Raman and X-ray diffraction study of Ag–In–S polycrystals, films, and nanoparticles

A Raman and X-ray diffraction (XRD) study of AgInS2 and Ag-deficient Ag–In–S nanoparticles produced by colloidal synthesis is performed in comparison with polycrystals and thermally evaporated films of similar compositions. The tetragonal and cubic structures of AgInS2 and AgIn5S8 polycrystals as well as the amorphous structure of the films are confirmed by XRD. Average size of the Ag–In–S nanoparticles (~ 2 nm) is estimated from the Scherrer equation. The Raman spectra of AgInS2 and Ag-deficient Ag–In–S nanoparticles reveal significant broadening due to phonon confinement and the contributions of surface phonons. A strong similarity of the spectra of ultrasmall Ag–In–S nanoparticles prepared with various precursor ratios is explained by the fact that in this case the nanoparticle sulphur-rich chemical composition is determined by the high amount of sulphur atoms on the nanocrystal surface, which simultaneously belong to the glutathione capping ligands.