Yingge Du

Understanding topotactic phase transitions in epitaxial oxide thin films

Yingge Du
Physical Sciences Division, Pacific Northwest National Laboratory

Thursday, Sept. 26
4-4:50 p.m.
Johnson 102

 

Abstract

Structurally ordered oxides exhibit a broad range of structural, compositional, and functional properties, which can be further tuned by means of judicious elemental doping, strain and defect engineering. As such, they have found widespread application in energy storage and conversion devices, particularly for use as electrocatalysts, cathodes, and solid state ionics. However, as-designed materials can undergo dramatic changes due to ion diffusion, which, in many cases, leads to performance degradation and device failure.

This talk will highlight our most recent effort aiming to modify complex oxides through heteroepitaxy to achieve tunable functional properties. Combining in situ and environmental transmission electron microscopy (TEM), 18O2 labeled time-of-flight secondary ion mass spectrometry (ToF-SIMS), and ab initio simulations, we elucidate the structural and chemical evolution pathways in selected materials systems and reveal how such changes impact their functional properties. The first part of my talk focuses on Brownmillerite (BM)-structured SrFeO2.5 (BM-SFO), and rhombohedral-structured SrCrO2.8 (R-SCrO), which are perovskite (ABO3)-associated structures that contain ordered oxygen vacancy channels. We show that at relatively low temperatures, a topotactic phase transition between BM-SFO (R-SCrO) and perovskite SrFeO3 (SrCrO3) can be promoted, delayed, or prohibited based on the interfacial strain conditions, highlighting the importance of interface engineering in designing robust and efficient ion conducting materials. In another example, I will present the epitaxial growth and in situ TEM studies of LiCoO2 with or without overlayers to understand the Li transport processes and device failure mechanisms. In both cases, the high spatial and temporal resolution offered by advanced electron microscopy allows the visualization of reaction onset, kinetics, intermediates, and final products, which is critical for the rational design of functional materials.

 

About Dr. Du

Dr. Yingge Du is a senior staff scientist in the Materials Group of the Physical and Computational Sciences Directorate. Upon receiving his PhD from the University of Virginia, he joined PNNL in 2007 and became a staff member in 2010. He served as technical lead in the acquisition and commissioning of a new state-of-the-art oxide molecular beam epitaxy (MBE) system for the EMSL user facility located at PNNL. His current research focuses on growth and characterization of epitaxial metal oxide films and superlattices for energy conversion and storage applications.

Dr. Du is the recipient of a 2016 DOE Early Career Award, which supports him to conduct basic research that aims to understand, predict, and ultimately control cation/anion ordering and topotactic phase transitions occurring in transition metal oxide thin films. Achieving so will enable energy materials (e.g., catalysts, electrodes, and electrolytes) with desired functionalities to be designed, synthesized, stabilized, and harnessed for technological benefits.

 

Identifying Active Surface Entities for Catalytic Conversion
by Multimodal Surface X-ray Probes

Hua Zhou 
Advanced Photon Source, Argonne National Laboratory  
 
Monday, Sept. 30 
4-4:50 p.m. 
Johnson Hall 102 
 

Abstract

Electrocatalysts are materials designed to provide a facilitating environment for electrochemical conversion and synthesis of materials and fuels from atmospheric molecules, which is one of the most important challenges facing societal need of energy in 21st century. One of the major hurdles developing electrocatalysts is the lack of holistic information of the evolving surface structure of materials during electrochemical operation. This is particularly formidable for oxygen evolution reaction (OER), where the oxidizing environment is corrosive and can significantly rearrange the electrocatalyst surface structure. Surface-sensitive X-ray probes from modern synchrotron sources including surface X-ray scattering and grazing incidence X-ray spectroscopy provide a very powerful suite of toolkits to decipher the surface subtlety and evolution. If utilizing these techniques in a well-coordinated approach, one can deliver thorough and deep fundamental insights of surface transformations (e.g. structural, chemical and electronic) during the electrocatalytic process.

