Hexagonally Shaped Two-Dimensional Tin(Ii)Sulfide Nanosheets: Growth Model And Controlled Structure Formation

Tin(II)sulfide (SnS) is a well-known representative of IV-VI semiconducting materials with a layered crystal structure. SnS is of great interest due to its low toxicity and its optical and electrical properties. Here, we report on the first colloidal synthesis of hexagonally shaped single crystalline SnS nanosheets with tunable dimensions. The SnS nanosheets crystallize in the thermodynamically preferred orthorhombic a phase. High-resolution transmission electron microscopy and electron diffraction were executed in order to determine the growth direction of these hexagonally formed nanosheets. The simple hot-injection approach comprises the injection of a sulfur-oleylamine complex into a hot solution mixture containing oleylamine, oleic acid, tin(II)chloride, and hexamethyldisilazane (HMDS). HMDS is an essential chemical for many colloidal syntheses of two-dimensional nanosheets, but its function is not well described until now. Here, we elucidate the function of HMDS as an essential additive for the formation of two-dimensional nanostructures. Furthermore, we identify the role of oleylamine and oleic acid on the formation mechanism and depict how size and thickness of the nanosheets, as well as the crystal structure of alpha-SnS to pi-SnS, can be changed by the ratio of oleylamine isomers or the amount of oleic acid. For our reaction system, we identified the growth mechanism to follow the law of Ostwald's step rule (Ostwaldsche Stufenregel) instead of the oriented attachment growth mechanism.