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Physical Sciences and Engineering

Functional Nanoscale Heterostructures

Our group explores the behavior of magnetic, ferroelectric and resistive switching structures at the nanoscale, in addition to optical nanocomposites and energy storage materials.
Magnetic induction in magnetic vortices (left) and an artificial spin ice lattice (center) and local capacitance behavior of as-grown and freestanding ferroelectric films

We use in-situ 3D microscopy and electronic transport measurement to visualize and understand the emergent properties of these materials.

We aim to understand how the energy landscape of nanoscale ferroic materials can be influenced through geometric patterning or confinement and through interfacial interactions. We aim to explore and control the formation of novel distributions of spin and charge, for example stable topological spin structures in nanoscale patterned magnetic films, effect of curvature on magnetic spin textures, magnetic frustration and monopole defects in artificial spin ices, as well as flux-closure and metastable domains, in ferroelectric nanostructures. We are also exploring how confinement and charged defects affect the charge distribution and transport in resistance switching oxides, including artificial nanoscale networks. Our goal is to understand the emergent physical phenomena that are observed in these systems in response to external stimuli, such as the synaptic behavior of the conducting filaments in resistive oxides and domain walls in artificial magnetic networks, and the behavior of magnetic skyrmions in heterostructures as well as 2D van der Waals materials.  We are also exploring freestanding epitaxial complex oxide ferroelectrics, which exhibit surprisingly different properties than their counterparts on strongly-bonded substrates. The unique boundary conditions of freestanding materials profoundly alter their intrinsic local charge, spin and lattice degrees of freedom. Our current efforts are unveiling the intricate relationships among domain wall motion, impedance,  flexo- and piezoelectric effects and quantum tunneling of electrons in steady- and nonequilibrium states.

A particular focus of our research is the use of in-situ 3D microscopy to visualize and understand this nanoscale behavior. Our approach involves a combination of aberration-corrected Lorentz transmission electron microscopy and advanced scanning force microscopy that we use to address the scientific questions related to ferroic nanostructure behavior and resistance switching oxides. We have developed in-situ techniques that allow us to visualize domain behavior, local structural and electronic environment, and transport behavior in nanostructures as a function of external stimuli such as applied fields, temperature and time. We combine these experiments with measurement of charge, potential and current at the mesoscopic length scale, and with simulations. We also apply the microscopy and electronic transport measurement techniques to explore materials for applications in batteries, solid oxide fuel cells and solar cell coatings.

More broadly, we interact with the wider imaging community at Argonne to develop experimental and computational capabilities for multi-modal imaging at the nanoscale, including incorporating machine learning approaches.