Phase-tuned tetrapod-shaped CdTe nanocrystals by ligand effect

We achieved extensive control of the morphology and phase of colloidal cadmium telluride (CdTe) nanocrystals (NCs) using two different types of capping ligands, namely, amines and phosphonic acids having various alkyl chains ranging from butyl (C4) to octadecyl (C18). Among the alkylamines, the largest tetrapods are preferentially produced using octylamine (U), suggesting that the steric hindrance of the alkyl chains optimizes the growth condition of the tetrapods. The phase of the tetrapod branches can be tuned from wurtzite to zinc blende by enhancing the steric hindrance of the tertiary alkyl phosphine used as the Te activating ligand. The in situ synthesis of tetrapod CdTe NCs on carbon nanotubes (CNTs) was performed using the two types of ligands. All of the CdTe NCs grown on the CNTs consisted of wurtzite phase, and the largest tetrapods are produced using phosphonic acid having the alkyl chain, C10.