Yunfeng Shi, Rensselaer Polytechnic Institute
Katharine Flores, Washington University
Tanguy Rouxel, University de Rennes
John Mauro, The Pennsylvania State University
CM02.01: Distinctions and Commonalities of Glasses
Monday AM, November 26, 2018
Hynes, Level 2, Room 200
8:00 AM - *CM02.01.01
The Continuous Random Network—A Review
Harvard University1Show Abstract
The continuous random network (CRN), introduced by Zachariasen for oxide glasses, became the paradigm for the structure of covalent, directionally bonded amorphous materials. Elemental amorphous Si and Ge, which form one of the simplest CRNs, have been studied for more than fifty years. We will review their structure, thermodynamic properties, phase transformations, flow and structural relaxation. We will revisit some striking features, such as their density being higher than that of the diamond cubic crystal, their negative activation volumes for crystallization, and the bimolecular kinetics of their structural relaxation.
8:30 AM - *CM02.01.02
Understanding Indentation Behavior of Oxide Glass from Molecular Dynamics Simulation
Rensselaer Polytechnic Institute1Show Abstract
To evaluate the damage resistance of glasses, instrumented indentation using sharp indenters is the method of choice, as it can mimic real-life damage incidents under controlled conditions. Furthermore, indentation provides a useful system to study crack initiation, as unstable crack propagation is prevented by the highly localized stress state. However, unravelling the nature of structural change under indentation is a formidable task in experiment because of the complexity that originates from the atomic-scale disorder of glass, and the experimental difficulties associated with the in-situ investigation at a local scale (tens of microns) under very high stresses. To this send, computer simulations can provide an important complement to experimental approaches. In this work, we carried out large scale molecular dynamics (MD) simulations to investigate the effect of quench pressuring during hot compression and chemical composition variation on the response of glass to nanoindentation. A rigid hollow Vickers indenter made of carbon atoms is used to indent the glass sample with a fixed loading rate, during which atoms in the indenter interact with the glass via a repulsive force field. To minimize the boundary condition effects in simulated nanoindentation tests, large samples of several hundred nm in lateral dimensions are used. The indenter angle is varied to study the effect of the indenter sharpness on the deformation of glasses, as what has been done in experiments. Short- and medium-range order of the plastically deformed glass are compared with those in the undeformed region. These simulated nanoindentation tests reveal how the stress field and glass structure evolve with the deformation underneath the indenter, which in turn shed light on the degree of densification and pile-up in different glasses.
9:00 AM - *CM02.01.03
Connecting Mechanical Properties of Amorphous Polymers to Chain Alignment and Entanglements
Mark Robbins1,Marco Galvani Cunha1
Johns Hopkins Univ1Show Abstract
Polymer glasses are frequently used in a form of additive manufacturing called fused filament fabrication (FFF). Melts are extruded onto previous layers and form a weld before the temperature drops below the glass transition temperature. Extrusion is typically fast enough to produce significant chain alignment that affects the welds formed by diffusion between layers and leads to a strongly anisotropic amorphous structure. Improved understanding of the structure property relations in printed parts is essential to optimizing FFF for structure-critical parts and FFF offers unique opportunities to create non-crystalline materials with continuously tunable local alignment and entanglement densities.
We have used molecular dynamics simulations of a generic polymer model to examine the relaxation of aligned melts, including the evolution of alignment and the entanglement density in bulk regions and at the interfacial weld. The mechanical properties of the resulting structures are then studied under tensile and shear loading. Local structure determines the initial yield stress while entanglements lead to strain hardening and crazing that strongly affects the total fracture energy. Alignment of chains along the deposition direction means that there are more weak van der Waals bonds in the perpendicular directions. This reduces the yield strength for shear and tensile failure perpendicular to the deposition axis. Alignment and changes in entanglement density also produce profound changes in the strain to failure and ultimate fracture energy. Welded regions are most affected by diffusion during cooling and may be stronger than adjacent bulk material which has higher entanglement density than the weld but is also strongly aligned.
9:30 AM - *CM02.01.04
Modeling Slip Statistics and Dynamics in Bulk Metallic Glasses, Granular Materials and Other Systems
Karin Dahmen1,Wendelin Wright2,Dmitry Denisov3,Todd Hufnagel4,Peter Liaw5,Peter Schall3,Jonathan Uhl6
University of Illinois at Urbana-Champaign1,Bucknell University2,University of Amsterdam3,Johns Hopkins University4,The University of Tennessee, Knoxville5,Los Angeles6Show Abstract
Slowly strained solids deform via intermittent slips that exhibit a material-independent statistics and dynamics. We compare predictions of a simple model for the plastic deformation, the slip statistics and dynamics, and time series properties to experiments on slowly deformed bulk metallic glasses and granular materials. We highlight measures that can be used to differentiate between different systems and explain connections to other systems with avalanches. Predictions for future experiments will be discussed. The results are important for transferring results across scales and material structures.
10:30 AM - *CM02.01.05
Tailoring Glass Structure to Break the Speed Record of Phase-Change Memory
Johns Hopkins University1Show Abstract
This talk describes our recent success (F. Rao et al., Science 2017) in controlling the amorphous structure of chalcogenide Sc-Sb-Te glass to accelerate its crystallization, reaching an unprecedented operation speed for memory and switch applications. Specifically, we have designed a new phase-change memory alloy with drastically reduced crystal nucleation stochasticity from the parent amorphous phase. The ultrafast transition between the two metastable states accomplishes sub-nanosecond switching for cache-type phase-change random-access memory (PCRAM) technology. This is a milestone in memory materials, because operation speed is currently a key challenge in PCRAM technology, especially for achieving sub-nanosecond high-speed cache-memory (such as SRAM). The limiting factor in the commercialized PCRAM products is the writing speed (~currently several tens of nanoseconds), which originates from the stochastic crystal nucleation during the crystallization of the amorphous Ge2Sb2Te5 glass. Here we use alloying into the parent glass to speed up the crystallization kinetics by orders of magnitude. The newly designed chalcogenide Sc-Sb-Te alloy enables a record-setting writing speed (as short as ~700 picoseconds) in a conventional PCRAM device, with no requirement for pre-programming or additional device design. This ultrafast crystallization stems from the reduced stochasticity of nucleation via geometrically matched and robust chemical bonds that stabilize crystal precursors in the amorphous state, which are found via ab initio simulations to exhibit long life-times, shortening the incubation time for crystallization. This discovery is an example of physical metallurgy principles in action, using atomic-scale insight into glass structures (bonding configurations and sub-critical nuclei) to control properties. For details, see F. Rao et al., Science 358 (6369), 1423 (2017).
11:00 AM - *CM02.01.06
The Interaction Between Stress, Light and Chemistry in Glass
Dalhousie Univ1Show Abstract
Application of mechanical stress to glass causes interesting changes in how it transmits light. This interplay is summarized by the elasto-optic tensor, the key metric for technological applications including zero stress-optic glass, and reduced stimulated Brillouin scattering glass. Fundamentally, these effects are controlled by the glass chemistry, and in particular the nature of the chemical bonds that make up the glass. We will summarize our approach to this problem, which is focused on both an empirical and ab initio approach to the structure-property relations governing the elasto-optic tensor. We will describe the control of the stress-optic response through judicious choice of glass chemistry, and also describe our current progress in understanding and developing glass with reduced stimulated Brillouin scattering. We will include discussion of both average properties and energy-dispersive effects. We will show how these effects may be computed ab initio, with a reasonable trade-off between accuracy and speed, and illustrate a bond-based model we are developing that attempts to put in simple terms the empirical relations we have discovered.
11:30 AM - *CM02.01.07
Ductility and Residual Liquidity in Metallic Glasses
Takeshi Egami1,2,Wojciech Dmowski1
Univ of Tennessee1,Oak Ridge National Laboratory2Show Abstract
Lack of ductility is one of the major shortcomings of bulk metallic glasses which hamper their wide application as structural material. Ductility is a complex mechanical property which is difficult to characterize precisely. In a sense metallic glass is always microscopically ductile, because applied shear stress can locally liquefy glass. But it has no work-hardening, thus often local yielding results in catastrophic shear failure. In order to achieve macroscopic ductility glass must be able to relax local stress concentration before it starts macroscopic shear band or crack. In our view the key is the residual liquidity in glass. The structure of supercooled liquid is heterogeneous, and the frozen-in structure at the glass transition contains weak liquid-like and strong solid-like regions. It is difficult to assess such heterogeneity directly from the structure itself, but it is possible to characterize it through the structural response to applied stress. We determined the anisotropic pair-density function (PDF) of various metallic glass samples under uniaxial stress by high-energy x-ray diffraction using the spherical harmonics expansion of the structure function S(Q) and the PDF. The measured anisotropic PDF at large distances agrees with the one expected for affine (uniform) deformation which determines the long-range strain e∞. However, at short distances it deviates from the affine deformation, and at the first neighbour the local strain, e1, is smaller than e∞. The deviation from the affine deformation occurs because of local liquid-like regions, so that the ratio G = e0/e∞ , or ΔG = 1 - G, characterizes the strength of residual liquidity in glass. We found that the ratio e0/e∞ is closely related to ductility. In particular, Gc = 0.77 is the threshold which separates brittle and ductile behaviors. If G > Gc the samples are brittle, whereas if G < Gc the samples are ductile. Thus we suggest that the percolation of the liquid-like regions results in ductile behaviour. This new parameter is compared to other criteria for ductility.
CM02.02: Structures of Glasses
Monday PM, November 26, 2018
Hynes, Level 2, Room 200
1:30 PM - *CM02.02.01
Network Structures and Dissolution Behavior of Specialty Oxide Glasses
Missouri University of Science and Technology1Show Abstract
Borate, phosphate, and borophosphate glasses have been developed for a variety of technological applications, including fast ion conductors, optical substrates, and biomedical devices. For the latter, compositions are often tailored to control the rate at which physiologically significant ions are released to induce the desired biomedical response. These reaction rates depend on the hydrolysis of bonds that link neighboring glass forming polyhedra as well as the hydration of bonds associated with other metal cations that modify the glass forming network, and so detailed understanding of the glass structure connects composition to design performance. For borate and borophosphate glasses, the network hydrolysis rates decrease with increasing fractions of tetrahedral borate. For phosphate glasses, hydrolysis is not significant in neutral pH physiological conditions, but the hydration rates of metal cations are faster when they are linked to chain-forming P-tetrahedra than when they are linked to a chain-terminating tetrahedron. Quantitative and qualitative structural information about Na-Ca-borate, phosphate, and borophosphate glasses, obtained by techniques like nuclear magnetic resonance spectroscopy, Raman spectroscopy, and ion chromatography, will be described and used to explain their bio-functionality.
2:00 PM - CM02.02.02
Progress in Scattering with the Neutron Electrostatic Levitator (NESL) at the Spallation Neutron Source
Oak Ridge National Laboratory1Show Abstract
There is great interest in a developing understanding of the relationships between structures and
dynamics in liquid and glassy systems. Metallic liquids, which exhibit a degree of short and medium range ordering, are well suited to scattering probes, but there are many difficulties associated with selecting the proper furnaces for such studies. The Neutron Electrostatic Levitator (NESL)  at the Spallation Neutron Source is a containerless environment developed for challenging systems, including high temperature alloys and undercooled liquids. It provides a high vacuum, high purity, non-contact environment for fundamental studies of materials at wide temperature ranges. Combined with x-ray scattering data and isotopic substitution, the system is well suited to structural characterization of liquids via pair distribution function analysis, as has been successfully demonstrated at the Nanoscale Ordered Materials Diffractometer (NOMAD) [2,3].
A series of upgrades has improved the stability of the levitator and enabled new avenues of exploration. Recently, the system has been operated at the Wide Angular Range Chopper Spectrometer (ARCS)  and is currently being commissioned at the Cold Neutron Chopper Spectrometer (CNCS)  for high resolution inelastic and quasi-elastic scattering, enabling non-contact probes of excitations in glass forming liquids as well as high temperature self-diffusion measurements. The current capabilities and characteristics of the levitation furnace, progress in inelastic scattering measurements, and early results from the commissioning at CNCS will be discussed.
 Mauro, N. A., A. J. Vogt, K. S. Derendorf, M. L. Johnson, G. E. Rustan, D. G. Quirinale, A. Kreyssig et al. "Electrostatic levitation facility optimized for neutron diffraction studies of high temperature liquids at a spallation neutron source." Review of Scientific Instruments 87, no. 1 (2016): 013904.
