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2017  Nov 1 - Dec 21

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2018  Apr 11 - Jun 4
2018  Proposal/BTR deadline: 2/1/18

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Talk Abstracts

 

 
"Modeling Microstructural Effects on Porosity Evolution"

Nathan Barton
Lawrence Livermore National Laboratory

Abstract: We present results from a computational investigation of microstructural effects on failure of ductile polycrystalline metals. The computational model makes use of a crystal mechanics based constitutive model that includes porosity evolution. The formulation includes nucleation behavior that is fully integrated into a robust numerical procedure, enhancing capabilities for modeling small length scales at which nucleation site potency and volume fraction are more variable. Anisotropic crystal response and interactions among the crystals produces heterogeneities that influence spall response and spatial resolution of the polycrystal allows for investigation of various types of nucleation site distributions. By focusing validation efforts on models that connect directly to experimentally measurable features of the microstructure, we can then build confidence in use of the models for components prepared under different processing routes, with different chemical compositions and attendant impurity distributions, or subjected to different loading conditions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (LLNL-ABS-664056).

 

 
"Impact of atomic structure and dynamics on solar cell performance of metal halide perovskite thin films"

Joshua J. Choi
University of Virginia

Abstract: Metal halide perovskites (MHPs) are revolutionizing the solar cell research field - the record power conversion efficiency of MHPs based solar cells has reached 22%, which rivals that of silicon solar cells. This represents the highest efficiency among all solution processable materials and the fastest rate of efficiency improvement in the history of all photovoltaic materials. Based on this trend, MHPs have been called the “next big thing in photovoltaics” and worldwide research efforts have grown explosively.

Despite the impressive solar cell performance demonstrations, the microscopic mechanisms of the high performance are poorly understood, precluding more rational progress toward further increase in efficiency. Also, the record solar cell efficiency demonstrations are based on small laboratory scale devices (not much bigger than a human fingernail) and scaling up of the device area while maintaining the high efficiency has not yet been achieved. This is primarily because the thin film growth processes of the MHP thin films are not well understood.

In this talk, I will present our recent work that employed temperature dependent X-ray and neutron scattering to characterize the atomic structure and dynamics in MHPs. We find that the rotation of organic cations in MHPs play a crucial role in determining the optoelectronic properties as well as structural phase stability that are directly relevant for solar cell performance. I will also present results from in-situ grazing incidence X-ray scattering studies on the MHP thin film formation processes. Our results reveal the sub-processes and mechanisms through which highly preferential crystallographic orientation of MHP films can be formed. We demonstrate methods to controllably tune the direction and degree of the preferential orientation. Impact of the degree of thin film orientation on solar cell performance will be discussed.

 

 
"Structural Basis for HIV Integrase Oligomerization and its Drug-induced Aggregation"

Kushol Gupta1, Grant Eilers2, Audrey Allen2, Vesa Turkki2*, Young Hwang2, Gregory D. Van Duyne1 and Frederic D. Bushman2
1From the Perelman School of Medicine, University of Pennsylvania. Department of Biochemistry and Biophysics 242 Anatomy-Chemistry Building Philadelphia, PA, 19104-6059 U.S.A. 2Department of Microbiology 3610 Hamilton Walk Philadelphia, PA 19104-6076 U.S.A.

