2014 TMS RF Mehl Medal Symposium on Frontiers in Nanostructured Materials and Their Applications: Keynote Session on Nanomaterials and Applications
Sponsored by: TMS Electronic, Magnetic, and Photonic Materials Division, TMS: Thin Films and Interfaces Committee
Program Organizers: Nuggehalli Ravindra, New Jersey Institute of Technology; Ramki Kalyanaraman, University of Tennessee; Haiyan Wang, Texas A & M University; Yuntian Zhu, North Carolina State University; Justin Schwartz, North Carolina State University; Amit Goyal, Oak Ridge National Laboratories

Monday 2:00 PM
February 17, 2014
Room: Ballroom E
Location: San Diego Marriott Marquis & Marina

Session Chair: Ke Lu, Institute of Metal Research; Dieter Wolf, Argonne National Laboratory

2:00 PM  Keynote
Colossal Injection of Catalyst Atoms into Epitaxial Silicon Nanowires: David Seidman1; Oussama Moutanabbir2; Dieter Isheim1; Horst Blumtritt3; Stephan Senz3; Eckhard Pippel3; 1Northwestern University; 2Ecole Polytechnique de Montreal; 31Max Planck Institute of Microstructure Physics
    The incorporation of impurities during growth of nanowires from the vapour phase alters deeply their basic properties with impacts on an extended range of emerging nanoscale technologies. Herein, we present an atomistic level and quantitative study of the phenomenon of catalyst dissolution by achieving three-dimensional atom-by-atom maps of individual aluminium catalyzed silicon nanowires using highly focused ultraviolet laser-assisted atom-probe tomography. Although the observed incorporation of the catalyst atoms into nanowires exceeds by orders of magnitudes the equilibrium solid-solubility and solid-solution concentrations in known non-equilibrium processes, aluminium impurities are homogeneously distributed and do not form precipitates or clusters. Besides inducing p-type doping, this kinetics-driven colossal injection also has direct implications for nanowire morphology. The current theories of solute trapping at moving interfaces cannot explain the observed phenomenon. Herein, a rate equation model is presented to describe catalyst atoms incorporation during step-flow growth of a silicon nanowire.

2:20 PM  Keynote
Solidification Mechanisms of Carbon as Graphene, Graphite and Diamond from Metal-carbon Melts: Reza Abbaschian1; Shaahin Amini1; 1University of California, Riverside
    The formation of three allotropes of carbon as graphene, graphite and diamond from supersaturated metal-carbon melts will be reviewed. For the formation of graphene, it is shown that a single sheet of carbon atoms with a honeycomb lattice nucleates and grows on the melt surface upon cooling. Beside the nano-crystalline layer, bulky flaky or spherical graphite may also form in the interior of the melt. Small solidification rates favor formation of flake graphite because of the limited 2-dimensional nucleation and spreading along basal facets. At higher rates, on the other hand, both basal and prismatic faces grow with a similar rate, leading to the spherical morphology. When the melt is exposed to exceeding pressures of 5.0 – 6.5 GPa, carbon crystallizes as diamond. The diamond crystal morphology and quality also strongly depend on the growth temperature and atomistic growth processes taking place at the diamond–molten metal interface.

2:40 PM  Keynote
Hierarchical Microstructural Architecture for High-performance Thermoelectrics: Vinayak Dravid1; 1Northwestern University
    The intellectual challenge for the next generation bulk thermoelectric materials revolves around synthesis and fabrication of hierarchically organized microstructure that does not appreciably compromise the innate high power factor of the chosen thermoelectric matrix systems but significantly reduces lattice thermal conductivity to enhance the overall figure of merit, ZT. An emerging strategy involves nanostructuring bulk thermoelectric materials; wherein nanoscale precipitates do not appreciably compromise charge transport (thus power factor) but significantly reduce the lattice thermal conductivity via phonon scattering pathways. Here, there are exciting opportunities for understanding and tailoring microstructural elements with attention to the hierarchical length-scale influence from atomic-, nano- and micro-meter dimensions. We demonstrate this intricate but tractable relationship between various microstructural attributes (atomic-scale, line and interfacial defects as well as associated elastic and plastic strain) and lattice thermal conductivity. The presentation will also cover strategies for next generation thermoelectrics based on hierarchical length-scale tailoring of microstructure.

