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 hy drazine has also been investigated. The CdS particle size, determined by X- ray diffraction, varied between 2 and 7 nm, depending on the reaction condi tions. 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 th e crystals decreased. The surface structure of the CdS nanocrystals was cha racterized by IR and NMR spectroscopy. The spectra of CdS particles prepare d with cadmium acetate and sulfur showed four types of binding sites at the crystallite surfaces: oxidized sulfur, acetate adsorbed to the surface cad mium in a bridging complex, oxygen-bound DMSO, and hydroxyl ions.