Electron-phonon coupling at complex grain boundaries in single layer MoS₂

Electron-phonon coupling is an intrinsic interaction in semiconductors that helps define the temperature dependence of optical band gaps. The coupling constant strongly depends on electron and phonon dispersions in the material, which should change in the presence of planar defects. While grain boundaries generally are the result of uneven growth during crystallization of individual grains, they often can be tailored in particular orientations to design materials with better electric current mobility and intragranular thermal transmission. Hereby, 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 the exciton decay rate as a function of their momentum. Simultaneously, we acquire the active Raman modes to probe the bonding covalence and calculate the phonon energy. Lastly, since mirror and tilt boundaries vary in the localized mid-gap states at the faceted interface, we employ aberration-corrected transmission electron microscopy (TEM) to correlate spectroscopic identities with alpha and beta defects along boundaries. This work details a step forward in energy harvesting of polycrystalline 2D materials for thermoelectric and optoelectronic devices.