Amorphous to crystalline transformation of indium sulphide powders on thermal treatment: Studies by x-ray photoelectron spectroscopy and Raman spectroscopy

Abstract Amorphous, partially crystalline and polycrystalline indium sulphide (In2S3) obtained on the heat treatment of wet-chemically synthesized In2S3 powders, at 373, 523 and 673 K temperatures respectively in argon atmosphere have been examined by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The binding energies of In(3d) and S(2p) electrons decrease on the transformation of the compound from its amorphous to polycrystalline (β-In2S3) state. The co-existence of amorphous and crystalline phases in the partially crystalline material is conclusively demonstrated by the occurrence of as many peaks in the In(3d) electron spectrum. The XPS measurements also indicate the prevalence of β-In2S3 in subtle amounts in the amorphous In2S3 powder and a certain content of amorphous In2S3 in the material heat treated at 673 K. The higher binding energies of In 3d5/2 electrons (446 eV) and S 2p3/2 electrons (163.3 eV) in amorphous In2S3 can be attributed to the lack of extra-atomic relaxation. The relative shifts of the binding energies suggest that the bonding is more ionic in the crystalline phase. The polycrystalline material has Raman spectrum typical of β-In2S3 indicating a crystal ordering initially with the formation of InS4 tetrahedra and subsequently with, InS6 octahedra as the temperature of the treatment is increased to 673 K. The Raman spectrum, too, points to the prevalence of a certain amorphicity in the compound.