Transition Metal Dichalcogenide MoS${}_2$: oxygen and fluorine functionalization for selective plasma processing

Abstract

Low-temperature plasma processing is a promising technique for tailoring transition metal dichalcogenides (TMDs). For chalcogen substitution processing, a key challenge is to identify the ion energy window that enables selective chalcogen removal while preserving the metal lattice. Using ab-initio molecular dynamics (AIMD), we demonstrate that oxygen and fluorine functionalization widen the processing window by significantly lowering the sulfur sputtering energy threshold ($E_{\text{sputt,S}}$) of MoS${}_2$ from $\sim 30$ eV to $\sim 10$ eV via formation of sputtering products such as SO${}_2$ and SF${}_n$. Additionally, we show that experimentally relevant cryogenic temperatures strongly affect $E_{\text{sputt,S}}$. The dependence is confirmed via AIMD and also predicted by a mechanistic parameter-free theory, suggesting that $E_{\text{sputt}}(T)$ generalizes to other TMDs, functionalization, and surface impacts in general. Our results highlight oxygen/fluorine functionalization, ionic impact angle, and material temperature to be key control parameters for selective, damage-controlled chalcogen removal in TMD processing.