Surface Ligand Dynamics in Growth of Nanocrystals

Abstract

Amine ligands were identified to bond on the surface of CdSe nanocrystals in a dynamic fashion under elevated temperatures in the reproducible growth domain of the specific designed growth reactions. The surface ligand dynamics was found to strongly depend on the growth temperature, the ligand concentration, and the ligand chain length. The strong chain-length dependence was originated from the interligand interactions in the ligand monolayer of a nanocrystal, provided fatty amines being weak ligands for CdSe nanocrystals. When the growth reaction was above the boiling point of an amine ligand, the surface ligand dynamics was violent, a quasi-gas-phase state, indicated by strong temperature-dependent and fast growth rates of the nanocrystals. Approximately below its boiling point, a significantly weak temperature dependence of the growth rate of the nanocrystals associated with the quasi-liquid state of the surface ligands was observed. A direct result of studying the surface ligand dynamics of this well-established nanocrystal system was the formation of high-quality CdSe nanocrystals under much reduced temperature, 150 degrees C, in comparison to the standard 250-350 degrees C temperature range. This was achieved by using fatty amines with a short hydrocarbon chain at a low ligand concentration in the solution. Preliminary results indicate that a similar temperature (160 degrees C) also worked for the growth of InP nanocrystals.