Intercalation is a powerful tool for inducing phase changes in transition metal dichalcogenides (TMDs). However, only the transition from a semiconducting 2H (hexagonal) phase to metallic 1T (octahedral, or semi-metallic 1T′, distorted octahedral) phase induced by lithium ion (Li+) intercalation in MoS2 is well-known, due to its versatile chemistry and rich physics with adjustable electronic and optical properties.

The team carried out the Li+ intercalation in an on-chip electrochemical cell (see panel b in the figure) with a 1T′-MoTe2 nanoflake as the cathode, a small piece of Li metal foil as the anode, and a complex blend of molecules as the electrolyte. The electrodes and electrolytes were encapsulated by a transparent case, with a coverslip serving as the top cover and SiO2/Si chip as the bottom substrate. A micro-cell such as this can not only provide a complete circuit to achieve the electrochemical intercalation but also allow for in situ electrochemical and spectroscopic testing.