Chemistry of tin monosulfide (δ-SnS) electrodeposition

The conditions of formation of a tin sulfide δ-SnS phase by galvanostatic deposition with tartaric acid were investigated, changing parameters such as pH (1.5 and 2.5) and temperature (50, 70, and 90°C). Uniform films were deposited at both pH's. Cyclic voltammetry data suggested that tin-tartrate complexes were crucial to film electrodeposition and also indicated reduction of sulfur species rather than tin. X-ray diffraction showed the δ-SnS structure to be a pure phase over the range of deposition temperatures (50-90°C) at pH 2.5. This observation was limited to 70°C for films deposited at pH 1.5. Impurities of Sn and α-SnS were found in films deposited at pH 1.5 and temperatures of 50 and 90°C, respectively, indicating that the α-SnS phase is more likely to be formed at lower pH's. All the films annealed at 350°C displayed the α-SnS phase. Scanning electron microscopy showed deposited particles increased in size and became more platelike with increasing temperatures of electrodeposition, but did not change morphology with annealing. UVvis spectrometry confirmed increased disorder in films deposited at 50°C and a direct allowed optical bandgap of lower energy for the δ-SnS phase compared to that of α-SnS.