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Special Topics Seminar: Harikrishnan KP, Cornell
February 5 @ 10:00 am – 11:00 am
Atomic-Scale Insights into Ferroic Materials with Electron Ptychography and 4D-STEM
Abstract
Recent advancements in detector technology and phase-retrieval algorithms have pushed the spatial resolution of electron microscopes to the fundamental limits set by atomic thermal vibrations and the sample’s dose tolerance. Leveraging these improvements, along with enhanced capabilities for imaging light elements and reconstructing 3D structural information, I demonstrate how dipoles in polar materials can now be mapped quantitatively. This approach overcomes multiple scattering and diffraction artifacts that have long challenged conventional imaging methods. Specifically, I will present a dipolar mapping of strain-engineered ferroelectricity in sodium niobate thin films and strain-gradient-engineered flexoelectricity in bent strontium titanate membranes, revealing an unconventional polar distortion dominated by oxygen displacements in both materials. Expanding on these findings, I will delve into the direct visualization of buried nano-domains in 3D, surface relaxations and interface reconstructions, shedding new light on atomic-scale structural distortions in diverse material systems.
Biography
Harikrishnan KP is a physicist specializing in materials characterization through advanced electron microscopy techniques. He is currently a PhD candidate in Prof. David Muller’s group in the Applied Physics program at Cornell University. His research focuses on pushing the limits of high-resolution imaging to investigate complex oxides and semiconductor devices. Before pursuing his graduate studies, he earned a bachelor’s degree in Engineering Physics from the Indian Institute of Technology (IIT) Bombay.
