Thursday, 16:00-17:00 April 22, 2021

Dr. Ismail El Baggari

Cryogenic STEM Visualization of Strongly Correlated Phases

Scanning transmission electron microscopy (STEM) is highly sensitive to lattice degrees of freedom and enables tracking of lattice displacements with sub- Angstrom resolution and picometer precision. This has ushered novel visualizations and discoveries of functional atomic displacements in ferroelectric materials, magnetoelectric oxides, and 2D materials. Due to stringent stability requirements, the overwhelming majority of high-resolution STEM measurements are limited to room temperature or above.

In many classes of correlated electronic materials, however, subtle and exotic ground states emerge exclusively below room temperature. Achieving cryogenic capabilities in STEM is therefore paramount to accessing and probing low temperature phases including high-temperature half-doped manganite, we address the long- standing question of whether charge order resides on the sites or bonds, discover an exotic intermediate state which breaks inversion symmetry, and find that non-linear couplings between distinct lattice distortion modes locally determine phase competition.

These cryogenic STEM results pave a clear path to imaging low temperature electronic phases with high resolution and precision.  Finally, I will discuss prospects of adding in-situ electrical contacts alongside cryogenic capabilities.

[1] El Baggari et al., Proceedings of the National Academy of Sciences 115.7 (2018): 1445-1450.

[2] El Baggari et al., Physical Review Letters 125.16 (2020): 165302.

[3] El Baggari et al., arXiv:2010.12610 (In Review)

[4] Schnitzer et al., Microscopy and Microanalysis 26.S2 (2020): 2034-2035.

Dr Michele Conroy

In-situ phase changes of Energy and Electronic Materials

 Most energy and electronic devices rely on the smooth transition between phases during device cycling.  At Bernal, there are several groups focused on nano-material synthesis and design for such applications. However, to truly harness the potential of these nano-materials we need our in- situ characterization at the atomic scale.

In this talk, I will show examples of how in-situ (S)TEM has been used to answer some questions our Bernal research community had about material phase changes. Additionally, I will briefly cover the in-situ (S)TEM options and expert staff we have at UL.

Finally, I will detail how to apply for national lab access for more specialized TEM equipment and expert TEM microscopist time.

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