Speaker: Ismail El Baggari, UBC

Time: 10:00-11:00am

Location: BRIM 311

Title: Scanning transmission electron microscopy (STEM) now routinely resolves the atomic structure and chemistry of materials with sub-angstrom resolution. Recent advances in instrumentation further allow spatially resolved mapping of subtle, picometer-scale atomic shifts that underpin emergent functional properties. In ferroelectrics, for example, polarization arises from tiny atomic displacements that break inversion symmetry; STEM can locally visualize these displacements and reveal novel polarization textures. 

Despite this potential, STEM applications have traditionally been restricted to room temperature (or higher) because of longstanding challenges in implementing stable liquid-helium cryogenic cooling, such as vibrations and inadequate temperature control. My group has been addressing these limitations by developing dedicated liquid helium cryogenic STEM instrumentation to probe materials whose emergent properties appear only at low temperatures. We have now overcome key technical hurdles and can cool samples inside the microscope to cryogenic regimes down to ~20 K. I will present recent applications of cryogenic STEM to imaging order and disorder in ferroelectrics. In particular, I will highlight quantum paraelectric SrTiO₃, a material that hovers on the verge of ferroelectricity yet remains paraelectric to the lowest temperatures due to quantum fluctuations. Using cryogenic STEM, we directly visualize emergent nanoscale polar textures and mesoscale correlations in this quantum paraelectric phase.

Zhang et al. “Inverse Melting of Polar Order in Chemically Substituted BaTiO3.” Physical Review Letters 134.25 (2025)

Rennich, et al. “Ultracold cryogenic TEM with liquid helium and high stability.” Proceedings of the National Academy of Sciences122.36 (2025)

Zhang et al. “Nanoscale Polar Landscapes in Quantum Paraelectric SrTiO₃.” arXiv:2509.24969 (2025).