 Neuefeind, Jörg, Mikhail Feygenson, John Carruth, Ron Hoffmann, and Kenneth K. Chipley. "The nanoscale ordered materials diffractometer NOMAD at the spallation neutron source SNS." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 287 (2012): 68-75.
 Johnson, M. L., M. E. Blodgett, K. A. Lokshin, N. A. Mauro, J. Neuefeind, C. Pueblo, D. G. Quirinale et al. "Measurements of structural and chemical order in Z r 80 P t 20 and Z r 77 R h 23 liquids." Physical Review B 93, no. 5 (2016): 054203.
 Abernathy, Douglas L., Matthew B. Stone, M. J. Loguillo, M. S. Lucas, O. Delaire, Xiaoli Tang, J. Y. Y. Lin, and B. Fultz. "Design and operation of the wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source." Review of Scientific Instruments 83, no. 1 (2012): 015114.
 Ehlers, Georg, Andrey A. Podlesnyak, Jennifer L. Niedziela, Erik B. Iverson, and Paul E. Sokol. "The new cold neutron chopper spectrometer at the Spallation Neutron Source: design and performance." Review of Scientific Instruments 82, no. 8 (2011): 085108.
2:15 PM - CM02.02.03
High-Resolution 3D Imaging for Drug Micro-Structure Characterization and Release Prediction
Merck & Co., Inc1Show Abstract
Modern drug delivery increasingly relies on micro- and nano-structures to achieve specific release rate and therapeutic target. The delivery systems modulate drug release via engineering control of the API domain and pore size. Other approaches involve the use of functional coating or performance-enabling excipients. The small-scale nature of pores, drug domains, and delivery vehicles demands higher resolution technique to characterize. High-resolution image-based characterization has been broadly utilized in drug product development for fundamental understanding on the process-property-performance interplay and optimizing formulation process and design. It finds applications in various novel drug release systems such as tailoring rate-limiting film coat thickness where the pore formation is critical to control drug release and interrogating the underlying mechanism of in-situ drug nanoparticle formation from amorphous solid dispersions in dissolution media for solubility enhancement. 3D micro-imaging can qualitatively visualize micro-structures, quantify their spatial and chemical distribution, and predict release behavior. In recent years, the emerging image-based numerical simulation has received significant traction and plays an important role on predicting drug release performance. Information-rich 3D images can be converted to characteristic drug transport parameters through intelligent analysis and applied to numerical simulation models to predict release performance. This image-based simulation approach represents a potential paradigm shift in drug design and evaluation, with significantly reduced evaluation time, improved release performance, and lowered in-vitro and in-vivo experiment cost.
2:30 PM - CM02.02.04
Nanoscale Imaging of Bulk Bottlebrush Polymers Using Helium-Ion Microscope
Nikolay Borodinov1,Alex Belianinov1,Dongsook Chang1,Jan-Michael Carrillo1,Matthew Burch1,Yuewen Xu2,Anton Ievlev1,Bobby Sumpter1,Olga Ovchinnikova1
Oak Ridge National Laboratory1,Kimberly-Clark Corporation2Show Abstract
Recently, bottlebrush polymers have attracted significant interest due to their potential applications in drug delivery and electronics. The tunability of their properties, stemming from the diversity of sidechains and their spatial arrangement, have emphasized their industrial potential as compared to the linear macromolecules. In this context, the structural information and organization of these systems play a major role in the rational design of functional bottlebrush polymers. Specifically, direct observation of the molecular organization can reveal inter-chain interaction phenomena and explain the fundamental physical properties of these systems. Here, we report a new method to analyze bulk macromolecular chain arrangement of bottlebrush polymers based on Helium Ion Microscopy (HIM). By using the HIM we were able to quantify structural nematic-type ordering in an amorphous polymer bottlebrush system. High-resolution imaging coupled with data analytics has proven to highlight the location and distribution of the polymer backbones, after oxygen plasma-generated height contrast; as well as map changes in the backbone spatial arrangement as a function of thermal annealing. Our experimental findings are corroborated by the coarse-grained molecular dynamics simulations. Overall, this approach can generate clear insights on the internal structure of amorphous materials and provides a complimentary information channel to scattering techniques and theoretical modelling.
This work was performed at the Center for Nanophase Materials Sciences, a US Department of Energy Office of Science User Facility. This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725. The authors acknowledge Scott Retterer at the Center for Nanophase Materials Science at Oak Ridge National Laboratory for helpful input and discussion
2:45 PM - CM02.02.05
Correlating Nanoscale Structural Heterogeneity to Glass Forming Ability and Mechanical Properties of Metallic Glasses
Soohyun Im1,Jared Johnson1,Gabriel Calderon Ortiz1,Menglin Zhu1,Pengyang Zhao1,Geun Hee Yoo2,Eun Soo Park2,Yunzhi Wang1,Jinwoo Hwang1
The Ohio State University1,Seoul National University2Show Abstract
We determine the nano-to-mesoscale structural heterogeneity in metallic glasses (MGs) using 4- dimensional (4D) nanodiffraction in scanning transmission electron microscopy (STEM). Structural heterogeneity in MGs has been suggested by both experiments and simulations previously. The heterogeneity must involve local structural ordering at the nanoscale, commonly known as medium range order (MRO), some of which has been studied using small electron probes in the past. However, the statistically reliable information on how such MRO constitutes the heterogeneity has remained difficult to determine. Our new approach to determine the MRO and structural heterogeneity involves 4D-STEM, which uses a new-generation pixelated fast STEM detector that allows for the continuous collection of the diffraction patterns from a large area of the MG sample. Using angular correlation and intensity variance analyses, the diffraction patterns can then be converted to real space maps of the local ordering, which we use to precisely determine the type, size, distribution, and volume fraction of MRO. We will present two cases of how the heterogeneity affects the important properties of MGs, one is the glass stability in Ti-based MGs, and the other is the ductility of Zr-based MGs. To connect the structural heterogeneity to ductility, we use a new mesoscale simulation that incorporates the experimentally determined heterogeneity, which can simulate realistic shear band formation and overall deformation that match the spatial and temporal scales of the deformation of real MGs.
3:30 PM - *CM02.02.06
Structure is the Organization Plan of Glasses—But Dynamics Might Bring Deeper Insight
Bernhard Frick1,Henriette Hansen1,2,3,Kristine Niss2
Institut Laue–Langevin1,Roskilde University2,Chalmers3Show Abstract
It is well known that for a large number of glass forming liquids the static structure factor, S(Q), shows no or only subtle changes when passing from the liquid into the glass. In contrast the dynamic structure factor S(q,ω) of simple or more complex glass forming liquids evidences in the GHz - THz frequency range and close to the glass transition clear and common signatures which have been addressed by several theories over the last decades. In spite of large experimental and theoretical activity in this field the glass transition is still not fully understood. Quasielastic neutron scattering plays a vital role for the experimental investigation of dynamic properties of disordered materials, glasses and undercooled liquids. We will give a brief overview over typical experimental findings near the glass transition and over recent instrumental progress on neutron spectrometers before presenting some examples. We then focus on our recent investigations on simple organic, hydrogen bonded and ionic liquids for which we have probed the dynamics near the glass transition by simultaneous dielectric and neutron spectroscopy. For these simultaneous experiments we have controlled both temperature and pressure which did allow us to map lines in the (P,T)-diagram along which the dynamics is unchanged and therefore is isochronous over a wide time range.
4:00 PM - CM02.02.07
Spatially Heterogeneous Dynamics in Metallic Glass Nanowires Imaged by Electron Correlation Microscopy
Debaditya Chatterjee1,Pei Zhang1,Jittisa Ketkaew2,Jan Schroers2,Paul Voyles1
University of Wisconsin–Madison1,Yale University2Show Abstract
We have used electron correlation microscopy (ECM) to image the nanometer scale heterogeneities in the relaxation dynamics of the supercooled liquid of a metallic glass forming alloy . The length and time scales of the heterogeneous dynamics are central to the glass transition and influence nucleation and growth of crystals from the liquid. Electron correlation microscopy (ECM) experiments use time-resolved tilted dark field transmission electron microscopy with sub-nanometer resolution for direct measurement of those length and time scales. ECM data on Pt-based metallic glass nanowires above the glass transition temperature (Tg) reveal a relaxation time scale that varies from a few seconds to hundreds of seconds and a length scale that varies from 0.8 to 1.4 nm. They also demonstrate the existence of a ~1 nm thick near-surface layer with an order of magnitude shorter relaxation time than inside the bulk which may influence crystallization of the wires. Additional measurements of the surface layer relaxation time below the bulk Tg, and its connection to enhanced surface diffusion in metallic glasses and surface crystallization will be discussed.
 P. Zhang, J. J. Maldonis, Z. Liu, J. Schroers, P. M. Voyles, Nat. Commun. 9, 1129 (2018)
4:15 PM - CM02.02.08
Kinetic Metallic Glass Evolution Model
Thomas Hardin1,Christopher Schuh1
Massachusetts Institute of Technology1Show Abstract
Metallic glass is a heterogeneous composite on the scale of a few nanometers; the structure of the glass on this scale governs its macroscopic thermo-mechanical response. This structure evolves in response to thermal and mechanical loading; this evolution is mediated by discrete kinetic events in which clusters of atoms locally rearrange themselves. We present a model of this structural evolution and mechanical response which consists of a thermodynamic state space, density of states, and models for relaxation and shear transformation events which move the glass through that state space. We implement this model in a homogenized statistical sense and compare to homogeneous relaxation and flow data previously in literature; we also implement it in a discrete mesoscale framework. We conclude with a discussion of gaps in the current understanding of the fundamental structure of metallic glass.
4:45 PM - CM02.02.10
Hierarchical Machine Learning to Decode Structural Origin of Heterogeneous Deformation in Disordered Materials
Qi Wang1,Anubhav Jain1
Lawrence Berkeley National Lab1Show Abstract
When subjected to external stimuli such as mechanical loading, atoms in disordered solids respond heterogeneously. Due to lack of representations to resolve the subtle packing difference around atom sites and approaches to deal with the long-range correlation involved, it is hard to quantitatively predict this heterogeneous, site-specific response solely from the structure. Here, by designing a robust hierarchical machine learning framework, we show that it is possible to predict the mechanical heterogeneity in disordered solids a priori, directly from the quenched structural state itself. We encyclopedically create a large pool of 810+ site descriptors, from 40+ sets of structural measures, spanning topological and chemical short- and medium-range order, and develop a novel hierarchical scheme to further extend the studied scale to an unprecedentedly long-range while still retaining good interpretability and generality. Impressive predictability is achieved in a fairly large strain regime, suggesting a long-lived inheritance of the quenched state until later obstructed by shear banding. The framework is robust over a range of compositions and processing conditions and can well detect the site environments tuned by these conditions. We also identify a bag of promising structural signatures unrevealed previously, with their predictability exhaustively benchmarked and discussed. This hierarchical learning framework is general and could potentially be applied to decode structural origin of any site-specific properties in the family of disordered materials.
CM02.03: Poster Session I: Structure-Property Relations in Non-Crystalline Solids
Monday PM, November 26, 2018
Hynes, Level 1, Hall B
8:00 PM - CM02.03.01
Microstructure Design for Ductile Glass Composite
Yanming Zhang1,Binghui Deng1,Liping Huang1,Yunfeng Shi1
Rensselaer Polytechnic Institute1Show Abstract
In this work we use molecular dynamics (MD) simulations to investigate glass composites constituted by two brittle model glasses with different stiffness. We show that tuning the stiffness ratio (SR), shape, volume fraction and distribution of the two brittle glass constituent scan trigger a brittle to ductile (BTD) transition. Such composite glasses can exhibit high strength, remarkable toughness and some work hardening. The highest failure strain of 80% can be reached in composite glasses as compared to 7% in monolithic model glasses. We also found that mechanical properties of such glass composites will not be deteriorated by introduction of pre-notch. Excellent load redistribution capability introduced by structural heterogeneity is responsible for high ductility in our composite glasses. Through a systematic analysis, we unveil the design principles that lead to the aforementioned BTD transition. We believe the current approach could enhance ductility and broaden the application of glasses as enabling structural materials.
