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Hua Zhou: Atomic Imaging Functional Heterostructures and Interfaces by Phasing Coherent Bragg Rods for Quantum Materials and Energy Systems

Argonne National Laboratory

Ubiquitous in a wide range of nature processes and technologies, a subtle modification (e.g. structurally, chemically, or electronically) near an interface can have a decisive effect on properties of the collective as well as each individual. A compelling case manifesting such subtlety is oxide heterostructures and heterointerfaces exhibiting fascinating emergent behaviours due to numerous combinative contributions of atomic structures and chemistries, which can be effectively harnessed for the design of advanced materials for information and energy applications and accelerating materials integration into advanced devices. Surface/interface X-ray scattering from modern synchrotron sources integrated with phase retrieval direct methods provides a very powerful toolkit to decipher the interfacial subtlety. This is essential to our ability to provide a quantitative and realistic description of the interfacial boundaries by which to engineer properties of functional interfaces using atomic structure-driven design principles in a reliable and controlled manner.

In this seminar, I will firstly give a brief introduction of how to obtain atomic mapping of multifunctional heterostructure and heterointerfaces with sub-Ångstrom resolution by phase retrieving coherent Bragg rods, wherein complete atomically structural information hidden, in particular on the COBRA method in combination with the difference map algorithm achieving unprecedented speed of convergence and precision. In the following, I will demonstrate some science cases in the exploration of oxide heterostructures and heterointerfaces for information and energy applications by applying the direct method, such as revealing structural motifs responsible for various quantum states (e.g. 2DEG/2DHG, interfacial superconductivity, polar metal and 2D skyrmions) adjacent with heterointerfaces, catching structural perturbations in response to internal and external electric fields, differentiating at the atomic-layer level the complicated cation distribution for enhancing oxygen reduction activities, and depth-resolved mapping oxygen-octahedral connectivity network essential with incipient ferroelectricity of heterostructures. In the end, I will give a short commentary on emerging opportunities in X-ray studies of multifunctional interfaces and heterostructures enabled by the exciting advancements towards ultimate storage rings, in particular with enhanced high-energy, coherence and ultrafast capabilities.