Controlled Synthesis of Two-Dimensional 1T-TiSe2 with Charge Density Wave Transition by Chemical Vapor Transport

Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs), such as 1T-TiSe₂, are ideal systems for exploring the fundamentals in condensed matter physics. However, controlled synthesis of these ultrathin materials has not been achieved. Here, we explored the synthesis of charge density wave (CDW)-bearing 2D TiSe₂ with chemical vapor transport (CVT) by extending this bulk crystal growth approach to the surface growth of TiSe₂ by introducing suitable growth substrates and dramatically slowing down the growth rate. Sub-10 nm TiSe₂ flakes were successfully obtained, showing comparable quality to the mechanically exfoliated thin flakes. A CDW state with 2 × 2 superstructure was clearly observed on these ultrathin flakes by scanning tunneling microscopy (STM), and the phase transition temperature of these flakes was investigated by transport measurements, confirming the existence of CDW states. Our work opens up a new approach to synthesizing 2D CDW and superconductive TMDCs for exploring new fundamentals and applications in novel electronics.