## 3 Synthetic Routes to SnS  
To understand the fundamental properties of any material, undoped single crystalline bulk material with negligible defects must first be produced and thoroughly characterised. Chemical vapour transport and the Bridgman-Stockbarger technique are the most commonly used methods for the synthesis of tin(II) sulfide single crystals. To grow high quality single crystals of SnS, one must consider the thermodynamic equilibrium and growth rate (slow growth means high purity, with fast growth rates corresponding to high defect levels). Single crystal growth processes occur at equilibrium; however, it may take several days to allow crystals to reach the equilibrium condition. Once single crystals are grown, these can be used to prepare mono- or few-layer SnS compounds via mechanical or liquid-phase exfoliation. [PERSON] et al. have synthesised single crystals of SnS using chemical vapor transport (CVT). In Table 2, experimental data and density functional theory (DFT) have been used to model the electronic structure and defect chemistry of three different tin chalcogenides (SnS, SnS\({}_{2}\) and SnS\({}_{2}\)S\({}_{3}\)) [41]. Stoichiometric amounts of tin and sulfur were crushed manually using a pestle and mortar and then placed in a silica ampoule. Iodine was also placed in the same ampule, as recommended by [PERSON] et al. [42], and the following chemical process occurs:  
\[Sn+S+I_{2}\to SnI_{2}+S\to SnS+I_{2}\]  
[PERSON] et al. have used the Bridgman-Stockbarger technique to produce single SnS crystals [43]. Two approaches were tested: (i) stoichiometric amounts of high purity Sn and S were sealed in a quartz ampoule. The ampoule was placed in a furnace and heated up in steps to 600 \({}^{\circ}\)C and left at this temperature until the S had fully reacted. Later, the temperature was increased to 900 \({}^{\circ}\)C and maintained for several hours and then switched off, allowing the furnace to cool rapidly. This method gives the pure stoichiometric SnS phases only; and (ii) the two-temperature method, where both Sn and S were kept at two different places within the ampule at two different temperature. The Sn was kept at 600 \({}^{\circ}\)C and S was at 200 \({}^{\circ}\)C. The reaction took place by evaporating the S; this method reduces the chances of an explosion of the ampoule, due to the reduced partial pressure of S. In this method, the main compound produced is SnS along with other phases such as Sn\({}_{2}\)S\({}_{3}\) or SnS\({}_{2}\). It is also reported that above 600 \({}^{\circ}\)C, a phase transition of SnS takes place, which indicates that the material undergoes a change of its lattice parameters. The change in the axial ratios due to temperature difference creates a mechanical stress during the cooling-down of the crystals to room temperature. As a result, nearly all ampoules and all crystals crack, which indicates the poor crystalline quality of the grown material. There are two possibilities to increase the crystal quality: (i) passing of the phase transition with less mechanical stress; and (ii) avoiding the temperature of the phase transition. Tin(II) sulfide thin films have been successfully deposited by aerosol-assisted chemical vapour deposition (AACVD). [PERSON] et al. have developed a series of symmetric and unsymmetric diorganotin dithiocarbamate complexes as molecular precursors to SnS. These are: (1): Sn(C\({}_{4}\)H\({}_{9}\))(S\({}_{2}\)CN(C\({}_{2}\)H\({}_{5}\))\({}_{2}\))\({}_{2}\); (2): Sn(C\({}_{4}\)H\({}_{9}\))(S\({}_{2}\)CN(CH\({}_{3}\))(C\({}_{4}\)H\({}_{9}\)))\({}_{2}\); and (3): Sn(C\({}_{4}\)H\({}_{9}\))(S\({}_{2}\)CN(C\({}_{4}\)H\({}_{9}\))\({}_{2}\))\({}_{2}\). These were dissolved in toluene and used for the deposition of tin(II) sulfide thin films on glass substrates at temperatures ranging from 400 \({}^{\circ}\)C to 530 \({}^{\circ}\)C (see in Table 3). This