Controlled synthesis of monodisperse nanocrystals by a two-phase approach without the separation of nucleation and growth processes

The synthesis of monodisperse nanocrystals is an important topic in the field of nanomaterials not only for practical applications, but also for scientific interest in fundamental research. In this feature article, we mainly focus on synthesis of monodisperse nanocrystals by a two-phase approach without the separation of nucleation and growth processes, and report some progress made recently in the observation and understanding of nucleation and growth of semiconductor nanocrystals. Firstly, a novel two-phase approach to monodisperse nanocrystals, which is different from the well-established synthesis models, is discussed. We demonstrate that the two-phase approach has a quite lengthy nucleation process, and can be applied to the synthesis of many kinds of binary monodisperse nanocrystals. Then, we provide a summary of recent research progress in the observation and understanding of nucleation and growth of semiconductor nanocrystals in one-phase and two-phase systems, and compare the nucleation and growth mechanisms of the two kinds of reaction systems. Although the lengthy nucleation process of the two-phase approach enables researchers to capture some useful information about the nucleation and growth processes, and the nucleation and growth processes have been studied by optical absorption spectra and transmission electron microscopy, there is little or no experimental data available on the atomic configurations of critical nuclei. Finally, the current difficulties and future challenges in synthesis and structural characterization of critical nuclei are presented.