Ion Exchange-Driven Controlled Transformation and Heterostructure Formation of Sn-Based Wafer-Scale 2D Layers

This study explores two synthesis strategies for tin (Sn)-based two-dimensional (2D) transition metal dichalcogenide (TMD) van der Waals (vdW) layers: (1) direct chemical vapor deposition (CVD) growths of wafer-scale tin diselenide (SnSe₂), tin disulfide (SnS₂), and tin telluride (SnTe), and (2) their post-CVD transformations employing anion exchange reactions. While as-grown 2D SnSe₂ layers are confirmed to be intrinsically semiconducting (i.e., bandgap of ∼1 eV and electron mobility of 1.57 cm²/V·s), their transformed counterparts in a form of SnX_n with controlled stoichiometries (i.e., <i>X</i> = Te (tellurium) or S (sulfur), and <i>n</i> = 1 or 2) exhibit distinct optoelectronic characteristics. For example, 2D SnTe layers transformed via a CVD telluirzation of 2D SnSe₂ layers display highly metallic properties, accompanying with an order-of-magnitude conductivity increase as well as preserving the intrinsic vdW structural integrity. This strategy of simultaneously modulating chemical, electrical, and optical properties enables the fabrication of "all-2D" Sn-based in-plane heterostructure arrays employing 2D/2D metal/semiconductor seamless interfaces.