Stability and electronic properties of edges of SnS2

Because of its two-dimensional structure and semiconducting properties, tin disulfide $({\mathrm{SnS}}_{2})$ is of interest for many applications, such as photocatalysis, photovoltaics, sensing, and electronics. While the atomic and electronic structure of bulk and monolayer ${\mathrm{SnS}}_{2}$ have been studied, much less is known about the edges of layers. Such edges could have a major influence on the performance of ${\mathrm{SnS}}_{2}$. This paper reports on density functional theory (DFT) simulations of the atomic and electronic structure of the edges of ${\mathrm{SnS}}_{2}$. We modeled several different edge terminations at various S coverages and orientations, as well as performed thermodynamic analysis of edge terminations. Our results show that edges with 0% and 50% S atoms are most stable and that higher S coverage are unstable. We directly link edge stability with environmental temperature and pressure, which will guide the experimental synthesis of ${\mathrm{SnS}}_{2}$ materials. We found all the edges to be semiconducting, unlike other metal chalcogenides, and that the band gap energy decreased with increasing S coverage. Semiconducting edges could lead to lower charge recombination rates and better photocatalytic performance. Our calculations also show that edges may have direct or indirect band gaps, depending on the edge termination. Finally, we examined the reactivity of edges through hydrogen dissociation and found edges to be more reactive than basal planes. Our work provides important details on the nature of ${\mathrm{SnS}}_{2}$ edges and how these edges influence the electrical and chemical features of ${\mathrm{SnS}}_{2}$.