Two-dimensional (2D) transition-metal dichalcogenides (TMDs) are new crystalline materials with exotic electronic, mechanical, and optical properties. Due to their inherent exceptional mechanical strength, these 2D materials provide us the best platform for strain engineering. In this study, we have performed first-principles calculations to study the effect of uniaxial strains on the electronic, magnetic, and mechanical properties of transition-metal dichalcogenides (TMDs) MX₂ (where M = Cr, Mo, W and X = S, Se), monolayers (2D), and armchair and zigzag nanoribbons (1D). For the mechanical strength, we determined the tensile strength (σ) and Young's modulus (Y) and observed that σ and Y are higher in monolayers (most in WS₂ML) as compared to nanoribbons where monolayers resist tension up to 25-28% strain while nanoribbons (armchair and zigzag) can be only up to 5-10%. Deformation potential (Δ _p ) in the linear regime near the equilibrium position(ϵ < 2%) has also been calculated, and its effect on monolayers is observed less as compared to nanoribbons. In addition, unstrained nonmagnetic monolayers are direct band gap semiconductors (D) which changed to indirect band gap semiconductors (I) with the application of strain. Ferromagnetic states of metallic zigzag nanoribbons (including up spin channel of 7-CrS₂NR and 7-CrSe₂NR) are greatly affected by strain and show half-metal-like behavior in different strain range. The magnetic moment (μ) that is predominantly observed in zigzag nanoribbons is 2 times higher than that of other nanoribbons. This magnetism in nanoribbons is mostly caused by transition-metal atoms (M = Cr, Mo, W). Thus, our study suggests that strain engineering is the best approach to modify or control the structural, electronic, magnetic, and mechanical properties of the TMD monolayer and nanoribbons which, therefore, open their potential applications in spintronics, photovoltaic cells, and tunneling field-effect transistors.

Spin-polarized density-functional theory (DFT) has been employed to study the effects of atmospheric gases on the electronic and magnetic properties of a defective transition-metal dichalcogenide (TMD) monolayer, MoX₂ with X = S or Se. This study focuses on three single vacancies: (i) molybdenum “V_Mo”; (ii) chalcogenide “V_X”; and (iii) di-chalcogenide “V_X2”. Five different samples of sizes ranging from 4 × 4 to 8 × 8 primitive cells (PCs) were considered in order to assess the effect of vacancy–vacancy interaction. The results showed that all defected samples were paramagnetic semiconductors, except in the case of V_Mo in MoSe₂, which yielded a magnetic moment of 3.99 μ_B that was independent of the sample size. Moreover, the samples of MoSe₂ with V_Mo and sizes of 4 × 4 and 5 × 5 PCs exhibited half-metallicity, where the spin-up state becomes conductive and is predominantly composed of $d_{xy}$ and $d_{{\mathrm{z}}^2}$ orbital mixing attributed to Mo atoms located in the neighborhood of V_Mo. The requirement for the establishment of half-metallicity is confirmed to be the provision of ferromagnetic-coupling (FMC) interactions between localized magnetic moments (such as V_Mo). The critical distance for the existence of FMC is estimated to be $d_c\cong$ 16 Å, which allows small sample sizes in MoSe₂ to exhibit half-metallicity while the FMC represents the ground state. The adsorption of atmospheric gases (H₂O, O₂, O₃) can drastically change the electronic and magnetic properties, for instance, it can demolish the half-metallicity characteristics. Hence, the maintenance of half-metallicity requires keeping the samples isolated from the atmosphere. We benchmarked our theoretical results with the available data in the literature throughout our study. The conditions that govern the appearance/disappearance of half-metallicity are of great relevance for spintronic device applications.

Two-dimensional transition metal dichalcogenides are promising sensing materials due to their tunable properties. Here, density functional theory is used to investigate hydrogen cyanide (HCN) adsorption on pristine and doped MoS 2 monolayers (X–MoS 2 , X = P, N, Si, Al, B, and Cl). Most dopants lead to weak physisorption with ultrafast recovery, while Al–MoS 2 exhibits strong chemisorption with an adsorption energy of − 1.459 eV, resulting in an impractically long recovery time. Among the single-doped systems, Si–MoS 2 shows a favorable microsecond-scale response. To overcome the recovery-time limitations associated with strong adsorption, dopant concentration effects are examined by substituting two and three sulfur atoms with P, Si, and Al. A non-monotonic trend is observed, wherein double doping enhances the adsorption strength, while symmetric triple doping weakens the interaction, enabling recovery-time tuning at room temperature. In particular, 2Si–MoS 2 exhibits a recovery time of 15.48 min along with strong electronic sensitivity, whereas 3Al–MoS 2 achieves balanced adsorption with a recovery time of 3.24 ms, accompanied by significant work-function modulation and enhanced electron emission current density. This dopant-engineering approach provides an intrinsic and safer alternative to temperature- or field-driven desorption strategies, offering practical design guidelines for chemiresistive, electrochemical, and ultraviolet-based HCN sensing using MoS 2 .

In this study, we examined the effects of iron doping on the electronic and magnetic properties of transition metal dichalcogenide (TMD) monolayers, specifically MoSe2 and WSe2, utilizing density functional theory (DFT). Our results demonstrate that strategic doping significantly alters the material properties. Structural analysis reveals that doped systems largely retain the original structure of MSe2ML (Mo, W), despite exhibiting minor lattice distortions. Total energy calculations indicate that these structures remain stable. The doping of Fe induces significant spin polarization in both MoSe2ML and WSe2ML. The spin-down and spin-up channels exhibit distinct band gaps: 1.09 eV (D) and 0.24 eV (I) for MoSe2ML, and 1.0 eV (D) and 0.27 eV (D) for WSe2ML, respectively. Iron doping also induces magnetization in these TMDs. Additionally, the introduction of spin polarization shows that neighbouring atoms around the impurity exhibit slight magnetization due to the localized effects of the dopant. The net magnetic moment for both MoSe2ML and WSe2ML with iron impurities is approximately 2 µB. The computer simulations enable precise doping which leads to improved and tunable properties of TMDs. Future development in electronics, spintronics and quantum computing are facilitated by the potential expansion of doped TMDs.