Characterizing crystal growth by oriented aggregation

Abstract

Oriented aggregation (OA) is a non-classical crystal growth mechanism by which uniquely shaped nanocrystals with tight size control can be produced. Primary crystallites attach with crystallographic order, leading to the formation of secondary, single crystals. Comprehensive characterization is critical for elucidating the fundamental processes of oriented aggregation. Transmission electron microscopy (TEM), cryogenic TEM, and in situ fluid cell TEM enable direct imaging of materials throughout the growth process. Correlative techniques, such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), dynamic light scattering (DLS), and UV-visible spectroscopy, as well as kinetic modeling, also lead to important insights. Each of these techniques has advantages and limitations; a combination of methods is required to push our understanding of OA forward.

Oriented Attachment and Nonclassical Formation in Iron Oxides

“…Finally, ultraviolet-visible (UV-Vis) spectroscopy can be used to determine size from size-dependent optical properties of some nanoparticles [89], though this technique has less applicability to nanoparticles (including some iron oxides) that do not change color or optical properties with size. An in-depth review of methods for characterizing growth via OA can be found in Penn and Soltis [28].…”

“…The detection of features such as crystal twinning, dislocations, and dimpled boundaries in TEM images can indicate relics of growth by OA [28]. Figure 11.4 shows a pair of TEM images of goethite synthesized from a ferrihydrite precursor [51].…”

“…Similarly, a lack of such features is also not sufficient evidence for crystal growth by coarsening, since rough surfaces and defects can effectively be erased by competing mechanisms. Thus, correlative methods, such as tracking particle size distributions using in situ light and X-ray scattering methods and in situ imaging methods, like cryogenic (cryo) and fluid cell TEM, are essential [28].…”

“…A fluid cell encloses a small amount of liquid sample between electron-transparent windows [28,70]. Some fluid cell holders can accommodate single-or dual-input flow cells, permitting mixing experiments, or incorporate electrochemical and thermal controls [70].…”

“…The particles can then irreversibly attach to form a continuous crystal (IV)." (Reproduced from [28], with permission of The Royal Society of Chemistry.) aggregation could not readily explain observed textures and shapes.…”