Nanoparticle Metamorphosis: An In Situ High- Temperature Transmission Electron Microscopy Study of the Structural Evolution of Heterogeneous Au Fe2O3 Nanoparticles

Baumgardner, William J., Yingchao Yu, Robert Hovden, Shreyas Honrao, Richard G. Hennig, Héctor D. Abruña, Tobias Hanrath, et al., 2014

Image courtesy of ACS Nano

Abstract

High-temperature in situ electron microscopy and X-ray diffraction have revealed that Au and Fe2O3 particles fuse in a fluid fashion at temperatures far below their size-reduced melting points. With increasing temperature, the fused particles undergo a sequence of complex structural transformations from surface alloy to phase segregated and ultimately core–shell structures. The combination of in situ electron microscopy and spectroscopy provides insights into fundamental thermodynamic and kinetic aspects governing the formation of heterogeneous nanostructures. The observed structural transformations present an interesting analogy to thin film growth on the curved surface of a nanoparticle. Using single-particle observations, we constructed a phase diagram illustrating the complex relationships among composition, morphology, temperature, and particle size.

Impact Statement

The observation of Au and Fe2O3 particles’ structural transformations through in situ electron microscopy and spectroscopy. The particles fuse together at temperatures below their size-reduced melting points. Under increasingly higher temperatures, the
fused particles transform from surface alloy to phase-segregated and finally core-shell structures. The in situ microscopy and spectroscopy provided the researchers with a more detailed view of the fundamental thermodynamic and kinetic aspects behind the
heterogeneous nanostructures’ formation.