Millisecond Conversion of Metastable 2D Materials by Flash Joule Heating

Controllable phase engineering is vital for precisely tailoring material properties since different phase structures have various electronic states and atomic arrangements. Rapid synthesis of thermodynamically metastable materials, especially two-dimensional metastable materials, with high efficiency and low cost remains a large challenge. Here we report flash Joule heating (FJH) as an electrothermal method to achieve the bulk conversion of transition metal dichalcogenides, MoS2 and WS2, from 2H phases to 1T phases in milliseconds. The conversions can reach up to 76% of flash MoS2 using tungsten powder as conductive additive. Different degrees of phase conversion can be realized by controlling the FJH conditions, such as reaction duration and additives, which allows the study of ratio-dependent properties. First-principles calculations confirm that structural processes associated with the FJH, such as vacancy formation and charge accumulation, result in stabilization of the 1T phases. FJH offers rapid access to bulk quantities of the hitherto hard-to-access 1T phases, a promising method for further fundamental research and diverse applications of metastable phases.