Illuminating microstructural effects on electron-phonon coupling in monolayer MoS2.

Electron-phonon interactions are the fundamental reason behind thermal-electric energy exchange, they depend on electron and phonon dispersions, which are altered by the inclusion of material defects. Material defects such as grain boundaries and point vacancies can be the result of conditions like uneven growth or exposure to irradiation, either of which can be tailored to produce a desired defect density. The strength of these interactions can be evaluated by examining the optical bandgap of a material, i.e. the photoluminescence signal corresponding to exciton recombination. In this work, we use a CryoRaman microscope to perform low-temperature measurements from 4K to room temperature using site-selective optical spectroscopy in single-layer MoS2 to analyze exciton decay rate as a function of momentum. Additionally, since differences in defect type vary localized mid-gap states, we employ aberration-corrected transmission electron microscopy (TEM) to correlate spectroscopic identities with specific defects in the regions of interest. This work helps us understand the fundamental mechanisms of thermal-electric energy conversion and will help optimize energy harvesting in polycrystalline 2D materials for thermoelectric and optoelectronic devices.