An Investigation of Lithium and Cobalt Intercalation Method in 2D Transition Metal Dichalcogenides

In recent studies, it has been confirmed that 2D van der Waals (vdW) materials, including magnetic elements such as CrI₃, Fe₃GeTe₂, Cr₂Ge₂Te₆, VS₂, and VSe₂, exhibit long-range ferromagnetic order. In addition, the previous studies have explored improving electrical properties by injecting magnetic dopants into 2D transition metal dichalcogenide (TMD) materials with semiconductor properties or chalcogen defects. However, the intercalation method of inserting a magnetic element between the van der Waals planes of 2D TMDs has rarely been explored.<br/>This study proposes implementing ferromagnetism by inserting Cobalt (Co) between layers of Molybdenum ditelluride (MoTe₂) using a wet chemical method that sequentially proceeds with Li intercalation and Co intercalation. n-Butyllithium diluted in hexane is widely used as a reagent for Li intercalated complexes because Li has a small atomic radius, high reactivity, and can react at room temperature. 2D TMD materials can exist in a 2H (semiconducting) or 1T' (metallic) phase. MoTe₂ typically exists in a 2H phase under atmospheric conditions and has the lowest equilibrium energy difference between 2H-1T' among TMD materials. Pristine 2H-MoTe₂ undergoes a phase transition to 1T'-MoTe₂ by Li intercalation for 48 hours. This phase transition is confirmed by the 1T' peak observed in the Raman spectrum and the change in gap distance from 6.97 to 6.95 Å measured by X-ray diffraction (XRD) analysis.<br/>Li-intercalated 1T'-MoTe₂ induces ionic exchange during secondary Co intercalation due to its strong reducing ability, effectively allowing zero-valent Co to settle within the vdW gap instead of Li ion. Dicobalt octacarbonyl, Co₂(CO)₈, is used as a precursor to provide Co.