Substrate-Driven Nanoscale Control of Photoluminescence and Raman Response in WS₂ Monolayers for Optoelectronic Applications

This study investigates the nanoscale optical and electronic behavior of a WS2 monolayer interfaced with Pt and SnS substrates, as well as a freestanding configuration. Using photoluminescence and Raman spectroscopy with nanometer-scale spatial resolution, we reveal how substrate-induced charge transfer, doping, and image-charge effects modulate exciton and trion properties. In the Pt-supported regions, significant hole accumulation enhances trion binding energy while suppressing excitonic responses, attributed to strong substrate coupling at the nanoscale. On SnS, moderate dielectric screening preserves excitonic properties while inducing p-type doping via type-II band alignment. The freestanding WS2 monolayer displays maximized exciton and trion binding energies, with minimal external perturbations. These findings provide critical insights into nanoscale control of charge interactions and exciton dynamics, enabling targeted design strategies for WS2-based optoelectronic and photonic devices.