Nanoparticle-Templated Thickness Controlled Growth, Thermal Stability, and Decomposition of Ultrathin Tin Sulfide Plates

Tin monosulfide (SnS) is a layered two-dimensional semiconductor that has attracted attention because of its potential applications, for instance, photovoltaics, optoelectronics, and valleytronics. However, these applications require synthesis of SnS flakes with a controlled thickness and shape. Here, we demonstrate the possibility of using Au nanoparticles to seed the nucleation, determine the position, and control the thickness of the growing SnS plates. Further, we use in situ transmission electron microscopy on individual ultrathin SnS flakes during annealing at high temperatures to establish their thermal stability and decomposition pathways, which is important due to the large surface areas of ultrathin flakes. We find that ultrathin SnS plates decompose rapidly at temperatures above 400 °C. The decomposition invariably starts at the edges of the flakes and is highly anisotropic. Real-time observations show that while the {010} and {110} facets are relatively stable and retract slowly, rapid removal of material along the directions leads to the fast decay of the {100} facets, which are thus replaced by the extended {110} facets. The comparison of shapes developed during growth and sublimation establishes that the typical crystal habits observed for SnS and related group IV monochalcogenides are indeed kinetic growth shapes rather than equilibrium (Wulff) shapes determined by different facet surface free energies. These findings can further guide the design of growth experiments for achieving particular shapes of flakes of SnS and related layered crystals