When 3:30 PM - 5:00 PM Sep 27, 2013
Where 1670 Beyster Building
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Structure and Chemistry at the Atomic Scale: A New Paradigm in Materials Characterization

James Lebeau
North Carolina State University, Department of Materials Science and Engineering

As “nano” becomes an ever-present prefix of daily life, demand has increased for analytical capabilities that reach beyond the nanoscale. Scanning transmission electron microscopy (STEM) has served as one of the most poIrful nanoscale characterization tools available to the materials scientist for this reason. Within the past decade, electron microscopy has been revolutionized by the advent of the aberration corrector. Aberration correction dramatically improves spatial resolution into the sub-ångstrøm regime, unlocking information about material defects previously just beyond reach. One technique in particular, atomic resolution high angle annular dark-field STEM (HAADF STEM), provides images that are directly interpretable and whose intensities depend sensitively upon the atomic species present. Furthermore, when aberration correction is combined with state-of-the-art energy dispersive X-ray spectrometers, atomic resolution chemical spectroscopy becomes possible. In this talk, I will show that aberration corrected STEM techniques have become indispensible for addressing a wide variety of materials science questions, and will explore the synergistic combination of atomic resolution STEM imaging and X-ray spectroscopy to study interfaces, defects, and phase evolution. As a prototypical example, I will discuss our recent study of a thin film of bismuth telluride, Bi2Te3, grown epitaxial on a GaAs substrate. In this case, HAADF STEM images could only provide an ambiguous determination of the interface structure. Through application of atomic resolution x-ray spectroscopy, direct identification of interface layers becomes possible, namely the replacement of As by Te; impossible to determine from the HAADF STEM images alone. Using this additional information, I will present a new model where a single layer of Ga2Te3 provides the platform for van der Waals epitaxial growth. Along the path to the new paradigm, I will survey recent results applying atomic resolution STEM imaging and spectroscopy to longstanding questions about solution-deposited ferroelectric films, oxide electronics, and ultra-high toughness ceramic composites.

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