Nucleation and Growth Kinetics of CdSe Nanocrystals in Octadecene

The growth kinetics of CdSe nanocrystals nucleated from TOPSe and cadmium oleate were investigated in octadecene, a non-coordinating solvent. The effects of temperature and the oleic acid concentration on the kinetics of both nucleation and particle growth were investigated. It was found that increasing oleic acid concentrations led to smaller numbers of nuclei, smaller initial nuclei size, and larger final particle sizes. The rate constant for steady-state CdSe deposition was found to be 2.2 × 10-6 cm s-1 at ≈ 265 °C, far slower than the diffusion limit. The number of growing particles remained constant following the initial nucleation step. The radius of the primary CdSe nuclei varied from 1.0 ± 0.1 nm down to 0.8 ± 0.2 nm at lower oleic acid concentrations. Between 2 and 8% of the available Cd was consumed during nucleation. From the residual TOPSe and cadmium oleate concentrations at the onset of Ostwald ripening, the solubility of 2.2 nm CdSe in octadecene is measured to be 6.4 × 10-5 M2 at 265 °C. The surface free energy of CdSe in octadecene was found to be 0.17 J/cm2, which leads to an estimate of a 9% size distribution in the nanocrystals at the moment of nucleation.