Preparation and surface structure of nanocrystalline cadmium sulfide (sulfoselenide) precipitated from dimethyl sulfoxide solutions

We present a method for the synthesis of CdS and CdSxSe1-x nanocrystals by precipitation from a solution of cadmium carboxylate in dimethyl sulfoxide (DMSO) with or without elemental S (Se). The reaction in the presence of hydrazine has also been investigated. The CdS particle size, determined by X-ray diffraction, varied between 2 and 7 nm, depending on the reaction conditions. The CdSxSe1-x crystal size varied between 5 and 10 nm. UV spectra of the particles showed an increase of the optical band gap as the size of the crystals decreased. The surface structure of the CdS nanocrystals was characterized by IR and NMR spectroscopy. The spectra of CdS particles prepared with cadmium acetate and sulfur showed four types of binding sites at the crystallite surfaces: oxidized sulfur, acetate adsorbed to the surface cadmium in a bridging complex, oxygen-bound DMSO, and hydroxyl ions.