Two dimensional (2D) layered materials such as graphene, metal dichalcogenides and black phosphorus are of increasing interest because of their unique optical and electronic properties. Black phosphorus has a variable band gap but is air-sensitive while graphene is limited by its zero bandgap. SnS has a similar crystal structure to black phosphorus but is stable in air. In addition, SnS is a p-type, 2D semiconductor with a direct band gap (~1.3 eV), indirect band gap (1.1 eV), and a high absorption coefficient (&gt;104 cm-1). It has potential applications in transistors, photovoltaics, photocatalysis, and lithium ion batteries. We have synthesized 3-60 nm thick and up to approximately 10 micron wide SnS nanoplates via decomposition of tin(IV) diethyldithiocarbamate upon hot injection into oleylamine (300-340 oC). The reaction products are characterized using a combination of electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), atomic force microscopy, and Raman spectroscopy. All characterization techniques confirm that the final reaction product is orthorhombic SnS (e.g., after 60 minutes at 340 oC). At low temperatures (300 oC) and short synthesis times (3 minutes) we also observe the presence of tin disulfide (SnS2) which suggests that decomposition of tin(IV) diethyldithiocarbamate first produces SnS2. SnS2 is subsequently reduced, likely by oleylamine, to SnS. The SnS nanoplate surfaces are covered with oleic acid ligands, which sterically stabilizes their dispersions in organic solvents. These ligands could be exchanged with K2S to charge stabilize them in water and other polar solvents. Orthorhombic SnS grows preferentially as plates, with the [001] direction normal to the plate surfaces. In fact, when plates are large (&gt;1 micron) XRD from films cast from colloidal dispersions in toluene show predominantly the (004) diffraction. The nanoplate size affects their optical properties. The flat surface on large nanoplates make them highly reflective when compared to smaller (&lt;1 micron) nanoplates as confirmed with reflectance and transmission measurements. Nanoplates are polarizable in electric fields and their dispersions respond to electric fields. They form spontaneous patterns in dispersions confined between two electrodes that are biased with respect to each other.

Morphology, structure, and optical properties of 2D SnS nanoplates synthesized via a hot-injection method

253rd National Meeting (2017)

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