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Materials Interfaces: Structure, Dynamics, and Charge Density Revealed with Improved Resolution
February 27, 2019 @ 10:00 am - 11:00 am
Speaker: Wenpei Gao
Affiliation: Department of Materials Science and Engineering, University of California, Irvine
Title: Materials Interfaces: Structure, Dynamics, and Charge Density Revealed with Improved Resolution
Recent advancement in electron microscopy techniques brings highly improved spatial resolution and energy resolution to characterize materials structures at the atomic scale. However, at materials interfaces, including those between metal nanoparticle and support, between liquid/gas and solid, and between complex oxides, resolving the structures and dynamics requires further technical improvement.
For example, at the metal-oxide interface in catalyst, the interfacial structure changes under different pretreatments, and has been proposed to impact the catalyst activity, selectivity and stability. Rebuilding the three-dimensional structure is critical to understand the catalytic mechanism at the atomic scale, however, three-dimensional imaging is challenging and beyond the capability of routine imaging condition, considering the complexity of the interfacial structure.
Another example is the growth of functional nanostructures, catalysts and colloidal nanoparticles. Controlling the morphology and properties of the nanostructures heavily relies on fine tuning the reduction kinetics of the precursor and manipulating the nucleation process. However, existing experimental studies only address the nucleation process as a whole, or at a scale larger than 1 nm; multiple hypotheses from classical theory also co-exist, each predicting different possible materials reduction trajectories. A microscopic picture detailing the intermediate reaction steps can help clarify the puzzle, however, is missing, because of the limitation on imaging beam sensitive chemicals at high resolution in electron microscopes.
Finally, in semiconductors and complex oxides, the charge distribution is closely related to their electronic structures and transport properties. However, the limited spatial resolution of current methods in probing charge density present significant obstacles in characterizing the charge redistribution in nanostructures and heterostructures, such as interfaces, domain walls, and grain boundaries, which are vital to the materials properties and device performance.
In this presentation, the efforts to overcome the limitations for imaging materials interfaces in electron microscopy will be described, which includes using depth sectioning to reconstruct the three-dimensional structures of interfaces in catalyst, combining low-dose with in situ imaging to probe the chemical reactions at atomic resolution in real space, and developing scanning diffraction to reveal the interplay among lattice, charge and field in oxides. The new possibilities in electron microscopy brought by going beyond imaging two-dimensional projection to three-dimensional structure, beyond resolving atomic structures to probe chemical reactions, and beyond seeing atoms to mapping field and charge will also be discussed.