Dual-metal precursors for the universal growth of non-layered 2D transition metal chalcogenides with ordered cation vacancies

Two-dimensional (2D) transition metal chalcogenides (TMCs) are promising for nanoelectronics and energy applications. Among them, the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surface and strong intralayer and interlayer bonding. However, the synthesis of non-layered 2D TMCs is challenging and this has made it difficult to study their structures and properties at thin thickness limit. Here, we develop a universal dual-metal precursors method to grow non-layered TMCs in which a mixture of a metal and its chloride serves as the metal source. Taking hexagonal FeS as an example, the thickness of the FeS flakes is down to 3 nm with a lateral size of over 100 μm. Importantly, we find ordered cation Fe vacancies in FeS, which is distinct from layered TMCs like MoS where anion vacancies are commonly observed. Low-temperature transport measurements and theoretical calculations show that 2D FeS is a stable semiconductor with a narrow bandgap of ∼60 meV. In addition to FeS, the method is universal in growing various non-layered 2D TMCs containing ordered cation vacancies, including FeSe, CoS, CrS, and VS. This work paves the way to grow and exploit properties of non-layered materials at 2D thickness limit.