## 7 Synthesis of Two-Dimensional SnS
The Hansen parameters for the solvents NMP, IPA and acetone are listed alongside those of SnS in Table 6.  
Figure 9: (**a**) Calculated band structure of SnS; (**b**) band structure of Pb\({}_{0.2}\)Sn\({}_{0.8}\)S; (**c**) thickness distribution of nanosheets centrifuged at 180\(\times\)\(g\); (**d**) thickness distribution of nanosheets centrifuged at 11,620\(\times\)\(g\); (**e**) high angle annular dark field scanning transmission electron microscopy (HAADF STEM) image of Pb\({}_{0.2}\)Sn\({}_{0.8}\)S; (**f**) S distribution; (**g**) Sn distribution; (**h**) Pb distribution of highly centrifuged nanosheets. Adapted with permission from _Chem. Sci._, **2019**, \(9\), 1035–1045. Potential future work could be focused on liquid-phase exfoliated SnS via aqueous surfactant solutions, eliminating the need for volatile, toxic, or costly solvents. This has been shown to work with materials such as black phosphorous. The exfoliation method utilised deoxygenated water and sodium dodecyl sulfide (SDS) to produce nanosheets with thicknesses under 10 nm [111]. An alternative top-down method is mechanical exfoliation, which can be used to produce nanosheets with a significant lateral size relative to thickness. This method has been used since the discovery of graphene [79] to produce high quality 2D materials, although lacks scalability. Relatively large flakes of SnS were created by [PERSON] et al. via the use of micromechanical exfoliation from bulk SnS using tape and Au exfoliation. The nanosheets obtained were found to be 13.8 nm, 10.5 nm, and 4.3 nm in thickness with a lateral size over several \(\upmu\)m, which is up to several orders of magnitude larger than those obtained from liquid-phase exfoliated few-layer SnS [1,106]. Oxygen annealing was then used to successfully thin the flakes down to close to monolayer thickness [88]. A comparison of tape and Au mediated exfoliation has been performed by [PERSON] et al. This showed that tape exfoliated SnS was found to have a lateral size of several \(\upmu\)m with a thickness in the range of tens of nm. Au exfoliated nanosheets were found to have a larger lateral size (tens of \(\upmu\)m) with thicknesses showing a wide distribution down to 1.1 nm. The increased lateral size for Au mediated exfoliation was attributed to the strong, semi covalent bonding between Au and S atoms. The produced Au exfoliated SnS had a thin SnO\({}_{\text{x}}\) layer, making it ideal for the creation of thin SnS/SnO\({}_{\text{x}}\) heterostructures, but ineffective for creating large area, pure SnS nanosheets [112]. SnS has been successfully separated into nanosheets via the use of lithium intercalation by [PERSON] et al. SnS was synthesised via the heating of Sn and S in a quartz ampoule at 950 \({}^{\circ}\)C for 6 h. Intercalation was undertaken via the addition of ethylene glycol and lithium hydroxide with heating in an autoclave at 200 \({}^{\circ}\)C for 48 h. The nanosheets were then added to aqueous tartaric acid and heated in an autoclave for 203 \({}^{\circ}\)C for 2 h to form porous SnS nanosheets. Finally, the polyaniline was synthesised around porous SnS to form the composite. The SnS produced was from 200 nm to 500 nm in lateral size. It was found via field effect TEM (FETEM) that the microhardness of the nanosheets changes from pristine (80 kgf mm\({}^{-2}\)) to porous (70 kgf mm\({}^{-2}\)). The nanosheet composite formed had a ZT value which increased with temperature up to 0.078 at 177 \({}^{\circ}\)C, which was 458-fold higher than the pristine nanosheet SnS [113]. Chemical synthesis is a versatile method of creating nanoscale materials, which has advantages of versatility of reactants and conditions, enabling a range of morphologies to be produced. However, in some cases dangerous reactants and conditions such as high temperatures may pose a risk. Chemical synthesis may also carry the risk of unwanted products and may require purification. Commonly, tin chloride is used as the source of Sn [103]. [PERSON] et al.