Tuning Phonon and Exciton Dynamics through alloying in 2D Transition Metal Dichalcogenides

Quasiparticles Phonons play a key role in thermal transport and electronic behavior in 2D materials, where dipole interactions and lattice dynamics can be tuned via compositional alloying. However, controlling momentum transitions of phonons, coupling strength of excitons, and their locality based on intrinsic stresses in the lattice remains a challenge. This is attributed to a limitation in bulk characterization techniques; they give global information that averages thousands of unit cells, making it impossible to correlate which bonds result in individual displacement modes or optical transitions. Hereby, we investigate how alloying in W_xMo_1-xS₂ modulates local dipole moments and phonon/exciton populations, with implications for thermoelectric performance. By varying stoichiometry across five compositions, we examine how vibrational properties evolve with atomic-scale disorder and dipole perturbation. Bulk vibrational modes were measured using Raman and Infrared (IR) spectroscopy, with Raman providing high superior energy resolution and enabling the collection of low-energy optical phonons. The optical spectrum was interpreted with photoluminescence (PL) to measure band transitions and splitting in the valence band. To access vibrational and optical behavior beyond the optical diffraction limit set by the wavelength of photons, we used monochromated electron energy loss spectroscopy (EELS) inside an aberration-corrected scanning transmission electron microscope (STEM), enabling atomic-scale mapping of phonon and exciton populations. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) confirmed chemical composition uniformity over micron and nanometer length scales. This combined approach reveals how alloying influences dipolar spin-orbit coupling and lattice vibrations, offering insight into heat thermal transport and informing structure property tunability of exciton-phonon coupling control in low-dimensional thermoelectric systems semiconducting platforms.