3:00 PM  Keynote
Coarsening of Nanoscale Precipitates in Al-Li Alloys: Martin Glicksman1; Ke-gang Wang1; Ben Pletcher2; 1Florida Institute of Technology; 2Select Arc Corp.
    Precipitates nucleate in dilute Al-Li alloys as a distribution of spherical nanoscale particles with diameters <10 nm. Analysis of their dynamic evolution via diffusion-limited coarsening allows quantitative evaluation of collective interactions called ‘diffusion screening’. Debye-Huckel theory and multiparticle simulations serve as predictive methods for interpreting late-stage coarsening kinetics in these precipitation-hardened alloys. Particle size distributions, growth kinetics, and maximum-allowed particle sizes were measured with automated TEM and HREM, and compared with theoretical and computational predictions. The dependence of the rate constants on precipitate volume fraction and their associated dynamically admissible size ranges were evaluated for the first time. Our experiments show that diffusion screening, a fundamental interaction among fine-scale dispersions, yields reasonable kinetic predictions of the observed δ′ (Al3Li) dispersions. Multiparticle simulations of precipitate evolution are compared with experiments. Diffusion screening theory and simulation models provide useful tools for the future design of two-phase alloys for elevated temperature applications.

3:20 PM Break

3:40 PM  Keynote
Fundamentals of Ion-solid Interactions in Ceramic and Structural Materials: Steven Zinkle1; 1Oak Ridge National Laboratory
    Ion bombardment can create a wide variety of novel nanostructures and nanoscale chemical profiles in materials, with resulting unique materials properties. The field of ion-solid interactions is one of numerous topics that have richly benefitted from the research by Jay Narayan. This presentation will summarize some of the defect architectures that can be created in ion-bombarded materials, including defect cluster patterning (cavities and dislocation loops) and solute precipitation (e.g., metallic colloid formation in insulators). The impact of these nanostructures on materials properties will be discussed and related to fundamental aspects of ion-solid interactions including the roles of irradiation temperature, damage rate, and primary knock-on atom spectra. Unresolved scientific issues including the role of ionization on point defect diffusion in nonmetals and the potential impact of one-dimensional glissile transport versus three-dimensional random walk diffusion of point defect clusters will be highlighted.

4:00 PM  Keynote
Plastic Deformation in Nanoindentation of a BCC Metal: Marc Meyers1; Carlos Ruestes1; Tane Remington1; Eduardo Bringa2; Bruce Remington3; Bimal Kad1; 1UCSD; 2CONICET/U. Nacional de Cuyo; 3LLNL
    Experiments and molecular dynamics calculations reveal the mechanisms of deformation under a nanoindentation in tantalum, chosen as a model BCC metal. Both molecular dynamics calculations and indentations are conducted for three monocrystal orientations: [100], [110], and [111]. The evolution of plastic deformation proceeds by the initiation through nanotwins and stacking faults, which evolve to shear dislocation loops. They expand into the material by the advance of the edge component. Simultaneously with this advance, the screw components of the loop cross slip and describe a cylindrical surface. When the opposite segments approach they attract each other and eventually cancel, forming a quasi-circular prismatic loop in the process composed of edge dislocation segments. The prismatic loops advance into the material along the <111> directions. Analytical calculations supplement the molecular dtynamics and experimental observations and provide a framework for the improved understanding of the evolution of plastic deformation under a nanoindenter.

4:20 PM  Keynote
Strengthening of Steels by Nanodispersoids: G Sundararajan1; R Vijay1; 1ARCI
    The strengthening of steels by micrometer sized dispersoids is well understood. However, only in the last decade, it has been possible to produce steels containing a high number density of nanometer sized dispersoids. These steels, normally designated as oxide dispersion strengthened (ODS) steels, display outstanding high temperature mechanical behaviour and in addition exhibit excellent fatigue and irradiation resistance. The objective of the presentation is to examine the evolution of nano dispersoids in Fe, Fe-9Cr and Fe-18Cr steels in terms of their structure and size, right through the processing steps, starting from atomisation, followed by milling and consolidation and finally by hot extrusion and subsequent annealing. The influence of nano dispersoids on the elevated temperature properties of the steels will be evaluated in terms of the applicable strengthening mechanisms. In addition, the reasons behind the substantial decrease in the yield strength beyond 600 deg C will be discussed.

4:40 PM  Cancelled
Role of Dislocations during Processing and Deformation of Nanocrystalline Materials: Farghalli Mohamed1; 1University of California,Irvine
    Nanocrystalline (nc) materials, which are characterized by grain sizes ≤ 150 nm, offer interesting possibilities related to many structural applications. Therefore, it is no surprise that considerable efforts have been devoted to investigating nc-materials over the past two decades. These efforts have resulted in major advances. Primary among these advances is the identification of the role that dislocations play not only in processing nc-materials via severe plastic deformation (SPD) but also in accounting for their mechanical behavior. Details of this role will be presented.