8:00 PM - CM02.03.02
Molecular Modeling of Stress Corrosion Behavior
Swastik Basu1,Liping Huang1,Yunfeng Shi1
Rensselaer Polytechnic Institute1Show Abstract
Glass is well known to be susceptible to stress corrosion cracking caused by chemicals in the environment, a phenomenon that can cause delayed failure of glasses due to growth of pre-existing surface defects in the presence of humidity. The complex macroscopic effects of stress corrosion, like fracture, occur due to microscopic interactions, which demand a study to replicate the microstructural interactions within a model, which should reproduce the macroscopic behaviors. The purpose of this research is to study the stress corrosion behavior of a model metallic glass system with a view towards representing the underlying atomic level mechanisms using a molecular dynamics approach.
8:00 PM - CM02.03.03
Liquid Metal Nanoscale Structures as Novel Platform for Characterization of Structural Relaxation of Metallic Glasses
Ziyang He1,Chen Liang2,Chenhao Qian3
Columbia University1,University of Liverpool2,Jiangnan University3Show Abstract
This poster firstly introduces a new microfluidic method for preparing nanostructures of gallium-indium liquid alloy systems. Due to its smaller nanometer size (50-100nm diameter), good self-healing behavior, strong oxide layer formed by spontaneous oxidation, rich changeable nanomorphology driven by voltage variation and large undercooling range, the alloy system has become a good platform for studying amorphous structure transformation and internal structure of liquids using in-situ characterization technology under current conditions. We have successfully discovered the presence of secondary structures in this liquid metal system through in situ TEM lithiation experiments and subsequent nanomechanical and electrical experiments. By comparing the structural relaxation of the same kinetic fragility liquid with or without the oxide layer structure, we found that the oxide layer structure could guide the dynamic non-uniformity of the nano-amorphous system to some extent. At the same time, we are also actively exploring the future application of this alloy system in liquid metal self-healing electrodes, nano-heat pipes, nanoscale self-propelled robots and other industrial fields.
8:00 PM - CM02.03.04
Self-Diffusion Mechanism of Atoms in Forsterite Glass
Junya Nishizawa1,Tomoko Ikeda-Fukazawa1
Meiji University1Show Abstract
Forsterite glass exists as dust grains in interstellar molecular clouds and young stellar objects . In interstellar molecular clouds, elements such as hydrogen, oxygen, carbon, and nitrogen deposit on dust grains, and form various molecules (e.g., H2O, CO, CO2, NH3, CH4, H2CO, CH3OH, and so on) . These molecules undergo chemical evolutions to organic molecules through various processes on the surface of dust grains . Dust grains are important materials governing the chemical and thermal evolutions in space. However, the transport coefficients of forsterite glass are less conclusive, because forsterite glass is easily to crystallize. To investigate the mechanism of self-diffusion of atoms in forsterite glass, molecular dynamics (MD) calculations were performed.
The MD calculations were performed using an atom-atom potential model with MXDORTO program . The potential parameters were empirically determined by constraining the model to reproduce the experimental results of density, thermal expansion coefficient, and bulk modulus . The transition point from glassy state of supercooled liquid state (Tg) for our potential model is 1567 K. A fundamental orthorhombic cell consisting of 160 Mg2SiO4 with three-dimensional periodic boundary conditions was used. The glass structure was prepared by quenching the liquid phase from 3000 K to 10 K with 0.4 K/ps in rate. The quenched glass was warmed to 3000 K with the same rate. The MD code was run with NTP ensemble. The pressure was kept at 0.1 MPa.
The self-diffusion coefficients of Mg, Si and O were calculated using mean-square displacement (MSD). To investigate the mechanisms of self-diffusion, the temporal variations of pair correlations functions for Mg were analyzed. The result shows that the jumping probability of Mg, which is located at a position with high Si and low Mg densities is high. Because of the strong Si–O bonds in the tetrahedral SiO4 units, the jump of Mg atom (or MgOx unit) was induced by structural distortion of the surrounded SiO4 units. From analyses of spatial distribution of MSD, it was found that the MSD values of Mg are inhomogeneous at temperatures just below Tg. Because the self-diffusion coefficient of Si is significantly low at < Tg, the distribution of Si in forsterite glass is inhomogeneous. Therefore, the diffusivity of Mg depends on surrounded Si distribution.
 J. P. Bradley, L. P. Keller, T. P. Snow, M. S. Hanner, G. J. Flynn, J. C. Gezo, S. J. Clemett, D. E. Brownlee, J. E. Bowey, Science, 285, 1716 (1999).
 N. Watanabe, A. Kouchi, Prog. Sur. Sci., 83, 439 (2008).
 K. Kawamura, MXDORTO, Japan Chemistry Program Exchange, #029 (1990).
 T. Ikeda-Fukazawa, J. Soc. Inorg. Mater. Jpn., 23, 130 (2016).
8:00 PM - CM02.03.06
Methods for Estimating Appearance of Metal-Like Plastic
Sun Chul Jin1,Hyungjin Roh1,Kiyong Kim1,Sunghawn Cho1
A plastic has a lower specific gravity than glass or metal and has many advantages such as lightweight and good mechanical properties.
These thermoplastics are rapidly replacing conventional glass and metal areas in fields such as electronic and automobile parts. Recently, as increasing need for environmentally friendly material, there is an increasing demand for plastic that can feel a metallic appearance similar to a metal without a spray process.
For the development of metal-feeling thermoplastics, it is well-known way to use metallic pigment. But because of difference in flowability between metal pigment and plastic, There is an appearance problem such as flow mark and weld-line. This is why metal-feeling plastic can’t be expanded. In order to solve these problems, much research have been studied to control the shape and aspect ratio of metallic pigment and to improve the surface coating of it. However, it is limited to improve the appearance problems such as aggregation and orientation.
In addition, there is no effective method for objectively estimating the appearance of the metallic feeling except for flop index. But the flop index can evaluate only the metallic brightness and the degree of defects such as flow mark and weld-line caused by the metallic pigment could not be evaluated. As a result, there is no method of evaluating the appearance that can represent the overall phenomenon caused by the metallic pigment as an objective numerical value. In this research, development of method for estimating appearance of metal-feeling plastic is studied. Through correction of flop index, new index named as ‘T/N_Flop_X’ was developed. Using this index, it is available to objective evaluation and comparison of metal-feeling. And using the CCD camera, it was studied that correlation of sparkle effect, metallic pigment’s orientation and weld-line.
Based on these studies, we found out sparkle index that could be explained about orientation and metal-feeling. Additionally we studied about control of metallic pigment for reduce an appearance problem. Orientation is important factor to determine weld-line degree and in a constant direction makes decrease it.
We found out factors that could control orientation especially additive having an affinity of polar and non-polar.
8:00 PM - CM02.03.07
Amphiphilic Modification of PDMS Surface with PVA/PSBMA Zwitterionic Semi-Interpenetrating Hydrogel for Marine Antifouling Application
Xingyang Xu1,Rongrong Chen1,Jun Wang1
College of Material Science and Chemical Engineering, Harbin Engineering University1Show Abstract
Marine biofouling is a highly complex process and a worldwide problem which involve a wide variety of species. The common techniques proposed inculde heavy metals (Cu2O), or organic biocide, are bring potential harm to marine environment and ecosystem. Therefore, the nontoxic approaches, particularly silicone-included low-surface-energy Fouling Release Coatings (FRCs) may be the alternatives to chemically active coatings and more environmentally friendly AF strategies. In this study, a facile and versatile approach to the formation of amphiphilic marine antifouling is reported. The approach used boric acid (BA) to mediate the the plasma treated PDMS elastomer and subsequent immobilization of polyvinyl alcohol/poly (sulfobetaine methacrylate) (PVA/PSBMA) zwitterionic semi-interpenetrating hydrogel on solid substrates. PVA/PSBMA was immobilized on the PDMS surface via hydrogen bond and chemical bond. The resulting substrates were tested for the algae attachment test and protein adsorption assay, in which diatom and protein adhesion was significantly inhibited compared to PDMS. Advantageously, this approach allowed marine antifouling coatings to be prepared by a simple immersion process under environmentally friendly conditions.
This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.
8:00 PM - CM02.03.08
The Effect of Arm Segment Length on Thermally Induced Self-Healing Behavior of Supramolecular Star Poly(ε-caprolactone)s Network
Woojin Lee1,Dae-Yeon Won1,Hyo-bin Wi1,Jae Woo Chung2,Seung-Yeop Kwak1
Seoul National University1,Soongsil University2Show Abstract
Supramolecular polymer is comprised of oligomers or polymers that are held together by reversible non-covalent supramolecular interactions. It is capable of responding to damage or crack and restoring the polymer`s performance without affecting the initial materials properties. The healing property of supramolecular polymer network depends on two factors, that is, the first being the supramolecular interactions, and the second being the chain dynamics of the individual polymer chains. In this study, we synthesize the simple supramolecular network consisted of ureidopyrimidinone (UPy) ends functionalized 6-arm star poly(ε-caprolactone)s and investigate the effect of arm length on thermally induced self-healing behavior of the supramolecular star poly(ε-caprolactone) network. The resulting materials can be healed several times at 90C during 10 minutes, and even can be healed at 60C after 40 minutes. We find the compromise between number of tie points by supramolecular force and chain dynamics related to sufficient mobility of network. Both supramolecular end clustery crystal and main chain crystal might affect the mobility of network. For the efficient healing behavior, the crystalline domain of supramolecular polymer network should be collapsed. Thus, the sufficient thermally induced healing behavior can be achieved through the enhanced mobility of network.
8:00 PM - CM02.03.09
Ab Initio Study of the Amorphous Cu-Bi System
Isaías Rodríguez2,David Hinojosa-Romero1,Alexander Valladares2,Renela Valladares2,Ariel Valladares1
IIM-UNAM1,Facultad de Ciencias-UNAM2Show Abstract
As a pure element, bismuth is a semimetal which possesses several interesting physical properties, not all of them well understood. The recent discovery of superconductivity , as predicted by our group , and the increasing superconducting transition temperature as the pressure applied increases, are some examples of its particularities. Also, the fact that the amorphous phase is superconductive with a transition temperature several orders of magnitude larger than the crystalline at ambient pressure is unusual . These phenomena have also motivated our predictions for the transition temperatures of Bi-bilayers  and the Bi-IV phase . When mixed with other elements, bismuth seems to contribute to the superconducting character of the resulting material. Here we study the binary copper-bismuth amorphous system which is known to superconduct in diverse compositions . Using ab initio molecular dynamics and the undermelt-quench method, we generate an amorphous structure for a 144-atom supercell corresponding to the Cu88Bi56 system. We shall report the calculated electronic and vibrational densities of states for this system and relate them to the superconducting properties of this alloy.
 O. Prakash, A. Kumar, A. Thamizhavel, S. Ramakrishnan. Evidence for bulk superconductivity in pure bismuth single crystals at ambient pressure. Science 355 (2017), pp. 52-55. DOI: 10.1126/science.aaf8227.
 Z. Mata-Pinzón, A. A. Valladares, R. M. Valladares, A. Valladares. Superconductivity in Bismuth. A New Look at an Old Problem. PLoS ONE 11 (2016), e0147645. DOI:10.1371/journal.pone.0147645.
 D. Hinojosa-Romero, I. Rodriguez, A. Valladares, R. M. Valladares, A. A. Valladares. Possible superconductivity in Bismuth (111) bilayers. Their electronic and vibrational properties from first principles. MRS Advances 3 (2018), pp. 313-319. DOI: 10.1557/adv.2018.119.
 A. A. Valladares, I. Rodríguez, D. Hinojosa-Romero, A. Valladares, R. M. Valladares. Possible superconductivity in the Bismuth IV solid phase under pressure. Scientific Reports 8 (2018) 5946 DOI:10.1038/s41598-018-24150-3.
 N. E. Alekseevskii, V. V. Bondar and Yu. M. Polukarov, Zh. Eksperim. i Teor. Fiz. 38 (1960), p. 294 [translation: Soviet Phys. - JETP 38 (1960), p. 213].
8:00 PM - CM02.03.10
Structural Commonalities in Different Classes of Non-Crystalline Solids—A Pair Distribution Function Analysis
Isaías Rodríguez1,David Hinojosa-Romero2,Renela Valladares1,Alexander Valladares1,Ariel Valladares2
Faculty of Science, UNAM1,IIM-UNAM2Show Abstract
In the past decades the research community has explored diverse structures and new fabrication methods of non-crystalline solids. Glassy materials that belong to the semiconductor realm and to the metallic type are the most studied both experimentally and simulationally. The present work investigates common structural trends whenever they exist and different trends among different classes. Amorphous semiconductors display Pair Distribution Functions (PDF) that are very similar among themselves and this indicates that these network forming materials have properties that are alike . Analogously metallic systems have comparable PDFs but different from the network forming materials, as it should be, since the properties between these two classes are very different .
