## 7 Synthesis of Two-Dimensional SnS
Stability is a prerequisite for nanoparticle processing into thin films or for use as an additive to polymer matrices (Figure 11) [121]. Figure 10: The dimension control strategies of SnS nanocrystals: (**a**) hot-injection method for 0D SnS NPs; (**b**) cool-injection method for 1D SnS NRs and 2D SnS NSs. Adapted with permission from _New J. Chem._, **2019**, _19_, 7457–7462. [PERSON] et al. have also prepared SnS nanosheets using trioctylphosphine and oleic acid as ligands. Tin(II) acetate (TA), oleic acid (OA) and trioctylphosphine (TOP) were dissolved in diphenyl ether (DPE) and the mixture was heated to 230 \({}^{\circ}\)C under nitrogen. Thioacetamide in dimethylformamide was when added and left to react for 5 min before cooling, centrifugation, and redesign in toluene. DFT (CP2K package) was also performed to determine the formation mechanisms using the PADE LDA functional, a DZVP basis set, GTH-PADE potential with a SnS nanocrystal consisting of 224 Sn and 224 S atoms. For the synthesis of square-like SnS nanosheets, TA was partly transformed to tin oleate. The synthesis of nanosheets begins with complexation of the tin precursor and OA followed by the synthesis of SnS nanocrystals via the reaction of Sn and S precursors; the growth step then occurs via the SnS nanocrystals. Lowering the amount of TA was found to form larger, thicker nanosheets due to the reduced number of nuclei formed. When TOP is added without OA, small, square nanosheets and nanoparticles are formed, indicating that TOP enhances the formation of (101) square facet nanosheets. Increasing the OA concentration was found to increase both the size and thickness. For the synthesis of hexagonal nanosheets, OA concentration must be above a certain threshold (2 mmol). The formation of large laterally sized, hexagonal nanosheets is due to the large absorption energy of OA ligands on (100) facets as opposed to (101) and (010) (Figure 12) [122]. Aside from producing thicker, bulk SnS films such as those produced by [PERSON] et al. [123], chemical vapour deposition (CVD) and other vapour deposition methods have been used to synthesise 2D and nanoscale SnS. CVD is an effective way to produce nanostructured SnS with a variety of morphologies and compositions, including composites. CVD also has the potential advantages of scalability. CVD can also utilise a range of chemical precursors and produce nanosheets of high quality. However, chemical vapour deposition often requires transfer between growth and transfer substrates, high temperatures, and carrier gases, as well as not being directly processable from solution [124]. Figure 11: Growth mechanism of SnS square nanoplatelel(c) via the assembly of spherical seed nanoparticles (**b**) formed upon injection of the sulfur precursor into a solution of the complexed Sn precursor (**a**). The competing pathway (**d**) can be suppressed by proper choice of the reaction conditions, as sholin (**e**), where the following parameters have been used: [Sn] = 0.143 M, SnS ratio 3:1, T = 150 \({}^{\circ}\)C, reaction time 5 min, leading to monodisperse nanoplatelets with a thickness of 4.4 \(\pm\) 0.5 nm and edge length of 14.4 \(\pm\) 1.2 nm (no size-selective precipitation was performed) [121]. Adapted with permission from _J. Am. Chem. Soc._**2015**, _31_, 9943–9952. [PERSON] et al. have developed a CVD method involving the use of SnO and S powders in separate boats with an Ar carrier gas with the furnace heated at 650 \({}^{\circ}\)C. The S boat was moved to the centre of the heating zone when the temperature was stable. The SnS nanosheets produced were square faceted, horizontally aligned nanosheets with 25 nm thickness with lateral sizes of 2 \(\upmu\)m; these nanosheets were used in photodetection [125]. Nanosheets have been produced via a similar method by [PERSON] et al. SnO\({}_{2}\) and S powders were evaporated onto a B-doped Si substrate at 550 \({}^{\circ}\)C under nitrogen within a tube furnace. The tube furnace had the temperature maintained for 40 min.