Shape control of CdTe nanocrystals synthesized in presence of in situ formed CdO particles

Abstract

The shape of semiconductor nanocrystals synthesized with wet-chemical approaches in many cases can be controlled by the concentration and the activity of the precursors. In this study, we introduce a possibility to influence these two factors in the colloidal synthesis of cadmium telluride nanoparticles synthesized in the presence of in situ generated cadmium oxide particles. By changing the composition of the solvent (a mixture of oleylamine and octadecene), different shapes of CdTe nanocrystals can be synthesized. In reactions with higher oleylamine concentration, we observed the formation of elongated nanoparticles: nanorods (~14 nm length) and nanowires (several hundred nm long), while CdTe nanodots formed, if octadecene was used in excess. Formation of CdTe in octadecene and oleylamine as solvent was studied by nuclear magnetic resonance (NMR) spectroscopy. Based on these results, the influence of the solvent composition on the shape of the nanocrystals was attributed to the interplay of several factors, such as enhancement of the carboxylate precursor activity in the presence of an amine and the possibility of the formation of additional Cd monomers by the dissolution of CdO. At later stages of the reaction with high oleylamine content, also oleic acid depletion, leading to a destabilization of the particles, influences the shape of the resulting nanocrystals and lead to the formation of nanowires.