Nucleation and Growth of CdSe Nanocrystals in a Binary Ligand System

The competing effects of two ligands, oleic acid (OA) and bis-(2,2,4-trimethylpentyl) phosphinic acid (TMPPA), on the nucleation rate and growth of CdSe nanocrystals in octadecene are reported. It is found that TMPPA acts as a high boiling point "nonsolvent" or "nucleating agent". Addition of TMPPA leads to higher initial particle yields and smaller particle diameters. Conversely, oleic acid inhibits nucleation and results in a drastic increase in "early time ripening" (ETR), a phenomenon that causes a rapid reduction in the number of particles within the first minutes of reaction. By controlling the number of nuclei formed with TMPPA and tuning the rate of ETR with oleic acid, high yields of particles can be obtained with sizes between 3 and 7 nm. Furthermore, in the absence of OA, the preparation of very small nanocrystals with diameters approximately 2 nm is facilitated.