Understanding and controlling the growth of monodisperse CdS nanowires in solution

Cadmium sulfide (CdS) nanowires with a monodisperse diameter of 3.5 nm and length of about 600 nm were successfully synthesized using a simple and reproducible hot coordination solvents method. Structural characterization showed that the one-dimensional nanowires grow along the [001] direction and have the wurtzite structure. The morphology of the nanocrystals is affected by the octadecylphosphonic acid to cadmium (ODPA-to-Cd) mole ratio, the precursor ratio (Cd-to-S mole ratio), the precursor concentration, the precursor injection process, and the type of ligands used in the synthesis. However, we propose that the ODPA-to-Cd mole ratio is the key factor affecting the morphology of the nanowires because it affects both the cleavage rate of the P=S double bond and the nucleation/growth rate of the anisotropic nanocrystals. In addition, it was found that Cd-ODPA complexes give rise to a low diffusion rate of the precursor and hence low reactivity. Therefore, ODPA is good for generating nearly monodisperse and high aspect ratio CdS nanowires. Our nanowires have a high degree of dispersibility and thus can be easily processed for potential applications as solar cells and transistors. Finally, the potential applications of these highly dispersible and high aspect ratio nanowires will also be discussed.