Understanding particle-mediated crystallization is critical to geoscience, material synthesis, catalysis, energy storage, environmental conservation, and even biological medicine. Using a combination of scanning/transmission electron microscopy (S/TEM), atomic force microscopy (AFM), and computational methods, we are investigating these phenomena for several metal oxide systems and their relationship to interfacial structure in vacuum, water vapor, and solutions. Here we discuss two cases. In the first, we explore the aggregation behaviors of hematite nanocrystals with different exposed facets including {001}, {012}, {104} and {116} in aqueous solutions at hydrothermal conditions (120-180 <sup>o</sup>C) via using high resolution TEM and STEM. The result indicates that hematite crystallization by nanoparticle aggregation occurs exclusively along [001] directions independent of crystal facets. We compare the result to the predictions of coupled plane-wave and classical density functional theory simulations to relate the behavior to surface interactions. In the second case, we report measurement of anisotropic forces between rutile TiO<sub>2</sub> (001) nanocrystals as a function of their azimuthal orientation and surface hydration extent using a combined environmental TEM-atomic force microscopy (AFM) technique. At tens of nanometers of separation, the attractive forces are weak and show no dependence on azimuthal alignment nor surface hydration. At separations of approximately one hydration layer, attractive forces are strongly dependent on azimuthal alignment and systematically decrease as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory and show that dispersion forces are capable of generating a torque between particles to align them.

Unravel particle-mediated crystallization pathways via using advanced transmission electron microscopy techniques

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.