Influence of the matrix on the chemical surface bonds of ZnS and CdS nanoclusters obtained by chemical synthesis

Abstract

AbstractCadmium sulfide (CdS) and zinc sulfide (ZnS) nanocrystals were grown following three different chemical synthesis routes. In particular, the nanocrystals were synthesized by in situ thermolysis (∼300 °C) starting from a metal thiolate (i) in a solventless way, (ii) by a novel route in trioctylphosphine oxide (TOPO), and (iii) by direct synthesis in a polystyrene matrix. The formation of cadmium sulfide (zinc sulfide) nanocrystals and the chemistry of the organic/nanocrystal (polymer/nanocrystal) composites were investigated in detail by X‐ray photoelectron spectroscopy (XPS). In addition, X‐ray diffraction analyses (XRD) were performed in order to determine the crystallographic structure and the average size of the nanocrystals.The precursor powders (Cd(SR)2 and Zn(SR)2) of both II–VI compounds were analysed after annealing in different atmospheres (air, nitrogen, vacuum) at 300 °C (in situ thermolysis) in order to establish the starting of the nanocrystal formation process.All the three chemical routes employed and investigated here, showed the formation of CdS (and ZnS) nanocrystals. X‐ray diffraction analyses evidenced that under optimized growth conditions single crystal nanoclusters of zinc‐blende structure and of diameter between ${\oslash} = 1.5$ and 3.0 nm (depending on the annealing temperature and time) are formed. Very good and promising results were obtained by the novel route in TOPO that revealed that sulfur has only one component on the S 2p unresolved doublet (at about 161.6 eV ±0.2) associated to the metal‐sulfide bond, i.e. the Cd(Zn)–S nanocrystals are capped by metal‐sulfide‐TOPO chains. CdS and ZnS nanocrystals embedded in a polystyrene matrix were also successfully prepared and the XPS analyses revealed, in particular, that the sulfur doublet signal is split at least into two peaks, compatible with S in CdS structure and with S bonded to organic residues with energies of 161.66 and 166.98 eV respectively. Copyright © 2006 John Wiley & Sons, Ltd.