Bottom-Up Confined Synthesis of Air-Stable Two-Dimensional SnS and SnS₂ between Hexagonal Boron Nitride Nanosheets

Hexagonal boron nitride (hBN), a two-dimensional (2D) insulator, can act as a barrier layer to protect 2D materials and to bring out their intrinsic properties. Encapsulation of 2D materials with hBN sheets can improve the properties of 2D materials and allow the observation of unique physical phenomena. Here, we demonstrate the confined synthesis of 2D tin sulfide (SnS) and tin disulfide (SnS 2 ) by the sulfurization of encapsulated Sn particles in the interlayer 2D space between large-area hBN sheets. First, we highlight the influence of the inert surface of hBN on the morphology of the deposited Sn. We found that using thin hBN as the bottom layer can prevent Sn agglomeration during encapsulation between hBN, making an ideal hBN/Sn/hBN structure for further sulfurization. Due to the high thermal stability, the hBN sheet can serve as a barrier layer, allowing Sn to be sulfurized without evaporation at high temperatures, resulting in the formation of 2D SnS and SnS 2 between hBN sheets. Furthermore, the controlled synthesis of SnS and SnS 2 can be achieved by encapsulating different amounts of Sn. This confined synthesis approach ensures clean interfaces and preserves the intrinsic properties of SnS and SnS 2, while the hBN encapsulation provides long-term air stability. We further fabricated field-effect transistor (FET) devices of hBN-encapsulated SnS and SnS 2, demonstrating semiconductor and ferroelectric properties. Our findings provide a strategy for the fabrication of hBN-protected air-sensitive 2D materials for applications in nanoelectronics and optoelectronics.