Growth Mechanism of Nanocrystals in Solution: ZnO, a Case Study

We investigate the mechanism of growth of nanocrystals from solution using the case of ZnO. Spanning a wide range of values of the parameters, such as the temperature and the reactant concentration that control the growth, our results establish a qualitative departure from the widely accepted diffusion controlled coarsening (Ostwald ripening) process quantified in terms of the Lifshitz-Slyozov-Wagner theory. Further, we show that these experimental observations can be qualitatively and quantitatively understood within a growth mechanism that is intermediate between the two well-defined limits of diffusion control and kinetic control.

Figure 1

UV-absorption curves obtained at equal intervals of time for a typical reaction carried out at 308 K with 100 mM of water.

Figure 2

The cube of the average diameter of ZnO nanocrystals shown as a function of time for different temperatures at a fixed water concentration (100 mM). The inset shows the variation of the activation energy with the concentration of water.

Figure 3

The average diameter of ZnO nanocrystals shown as a function of time for different temperatures at a fixed water concentration (100 mM). The solid (dashed) lines show the best fits obtained over the entire data range using the form $B{d}^3+C{d}^2+D$ ($B{d}^3+D$). The inset shows the dependence of the activation energy on water concentration.

Figure 4

The constant $B$ scaled by the square root of water concentration, as a function of temperature for different water concentrations.