Here we pay attention to the Short-Range Order (SRO) and Intermediate Range Order (IRO) of these two classes. In particular, the first peaks of the structures studied are contrasted, while the second peaks are shown to differ considerably. Whereas the semiconductor structures display a simple first and second peak with a near-zero value between them, the metallic systems have a very well defined non-zero value between the first and second peaks and they also display what we have come to identify as an “elephant” second peak . To manifest the uncommonalities with amorphous semimetals we recall calculations carried out by our group for bismuth where the elephant peak does not appear but the non-zero behavior between the first and the second peak is present . The Plane Angle Distribution (PAD) functions are also reported.
 A. A. Valladares, J. A. Díaz-Celaya, J. Galván-Colín, L. M. Mejía-Mendoza, J. A. Reyes-Retana, R. M. Valladares, A. Valladares, F. Alvarez-Ramirez, D. Qu and J. Shen, New Approaches to the Computer Simulation of Amorphous Alloys: A Review. Materials, 4, 716-781 (2011).
 C.U. Santiago-Cortés, Simulación de sistemas metálicos amorfos y porosos de elementos nobles, Thesis (PhD), Universidad Nacional Autónoma de México, México (2011).
 I. Rodríguez, R. M. Valladares, A. Valladares, A. A. Valladares, to be published (2018).
 A. de Saint-Exupéry, Le Petit Prince, Reynal & Hitchcock, pp 1-2 (1943).
 Z. Mata-Pinzón, A. A. Valladares, R. M. Valladares, A. Valladares, Superconductivity in Bismuth. A New Look at an Old Problem. PLOS ONE, 11(1): e0147645 (2016).
8:00 PM - CM02.03.11
Dependence of Modulus on the Annealing Conditions of Pt57.5Cu14.7Ni5.3P22.5 Bulk Metallic Glass
Zheng Chen1,Amit Datye1,Jittisa Ketkaew1,Sungwoo Sohn1,Jan Schroers1,Udo Schwarz1
Yale University1Show Abstract
The mechanical properties of bulk metallic glasses are often tuned by annealing, which influences these properties by adjusting the relaxation or crystallization status of the glasses. Here, we studied the modulus of Pt57.5Cu14.7Ni5.3P22.5 bulk metallic glass (Pt-BMG) annealed at different temperatures in the metastable regime by nanoindentation, where the annealing gives the BMG different fictive temperature and fractions of crystallization. We find the modulus of the investigated BMG samples exhibits a “V trend”: As the annealing temperature increases, we first observe a decrease that is followed by an increase until saturation is reached. This phenomenon can be explained as a result of the combination of the glasses relaxation and the glasses crystallization: Relaxation caused by higher fictive temperatures lead first to higher free volumes, which leads to lower moduli, while past a specific temperature, crystallization generates new, denser phases with higher moduli. The latter finding is confirmed by nanoindentation measurements at which fully amorphous Pt-BMG samples with different fictive temperatures are compared with partially crystalline samples featuring the same fictive temperature.
8:00 PM - CM02.03.12
Theoretical Support to Hydrogen Elimination Monitoring by Ultraviolet Photodissociation Mass Spectrometry Using Density Functional Theory
Wenrui Chai1,Lindsay Morrison1,Jake Rosenberg1,Graeme Henkelman1,Jennifer Brodbelt1
The University of Texas at Austin1Show Abstract
Mass spectrometry (MS) has became an increasingly popular and useful in analyzing structures of proteins. Initially only information of low resolution and of the whole protein in general can be obtained. Many techniques that utilize property differences between parts of the protein to produce signature fragmentation patterns and products have been developed to gain more information on local geometry, such as collision induced dissociation (CID), electron transfer dissociation (ETD), electron capture dissociation (ECD) and ultraviolet photodissociation (UVPD). A new method called hydrogen elimination monitoring (HEM) was invented by Brodbelt et. al, to overcome disadvantage of other methods. For example, CID disrupts protein structure prior to fragmentation therefore higher order structural information is lost and ECD cannot differentiate highly ordered surface regions with internal buried regions. HEM aims finding out higher order structure anywhere in the protein by using hydrogen elimination information after fragmentation to determine the level of hydrogen binding prior to fragmentation, therefore determining local geometry. Experiments have demonstrated that hydrogen elimination correlates strongly to absence of backbone hydrogen bonding yet the underlying process and reason to this correlation is unknown. DFT studies of model peptides at ground state can help in illustrating the process and in providing theoretical support to HEM method.
In the computational study complementary to experimental findings, we used 3 structures of Ala8 peptide models with increasing amount of hydrogen binding: an unstructured linear peptide, a hairpin turn and a helix, to study the thermodynamics as well as the kinetics of the fragmentation process, by finding out the enthalpy change of the fragmentation reaction and the minimum energy pathways (MEPs) for the processes. The thermodynamics show that fragmentation products without hydrogen elimination are much higher in energy compared to products with hydrogen elimination, and therefore extremely unfavorable. The MEPs revealed reasons why the thermodynamic favorable product may not always form. In the unstructured peptide, hydrogen elimination always take place at the same time as the C-C back bone is cleaved. In the hairpin turn and helix structure, however, the MEP show that C-C cleavage takes place first and produces spatial separation that could prevent hydrogen elimination. This finding shows the underlying principle of the correlation between hydrogen elimination and amount of hydrogen binding prior to fragmentation, and therefore supports HEM as an effective method for analyzing protein structure.
8:00 PM - CM02.03.13
The Molecular Influence on High Strain Rate Microscale Impact Response of Synthetic Polymeric Materials
Yuchen Sun1,David Veysset1,Alex Hsieh2,Steven Kooi1,You-Chi Wu1,John Mikhail1,A. Maznev1,Jan Andzelm2,Gregory Rutledge1,Timothy Swager1,Keith Nelson1
Massachusetts Institute of Technology1,U.S. Army Research Laboratory, RDRL-WMM-G2Show Abstract
The deformation of materials in extreme dynamical environments such as high-velocity microparticle impact is a challenge to understand though important for many areas of science and technology from space exploration to sand erosion. While impact dynamics of macroscale projectiles have been studied in real time using high-speed imaging, investigations of microscale impact have been essentially limited to post-mortem analysis of impacted specimens. Here, we present real-time observations of supersonic microparticle impacts using multi-frame imaging. In a laser-induced projectile impact test, a microparticle is accelerated by laser ablation from a sacrificial gold layer on a glass substrate. These particles can be accelerated into free space with controllable speeds up to 1.0 km/s depending on laser pulse energy and particle characteristics. The particles are monitored in flight and during impact with an ultra-high-speed camera that can record up to 16 images with a minimum interframe time of 3 ns. We investigated the high-velocity impact deformation response of elastomers to further the fundamental understanding of the molecular influences on high strain rate elastomeric response. The types of materials that were synthesized and tested are glassy polymers, graft copolymers, and other materials. We show the dynamic stiffening response of various elastomers including poly(urea urethane) upon impact at strain rates of ~108 s-1 and demonstrate the significance of molecular constitution in the response. These results provide an impetus for modeling the molecular influence on high strain rate microscale impact responses in these polymeric materials.
8:00 PM - CM02.03.14
Enhancing the Mechanical Properties of Biodegradable PLA Using Ternary Polymer Blends
Xianghao Zuo1,Yuan Xue1,Elena Urquiola2,Ruilin Yin3,Jinghan Tang4,Miriam Rafailovich1
Stony Brook University1,Hunter College High School2,St. Anthony's High School3,Mater Dei High School4Show Abstract
Acrylonitrile butadiene styrene (ABS) has a similar matrix structure to the styrene acrylonitrile copolymer but has additional distribution of polybutadiene which strengthens it and allows ABS to surpass the properties of traditional commercial polymers. PLA is a 100% biodegradable polymer which can be regarded as a replacement to many current commercial plastics. However, it’s brittleness limited its application in the industrial processing. Commonly, binary blends including PLA and another polymer additives are created to enhance the mechanical properties of PLA, but this has been found to be ineffective due to the poor interfacial reaction between the polymers. Previous studies have determined that a 70:30 PLA: ABS ratio effectively balances the bio-based properties of PLA with the exceptional mechanical properties of ABS. Many have observed that the binary PLA/ABS blend actually has worse mechanical properties than just the PLA alone. Therefore, an efficient compatibilizer with good affinity with both PLA and ABS is a key factor to solve this problem. In our previous work, we have certified that PMMA is miscible with PLA and considering the structure of ABS, we hypothesis PMMA should be an excellent compatibilizer to the blend.
To create the ternary blends, the polymers were added to a C.W. Brabender and then molded into the tensile and impact test shapes using a Carver Hot Press. The blends were also run through an extruder to create filaments for 3D printing. A 286% increase for the molded sample in the impact test was observed when 4% by weight PMMA was used with the 70PLA/30ABS blend. Mechanical tests also showed that this ternary polymer material can maintain high mechanical properties even when 3D printing, as the mechanical properties of the 3D printed surpassed the pure PLA sample and PLA/ABS binary blend by 24.3% and 55.5% respectively. SEM and TEM imaging were used to verify the location of PMMA phase. And contact angle tests show that ABS has a higher affinity with PMMA than PLA.
The ternary blends reached their peak mechanical properties with less than 5% by weight of compatibilizer added, suggesting the economic efficiency of this blend for industrial use. For future study, interfacial properties in the ternary blends could be investigated using secondary ion mass spectrometry (SIMS) analysis to reveal interactions that contribute to mechanical strength.
8:00 PM - CM02.03.15
Enhancing Impact Resistance of Polymer Blends via Self-Assembled Nanoscale Interfacial Structures
Xianghao Zuo1,Yuan Xue1,Yichen Guo1,Miriam Rafailovich1
Stony Brook University1Show Abstract
We have designed and engineered ternary polymer blends with the mechanical properties comparable to high impact resistant conventional polymers under the guidance of the lattice self-consistent field model. Tow formulas were used to study the mechanical properties. In one system, poly (methyl methacrylate) (PMMA) was used as the compatibilizer for the widely studied biodegradable polymer blend, poly (lactic acid) (PLA)/Poly (butylene adipate-co-butylene terephthalate) (PBAT) blend. We characterized the compatibility of those components and found PMMA was miscible with PLA and partially compatible with PBAT, which allowed it to self-assemble to a nanoscale interfacial layer on the PLA/PBAT interface. This PMMA layer can significantly decrease the interfacial energy and strongly entangle with either PLA or PBAT, resulting in the strengthening of the interface and dramatically enhancement of the impact resistance of the ternary blend. The optimal mechanical performance was achieved when the total PMMA concentration was less than 10 wt %. Higher PMMA content embrittled the blend since the additional PMMA did not contribute to the minimization of the interfacial energy but remained in the PLA phase, increasing the glass transition temperature of the matrix. In the other system, as in our previous study, PMMA is miscible with PLA and PS is totally miscible with styrenic polymers such as HIPS and ABS, therefore, PLA/Styrene Acrylic Copolymers (SMMA) with different styrenic polymers were blended during the study. SMMA will self-assemble to become an interfacial layer on the PLA/PS (or HIPS or ABS) interface at very low concentration (SMMA concentration less than 2%), and enhance the impact resistance of the ternary blend up to 50% compared to the binary blend of PLA/styrenic polymers. Increasing the SMMA concentration will form a third phase domain in the polymer matrix which will embrittle the whole system.
8:00 PM - CM02.03.16
Electronic Transport in Aperiodic Labyrinth Lattices
Vicenta Sanchez1,Fernando Sanchez1,Chumin Wang1
Universidad Nacional Autonoma de Mexico1Show Abstract
The search for a simple and direct relationship between atomic scale arrangement and macroscopic properties of a material constitutes a principal task of the materials science. For example, the Bloch theorem establishes extended electronic wavefunctions and then a ballistic conduction if the atoms of a crystalline material are periodically ordered. At the other extreme, one- and two-dimensional amorphous solids with randomly arranged atoms possess only exponentially localized eigenstates . Nowadays, the study of electronic transport in artificial structures is of great importance in condensed matter physics, because such structures introduce many new physical properties essential for technological applications of atomic-scale devices. In this work, we report a new convolution theorem developed for the Kubo-Greenwood formula in Labyrinth tiling by transforming the original two-dimensional lattice into a set of independent chains with rescaled Hamiltonians . Such transformation leads to an analytical solution of the direct-current conductance spectra, where quantized steps with height of 2g0 are found in Labyrinth tiling with periodic order along the applied electric field direction, in contrast to the step height of g0 observed in the corresponding square lattices, being g0 the conductance quantum. When this convolution theorem is combined with the real-space renormalization method , we can address in a non-perturbative way the electronic transport in macroscopic aperiodic Labyrinth tiling based on generalized Fibonacci chains . Furthermore, we analytically demonstrate the existence of ballistic transport states in such aperiodic Labyrinth tiling. This finding suggests that the periodicity should not be a necessary condition for the single-electron ballistic transport even in multidimensional fully non-periodic lattices.
