## 7 Synthesis of Two-Dimensional SnS
have developed a novel hydrothermal synthesis method to produce 2D single crystalline nanosheets with micron scale lateral sizes. The reaction was undertaken via the use of SnCl\({}_{2}\)H\({}_{2}\)O, thioglycolic acid (TGA) and Na\({}_{2}\)S heated in an autoclave at 200 \({}^{\circ}\)C for 48 h with different morphologies obtained from changing the Sn/S ratio. Nanosheets up to micron scale were produced with TEM showing a 2D morphology. It was determined via XRD that SnS grows preferentially perpendicular to the (111) direction. The inclusion of TGA prevented nanosheets from aggregating, allowing improved control over nucleation \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Solvent/Material** & \(\mathbf{\delta_{d}}\) & \(\mathbf{\delta_{P}}\) & \(\mathbf{\delta_{h}}\) & **Reference** \\ \hline SnS & 18.1 & 14.7 & 13.8 & [109] \\ \hline NMP & 18.4 & 12.3 & 7.2 & [110] \\ \hline Acetone & 15.5 & 10.4 & 7.0 & [110] \\ \hline IPA & 15.8 & 6.1 & 16.4 & [110] \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Hansen parameters of SnS and the solvents used for liquid-phase exfoliation. and growth. The formation of the initial SnS nuclei for nanocrystal growth came from the reaction: SnCl\({}_{2}\) + Na\({}_{2}\)S \(\rightarrow\) SnS + 2 NaCl [103]. The hydrothermal method has also been used by [PERSON] et al. to produce microbelts with a thickness of 700 nm and a length of 15 \(\upmu\)m. The microbelts were synthesised using SnCl\({}_{2}\).2H\({}_{2}\)O in distilled water and thiourea in an autoclave at 200 \({}^{\circ}\)C for 24 h. The microbelts produced were then utilised as photodetectors [114]. Hydrothermal synthesis requires the use of consistent high temperature over a long period, however is capable of producing high quality, single crystalline nanomaterials with the possibility of bridging the gap between bulk and 2D SnS with the possibility of creating high quality microstructures. A film consisting of 2D nanobelts of SnS with a thickness of 20-30 nm with lengths 3-5 \(\upmu\)m length and widths ranging from 300-400 nm was produced by [PERSON] et al. via a simple chemical bath deposition. SnCl\({}_{2}\).2H\({}_{2}\)O and thioacetamide (TAA) in distilled water were reacted together for 1-2 h at 80 \({}^{\circ}\)C, and sulfuric acid was used to keep pH between 0.4-1.0. The reaction occurs by the release of Sn\({}^{2+}\) and S\({}^{2-}\) ions, which are obtained by the dissolution of Sn salt and decomposition of TAA, respectively. This step is followed by condensation of the ions onto substrates. Similarly, this method also relies on nucleation and growth steps. Phase-pure, single crystalline SnS was formed with morphology changing depending on pH and TAA concentration. A greater concentration of TAA leads to the creation of a more compact film due to the increased S\({}^{2-}\) concentration. Higher pH led to the creation of thinner, looser nanobelts due to decreased S\({}^{2-}\) release and increased precipitation of Sn(OH)\({}_{2}\). The SnS produced had a band gap of 1.41 eV and 1.39 eV for 1 h and 2 h deposition, respectively, as determined by Tauc plots from UV-Vis [115]. Thin films consisting of SnS nanosheets have been synthesised by [PERSON] et al. with individual sheet thicknesses of 200-400 nm. The SnS was synthesised by the reaction of SnCl\({}_{2}\).2H\({}_{2}\)O and thioacetamide at a pH range of 0.2-1.5, which was adjusted using sulfuric acid. The reaction was undertaken at 120-180 min at 80 \({}^{\circ}\)C. Sheet-like morphologies were obtained from pH 0.2-0.7 with film thicknesses of 4.37 \(\upmu\)m, 4.03 \(\upmu\)m, and 2.14 \(\upmu\)m for pH 0.2, 0.4, and 0.7, respectively. Thinner films are produced at higher pH due to the precipitation of Sn(OH)\({}_{2}\)[116]. The SnS is produced by the release and reaction of Sn\({}^{2+}\) and S\({}^{2-}\) ions, similar to the reaction undertaken by [PERSON] et al. [115]. The SnS was used in the creation of an FTO/SnS/CdS/Pt photocathode. [PERSON] et al.