Etching anisotropy in two-dimensional SnS layered crystals using a thiol-amine solvent mixture as an etchant

Etching anisotropy (or crystal-facet selectivity) is a common phenomenon in chemical etching and has widely been implemented to tailor micro/nanostructures with fascinating morphologies, architectures and properties. We here demonstrate for the first time the anisotropy in wet etching of layer-structured two-dimensional (2D) tin monosulfide (SnS) polygonal microflakes. A thiol-amine mixture solvent (ethanedithiol-ethylenediamine, EDT -en) is used as an etchant, which dissolves SnS by the formation of a soluble Sn(II) dithiolate coordination ions. Detailed analyses on the layered crystal structure and SEM/HRTEM images reveal that SnS polygonal microflakes are enclosed by the undercoordinated {0 1 0}, {001}, and {0 1 1} facets at the lateral surfaces and by the fully -coordinated {1 0 0} facets at the upper and lower surfaces, which enables a preferential etching of lateral-surface, undercoordinated vertices and edges to transform polygonal microflakes into curved or nearly-rounded and then into irregular-shaped micro-/nanoflakes. Meanwhile, a relatively slow etching occurring at the upper/lower surfaces decreases the thickness of SnS 2D crystals. This work opens up the feasibility to make 2D layered crystals of inorganic-nonmetallic chalcogenides with specific size, shape, and crystal surface by means of etching chemistry in suitable etchants.

Automated summary

Etching anisotropy is a common phenomenon used in chemical etching to create micro/nanostructures with specific shapes and properties. In this study, we demonstrate the anisotropy in wet etching of 2D tin monosulfide microflakes. The use of a thiol-amine mixture solvent as the etchant enables the preferential etching of specific surfaces and vertices of the microflakes, resulting in the transformation of their shape. This work opens up possibilities for tailoring the size, shape, and crystal surface of inorganic-nonmetallic chalcogenides using etching chemistry.