James LeBeau
Materials Science & Engineering
North Carolina State University

Putting a New Spin on Electron Microscopy: Towards Absolutely Quantitative Atomic Scale Imaging

Location: EB1 Room 1011

Friday, October 2nd 2015 - 11:00 am

Within the past fifteen years, electron microscopy has been revolutionized by the advent of the aberration corrector. Aberration correction dramatically improves spatial resolution into the sub-ångstrom regime, unlocking previously inaccessible information about material structure. While these recent advances have proven essential to the atomic scale characterization of materials, real-space measurements have remained largely qualitative. In particular, accuracy and precision for scanning transmission electron microscopy (STEM) was significantly hampered by the presence of sample drift and scan distortion. Until recently, this limitation has obscured the capabilities to characterize minute changes to the atomic structure that can ultimately define material properties.

In this talk, I will introduce revolving scanning transmission electron microscopy (RevSTEM). The method uses a series of fast-acquisition STEM images, but with the scan coordinates rotated between successive frames. I will provide a theoretical basis for the approach and demonstrate that the technique is capable of achieving sub-picometer accuracy and enables real-space crystallographic measurements in STEM. Multiple case studies will be presented to demonstrate the power of this new technique to characterize materials. For example, I will show how picometer precise measurements enable the capability to directly observe static atomic displacements within a complex oxide solid solution, highlighting differences in local bonding. Furthermore, using ferroelectric HfO2 thin films, I will also show how RevSTEM images can be used to accurately determine crystallographic parameters in real-space, and to determine the structural origins for spontaneous polarization in these materials. These results open a new world of atomic scale exploration that was previously just beyond our reach.

North Carolina State University