ABSTRACT
Figure 1.1 (A) The stages of nucleation and growth for the preparation of monodisperse NCs in the framework of the La Mer model. As NCs grow with time, a size series of NCs may be isolated by periodically removing aliquots from the reaction vessel. (B) Representation of the simple synthetic apparatus employed in the preparation of monodisperse NC samples. Reproduced from 16.
Further modification of this approach was developed by Alivisatos et al. [17]. The principal difference between the preparations was the injection temperature, which affects the time evolution of the nanocrystal growth as well as their crystallinity and shape. In this synthesis the TOPO was heated to 350°C under argon before injection (it was noted that this temperature was well above the flash point for TOPO and all manipulations were undertaken with extreme care) and after injection, the temperature was reduced to yield monodisperse ensembles. This change in temperature was utilised to distinctly separate both the nucleation and growth phases and resulted in high-quality crystalline, nearly monodisperse QD nanocrystals. This work has been followed by other groups [18] and has been tweaked somewhat by Talapin et al. [19] in an effort to further reduce the amount of “defocusing” or Ostwald ripening occurring during the growth period (Fig. 1.2). This group prepared CdSe using a three-component hexadecylamine-trioctylphosphine oxide-triocty-lphosphine (HDA-TOPO-TOP) mixture which provided much better control over the growth dynamics.