Abstract: The major effect of allosteric HIV integrase (IN) inhibitors (ALLINIs) is observed during virion maturation, where ALLINI treatment results in IN aggregation and the formation of aberrant particles. We previously crystallized full-length HIV IN bound with an ALLINI and determined the structure of this complex at 4.4 Å resolution. We have extended these ongoing structural studies to include new crystallographic structures with additional representative ALLINIs and resistance mutations. The structures reveal the formation of an open polymer, with dimers of IN interacting in a head-to-tail manner. An interface between the catalytic core domain of one dimer with the C terminal domain of an adjacent dimer forms around the ALLINI, which is deeply buried by IN surfaces. These surfaces are rich in residues that convey resistance to ALLINIs, as identified by serial viral passage experiments. Escape mutants were found to decrease drug-induced aggregation, and crystallographic studies of escape mutants support a model where ALLINIs disrupt virion maturation by inducing the formation of the polymer observed in the IN-ALLINI crystal structure. Biophysical analyses informed by these structures using Evolving Factor Analysis-Singular Value Decomposition (EFA-SVD) analysis of SEC-SAXS data suggests a structure for the IN tetramer in the absence of DNA and a novel structural model for IN oligomerization that is stimulated by the ALLINI class of molecules. Characterization of oligomeric intermediates, higher order IN-ALLINI complexes, and resulting escape mutants provides important data for optimizing ALLINI drug design and understanding mechanisms of resistance.

 

 
"A New in situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment: Application to Micromechanics of Biaxial Dwell Fatigue in Ti-7Al"

G.M. Hommer, Graduate Research Assistant, Mechanical Engineering Department, Colorado School of Mines, Brown Hall W350, 1610 Illinois Street, Golden, CO 80401
J.S. Park, Materials Physics and Engineering X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Ave, Building 431-A004, Lemont, IL 60439
P.C. Collins, Al and Julie Renken Associate Professor, Materials Science and Engineering, Iowa State University, 2240 Hoover Hall, 528 Bissell Road, Ames, IA 50011-1096
A.L. Pilchak, Materials Research Engineer, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433
A.P. Stebner, Assistant Professor, Mechanical Engineering Department, Colorado School of Mines, Brown Hall W350, 1610 Illinois Street, Golden, CO 80401
 

Abstract: A custom planar biaxial load frame capable of in situ X-ray diffraction experimentation has been built to study the three-dimensional micromechanics of advanced structural alloys exhibiting anisotropic, asymmetric and path dependent mechanical behaviors. The experimental setup, capabilities, sample design and current applications will be reviewed, with emphasis on the study of tension-tension dwell fatigue in Ti-7Al.

 

 
"Synchrotron Based X-Ray Computed Tomography for Damage Evolution Studies"

James Hunter
Los Alamos National Laboratory

Abstract: As part of its materials science mission Los Alamos National Lab uses synchrotron x-ray beamlines to study damage evolution in material samples. These materials range across the periodic table and damage mechanisms vary from thermal and mechanical to shock and radiation. The use of x-ray computed tomography as a 3D imaging tool at these beamlines is a key element of this work. This talk will discuss a range of projects covering multiple damage mechanisms and materials which used synchrotron CT for damage analysis at several different synchrotrons (CHESS, APS and DIAMOND). In addition to discussing what can be seen, this talk will also highlight limits in computed tomography and areas where complimentary techniques fit into a larger experimental materials analysis framework.

 

 
"Understanding Mechanics and Stress Transmission in Granular Solids by Combining 3D X-ray Diffraction and X-ray Computed Tomography"

R. C. Hurley
Lawrence Livermore National Laboratory, Johns Hopkins University
Collaborators: E. B. Herbold, S. A. Hall, J. Wright, D. C. Pagan, J. Lind, M. A. Homel, R. S. Crum., M.C. Akin

Abstract: Granular materials play a central role in various disciplines, including defense, agriculture, mining, and civil engineering. Despite their prevalence, understanding and modeling the behavior of granular solids remains a major challenge within the mechanics community. No unifying constitutive law has been proposed for granular materials and various approaches – statistical physics, critical state soil mechanics, plasticity theory – have been used to describe them. Some fundamental directions in the study of granular media include: the nature of inter-particle force transmission and its influence on macroscopic response; the length scale at which grains behave as a continuum; relationships between structure and properties; the origin and nature of highly-localized strain during deformation. Overcoming these challenges may enable profound advances in predictive modeling for granular materials and facilitate development of unifying constitutive laws.

