Designing a functionalized 2D-TMD (MoX₂, X = S, Se) hosting half-metallicity for selective gas-sensing applications: Atomic-scale study

Half metallicity is a desirable property not only for spintronic devices but also for selective gas sensing applications. The scope of the present investigation is to search/design transition-metal “TM” doped transition-metal dichalcogenide “TMD” monolayers (MoX₂, X = S, Se) that can host half-metallicity. The screening of various TMs, using spin-polarized DFT calculations, yielded positive results on (Mn, Fe, and Ni)-doped MoS₂ MLs and (V, Mn, Fe, and Co)-doped MoSe₂ to host half-metallicity when smaller samples of sizes 4 × 4, 5 × 5, and 6 × 6 primitive cells (PCs) are considered. The half-metallicity disappears for larger samples. The origin of this phenomenon can be attributed to the existence of ferromagnetic-coupling (FMC) interactions, governing the ground-state, involving the TM-dopant with its six mirror images, formed by the periodic-boundary conditions. The disappearance of half metallicity is also associated with a drastic change in magnetization (|ΔM|≫ 0). The critical length for the existence of FMC is found to be dependent on both the host crystal and the type of magnetic impurity; at the average is of the order of L_c ∼ 20 Å. Furthermore, we investigated the relevance of half-metallicity to gas-sensing applications (e.g., specifically, MoSe₂:Mn ML was taken as an example). In this latter particular case, our results showed the half-metallicity to be a useful property that can be explored for selective gas-sensing of NO₂ gas molecules. Our theoretical results are benchmarked to the available data in literature and found to be in good agreement with them.