Investigation of nanocrystalline CdS-glutathione particles by radial distribution function

Using high-energy synchrotron radiation, powder diffraction experiments were carried out on CdS nanocrystals stabilized with glutathione. The radial distribution function was calculated from the data and analysed. The nanoparticle core, of diameter estimated as 15-20 Å, consists of Cd and S atoms in the proportion 1:1. Inside the core, both Cd and S atoms coordinate each other approximately tetrahedrally. The surface S atoms are connected to just two or three Cd atoms of the core and belong to the glutathione molecules of the particle shell. These S atoms are also a part of the core structure and contribute about one half of the total number of S atoms per particle. First-neighbour Cd-S distances are 2.523 Å with a narrow distance distribution. No difference is observed between the lengths of Cd-S bonds involving the sulfur of the glutathione molecules and the sulfur atoms which are solely bound to Cd. The bond angle Cd-S-Cd at the surface bridging S atoms of glutathione is ca 99.5°, i.e. significantly smaller than an average one of 109.5° characteristic of the Cd and S atom packing inside the core. Beyond the range of the near interatomic distances, the influence of the surface and the defects cause a significant distinction of the particle core structure from those of zincblende and wurtzite, characteristic of bulk CdS.