Selective Synthesis of Large-Area Monolayer Tin Sulfide from Simple Substances

Both tin monosulfide (SnS) and tin disulfide (SnS₂) are thermodynamically stable layered materials with the potential for spin-valleytronic devices and photodetectors. Notably, SnS, owing to its low symmetry, exhibits interesting properties such as ferroelectricity, shift-current, and a persistent spin helix state in the monolayer limit. Unlike SnS₂, however, creating large-area atomic-thickness crystals of SnS is challenging, owing to the enhanced interlayer interactions caused by lone pair electrons. Here, we demonstrate that p-type SnS can be selectively grown by varying the sulfur vapor concentration relative to tin using high-purity elemental precursors in a chemical vapor deposition setup. Based on that, we further show that monolayer SnS crystals, up to several tens of micrometers in lateral scale, can be obtained by controlled sublimation of bulk SnS crystals. These findings pave the way for device applications based on high-quality tin sulfide.