Vapor-Phase Synthesis of Ti2CCl2 MXene.

The vapor-phase synthesis can produce 2D transition metal carbides and nitrides (MXenes) from abundant precursors, bypassing MAX phase synthesis. However, little progress was made after the initial report by Talapin's group on the chemical vapor deposition of MXenes on titanium foil, as the growth mechanisms remained poorly understood. Here, a scalable vapor-phase synthesis of high-quality Ti2CCl2 MXene from Ti, TiCl4, and CH4 is demonstrated, and the key features of the growth mechanism are elucidated. Increasing the Ti surface area while confining the reaction volume enables vapor-phase formation of Ti2CCl2 on quartz substrates. Supersaturation of TiCl2 increases gas-phase collision frequency, promoting nucleation and subsequent growth of 2D MXene flakes. The as-synthesized lamellae self-organize into spherulites with diverse morphologies, forming a porous nanocrystal network consistent with the gas-to-solid process. The continuous lateral growth into larger flakes is observed as synthesis time increases, suggesting the feasibility of wafer-scale synthesis. This study provides a practical synthesis route for Ti2CCl2 MXenes, accelerating MXene research and applications in quantum technology, optics, and electronics, where 2D crystals with low defect density are required.