CHEMICAL AND STRUCTURAL CHARACTERIZATION OF SNS2 SINGLE-CRYSTALS GROWN BY LOW-TEMPERATURE CHEMICAL VAPOR TRANSPORT

Chemical and structural characterization has been performed for thick (100-600-mu-m) and thin (10-100-mu-m) 2H/4H inter-polytype SnS2 crystals grown by low-temperature chemical vapour transport in the reverse temperature gradient geometry. X-ray diffraction shows that the 2H/4H-SnS2 phase transforms to single-crystal 2H-SnS2 in 6-12 months. The S/Sn ratio is 2.02 +/- 0.01 in thick crystals and 2.01 +/- 0.01 in thin crystals. Thermogravimetric/differential thermal analysis and the other characterization techniques show no difference between the two types of crystal. Extremely small quantities of carbon and oxygen and some chlorine were detected by secondary ion mass spectroscopy and/or X-ray photoelectron spectroscopy (XPS). These elements are concentrated at the surface. The XPS data show a chemical shift of tin and sulphur in the surface layer, which is probably caused by the adsorbed carbon and oxygen; however, it cannot be explained by the formation of the usual oxides of tin and sulphur.