## 7 Synthesis of Two-Dimensional SnS  
A range of methods have been developed for the creation of nanoscale SnS, ranging from liquid-phase chemical synthesis methods using a variety of different chemicals and reaction conditions including hydrothermal, solvothermal, aqueous solution and hot injection methods. Physical and chemical vapour deposition methods are also used for nanoscale SnS production as well as exfoliation directly from bulk SnS using mechanical and liquid-phase processes with a variety of solvents including \(N\)-methyl pyrrolidone (NMP), acetone, and isopropanol, among others. The two broad methods of synthesis for nanomaterials are top-down and bottom-up methods. Top-down methods involve the breaking down of bulk material into nanoscale materials via liquid-phase and mechanical exfoliation. Bottom-up methods involve the direct synthesis of nanomaterials, which includes methods such as chemical and physical vapour deposition as well as wet chemical synthesis methods. Tin(II) and tin(IV) chloride (SnCl\({}_{2}\) and SnCl\({}_{4}\)) are commonly used as reagents for the synthesis of nanoscale SnS, appearing in several published methods [73,103]. Few-layer SnS was first produced from bulk SnS via liquid-phase exfoliation by [PERSON] et al. (Figure 8) [1] Liquid-phase exfoliation has significant advantages, such as being directly processable from solution, allowing rapid device fabrication as well as scalability, as shown for other materials such as graphene with a 100 litre scale being obtained, and production rates of 5.3 g h\({}^{-1}\)[104], although it has several disadvantages, the main ones typically being the small sheet size and low monolayer yield [105]. [PERSON] et al. exfoliated bulk SnS for 24 h in NMP in an ultrasonic bath followed by centrifugation at 180 \(\times\)\(g\) (centrifugal \(g\) force) and then 11,620\(\times\)\(g\). Two-dimensional SnS nanosheets with an averagethickness of 4.1 nm (corresponding to 3-4 bilayers) and a corresponding band gap value of 1.65 eV were obtained [1]. The lateral sizes obtained were between 50 and 100 nm, the larger lateral size due to the weak interlayer bonds relative to the in-plane bonds. The small number of sheets inspected by lattice resolution HAADF STEM imaging appeared to be mostly free from defects. SnS nanosheets from liquid-phase exfoliation have a high aspect ratio (proportional relationship of lateral dimensions) of lateral nanosheet length: lateral width due to anisotropy in the a-b plane, enabling the covalent bonds within the SnS layers to be preferentially broken perpendicular to the weaker zigzag direction [1]. Further separation and isolation of different band gaps has been obtained by [PERSON] et al. via exfoliation in NMP and further centrifugation steps in a liquid-phase cascade centrifugation method. SnS was first ground in a pestle and mortar followed by the addition of NMP and probe sonication at 200 W for 4 s om/4 s off cycles for 8 h under an argon atmosphere. This was then bath-soniacted at 400 W for 48 h. SnS was then centrifuged at speeds of 2000-4000 rpm, 4000-6000 rpm and 6000-8000 rpm, respectively. The SnS produced had band gap values of 1.32 eV, 1.59 eV, and 1.71 eV, corresponding to average nanosheet thicknesses of 45.9 nm, 22.7 nm, and 6.1 nm, respectively [106]. Lead (Pb)-doped SnS nanosheets with the formula Pb\({}_{0.2}\)Sn\({}_{0.8}\)S were synthesised by the dithiocarbamate melt reaction of [Pb(S\({}_{2}\)(Net\({}_{2}\))\({}_{2}\)] with [Sn(S\({}_{2}\)(Net\({}_{2}\))\({}_{2}\)\({}^{n}\)Bu\({}_{2}\)] at 450 \({}^{\circ}\)C under argon, the products of which were then exfoliated using NMP and separated by centrifugation at 180\(\times\)\(g\) and 11,620\(\times\)\(g\) by [PERSON] et al. HAADF STEM and EDX of nanosheets showed an even distribution of Sn, Pb and S across the crystalline flakes, suggesting successful alloying at the nanoscale. Before high-speed centrifugation, the nanosheets had a length of 134 \(\pm\) 45 nm and a thickness of 10.9 \(\pm\) 7.7 nm.