Chemistry of δ-SnS: New Tin Monosulfide Polymorph Thin Films from Galvanostatic Electrodeposition

摘要

Galvanostatic deposition of tin monosulfide thin films (δ-SnS phase) on transparent conductive glass was studied. Uniform films were deposited in aqueous baths with tartaric acid. Cyclic voltammetry suggested tin-tartrate complexes were crucial to film electrodeposition, suppressing tin metal reduction in favor of sulfur species reduction. X-ray diffraction showed primitive orthorhombic symmetry for δ-SnS (a = 11.380 A, b= 4.029 A, c = 4.837 A). 5-SnS was converted to α-SnS (a = 11.172 A, b = 3.994 A c = 4.311 A) following annealing at ～ 270 ℃ in Ar_((g)). Characterizations of the as-deposited films confirmed 1:1 Sn/S. The 5-SnS structure was consistent over a range of deposition temperatures (50, 70, and 90 ℃). UV/Vis spectrometry confirmed increased disorder in films deposited at 50 ℃. A direct allowed optical band gap transition of lower energy for the 5-SnS phase (1.05 eV) was obtained compared to that for a-SnS (direct, 1.2 eV).