Insights into the multifunctional applications of strategically Co doped MoS2 nanoflakes

Abstract

Simultaneous tuning of magnetic, transport and electrochemical properties through strategic doping of cobalt (Co) ions in hydrothermally treated multi-layered MoS₂ nanoflakes (NFs) without having a secondary phase has been regarded as cutting-edge research. In our study, we have successfully incorporated Co into MoS₂ NFs at various percentages (0%, 2%, 4%, 6%, 8%) with a significant presence of defects, strain and sulfur vacancies, enabling prompt transformation of the surrounding 2H-MoS₂ local lattice into a trigonal (1T-MoS₂) phase. Effective amplification of magnetic property (ferromagnetic coupling on the scale of p_eff ∼ 4.37μ_B) in 8% Co-doped MoS₂ NFs has been evidenced from VSM measurements. The key reasons are probably attributed to the doping induced 1T phase, the presence of zigzag edges well-established from TEM and Raman measurements, and exchange interactions between ferromagnetically ordered sulfur vacancies and Mo⁴⁺ and Co²⁺ ions. The experimental observations on magnetic measurements have been fitted well with the well-known density-functional theory (DFT) computation. Further, the effect of intentional doping on transport property has been evaluated by employing a four probe linear geometry setup. The increased carrier concentration and decreased resistance result in improved transport properties. Various transport models such as variable range hopping (VRH) and nearest neighbour hopping (NNH) of the Co-doped MoS₂ systems have been successfully fitted in different temperature regimes with a tunable temperature coefficient of resistance (TCR) ∼ 3.0 × 10⁻² K⁻¹. Additionally, electrochemical measurements revealed a significant increase in electrochemical activity with the highest proportion of Co doping (8% Co), which is likely due to increased defect levels and active surface area with expanded interlayer separation, as well as exposure of the electrochemically more active metallic (1T phase) Mo atoms in the edge planes. Therefore, our approach in achieving mixed-phase defect-rich (1T and 2H) Co-doped MoS₂ NFs exhibiting room-temperature ferromagnetism, high TCR and improved electrochemical performance makes them an excellent multifunctional candidate in spintronics, infrared (IR) detection and energy storage devices.