## 3 Synthetic Routes to SnS
reported the synthesis of diphenylltin bis(2-methoxyethylxanthatate) and diphenylltin bis(iso-butylxanthatate) xanthates and used these as single-source precursors to deposit tin chalcogenide thin films using AACVD. The orthorhombic phase of SnS is obtained when diphenylltin bis(iso-butylxanthatate) is used as a single precursor solution in tetrahydrofuran (THF), whilst the films deposited using diphenylltin bis(2-methoxyethylxanthatate) at temperatures of 400 and 575 \({}^{\circ}\)C produce a nanocomposite of SnS/SnO\({}_{2}\). Investigations were performed to identify the presence of SnO\({}_{2}\) in the system, and it was found that a second oxygen in the diphenylltin bis(2-methoxyethylxanthatate) chain is responsible for the production of SnO\({}_{2}\) under anaerobic deposition conditions as opposed to the xanthato oxygen; this was proven by the synthesis of a second diorganotin(IV) xanthate, diphenylltin bis(iso-butylxanthatate) which only produced SnS under the same reaction conditions [46]. [PERSON] et al. have reported the synthesis of phase-pure films of SnS on a variety of substrates including Mo, fluorine-doped tin oxide (FTO), and Si, as well as glass substrates, by AACVD using the (dimethylamido)(N-phenyl-N\({}^{\prime}\),N\({}^{\prime}\)-dimethylthiourate)tin(II) dimer (Sn((C\({}_{6}\)H\({}_{5}\))NCSN[Me\({}_{2}\)])(NMe\({}_{2}\))) as a single source precursor. It was reported that the formation of either orthorhombic-SnS (\(\alpha\)-SnS) or zinc blende SnS (ZB-SnS) could be controlled by the temperature at which the deposition proceeds. Figure 3 shows the optimal temperatures for \(\alpha\)-SnS and ZB-SnS were 375 \({}^{\circ}\)C and 300 \({}^{\circ}\)C, respectively. The ambipolar behaviour of ZB-SnS has also been reported [47]. [PERSON] et al. have used atmospheric pressure chemical vapour deposition (APCVD) to deposit tin(II) sulfide films on glass substrates from the reaction between tin(IV) chloride and hydrogen sulfide (H\({}_{2}\)S). The films produced had different colours, compositions, and thicknesses, which could be changed by altering the deposition temperature. No film deposition took place in the temperature range from 25 \({}^{\circ}\)C to 200 \({}^{\circ}\)C; however, at 545 \({}^{\circ}\)C, phase-pure films of orthorhombic SnS were formed [48]. In another study, [PERSON] et al. reported the deposition of tin(II) sulfide (SnS) on a glass substrate using APCVD using a reaction of as-synthesised tri-n-butyltin trifluoroacetate (Bu\({}^{3}\)SnO\({}_{2}\)CCF\({}_{3}\)) with H\({}_{2}\)S at 350-600 \({}^{\circ}\)C under nitrogen [49]. There are several other methods used in the deposition of SnS films including conventional chemical vapour deposition [49; 50; 51; 52; 53], chemical bath deposition [54] including 2 stage immersion in SnI\({}_{2}\) and Na\({}_{2}\)S [55], electrochemical deposi  
Figure 3: (**a**) Plan view scanning electron micrographs of SnS thin films grown on (100) silicon wafers at 450, 400, 375, 350, and 300 \({}^{\circ}\)C, respectively. (**b**) Cross-section micrographs of SnS films grown at 300 and 375 \({}^{\circ}\)C (40 min). All scale bars = 500 nm [47]. Adapted with permission from _Chem. Mater._**2015**, 22, 7680–7688. tion [56], atomic layer deposition [57; 58], spray pyrolysis [10; 59; 60], and successive ionic layer adsorption and reaction (SILAR) [61]. Review articles on the synthetic strategies towards SnS thin films, nanocrystals and single crystals are available [35; 62; 63]. Other methods of SnS synthesis include mechanochemical synthesis by high energy milling which involves the tribological reaction between stoichiometric amounts of elemental Sn and S in a ball mill. The SnS produced was nanocrystalline which formed into aggregates with typical length scales of 30-50 \(\upmu\)m [64].