Plasma-induced process for oxygen replacements in 2D WS₂ and its effect on the excitonic behavior

Atomic defects and lattice reordering play an instrumental role in assessing the physical properties of two-dimensional (2D) transition-metal dichalcogenides (TMDs). We study here the impact of plasma-induced oxygen (O) replacement process on WS₂, both experimentally and theoretically. We developed a plasma treatment process to remove the top-layer S atoms and replace them with oxygen atoms. In addition, we conducted atomistic molecular dynamics (MD) simulation of the relaxation process of the lattice when top-layer S atoms are removed and replaced by O atoms, which showed that this treatment induced atomic reordering and significant lattice strain that can reach ∼1%. We employed various experimental techniques, including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL). Experimental analyses confirmed the lattice modifications, as we observed significant lattice deformation and estimated sub-percentage strains, a reduction in S atom concentration, and enhanced oxygen replacements. Also, while A-excitons dominated the light emission, we observed noticeable defect-induced emission, whereas Raman analysis reflected the lattice deformation through E_2g mode shift. Owing to the isovalence of S and O atoms, the electron density remained unchanged. Therefore, we uncover the interplay between S vacancies, O replacement, and excitonic properties via a defect-engineering approach, thereby opening the path to the development of tailored optoelectronic and light-emission applications.