This work has been partially supported by UNAM-IN114916, UNAM-IN106317 and CONACyT-252943. Computations were performed at Miztli of DGTIC, UNAM.
 E. Abrahams, et al., Phys. Rev. Lett. 42, 673 (1979).
 F. Sánchez, V. Sánchez, C. Wang, Eur. Phys. J. B (2018) doi: 10.1140/epjb/e2018-90070-4.
 V. Sánchez and C. Wang, Phys. Rev. B 70, 144207 (2004).
 F. Sánchez, V. Sánchez, C. Wang, J. Non-Cryst. Solids 450, 194 (2016).
8:00 PM - CM02.03.17
Fracture Tensile Test for Brittle Diamond-Like-Carbon at the Nanoscale
Dahye Shin1,Dongchan Jang1
Korea Advanced Institute of Science and Technology1Show Abstract
Ceramics are well used in various fields as functional materials and their property range is a way more expanded these days by adding new nanoscale properties. Even though a number of studies have been achieved for investigating electronic, magnetic, optic properties etc. at nanoscale, the fracture behavior is not reached to the same level of evaluation. It is in need of investigating the fundaments of fracture mechanics for nano-sized ceramic materials to guarantee the reliability of the systems adding to enjoy the newly enhanced nano-properties at the same time. Brittle failure of ceramics is usually mediated by a rapid crack propagation due to the lack of intrinsic crack tolerant mechanism which requires extremely high critical stress for its activation, usually never been reached before the total failure in bulk scale. However, in some theoretical studies, fracture of nanomaterials becomes insensitive to flaws when they shrink below a certain critical size and enables to reach almost theoretical strength of the material . Getting ideas from this, here we present an unwonted roll of cracks at the nanoscale as an activator of a fracture resisting mechanism not as an enemy of brittle ceramics through nanoscale tensile experiments and finite element methods analysis. In situ SEM tensile fracture tests with different crack geometries were carried out. Diamond-like-carbon (DLC) was chosen to be conductive for SEM image quality, isotropic, and brittle material to eliminate any complicate material issues and to make the best focus on the mechanical analysis. Single-edge-notched-tension (SENT) and double-edge-notched-tension (DENT) samples with pre-notch size of 60 nm and thickness of 200 nm were fabricated in mushroom like shape with head size of ~2 μm using Focused Ion Beam (FIB) on DLC film of ~1.5 μm coated on Si wafer. The head part was grabbed and pulled by a self-produced claw-like tip. In short, we observed that the DENT samples were deviated from the expectations based on classical linear elastic fracture mechanics showing 150% higher fracture strength even with 60% of total crack length out of thickness. It is explained by the interaction between the two stress fields of each crack that activates additional fracture resisting mechanism in the neck region of the specimen preventing the whole sample from the failure.
 Gao, Huajian, et al. "Materials become insensitive to flaws at nanoscale: lessons from nature." Proceedings of the national Academy of Sciences 100.10 (2003): 5597-5600.
8:00 PM - CM02.03.18
Studies of Photo-Thermal Dual Curing Behaviors of Acrylate Monomers with FTIR and Photo-DSC
Hyuck Sik Wang1,Seung Hyuk Lee1,Seok Hyung Bu1,Kigook Song1
Kyung Hee University1Show Abstract
The photo-curing behaviors of acrylate monomers capable of urethane thermal reaction were investigated using time-resolved FTIR spectroscopy and photo-DSC (Differential Scanning Calorimetry). Faster photo-reaction and lower conversion of acrylate reactions were observed in the thermal-photo dual curing process compared to the photo-curing only process. In the case of the acrylate system with long chain oligomers, faster photo-reaction was also observed in the dual curing process although no difference was found in the degree of conversion of acrylates between two photo-curing processes. The photo-curing process of three acrylate monomers was investigated using ATR-FTIR spectroscopy with a deuterated acrylate compound. In the free-radical terpolymerization, the conversion of three acrylate monomers into terpolymer as a function of time was monitored by observing the characteristic FTIR peaks of each component. In order to identify the acrylate components involved in the free-radical terpolymerization, careful peak assignments were made for the acrylate terpolymer such that characteristic FTIR bands from different monomers chosen for quantitative analysis should not overlap with one another. The use of deuterium substituted acrylate monomer as an aid in the interpretation of the FTIR spectra of three component systems has been demonstrated in this study.
8:00 PM - CM02.03.19
Fluorescent Carbon Particles Formed from Concentrated Glucose Solutions
Tomilola Obadiya1,Harsh Uppala1,David Sidebottom1
Creighton University1Show Abstract
Carbon dots (C-dots) are a class of low-dimensional carbon-based particles which exhibit a signature photoluminescence (PL) consisting of a red-shifted emission when irradiated with uv-visible light. This Photoluminescence (PL) has been explained as either the effects of quantum confinement, or of energy traps on the particle surface. Recently, several groups have reported the synthesis of C-dots directly from the thermal treatment of aqueous solutions of simple sugars (e.g., glucose, sucrose) either in a conventional autoclave or in a microwave oven. These studies have looked exclusively a preparation from low concentration (less than 10 wt% sugar) solutions reacted at rather high temperatures (between 160 to 200 C). We report the synthesis of fluorescent carbon particles produced from viscous glucose solutions of a much higher concentration heated at much lower temperatures. Analysis by photon correlation spectroscopy (PCS) reveals the particles form immediately with a size (approximately 300 nm) that is nearly 100 times larger than the precursor clusters of sugar but which decrease slightly in size with additional heating. Despite their larger size, PL shows emission similar to that of smaller C-dots but with clear indications of fine structure suggesting a set of discrete surface energy levels likely associated with different functional groups attached to the particle's surface.
8:00 PM - CM02.03.20
Modeling of the Resistance Drift Phenomenon in Chalcogenide-Based PCMs
Military University of Technology1Show Abstract
Chalkogenide phase change materials (PCM), such as those based on Ge-Sb-Te alloys, have been shown to have unique properties that have been used for a long time in optical memories (DVD), and, more recently, in non-volatile resistive memories [1, 2].
Nonetheless, several challenges must be overcome if PCM memory technology is to enter the market. The most critical of these challenges is that the resistance of the PCM amorphous phase increases with time (so-called "resistance drift phenomenon") due to the ageing of the material, and this drift has a negative effect on the storage of information.
The basic physical mechanisms underlying drift phenomena are still unclear and are currently the subject of intense discussion. Different and sometimes contradictory mechanisms have been proposed, such as : increasing  or reducing [5, 4] disorder during drift; increase  or decrease  density of defect states during drift; impact  or no effect  of stress on drift.
Despite all the recent research efforts, we do not yet have a clear picture of the structural mechanism of relaxation occurring during the ageing of the amorphous PCM phase, and further research is needed.
Discussion and analysis of different mechanisms proposed for increasing of the resistivity of the chalcogenide based PCM amorphous phase with time is presented – taking into account recent reported results of measurements and concepts, eg: clustering of Ge atoms in the amorphous phase of GeTe during ageing ; thermal excitations of electrons trapped in defect states within the electronic gap ; correlation between drift coefficient and activation energy ; increasing of the band gap during ageing ; increase in the proportion of homopolar Ge-Ge bonds with ageing ; densification of the films during ageing ; localization of the gap states during ageing [13, 14]; formation of Ge-Ge bonds upon ageing in thin films .
Structural and quantum chemical analysis was carried out using modified procedures described eg in .
Noé P et al 2018, Semicond. Sci. Technol. 33, 013002];  Kolobov AV et al 2017, Semicond. Sci. Technol. 32, 123003;  Fantini P et al 2012, Appl.Phys. Lett. 100 213506;  Ielmini D et al 2009, Microel. Eng. 86 1942; [5 ] Gopalakrishnan K et al 2010 Symp. on VLSI Tech. Dig. pp 205; [6 ] Pirovano A et al 2004, IEEE Trans. El. Dev. 51 714; [7 ] Ielmini D et al 2008, Appl.Phys. Lett. 92 193511; [8 ] Mitra M et al 2010, Appl.Phys. Lett. 96 222111; [9 ] Rizzi M et al 2011, Appl. Phys. Lett. 99 223513;  Noé P et al 2016, J. Phys. D: Appl.Phys. 49 035305;  Mitrofanov K V et al 2014, J. Appl. Phys. 115 173501;  Kalb J et al 2003, J. Appl. Phys. 94 4908;  Gabardi S et al. 2015, Phys. Rev. B 92 054201;  Sosso G et al 2012, Phys. Stat. Sol. B 249 1880;  Luckas J et al 2013, J. Appl. Phys. 113 023704;  Plucinski K J et al 2015, Mat. Sci. in Sem. Proc, 38, 184-187.
8:00 PM - CM02.03.21
The Relationship Between Photoluminescence and Short-Range Order Structure in SrTi1-xAlxO3 Amorphous Compounds
Valmor Mastelaro1,Yajaira D.R. Jerez1,Lauro Maia2,Alain Ibanez3
University of Sao Paulo1,Federal University of Goias2,Institut NÉEL - CNRS3Show Abstract
Although compounds exhibiting the perovskite structure, and particularly SrTiO3, have been very well studied concerning their photoluminescence (PL) properties, to our knowledge, the effect of water purity used and the addition of aluminum substituting partially titanium atoms on the PL properties have not yet been studied. To complete the previous studies, samples of SrTi1-xAlxO3 composition with x ranging from 0.005, 0.01, 0.03 and 0.05 were prepared by the modified polymer precursor method under different water purity. SrTi1-xAlO3 (STAO) composition samples with the amounts of aluminum equal to x = 0.005, 0.01, 0.03 and 0, 05 were synthesized by the modified polymer precursor method. The obtained resins were subsequently thermally treated at 250 °C at a heating rate of 10 °C/min for 4h under air atmosphere and subsequently ground to obtain fine black amorphous powders. Different temperatures of heat treatments between 450 ~ 500 ° C were selected as well as different calcination times between 2h and 8h. XANES spectra were collected at Ti K-edge using the transmission mode at the XAFS2 beam line of Brazilian storage ring. The pre-edge region of the XANES spectra on the Ti K-edge presents four transitions. They were attributed to a quadrupolar excitation of the 1s electron level to the octahedron t2g orbitals; a transition of the 1s electron to unoccupied 3d level; transitions attributed to the dipole excitation of the 1s electron level to the t2g and eg orbitals of the neighboring octahedron. Significant differences in the intensity of the pre-edge transition for samples containing 3% and 5% of aluminum were observed indicating that in these samples the local symmetry around titanium presents a greater distortion or a greater degree of disorder. This distortion or disorder may originate from the existence of sites with titanium pentacoordinate (Ti) or hexacoordinated (Ti). The comparison of the intensity of the transition present in the pre-border region of the XANES spectra of the samples versus the value of the PL intensity area, in agreement with literature data, shows a clear evolution of PL emission with the relative proportions / amounts of pentacoordinate and hexacoordinated symmetries and also the PL decreasing with the beginning of the crystallization process.
8:00 PM - CM02.03.22
Modifier Cations in Silicate Glasses—Possible Changes of the Local Structures During the Very Early Stages of Crystallization
Valmor Mastelaro1,Edgar Zanotto2
University of Sao Paulo1,Federal University of São Carlos2Show Abstract
Crystallization is a key issue in understanding glass and plays a fundamental role in the development of advanced glass-ceramics. In the absence of catalyzing agents, most supercooled liquids crystallize heterogeneously from the external surfaces; only a few systems crystallize homogeneously in the interior. , it is essential to follow the formation of the first nuclei. Is the whole local structure around the cations modified well before crystallization is completed? The precise role of nucleating agents in glass-ceramic formation will likely only be understood by investigating the very first stages of crystallization with a strictly local structural probe having atomic selectivity. The X-ray Absorption Fine Structure (XAFS) technique is quite appropriate to characterize the local structure of specific cations present in glassy samples from the earliest stage of crystal nucleation. In this work, partially crystallized and fully crystallized samples were obtained after treatment at temperatures and times defined in previous studies. The XANES and EXAFS spectra of selected cations ions in the BaO-SiO2, Ba2TiSi2O7, CaMgSi2O6 – 9 mol% Fe2O3, MgO-SiO2, 1NaO-2CaO-3SiO2 and 2NaO-1CaO-3SiO2 glassy systems were collected at room temperature by using the transmission and total electron yield modes. A preliminary analysis of the data indeed showed modifications in the local order around some cations as the time of crystallization increased. The results will be fully discussed.
