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Nanocrystal Growth by Oriented Aggregation

Recent Research from the group of Professor R. Lee Penn.

Oriented aggregation is an important, nonclassical crystal growth mechanism by which nanocrystals grow, defects are formed, and unique - often symmetry-defying - crystal morphologies can be produced. This growth mechanism involves the irreversible and crystallographically specific self-assembly of primary nanocrystals and results in the formation of new single crystals, twins, and intergrowths. It offers a route by which nanocrystal size, morphology, and microstructure can be controlled. Recently, the Penn group demonstrated particle size control by exploiting oriented aggregation in the formation of goethite (alpha-FeOOH) nanorods from ferrihydrite nanoparticles. Specifically, they showed that the size of the goethite nanocrystals formed depends directly on the size of the precursor ferrihydrite nanoparticles (figure 1). Growth by oriented aggregation is consistent with second-order kinetics with respect to the concentration of the primary nanoparticles, and the Penn group has further shown that the overall rate constant for growth by oriented aggregation is strongly size dependent (figure 2). These results explain the common observation that early nanocrystal growth in solvothermal conditions is dominated by oriented aggregation and that its contribution to overall growth slows as a function of continued crystal growth.

Figure 1: Transmission electron micrographs of goethite nanorods (right) produced from ferrihydrite nanodots (left). Smaller nanorods are produced by oriented aggregation of the smaller nanodots (upper), and larger nanorods are produced by oriented aggregation of the larger nanodots (lower). Ref. Penn et al., 2006.

Figure 2: Plot of the log of the rate constant for oriented aggregation (log(k)) versus average particle length demonstrating the strong size dependence of the kinetics of growth by oriented aggregation. The linear relationship between log(k) and size is consistent with DLVO predictions. Ref. Penn et al., IN PRESS.


Size Dependent Kinetics of Oriented Aggregation. R. L. Penn, K. Tanaka, and J. J. Erbs (IN PRESS) Journal of Crystal Growth.

Controlled growth of alpha-FeOOH nanorods by exploiting oriented aggregation. R. Lee Penn, J. Erbs, and D. Gulliver, (2006). Journal of Cyrstal Growth, 293, 1-4.

Undergrad authors are shown in BOLD.

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