Morphology-Dependent Properties of Semiconducting SnS Nanomaterials and Evidence for a Structural Distortion at the Nanoscale

The synthesis of semiconducting nanomaterials with controlled size, structure, and morphology using solution-based methods has emerged as an active field of research due to their excellent properties. Tin(II) sulfide is a intermediate band gap semiconductor that has received markedly less attention than other related compounds despite its non-toxic and earth-abundant constituent elements, as well as its comparably low cost and favorable electronic properties. Here we present a novel route for the solution synthesis of 2D SnS nanosheets as well as monodisperse 0D colloidal SnS nanocubes and spherical nanopolyhedra. The sheets are $\sim$ 270 nm squares with an orthorhombic crystal structure matching that of bulk $\alpha $-SnS. The cubes and spherical polyhedra are $\sim$ 10 nm, below the exciton Bohr radius of SnS, allowing them to act as ``quantum dots.'' An inability to reconcile incongruences in the diffraction patterns of the 0D nanocrystals with the 2D nanosheets leads us to propose that these SnS quantum dots crystallize in a distorted pseudotetragonal structure, which is confirmed by detailed crystallographic characterization and modeling. We interrogate the optoelectronic and photocatalytic properties of these materials to display that they are size-, shape-, and structure-dependent.