8:00 PM - CM02.03.23
Shear Band Nucleation and Propagation in Metallic Glass Matrix Composites
Jonathan Gentile1,Douglas Stauffer2,Jason Trelewicz1
Stony Brook University1,Bruker Nano2Show Abstract
Metallic glass matrix (MGM) composites combine high-strength amorphous metals with ductile crystalline inclusions to overcome the inherent brittleness of metallic glasses. While the crystalline heterogeneities have been shown to influence the process of shear localization, the underlying mechanisms are not well understood especially since they seemingly operate at disparate length scales. To explore the role of crystalline inclusions in the process of strain delocalization, we employ instrumented nanoindentation, which is particularly suited to study the deformation physics of these composite materials due to its ability to detect individual shear band propagation events and its precise control over plastic zone size. Using nanoindentation, we focus on elucidating three specific phenomena including the onset of plasticity through the formation of shear bands, the propensity for shear localization and its dependence on indentation strain rate, and the nature of shear band propagation. In this presentation, we describe instrumented Hertzian contact experiments that provide quantitative evidence for enhanced shear band nucleation as the shear band trajectory evolves with indentation depth to encompass the crystalline phase. Additionally, by measuring the fraction of discrete plastic events deriving from shear band plasticity during loading, we outline a transition from discrete to continuous deformation with increasing indentation strain rate, which is consistent with the behavior of monolithic metallic glasses. Through comparison of the propensity for shear localization with microstructural length scales of the MGM composites, we show that the presence of amorphous-crystalline interfaces simultaneously limit shear band propagation and promote a more homogeneous response through the partitioning of shear strain to the crystalline phase.
8:00 PM - CM02.03.26
Atomistic Simulation of Nearly Defect-Free Models of Amorphous Silicon—An Information-Based Hybrid Approach
Dil Limbu1,Raymond Atta-Fynn2,Parthapratim Biswas1
The University of Southern Mississippi1,The University of Texas at Arlington2Show Abstract
We present an information-based total-energy optimization method to produce nearly defect-free structural models of amorphous silicon. Using geometrical, structural and topological information from tetrahedral networks, we have shown that it is possible to generate structural configurations of amorphous silicon, which are superior than the models obtained from conventional reverse Monte Carlo methods involving structural constraints and total-energy optimization. The new static (i.e. relaxation-based) approach presented here is capable of producing atomistic models with structural properties which are on a par with those obtained from the modified Wooten-Winer-Weaire (WWW) models of amorphous silicon. Structural, electronic, and vibrational properties of the hybrid models are compared with the best dynamical models obtained from using machine-intelligence-based algorithms and efficient molecular-dynamics simulations, reported in the recent literature. We have shown that, together with the WWW models, our hybrid models represent one of the best static models so far produced by total-energy-based Monte Carlo methods in conjunction with experimental diffraction data of amorphous silicon.
8:00 PM - CM02.03.27
Metastable Hydrogenated Amorphous Silicon (a-Si:H) as Reversible Programmable Photonic Material
Mahir Mohammed1,Ripalta Stabile1,Jimmy Melskens1,Wilhelmus (Erwin) Kessels1,Oded Raz1
Eindhoven University of Technology1Show Abstract
Hydrogenated amorphous silicon (a-Si:H) is known to exhibit light-induced metastable properties that are reversible upon annealing. Although these metastable properties suggest the existence of reversible optical properties of a-Si:H as well, very little is known about this effect. If indeed properly identified and characterized, such reversible optical properties may find application in the reversible programmable photonic integrated circuits (PICs) that can enable multiple functionalities on the same chip, similar to field-programmable gate arrays (FPGAs). However, the required reversible effective refractive index change due to light soaking and annealing has not been reported yet nor has it been thoroughly investigated. Therefore, the effects of prolonged high intensity light soaking and annealing on a-Si:H on the near infrared (NIR) optical properties are studied in this work. A thin-film interferometric technique was developed to detect minute changes probed using a NIR laser source (1465-1575 nm). Using this approach, an increase in refractive index resulted in a red shift of the sharp reflection minimum and a blue shift for the decrease in refractive index. To detect the changes in optical properties more precisely, double-layered thin films were used: a-Si:H was deposited by inductively coupled plasma-enhanced chemical vapour deposition (ICP-PECVD) on SiO2, which was in turn deposited by PECVD on a crystalline silicon substrate. The a-Si:H deposition temperature was set to 80 °C and 300 °C, such that significantly different structural properties, e.g. hydrogen content and density, could be achieved. An irreversible blue shift was observed during the first cycle of annealing and light soaking after the deposition. However, from the second cycle onwards, a red shift of the spectrum due to light soaking, i.e. reversal of the annealed state was observed. It appeared that the initial irreversible changes are inevitable and only after these changes reversibility is observable. The reversibility was sustained after further cycles of annealing and light soaking. The reversibility appears for both a-Si:H deposited at 80 °C and 300 °C. However, the magnitude of the reversibility for a-Si:H deposited at 80 °C is significantly larger when compared to a-Si:H deposited at 300 °C. This suggests a correlation of the metastable properties of a-Si:H on the hydrogen content and density of the material, i.e. porous films (deposited at 80 °C) are more susceptible to light-induced change than dense films (deposited at 300 °C). The magnitude of the reversibility in refractive index for a-Si:H deposited at 80 °C is estimated to be around 0.03%. Although small, this metastable change should be sufficient for an application in reversible programmable optical switch. These results therefore indicate that a-Si:H has potential in enabling reversible programmable PICs and work to implement this material in a photonic device is currently ongoing.
8:00 PM - CM02.03.28
Ag+ Ion Emission from Sharp-Edged Ag+ Ion Conducting Glasses and Two Emission Mechanisms
Yusuke Daiko1,Hiroki Mori1,Sawao Honda1,Yuji Iwamoto1
Nagoya Institute of Technology1Show Abstract
Ion implantation is an effective method for surface modification of materials, and that has been used in various fields such as the semiconductor and metal industries, and bio-technology.In general, a discharged plasma (gas) or liquid (e.g., liquid Ga for a focused ion beam) is used as the ion source so far. However, in these cases, side reactions (generation of radicals or various ions with different mass, e.g. in the case of H+ emission, H2+ and H3+ etc. are also generated) are unavoidable. Also, ion accelerators are huge and expensive.
On the other hand, ion emissions from high ion conducting solid electrolytes have also been investigated because in a good solid electrolyte the mobile ions can move almost as freely as those in a liquid. The emission of O−ions from O2−-ion-conducting yttria-stabilized zirconia (YSZ) was first reported in 1997. Similarly, continuous Ag+ion emissions for a few days were reported using Ag-ion-conducting (AgI)0.5(AgPO3)0.5or RbAg4I5[8,9]. For 12CaO-7Al2O3(C12A7) clathrate crystals, it was found that not only electrons but also ions such as O−, H−, and F−ions can incorporate inside cages, and emissions of these anions from C12A7 pellets were also observed. In this ion emission method, a plasma is not required for ionization and the ion emission apparatus becomes simple.
We have studied ion emissions from various types of ion-conducting glasses [1-3]. One advantage of utilizing glass is its formability for tip sharpening because the electric field strength is proportional to the inverse of the curvature radius of the tip. Here we report Ag+ ion emission from a sharpened Ag+ ion conducting glasses. An aluminum phosphosilicate glasses Ag2O-Al2O3-P2O5-SiO2 show Ag+ ion conductivity of 3×10−3 S/cm at 300 °C, and an ionic current of Ag+ ion emission was successfully observed at 300 °C and 1×10−5 Pa. A good linear correlation is obtained between the log(current) and the square root of the acceleration voltage, suggesting the emission of Ag+ ion from the tip of glass fiber is expressed by Schottky model similar to a thermionic electron emission. On the other hand, in the case of AgI-B2O3-Ag2O glasses known as a super-ion-conducting glass, an Ag+ ion conductivity was higher than 5×10−3 S cm−1 at room temperature, and Ag+ ion emission was observed for the first time at room temperature and non-vacuum atmosphere. The relationship between the emission current and voltage is expressed by space-charge limited current model, in which the current is proportional to the (voltage)3/2. Ag+ ion emission mechanisms are discussed in relation with these two models. We also tried a cell adhesion test using the palm-sized Ag+ion emission gun as a first step of an application for a bioengineering field.
 Y. Daiko et al., J. Sol-Gel. Sci. Technol.,83(2017) 252-258.  Y. Daiko et al., Solid State Ionics, 322(2018) 5-10.  Y. Daiko et al., Adv. Eng. Mater.,20(2018) 1800198.
8:00 PM - CM02.03.29
Enhancement of Creep Deformation Induced via Proton Implantation for Phosphate Glasses Monitored Utilizing an Electrochemical Indenter
Yusuke Daiko1,Sawao Honda1,Yuji Iwamoto1
Nagoya Institute of Technology1Show Abstract
Intermediate temperature fuel cells (IT-FCs) operating around 400-500 °C have attracted much attention as next-generation energy source owing to their high conversion efficiency and low fabrication cost. Our group successfully prepared a fast proton conducting phosphosilicate glass using conventional melting method, and we confirmed fuel cell operation using H2 and O2 at the intermediate temperature (~5 mW/cm2) [1,2]. Similar to typical oxide glasses, our glass has quite few H+ (OH groups) just after quenching the melt. However, based on originally developed in-situ FTIR measurement, we found a proton implantation into the phosphosilicate glass occurs under fuel cell operating condition . We anticipated such proton implantation affects mechanical properties of glass. In this study, creep behavior of proton conducting glass in fuel cell atmosphere is reported.
A new electrochemical indentation apparatus was developed, in which we can control measuring conditions including atmosphere (H2, N2, air and relative humidity), temperature, and electrical field. A spherical Inconel 625 indenter was used as an electrode simultaneously, and we evaluated in-situ creep behavior under the proton implantation. Proton conducting glass was prepared by conventional melting method with composition of 7.5Na2O･7.5K2O･35P2O5･50SiO2 (mol%). After polishing the glass with ~1 mm thickness, Pt ring-electrode was sputtered on a side of the glass plate. Atmosphere was controlled by flowing a humidified H2gas (4%H2-96% Ar), heating up to 200 oC, and applying DC 5 V between the Pt ring and Inconel electrodes. This condition is similar to the anode reaction of fuel cell (H2 -> 2H++ 2e-), and proton implantation occurs. We conducted an indentation creep experiment under the reaction. We also carried out same experiments in N2 atmosphere as comparison. Humidity effects were also investigated using humid gas (relative humidity ~1%).
The phosphosilicate glass showed typical creep behavior in N2 atmosphere at 200 oC. Interestingly, the creep displacement increases remarkably in H2 atmosphere, and we obtained a longer relaxation time for creep in H2 atmosphere compared with that in N2. These results suggest that proton implantation affects significantly for mechanical properties of glass. Results including Raman spectroscopy will be shown and discussed at the presentation.
 Y. Daiko, et al., Electrochem.SolidState Lett. 14, B63 (2011)  Y. Daiko, et al., Electrochemistry,82, 901 (2014)  Y. Daiko et al., J. Ceram. Soc. Jpn, 121, 539 (2013).
8:00 PM - CM02.03.31
Thermal Stability and Nucleation Dynamics by Flash DSC in Zn-Based Metallic Glass
John Perepezko1,Meng Gao1
University of Wisconsin–Madison1Show Abstract
Zn-based metallic glasses (Zn40Mg11Ca31+xYb18-x, x=0-4) are strong glass forming alloys with low glass transition temperatures that enable metallic plastic behaviors. While the crystallization onset temperature is also low, the crystallization kinetics have not been examined and analyzed quantitatively. In this work, for one Zn-based metallic glass of Zn40Mg11Ca31Yb18, the thermodynamic properties and nucleation dynamics have been determined based on the application of the novel Flash DSC with ultrafast heating and cooling rate. The critical cooling rate range for glass formation was measured along with the critical heating rate for preventing crystallization and the kinetic fragility. A unique double-nose-shaped temperature-time-transformation (TTT) diagram between the glass transition temperature and the melting temperature was obtained by isothermal tests and it was verified to be induced by two different nucleation sites for the same crystallization products. To further investigate the properties of the two nucleation sites, a heterogeneous nucleation model was developed to simulate the experimental TTT diagram and reveal the novel nucleation pathway of Zn-based metallic glasses. This study provides a novel insight in the influence of spatial heterogeneity on crystallization dynamics in amorphous materials.