In this talk, we will firstly render a brief survey of various surface sensitive X-ray techniques to specifically probe structural and chemical aspects of electrocatalytic materials, in particular the combined approach to differentiate the contribution from surface and bulk layers. Following the survey, we would like to present a few prototypic studies of model systems (e.g. functionalized graphene and metal oxides) for surface catalytic processes. First example is the detailed understanding of the noncovalent functionalization of graphene by small molecule aromatic adsorbates (e.g. phenanthrenequinone), which demonstrates persistent redox activity associated with proton‐coupled‐electron‐transfer reactions. Surface X-ray scattering analysis integrated with ab-initio calculations reveals how the prior introduction of defects and oxygen functionality (hydroxyl and epoxide groups) to the graphene basal plane effectively stabilizes its noncovalent functionalization. The second major demonstration is to present a comprehensive study of the emergent surface transformation of SrIrO3, the most active OER electrocatalyst reported to date, especially the amorphous boundary layer that forms from the pristine crystalline structure on the surface with OER cycling. In virtue of multimodal X-ray probing, a step-by-step transformation mechanism of the amorphization process could be explicitly illuminated. Our X-ray results show that the amorphization is triggered by the lattice oxygen activation and the structural reorganization facilitating coupled cation and anion diffusions is key to the realization of the OER active structure in the final SryIrOx form which exhibits stronger disorder than conventional amorphous IrOx, explaining its champion OER activity. In the end, I will give a short commentary on future opportunities in X-ray studies of multifunctional surfaces and interfaces for energy conversions enabled by the exciting advancements towards ultimate storage rings, in particular with enhanced high-energy and coherence capabilities.

 

About Hua Zhou 

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 120 peer-reviewed publications. He has presented about more than 30 invited speeches in international conferences, universities and national labs.

Development of Alternative Water Supplies:
Innovative Technologies for Water Reuse and Desalination

Pei Xu 
Department of Civil Engineering, New Mexico State University
 
Monday, Oct. 7
4-4:50 p.m. 
Johnson Hall 102 

 

Abstract

Water scarcity and the need to meet the increasing water demands have driven the development of alternative water supplies including seawater, brackish water, agricultural, municipal and industrial wastewaters. Given the energy intensity of existing water infrastructures, it is critical to develop sustainable paradigms for water and wastewater engineering that will balance energy consumption, economic benefits, ecological impacts, and social acceptance. This presentation will highlight a number of innovative technologies for improving process efficiency, reducing carbon footprint, recovering resources from wastewater, generating water with quality tailored for various uses, and an integrated decision support tool for produced water treatment and reuse.

 

About Dr. Xu

Dr. Pei Xu is a professor in the Department of Civil Engineering at the New Mexico State University. She teaches courses in introduction to environmental engineering, physical/chemical/biological treatment processes, environmental engineering field session, advanced water treatment and reuse, sustainability in food-water-energy-environmental systems, and capstone design projects. Pei's research focuses on water reuse, desalination, and concentrate treatment for inland applications. The goal of her research is to address critical water shortage challenges in arid and semi-arid regions. Her work has been funded by NSF, DOE, BoR, USGS, Water Research Foundation, NASA, and water industry. She currently is a member and co-lead of the Engineering Thrust of the NSF Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt). She was recently selected as the AAAS Leshner Fellow on Food and Water Security, PESCO Endowed Professorship and C. Herb Ward Family Endowed Interdisciplinary Chair at NMSU.

Owen McCarty

The blood microenvironment: The good, the bad, and the sticky

Owen McCarty
Department of Biomedical Engineering, Oregon Health & Science University

Monday, Oct. 28
4-4:50 p.m.
Johnson 102

 

Abstract

Hemostatic plug formation upon blood vessel breach is initiated by platelet recruitment, activation and aggregation in concert with thrombin generation and fibrin formation. However, a similar process can also lead to pathological processes including deep vein thrombosis, ischemic stroke, or myocardial infarction, among others. We have developed narrow mechanism-specific agents targeting the intrinsic pathway of coagulation and demonstrated that experimental thrombosis and platelet production in primates is interrupted by selective inhibition of activation of coagulation factor (F)XI by FXIIa. In this seminar, I will present new data on the role of the endothelium in inactivating FXI, as well as studies on whether inhibiting FXI is beneficial in a non-human primate model of sepsis. I will present our first data from our clinical trial on the safety of inhibition of FXI, and plans to test the efficacy of FXI inhibition in dialysis. The understanding of the mechanisms by which the intrinsic pathway of coagulation promotes thrombus formation may support the rationale for the development of selective, safe and effective antithrombotic strategies targeting FXI.

 

About Dr. McCarty

A native of Rochester, Dr. McCarty received his B.S. in Chemical Engineering from SUNY Buffalo, and a Ph.D. degree in Chemical Engineering from Johns Hopkins University, where his research focused on the identification and characterization of tumor cell receptors for blood platelets and leukocytes. He performed his postdoctoral research on platelet cell biology in the Pharmacology Department at the University of Oxford and University of Birmingham, UK in the group of Dr. Steve Watson. Dr. McCarty joined Oregon Health & Science University in 2005, where he holds an appointment as a Professor in the Departments of Biomedical Engineering and Cell, Developmental & Cancer Biology and the Division of Hematology & Medical Oncology in the OHSU School of Medicine. Dr. McCarty serves as the Chair of the Biomedical Engineering Department and a fellow of the American Heart Association.