of chemical vapor deposition grown transition metal dichalcogenide monolayers

Transition Metal Dichalcogenides (TMDs) present unique optoelectronic characteristics arising from tightly bound excitons that make them suitable for diverse applications for next-generation devices. Understanding their electronic and optical properties under external stimuli - temperature and strain - is essential for their performance. Chemical vapor deposition (CVD) offers scalable synthesis of high-quality TMD monolayers, where slight adjustments of the growth parameters can induce controlled variations in their properties through their intrinsic strain. One fundamental challenge in the application of CVD grown TMDs, lies in developing a fast and reliable in situ characterization method, that is non-destructive. The combination of resonant Raman and photoluminescence (PL) spectroscopies, present a reliable approach to assess TMD samples, both in terms of their defect density and intrinsic strain, while also remaining a non-destructive method. However, the intensity of the Raman signal can be quite weak, even under resonant conditions, hindering its use for fast sample analysis. In this work, we systematically investigate the influence of SiO₂ layer thickness on Si substrates as a reliable way to enhance Raman and PL intensities of monolayer MoS₂ and WS₂. By analyzing the intensity of the first and second-order bands as a function of the SiO₂ thickness, we identify substrate thicknesses that maximize interference-based enhancement, enabling faster defect characterization and improved signal strength. We further demonstrate how intrinsic strain of CVD-grown MoS₂ and WS₂ samples modifies these enhancement effects, providing insight into the interplay between strain, optical interference, and excitonic resonance.