Date: Monday, Feb 24th
Presenter: Dr. Jeffery Aguiar, Los Alamos National Laboratory
Recent developments within the nuclear materials community have lead researchers to hypothesize that model composite materials can address concerns regarding nucleation, growth, migration, and fission product evolution at higher temperatures and radiation environments. Advanced microscopy allows for unprecedented insight into the underlying physical mechanisms responsible for the improved performance of these materials. To extend our understanding of radiation tolerance, and connect macroscale properties with changes in electronic and atomic structure, the use of analytical microscopy is a necessary tool. Studying nanocomposite ceramic interfaces offers opportunities to understand inherently complex phenomena in connection with material performance and behavior. Tailoring ceramic interfaces considers a variant of structural and chemical properties. Differences in crystal structure are selected to regulate changes in interfacial structure, misfit dislocation spacing, and the concomitant role of vacancy-interstitial energetics. In the later, for example the termination layer at the interface can play a major factor in determining the interfacial energetics. The same energetics are responsible for the structural evolution at interfaces and the concomitant role on radiation tolerance. Studying the structure, chemistry, electrostatics, and response before, during, and after irradiation thereby leads to fundamental studies at micron to sub-Ångstrom level aimed at both understanding and controlling radiation tolerance. In this presentation, we will examine both the evolution of structure in connection with the formation of intergranular films following light ion irradiation at structured interfaces. Combining controlled epitaxial growth of thin films and ion beam radiation, we have performed aberration corrected transmission electron microscopy coupled with spectral imaging on a series of irradiated CeO2-STO and STO-MgO oxide interfaces to address both simultaneous changes in atomic structure and chemistry. Studying the effects of transmutation, we will specifically present recent experiments using analytical aberration corrected transmission electron microscopy (TEM) to study the synthesis. These novel results are compared to complementary theoretical calculations, which ultimately will allow for predictions of structural stability as function of compositional evolution beyond equilibrium conditions.
Jeffery Aguiar received his undergraduate degree in Engineering Physics from the University of the Pacific, and his Ph.D. in Materials Science from the University of the California-Davis (UCD). After completing his Ph.D. in 2005, he joined the Materials Science and Technology Division at Los Alamos National Laboratory (LANL) as a postdoctoral research associate. Previously, before taking the postdoctoral position at LANL he interned in the Energy and Environmental Technologies Division (EETD) at Lawrence Berkeley National Laboratory from 2002 to 2005. In 2005, he moved to the Department of Chemical Engineering and Materials Science at the University of California-Davis (UCD) to pursue a doctorate degree and also held a joint graduate fellow research appointment at Lawrence Livermore National Laboratory (LLNL). During his Ph. D at UCD and LLNL, Jeffery focused on the use of analytical electron microscopy to study a variety of materials and their interfaces, including irradiated ceramics, alloys, and interplanetary space dust collected during the NASA Stardust mission. Now, at LANL his research is focused on the development of new methods in electron microscopy and materials to study irradiated nanocomposites and high-level radioactive waste forms with high spatial, temporal and spectroscopic resolution within the Energy Frontier Research Center (EFRC).