Synthesis of In-Plane Oriented Tin Sulfides by Organosulfur-Mediated Sulfurization of Ultrathin SnO₂ Films

Transition metal dichalcogenides (TMDs) have received great attention over the past decade due to their wide range of optoelectronic properties and intrinsic compatibility with ultimately downsized devices (as ultrathin or even 2D layers), making them desirable for next-generation technologies. To obtain TMDs with satisfying optoelectronic properties, very high process or annealing temperatures are generally applied (above 550 °C), requiring a dedicated growth substrate followed by a mechanical transfer of the TMD layer onto the target device. Hexagonal tin­(IV) disulfide (SnS₂) and orthorhombic tin­(II) monosulfide (SnS) are another class of layered semiconducting metal chalcogenides displaying n-type and p-type conduction, respectively. Unlike early-transition-metal TMDs, highly crystalline SnS₂ and SnS layers can be grown at relatively low temperatures (below 400 °C), which make them more suited for direct implementation on integrated circuits. In this article, we demonstrate the relevance of volatile and nontoxic liquid organosulfur compounds as a safe and convenient alternative to both elemental sulfur and H₂S for producing either SnS₂ or SnS ultrathin layers with good crystallinity. Between 300 and 400 °C, atomic layer deposited SnO₂ is directly converted into 2H-SnS₂ by using tert-butyl disulfide (TBDS). If tert-butylthiol (TBT) is used, the α-SnS phase is obtained. At 250 °C, TBDS converts α-SnS into SnS₂, and the zip mechanism allowing this transformation is analyzed at the atomic scale by using super-resolved transmission electron microscopy.