8:00 PM - CM02.03.33
Stress-Induced Martensitic Transformation of Cu50Zr50 Shape Memory Alloy Optimized Through Microalloying and Co-Microalloying
Paul Nnamchi2,Francois de Luca1,Abdurauf Younes2,A. T. Fry1,Sergio Sanchez2
National Physical Laboratory1,Northumbria University2Show Abstract
The stress-induced martensitic transformation of Cu50Zr50 at. % shape memory alloy was controlled through microalloying and co-microalloying and the performance compared at macro and nano scale. Nanoindentation (P/h)-h curves indicate that there is a change in deformation mode from dislocation slip to martensitic transformation during the loading. This change in mode is demonstrated from the change in slope at the initial stages of deformation. The maximum slope of 1.24 is attained for Cu49Zr50Ni1 at. % compared to about 1.07 for the parent Cu50Zr50 alloy and 0.48 for Cu49Zr50Co1 at. % thus suggesting that 1 at. % Ni promotes the martensitic transformation while 1 at. % Co decreases the effectiveness of the transformation compared to that of the parent alloy. For the co-microalloyed composition, Cu49Zr50Co0.5Ni0.5 at. %, the slope is about 0.88 and therefore intermediate. A similar trend is obtained by measuring the plasticity index values obtained from the ratio of plastic deformation area and total area under the P-h curves since it is minimum for the alloy with 1 at. % Ni (i.e., 0.49) and maximum for 1 at. % Co (i.e., 0.54) compared to that of Cu50Zr50 (i.e., 0.52). The effect of the microalloying elements on the twinning propensity of the parent alloy has also been assessed from measurements at macroscale from differential scanning calorimetry (measuring the shift of the transformation temperatures) and X-ray diffraction (relative intensity change of austenite and martensite peaks before and after pre-compression) studies.
8:00 PM - CM02.03.38
High Pressure-High Temperature Phase Diagram Using Electrical Resistance Measurements in a “Paris-Edinburgh” Large Volume Press
Moran Emuna1,Yaron Greenberg2,Eyal Yahel2,Guy Makov1
Ben-Gurion University of the Negev1,NRCN2Show Abstract
We present a novel experimental design for high sensitivity measurements of the electrical resistance of samples at high pressures (0-6GPa) and high temperatures (0-1000K) in a ’Paris-Edinburgh’ type large volume press. Uniquely, the electrical measurements are carried out directly on a small sample, thus greatly increasing the sensitivity of the measurement. The sensitivity to even minor changes in electrical resistance can be used to clearly identify phase transitions in material samples. Electrical resistance measurements are relatively simple and rapid to execute and the efficacy of the present experimental design is demonstrated by measuring the electrical resistance of Pb, Sn and Bi across a wide domain of temperature-pressure phase space and employing it to identify the loci of phase transitions. Based on these results, the phase diagrams of these elements are reconstructed to high accuracy and found to be in excellent agreement with previous studies. In particular, by mapping the locations of several well-studied reference points in the phase diagram of Sn and Bi, it is demonstrated that a standard calibration exists for the temperature and pressure, thus eliminating the need for direct or indirect temperature and pressure measurements. The present technique will allow simple and accurate mapping of phase diagrams under extreme conditions and may be of particular importance in advancing studies of liquid state anomalies.
8:00 PM - CM02.03.41
Mechanically Strong and Thermally Conductive Ultra-High Molecular Weight Polyethylene Sheets
University at Buffalo, The State University of New York1Show Abstract
Ultra-high molecular weight polyethylene (UHMWPE) is of great interest as a next-generation body armor material due to its superior mechanical properties. However, such unique properties depend critically on its microscopic structure characteristics, including the degree of crystallinity, chain alignment and morphology. Here we present a highly aligned UHMWPE and of its composite sheets containing uniformly dispersed boron nitride (BN) nanosheets. The dispersion of BN nanosheets into the UHMWPE matrix increases its mechanical properties over a broad temperature range. Experiments and simulation confirm that the alignment of chain segments in the composite matrix increases with temperature, leading to an improvement in mechanical properties at high temperature. Together with the large thermal conductivity of UHMWPE and BN, our findings serve in expanding the application spectrum of highly aligned polymer nanocomposite materials for ballistic panels and body armor over a broad range of temperatures.
8:00 PM - CM02.03.44
Toughening PDMS Through Entanglements
Deborah Ehrlich1,Junpeng Wang1,Jeremiah Johnson1
Massachusetts Institute of Technology1Show Abstract
There is a need for tough PDMS that maintains its optical clarity and high temperature resistance. Fillers increase the modulus, toughness, and tear resistance of PDMS, but diminish optical clarity. Entanglements can be used to improve the mechanical properties of PDMS, without impacting desirable properties. By enhancing entanglements, we can further increase the modulus, toughness, and tear resistance of PDMS elastomers while maintaining optical clarity and high temperature resistance. Here we discuss our efforts to synthesize novel PDMS network architectures with entanglement promoted toughness.
8:00 PM - CM02.03.45
Combining Raman Spectroscopy with Rheology to Correlate Physical and Chemical Properties of Polymers
Reinier Blok1,Richard Larsen1,Frederik Fleissner2,Boris Wezisla2,Georg Krenn3,katharina Napp2
Anton Paar1,Anton Paar OptoTec2,Anton Paar GmBH3Show Abstract
During chemical reactions such as polymerizations, the physical as well as chemical properties of a material change. While the viscoelastic properties usually can be characterized with a rheometer, no chemical information is obtained by the mechanical testing. The interpretation of rheometric results often relies on empirical models and a more phenomenological approach. For directly relating the changes in rheological behavior to chemical changes, Raman spectroscopy is employed in-situ with rheology. Raman is a spectroscopic technique based on inelastic light scattering from the sample molecules. By measuring the presence and intensities of molecular vibrations, Raman spectroscopy provides information on the chemical composition and structure of the sample. Furthermore, the Raman spectrum reflects internal molecular parameters such as bond strengths and the structural arrangement of the molecules within the material.
The combination of both techniques enables the simultaneous correlation of the mechanical properties and the molecular structure to obtain a better understanding of the sample.
The Anton Paar MCRxx2 (Modular Compact Rheometer) series of rheometers can be easily combined with the Anton Paar Cora Raman spectrometers via an optical fiber probe. For the applications presented here, a high temperature probe with an extended working distance of 10 mm was used to obtain measurements through the lower measurement plate of the rheometer system. To demonstrate the possibilities of a combined Rheo-Raman system, we investigated resin hardening as well as the melting behavior of polyethylene. First, the hardening of an epoxy resin was monitored providing insight into the chemical and physical changes during the reaction. Specifically, the reaction induced changes in the flow characteristics over time were characterized. In the Raman spectrum, the chemical changes can be found in the decrease of vibrational bands belonging to the epoxy group of the reaction component. Secondly, the phase transition from the crystalline to amorphous state in HDPE (High Density Polyethylene) was monitored while the polymer was heated. This resulted in a higher viscosity as well as alteration of vibrational bands in the Raman spectrum reflecting the conversion from a crystalline to an amorphous structure.
Having both viscoelastic and spectroscopic information on a sample allows a more detailed characterization of the observed sample. As a result, sample behavior can be analyzed in all its facets for better quality control as well as optimizing the process properties of materials.
8:00 PM - CM02.03.46
A Compressive-Sensing Pixelated Direct Detector for 4D-STEM
Robert Monteverde1,Benjamin Bammes1,Robert Bilhorn1
Direct Electron, LP1Show Abstract
Use of a pixelated detector in scanning transmission electron microscopy (STEM) enables the simultaneous acquisition of both the conventional annular dark-field (ADF) signal and the coherent bright-field (BF) diffraction pattern at every probe position. By detecting the scattering angle of nearly all the primary electrons that interact with the specimen, this “4D-STEM” technique promises to provide much more information about the specimen than conventional STEM using only an ADF detector.
An acute challenge for acquisition of 4D-STEM data is the relatively slow speed of pixelated detectors for capturing the coherent BF signal. Slow acquisition of STEM data introduces deleterious artifacts from specimen drift and thus forces users to acquire a severely limited the field-of-view—a significant problem for non-crystalline specimens.
One strategy to improve the speed of these detectors, is to reduce the number of pixels in the pixel array. However, this strategy prevents acquisition of the low- and medium-angle DF signal on the pixelated detector and it may also undersample the BF diffraction pattern and reduce its usefulness for differential phase contrast (DPC) or ptychography. This is especially problematic for complex specimens, such as specimens containing light atoms.
To address this challenge, we have implemented a new compressive-sensing readout mode—called Arbitrary Kernel Row Addressing (AKRA)—on our DE-16 direct detection camera. In AKRA readout mode, the user can specify any arbitrary combination of kernel rows from the detector to readout; all other kernel rows are skipped. By reading out fewer pixels, the detector framerate can be increased, enabling STEM imaging of a larger field-of-view. But since the “missing” pixels are scattering across the detector, the pixelated detector still captures a large area of the BF diffraction pattern and surrounding DF signal, with the “missing” pixels reconstructed using compressive-sensing algorithms. Therefore, AKRA enables fast 4D-STEM acquisition with a large pixelated detector so that rich structural information can be collected for large regions-of-interest of complex specimens.
8:00 PM - CM02.03.47
Size-Dependent Properties of Nano-Crystalline Oxides
Columbia University1Show Abstract
A number of oxides, when prepared in nano-scale crystallites, exhibit a larger than bulk lattice parameter. A couple of these nano-oxides also show decreasing thermal expansion as well as stiffness constants as crystal-size goes beyond 10nm. We will discuss the physics and the materials science behind such an extraordinary behavior and the implications for solid-state chemistry and physics in nanoscale.
8:00 PM - CM02.03.48
Fluorinated Polyurethane Resin with Fold Shape Structure and the Cavitation Erosion Resistance Performance
Haocheng Yang1,Rongrong Chen1,Jun Wang1,Xuejie Guo1,Kazunobu Takahashi1
College of Materials Science and Chemical Engineering, Harbin Engineering University1Show Abstract
Cavitation erosion is a common mode of propeller surface damage, which seriously affects the hydrodynamic performance of propeller. In industrial applications, it is a surface treatment technology can effectively improve the cavitation erosion resistance performance by spraying elastomer organic coating on hydraulic components. Fluorinated polyurethane is a good elastomer which not only has excellent mechanical properties, but also has good ability of anti-biofouling. Herein, hydrophobic fluorinated polyurethanes (FPU), which combination of cavitation erosion resistance and biological fouling resistance coating were prepared by using the method of introducing fluorine with perfluoroalkyl ethanol (TEOH-10) for modification of isophorone diisocyanate (IPDI) and controlling the IPDI adding dosage and time. The chemical structure of FPU was investigated by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectrum (NMR) and gel permeation chromatography (GPC). The bonding strength between top coating and metal interlayer is significantly excellent(>4 MPa). Cavitation erosion tests were performed on Ultrasonic bubble generator for 10h. The mass loss of different cavitation time was examined by balance analysis. Surface morphology of the specimens was observed by Contour GTX and scanning electron microscope (SEM), respectively. Six-months marine field test in the Yellow Sea revealed that the FPU coatings exhibited excellent antifouling/fouling release performance. (This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.)
8:00 PM - CM02.03.49
Cryo-EM Characterization of Chalcogenide Glass Solution Structure
Nikita Dutta1,Craig Arnold1
Princeton University1Show Abstract
The unique optical properties of solution-processed chalcogenide glasses have long been of interest for photonic devices; a common test system is arsenic (III) sulfide (As2S3) in amine solvents. It is widely accepted that As2S3 takes on nanoscale structures in solution, and our ability to control properties when processing for devices is limited by our lack of a full understanding of these structures and the factors that influence them. This, in turn, is limited by the difficulty of characterizing the material in its dissolved state. This is a challenge faced commonly in structural biology, where cryo-electron microscopy (cryo-EM) has become the method of choice for determining the structure of hydrated biological molecules. We adapt this novel characterization technique for the chalcogenide samples and employ it alongside liquid cell electron microscopy and other more traditional methods to explore the in-solution structure of As2S3 in n-propylamine. Our results provide the first visuals of a long hypothesized structure and begin to reveal its dependence on core processing parameters like solution concentration and solvent type.
