Dr. Hua Zhou [APS in Argonne National Laboratory, USA]

Title: Atomic Imaging Functional Heterostructures and Interfaces by Phasing Coherent Bragg Rods for Correlated Materials and Energy Systems

Time: 9:00 - 10:00 AM, Wednesday May 23, 2018

Place: Conference room 410, HPSTAR (Shanghai)

Host: Wenge Yang

Polycom: 02120004

Abstract:

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 a few recent studies 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, superconductivity and polar metal) adjacent with heterointerfaces, catching structural perturbations in response to internal and external electric fields, differentiating at the atomic-layer level the complicated cation distribution relevant with creating new polar order and enhancing oxygen reduction activities, and depth-resolved mapping oxygen-octahedral connectivity network essential with incipient functionalities of heterostructures. In the end, I will give a short commentary on future 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 and coherence capabilities.

Biography of the Speaker:





Dr. Hua Zhou is a staff physicist at the Advanced Photon Source (APS) in Argonne National Laboratory. He has managed and developed scientific programs dedicated for in-situ/operando and real-time X-ray studies of advanced materials synthesis, functionality and applications, in particular on surface/interface phenomena and processes in complex environments (e.g. thin film deposition of epitaxial nanostructures and heterostructures, emergent physics of strongly correlated condensed matters, versatile solid/liquid/gas interfaces for electrochemical energy storage and conversion systems) at the APS since 2011. He has extensive research experience using synchrotron-based X-ray techniques to characterize and uncover surface/interface structural modifications and dynamics of epitaxial thin films and heterostructures by using phase retrieval direct methods. Before he joined the APS, he was a postdoctoral fellow in National Synchrotron Light Source at Brookhaven National Laboratory and in Chemical Science and Engineering Division at Argonne National Laboratory. He received his Ph.D. degree in Materials Science from University of Vermont in late 2007. His work and contributions on thin films/heterostructures and surface/interface X-ray scattering techniques have been featured in book chapters, reviewers and more than 90 peer-reviewed publications. He has presented about 30 invited speeches in international conferences, universities and national labs.