Dongsheng Li
Pacific Northwest National Laboratory, USA
Title: In situ investigations of particle-mediated crystal growth
Biography
Biography: Dongsheng Li
Abstract
Assembly of molecular clusters and nanoparticles in solution is now recognized as an important mechanism of crystal growth in many materials, yet the assembly process and attachment mechanisms are poorly understood. To achieve this understanding we are investigating nucleation and assembly of iron and titanium oxides using in situ and ex-situ TEM, and the forces that drive oriented attachment between nanocrystals and the factors that control them via AFM-based dynamic force spectroscopy (DFS). Our hypothesis is that attachment is due to reduction of surface energy and the driving forces that bring the particles together are a mix dipole-dipole interactions, van der Waals forces, and Coulombic interactions. Therefore they can be controlled via pH, ionic strength (IS), and ionic speciation. In-situ TEM shows that, in the iron oxide system, primary particles interact with one another through translational and rotational diffusion until a near-perfect lattice match is obtained either with true crystallographic alignment or across a twin plane. Oriented attachment then occurs through a sudden jump-to-contact. Analysis of the acceleration during attachment indicates it is driven by electrostatic attraction. Ex-situ TEM analysis shows that the TiO2 nanowire branching occurs through attachment of anatase nanoparticles to rutile wires on a specific crystallographic plane for which the anatase-to-rutile transformation leads to creation of a twin plane. Initial DFS measurements of the forces between (104) planes of CaCO3, (001) crystal basal planes of mica, and (001) planes of ZnO show that the forces have strong relationship to pH, IS, and crystal orientation.