Nucleation kinetics vs chemical kinetics in the initial formation of semiconductor nanocrystals.

The initial formation of semiconductor nanocrystals/nanoclusters, that is, nucleation in the classic literature, was examined both theoretically and experimentally. An experimental method based on determining the initial reaction rate for the formation of nanocrystals/nanoclusters with fixed size and size distribution was developed using InP and CdS nanocrystals/nanoclusters systems, especially the InP one. This experimental strategy relies on the size-dependent absorption spectra of these semiconductor nanoparticles as quantitative probes. The experimental results along with theoretical analysis indicate that the classic nucleation model was unlikely relevant for such crystallization systems, whose bulk crystal solubility in a solution is extremely low. Instead, the formation process was found to match a reaction-controlled kinetics model. The results further imply that understanding of crystallization and development of controlled synthesis of high quality colloidal nanocrystals are both closely related to identifying the molecular mechanism and chemical kinetics.