In this talk, I will discuss our recent work that addresses some of the fundamental challenges described above. We have subjected various samples of granular materials to uniaxial and multiaxial loading at synchrotron X-ray sources and combined 3D X-ray diffraction and X-ray computed tomography to make grain-resolved in situ measurements. These measurements provide intra-grain strain tensors and contact fabric between grains, permitting quantification of stress and strain fields, inter-particle forces, and local porosity evolution. We have employed these quantities to study inter-particle force transmission and its relation to macroscopic response, microscopic structure-response relationships, local constitutive laws and related length scales, and in situ grain-fracture mechanics. I will highlight very recent work focused on understanding shear bands, or highly-localized strain, during triaxial compression tests of a granular sample. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

 

 
"Using Synchrotron Characterization to Support Technology Development:
Evolution of Contacts in Advanced CMOS"

Christian Lavoie and Jean Jordan-Sweet
IBM T.J. Watson Research Center, Yorktown Heights, NY

Abstract: Since the early 1980s, IBM has maintained a strong effort in synchrotron-based research, from characterizing exploratory materials to troubleshooting yield problems in early manufacturing. While our involvement with these facilities has been multi-faceted, we have leveraged our impact through two main avenues: the development of unique high-throughput instrumentation and the promotion of collaborations with academia. This has first enabled a continuous learning, which increases our understanding of the science behind the materials and processes used in microelectronics. Importantly, our developed instrumentation also enables us to quickly react to unexpected yield or reliability problems, often seen in production environments, in order to determine root cause and rapidly find possible solutions.

In this presentation, we describe the evolution of materials used for contact to CMOS devices over more than 20 years, and focus on a few examples where our synchrotron-based research led to direct impact on our technology. Over this time period, sustained size reduction drove the sequential implementation of Ti, Co and Ni silicides through about a dozen IBM CMOS generations. This size reduction and the complications associated with the introduction of non-planar devices, have recently led to drastic modifications in process flow for the contacts. As a result, the industry has returned to a thin Ti-based contact. Material and process selections are now primarily guided by the interfacial contact resistivity (ρc), with an emphasis on morphological stability. Contact lengths of current devices are now reaching below 20 nm, a scale at which dimensions of material microstructure (grain size) become similar to contact size, and interface quality becomes critical to device performance. We will also discuss recent synchrotron measurements performed on titanium thin films when annealed under advanced treatments. In these samples the metal film thickness is reduced below 10 nm to match conditions used in today’s most advanced processors.

 

 
"Towards an integrated experimental/modelling framework to account for microstructural effects on ductile damage evolution"

Ricardo A. Lebensohn and Reeju Pokharel
Materials Science and Technology Division, Los Alamos National Laboratory

Abstract: In-situ non-destructive 3-D characterization and micromechanical formulations that can use direct input and be validated by those emerging methods are enabling the discovery and modelling of microstructural effects on mechanical behavior of polycrystalline materials. In this talk we report the synergistic combination of Fast Fourier Transform-based methods (e.g. [1]), which can efficiently use the voxelized microstructural images of heterogeneous materials as input to predict their micromechanical response, and High Energy Diffraction Microscopy (HEDM) (e.g. [2]) obtained in metallic aggregates developing porosity during plastic deformation that allowed us to study how microstructure affects ductile damage in these materials.

References

[1] Lebensohn R.A., Escobedo J.P., Cerreta E.K., Dennis-Koller D., Bronkhorst C.A. and Bingert J, 2013, "Modelling void growth in polycrystalline materials". Acta Mater. 61, pp. 6918-6932.

[2] Pokharel R., Lind J., Li S.F., Kenesei P., Lebensohn R.A., Suter R.M. and A.D. Rollett, 2015, “In-situ observation of bulk 3-D microstructure evolution of polycrystalline Cu using synchrotron radiation”. Int. J. Plasticity 67, pp. 217-234.

