Substrate-induced charge transfer and optical quenching in monolayer semiconducting TMDCs

Abstract The optical and electronic properties of a two-dimensional (2D) material are profoundly influenced by the nature of its underlying substrate, thereby making the substrate-material interactions a vital factor for both fundamental studies and technological applications. These interactions can significantly modify the electronic structure and optical response of the 2D system, providing a powerful means to tailor and optimize their properties. In this study, we employ optical spectroscopy, including Raman and photoluminescence (PL) measurements, to probe the effects of the substrate on monolayer transition metal dichalcogenides (TMDCs): tungsten disulfide (WS 2 ) and tungsten diselenide (WSe 2 ). The films were synthesized by the laser-assisted synthesis technique (LAST) on silicon/silicon dioxide (Si/SiO 2 ) substrates and subsequently transferred onto interdigitated Si–Si/SiO 2 platforms to study the effects of bare Si and Si/SiO 2 surfaces on these materials. The optical response of the 2D single crystals on bare Si and Si/SiO 2 substrates reveals pronounced substrate-induced modifications, underscoring the critical influence of the supporting surface. Portions of the monolayers of WS 2 and WSe 2 on the Si/SiO 2 areas of the interdigitated substrate showed strong Raman and PL signals, while on the bare Si regions, these signals were relatively weaker or strongly suppressed. Additionally, strong PL quenching, approximately 10-fold for WS 2 and 13-fold for WSe 2 , was evident. A slight shift in the PL peak was also observed, which was more pronounced in WSe 2 . We rationalize these observations via first-principles calculations identifying band alignments and surface interactions as the mechanisms producing the PL quenching in TMDCs on Si substrates. Our findings highlight the potential of substrate engineering to tune the optoelectronic performance of 2D materials for advanced device applications, thereby opening new perspectives in microelectronics.