Investigations of the growth kinetics of capped CdSe and CdS nanocrystals by a combined use of small angle X-ray scattering and other techniques.

The growth of capped CdSe and CdS nanocrystals formed by the reaction of selenium or sulfur with cadmium stearate in toluene solution in the presence of dodecanethiol or trioctylphosphine oxide and tetralin, has been investigated by a variety of techniques to obtain reliable data. Whereas small angle X-ray scattering has provided statistically satisfactory data on the variation of size distribution with time, TEM has been used as a direct probe of the particle size, although with a limited sampling size. UV/Vis and photoluminescence spectroscopies have also provided information about the time evolution of the average diameter (D) of the nanocrystals. By employing all these techniques, we have obtained the D(t) data and fitted then to various growth models. Although certain qualitative observations suggest growth of the nanocrystals to be controlled by diffusion-limited Ostwald ripening, we have found it is necessary to include the surface reaction term in the growth equation. Thus, the growth of CdSe and CdS nanocrystals has contributions from both diffusion and surface reaction, with a D(3)+D(2) type behavior, independent of the capping agent.