 

 
"Real-time synchrotron X-ray characterization of phase transformations and deformation in metals and alloys"

Ryan Ott
Ames Laboratory

Abstract: Developing a fundamental understanding of the rate controlling mechanisms of phenomena such as the devitrification of amorphous metals or the plastic deformation of nanostructured alloys requires characterizing these processes in real-time. The advent of high-brightness synchrotron sources, coupled with rapid-acquisition detectors has greatly expanded the potential for probing different materials behavior in real-time. Here, we discuss utilizing combined wide-angle and small-angle X-ray scattering (WAXS/SAXS) to examine the phase evolution during annealing of glassy metal alloys. By coupling the two different methods, metastable crystalline phases can be identified by WAXS, while the associated chemical fluctuations on the nano-scale can be seen via SAXS. Additionally, we have combined bulk mechanical testing with real-time synchrotron measurements to explore the deformation behavior in several nanostructured alloys. We discuss how different plasticity mechanisms such as dislocation-mediated plasticity and twinning can be identified through these experiments.

 

 
"Advanced in situ loading environments for high energy synchrotron x-ray experiments"

Paul Shade
Air Force Research Laboratory

Abstract: High energy x-ray characterization methods hold great potential for gaining insight into the behavior of materials and providing comparison datasets for the validation and development of mesoscale modeling tools. A suite of techniques have been developed by the x-ray community for characterizing the 3D structure and micromechanical state of polycrystalline materials; however, combining these techniques with in situ mechanical testing under well characterized and controlled boundary conditions has been challenging due to experimental design requirements. In this presentation, we describe advanced sample loading and heating environments that have been developed for in situ high energy synchrotron x-ray experiments. Example datasets that were collected utilizing this hardware will be described.

 

 
"Resonant x-ray scattering studies of competing order in spin-orbit Mott states"

Stephen Wilson
University of California Santa Barbara

Abstract: Numerous new states have been predicted at the interface between correlated electron and strong spin-orbit coupling physics. At the heart of this interface is the spin-orbit assisted Mott state which relies on both strong on-site Coulomb repulsion as well as spin-orbit driven quenching of orbital degeneracy. The resulting J_{eff}=1/2 insulating ground state of these new Mott materials is predicted to reside in close proximity to a number of unconventional phases such as topological Weyl semimetals, quantum spin liquids, and high temperature superconductivity. In this talk I will present our work using resonant x-ray scattering techniques to explore for some of these nearby competing states. In particular, I will discuss our work studying the electronic responses of the spin orbit Mott insulators Sr2IrO4 and Sr3Ir2O7 as electron-doping drives the collapse of their parent insulating states. Evidence suggesting the presence of anomalous competing states in close proximity to the J_{eff}=1/2 Mott insulting state will be presented.

 

 
"Chemical Integration of Circadian and Photoperiodic Clocks in Plants"

Brian Zoltowski
Southern Methodist University

Abstract:  Nearly all organisms have evolved elaborate mechanisms to measure day length and coordinate growth and development with diurnal rhythms. These circadian clocks are present in all cell types and are synchronized by integrating diverse external stimuli into regulation of gene transcription. Whereas in vertebrate systems the sensory and signaling networks are complex and not well understood, in plants blue-light is the primary factor dictating adaptive responses to changes in environmental variables. In particular, two Light-Oxygen-Voltage (LOV) domain proteins, ZEITLUPE (ZTL) and FLAVIN-BINDING, KELCH REPEATS, FBOX-1 (FKF1) integrate diurnal variations in blue-light into regulation of protein stability and organism development. Although the biological activities of these proteins are well studied, molecular details indicating how photon-absorption regulates signal transduction is not well characterized. Moreover, how photic cues are integrated with metabolic signals and oxidative stress is poorly explored. Using a combination of chemical and structural biology approaches we have delineated signal transduction pathways that distinguish ZTL and FKF1. These hinge on multiple signaling interfaces that enable stimuli-dependent selection of specific protein-protein interactions. These studies indicate that ZTL and FKF1 act in an antagonistic manner with FKF1 active during the day and ZTL activated shortly after dusk. These antagonistic functions enable proper measurement of day length and regulation of circadian function. Tuning of these pathways has identified chemical and structural variants that disable circadian and photoperiodic timing in a selective manner.