Date: Monday, Mar 2nd
Presenter: Dr. Melissa Santala, Lawrence Livermore National Laboratory
The crystallography and atomic structure of hetero-interfaces can exert a profound effect on a wide range of multiphase-material properties. The properties of oxide-metal interfaces are important to a large variety of applications, ranging from thermal barrier coatings to sensors to catalysts, but few have been well characterized due to challenges involved in experimentally determining the atomic structure at interfaces of dissimilar materials. This talk will describe the use of conventional and aberration-corrected TEM to determine relative interfacial energies and atomic structure of interfaces in a representative oxide-metal system. Ion implantation and thermal annealing was used to control Pt distribution within alpha-Al2O3, a model structural ceramic (though similar processing could be used as a novel route to study catalytically active phases of alumina). The quantitative characterization of the morphology of Pt inclusions in alpha-alumina was used to determine the relative interfacial energies of select alpha-alumina/Pt interfaces and relative surface energies of Pt-saturated alumina surfaces. The thermodynamics and atomic structure of alpha-alumina/Pt interfaces were also studied through a combination of aberration-corrected high-resolution TEM and first-principles calculations. Density functional theory (DFT) calculations were performed to identify energetically favorable configurations of an alpha-alumina/Pt interface for three different alumina terminations and interfacial energies and stability ranges for a range of oxygen partial pressures were calculated. Comparisons between the reconstructed phase images from the TEM experiments and the DFT-based calculations allowed the interface termination to be established. Potential applications of the processing and TEM techniques used in this work and of recently developed in situ TEM techniques will be presented.
Dr. Melissa K. Santala is a staff scientist in the Materials Science Division at Lawrence Livermore National Laboratory. After a brief career as a painting conservator, she decided to study materials science. She received her B.S. and M.S. in Materials Science and Engineering from the University of California at Berkeley. She was a recipient of a National Science Foundation Graduate Research Fellowship and earned her Ph.D. in Materials Science and Engineering at UC Berkeley in 2009. Her graduate research focused on fundamental studies of the thermodynamic and kinetic properties of surfaces and interfaces in ceramic and ceramic-metal systems. She joined Lawrence Livermore National Laboratory as a post-doctoral researcher and there she has been using photoemission TEM for in situ studies on the kinetics of highly-driven phase transformations in various materials systems, including semiconductors and chalcogenide-based phase change materials.