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

Abstract

Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs), such as 1T-TiSe, 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 TiSe with chemical vapor transport (CVT) by extending this bulk crystal growth approach to the surface growth of TiSe by introducing suitable growth substrates and dramatically slowing down the growth rate. Sub-10 nm TiSe 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.

Chemical Vapor Transport Reactions for Synthesizing Layered Materials and Their 2D Counterparts

“…It should be mentioned that the formation of bulk TMD crystals is typically an endothermic process, and thus the sublimation temperature T 1 is mostly set higher than the deposition temperature T 2 . The CVT based methods are now regarded as one of the most reliable approaches to grow common bulk TMD crystals for both research and commercial purposes …”

“…From this point of view, source materials and the mineralizer can be regarded as the most decisive factors in the growth of TMD crystals. Thereafter, the reaction conditions could be optimized case by case, typically in an empirical way, and some representative reactions are summarized in Table 1 …”

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

“…Bulk CDW materials such as 1T-VSe 2 [50], 1T-TaSe 2 [28], 2H-TaSe 2 [5,51] and 2H-NbSe 2 [52] have been reported by the CVT method in recent years. For synthesis of 2D CDW materials, recently, J. Wang et al reported controlled synthesis of two-dimensional 1T-TiSe 2 on sapphire substrates with sub-10-nm thickness [53] (Figure 5). It is essential to introduce a growth substrate to guide the 2D growth of TMDs and dramatically slow down the growth of the bulk counterpart in the CVT method.…”

Monolayer Tungsten Disulfide (WS2) via Chlorine‐Driven Chemical Vapor Transport

“…Although CVT is ubiquitously used to synthesize bulk crystals, it was only recently reported that atomically thin TMDs, including WS 2 , can be grown using CVT in a sealed ampule by carefully controlling mass transport . While using I 2 and metal chlorides as transport agents, the presented closed‐tube technique still requires metal oxides and sulfur as precursors, akin to CVD where stoichiometry is always a consideration.…”