8:00 PM - CM02.03.51
Extensive Plastic Deformation in Vitreous Silica in Micropillar Compression Tests
Shefford Baker1,Zachary Rouse1,Sanjit Bhowmick2,Syed Asif2
Cornell University1,Bruker Nano Surfaces Division (formerly Hysitron Inc.)2Show Abstract
Pure SiO2 glass is generally considered to be brittle, yet it is known that it can be deformed plastically in indentation or scratch tests. Understanding this plastic deformation is important in the development of devices with improved resistance to mechanical failure, but very little is known about the atomic scale mechanisms that control plasticity. Most work in this area has depended on indentation experiments, where complex inhomogeneous stress state makes interpretation difficult. To study plastic deformation quantitatively, we have developed silica glass micropillars having highly ideal geometries and tested them in compression in-situ in a scanning electron microscope. We characterized yield behavior, strain hardening, and strain rate sensitivity. Many behaviors are evident that are not accessible in indentation tests, including strain softening. Extremely large plastic strains were observed. Plastic deformation mechanisms and the possible role of electron illumination in plasticity is elucidated.
Yunfeng Shi, Rensselaer Polytechnic Institute
Katharine Flores, Washington University
Tanguy Rouxel, University de Rennes
John Mauro, The Pennsylvania State University
CM02.04: Deformation of Glasses I
Tuesday AM, November 27, 2018
Hynes, Level 2, Room 200
8:00 AM - *CM02.04.01
Fracture Toughness of Modern and Ancient Glasses as Measured by the SCF and SEPB Methods
George Quinn1,Jeffrey Swab2
National Institute of Standards and Technology1,U.S. Army Research Laboratory2Show Abstract
The fracture toughness of eight glasses was measured by the surface crack in flexure (SCF) and single-edged precracked beam (SEPB) methods. These include four soda lime silicas including a common plate glass form, two low iron modern forms, and one ancient Roman glass, a fused silica, a borosilicate crown (BK-7) optical glass, and two other borosilicate glasses for armor applications. The historical soda lime silica glass was made in an ancient Roman glass factory that operated in Palestine until 383 AD. This glass was exposed to the environment for almost sixteen centuries. The two SCF and SEPB methods have different susceptibilities to environmentally-assisted slow crack growth, that can be a major interference in measuring fracture toughness in ambient testing environments. A new definition for fracture toughness of glasses is proposed.
8:30 AM - CM02.04.02
Fracture Toughness and Atomic Bonding Character in Glass
Tanguy Rouxel1,Fabrice Celarie1,Theany To1
University de Rennes 11Show Abstract
The fracture surface energy (γ) and the fracture toughness (KIc) of glass were estimated from the nominal composition by means of a simple approach to the structure at the atomic scale. The theoretical values are compared with the experimental ones, as obtained by means of self-consistent methods such as the Single Edge Pre-crack Beam (SEPB) and Chevron Notch (CN) ones, when available. A remarkable agreement is observed for ionocovalent glasses. In comparison, indentation cracking methods are found to mostly overestimate KIc by up to 50 %. In the case of metallic glasses, the theoretical values are much smaller than the experimental ones, which supports the occurrence of crack tip plasticity and shielding effect. Toughness (or ductility) is chiefly governed by the average coordination number, the bond directionality, and the atomic packing density.
8:45 AM - CM02.04.03
Intrinsic Ductility of Glassy Solids
Rensselaer Polytechnic Institute1Show Abstract
Glasses are usually brittle, seriously limiting their practical usages. Recently, the intrinsic ductility of glass was found to increase with the Poisson’s ratio (v), with a sharp brittle-to-ductile (BTD) transition at vBTD=0.31-0.32. Such a correlation between far-from-equilibrium fracture and near-equilibrium elasticity is unexpected and not understood. Via force-field tuning technique, metallic glasses, amorphous silicon, silica glasses, and polymeric glasses have been investigated, showing BTD transition accompanied by an increase in their Poisson’s ratio. Interestingly, beyond monolithic glasses, the Poisson’s ratio of glassy composites embedded with crystallites also correlate to the intrinsic ductility. The Poisson’s ratio, although defined elastically, reflects the bonding covalency and structural disorder, as well as microstructure heterogeneity.
9:00 AM - CM02.04.04
Stresses and Strains in Colloidal Glass
J. Zsolt Terdik1,David Weitz1,Frans Spaepen1
Harvard University1Show Abstract
Micron-sized hard-sphere colloidal particles can be used to form dense amorphous packings. Due to the large size and slow dynamics of colloidal particles, confocal microscopy can be used to investigate the 3D structure and dynamics of these glasses at the particle level. Previous studies have directly visualized both the inhomogeneous particle level strains in deformed colloidal glasses (i.e. STZs), and surrounding continuum strain fields. Measuring the stress in colloidal glasses during deformation, however, is a significant challeng; due to the large size and thermal interaction energies, colloidal solids have very small elastic moduli, on the order to 10-100mPa. We introduce a new technique, traction force rheology, to directly measure the mechanical response of colloidal glasses while simultaneously visualizing the microstructure using a confocal microscope. The method consists of a bilayer of colloidal glass atop a well calibrated soft polymer gel of slightly greater shear modulus. The composite bilayer is sheared and the shear stresses are inferred from the displacement of embedded tracer particles in the calibrated polymer gel. Using these stress measurements, we show that under cyclic applied shear the colloidal glass goes through a sequence of reversible and irreversible microscopic rearrangements which are related to the spatially correlated heterogeneities in the stress field.
9:15 AM - CM02.04.05
High Strain Rate Compression Testing of Amorphous Silica Micropillars
Rajaprakash Ramachandramoorthy1,Jakob Schwiedrzik1,Laszlo Petho1,Damian Frey2,Jean-Marc Breguet2,Johann Michler1
Mechanical testing of bulk materials at high strain rates is a well-established field of research over the past multiple decades. Recently in the past decade, the field of micromechanics has been established and it is now recognized that a reduction in sample dimensions to the micro- and nano- scale leads to enhanced material properties such as strength and ductility. Until now, the micromechanical experiments such as indentation and micropillar compression has been conducted only at quasi-static strain rates. This limitation of low strain rate testing (<~0.1/s) at the microscale arises primarily due to the lack of high strain rate testing platforms capable of simultaneous high-speed actuation and high-speed sensing of microscale displacements and millinewton loads. Thus, the micromechanical properties and the deformation mechanisms for almost every material at strain rates above 0.1/s remains largely unknown.
This presentation will report, for the first time, a piezo-based experimental methodology for conducting high strain rate in situ micropillar compression testing at rates upto ~1000/s inside a scanning electron microscope. The strain rate achieved in this study is an increase of approximately four orders of magnitude compared to the current state-of-the-art micromechanical testing. The advantages and unique challenges of conducting micromechanical testing at high strain rates, with a particular focus on wave phenomena, inertia and sample recovery capability at particular strain, will be compared against traditional macroscale high strain rate tests conducted using kolsky bars.
Subsequently, a case study on the high strain rate micromechanical characterization of amorphous silica or glass, a commercially relevant classic material, will be presented. The rate dependent mechanical properties of ~1µm diameter amorphous silica micropillars will be presented as a function of strain rate across eight orders of magnitude, from 0.0001/s to 1000/s. Remarkably, the amorphous silica micropillars undergo a unique ductile-brittle-ductile transition in failure mechanism as the strain rate is increased from quasi-static to 1000/s. The stress-strain curves become serrated at strain rates between 0.01 and 10/s, a typical mechanical response of amorphous materials. Using the extracted velocities of the load drops in the serrated stress-strain curves, analytical calculations based on adiabatic heating and atomistic simulations reported in literature, an explanation for the anomalous plasticity behavior of amorphous silica at different strain rates will be presented. Also, it will be shown, for the first time, that the yield stress increases as the strain rate is increased till 10/s and then saturates as the strain rates are increased further till 1000/s. Finally, a comparison between the macro-scale and micro-scale mechanical response of amorphous silica at high strain rates will be used to demonstrate their startling differences.
9:30 AM - *CM02.04.06
Effect of Aging and Cryogenic Temperatures on the Mechanical Response of Sputtered Zr-Ni-Al Metallic Glass Nano Structures
Julia Greer1,Rachel Liontas2,Anthony Kwong1,Yongwei Zhang3
California Institute of Technology1,Intel Corporation2,IHPC3Show Abstract
Brittleness of metallic glasses (MGs) is a major drawback for their structural use at bulk scale. It has been shown that when reduced to ~100nm, some metallic glasses undergo a brittle-to-ductile transition and become plastically deformable. To harness this ductility emergent only at nano-scale and proliferate it onto materials with macroscale dimensions, we produced hollow-tube octet-truss nanolattices made out of sputtered NiAlZr with median wall thicknesses of ~10 to ~100nm, which results in a relative density of ~5% and renders them to be 20x lighter than their bulk counterparts.
In-situ uniaxial compression experiments conducted inside an SEM reveal a transition from brittle, catastrophic failure in thicker-walled nanolattices (>60 nm) to deformable, gradual, layer-by-layer collapse in thinner-walled nanolattices (<40 nm). We explain the brittle-to-deformable transition as wall thickness decreases in terms of the "smaller is more deformable" material size effect that arises in nano-sized MGs. We further irradiated ZrNiAl nano-architectures with 12 MeV Ni4+ ions and found that the thickest-walled nanolattices (~88 nm) withstood irradiation; all other substantially shrunk and collapsed. In-situ nanomechanical experiments reveal significant improvement in mechanical response upon irradiation, with a ~36% increase in average yield strength and enhanced deformability. Irradiated nanolattices deformed via a layer-by-layer collapse in contrast to catastrophic failure in equivalent as-fabricated samples.
Shortage of literature on mechanical properties and structural analysis of sputtered MGs motivated fundamental study of NiAlZr. We measured as-sputtered thin film to have a Young’s modulus of 70 GPa and a yield strength of 1.8 GPa and discovered that room temperature aging for three years increased modulus by ~15% and yield strength by ~25%. In-situ tensile experiments on individual nano-samples uncovered their ductility to be larger than reported for other MGs, reaching >10% engineering strains, >150% true strains, and necking down to a point in relatively large, 150nm-wide, samples. Ductility was dependent on specimen size and annealing conditions, with highest ductility of ~150% true strain in ~90 nm wide samples; all annealed specimens of equivalent dimensions were substantially less ductile. We present molecular dynamics simulations, TEM microstructural analysis, and synchrotron XRD characterization to explain observed mechanical behavior in the framework of β-relaxation, free volume reduction and a concomitant increase in short- and medium- range order upon annealing and aging. These findings illustrate key role of the presence and distribution of free volume in governing mechanical deformation of MGs. Our work demonstrates the importance of sample dimensions, fabrication method (sputtering), post-processing conditions (annealing, aging, and irradiation), as well as nano-architecting, in tuning mechanical properties of MGs.
10:30 AM - *CM02.04.07
Mechanical Glass Transition Revealed by the Fracture Toughness of Metallic Glasses
Jan Schroers1,Jittisa Ketkaew1,Eran Bouchbinder2,Takeshi Egami3
Yale University1,Weizmann Institute of Science2,The University of Tennessee, Knoxville3Show Abstract
The fracture toughness of glassy materials, despite its central role in glass science and technology, remains poorly understood. In large part, this is due to the disordered, intrinsically non-equilibrium nature of the glass structure which challenges its theoretical description and experimental determination. By meeting some of these challenges, we show that the notch fracture toughness of metallic glasses exhibits an abrupt toughening transition as a function of a well-controlled fictive temperature Tf, which characterizes the glass structure. The ordinary temperature, which has been previously associated with a ductile-to-brittle transition, is shown to play a minimal role. The observed transition is interpreted to result from a competition between the Tf-dependent plastic relaxation-rate and an applied strain-rate. Consequently, a similar toughening transition as a function of strain-rate is predicted, which is demonstrated experimentally here. The observed mechanical toughening transition bears strong similarities to the ordinary glass transition and explains previously reported large scatter in fracture toughness data and ductile-to-brittle transitions.
11:00 AM - CM02.04.08
Cyclic Shear in a Mesoscopic Model of Amorphous Plasticity
Kareem Khirallah1,Botond Tyukodi1,Craig Maloney1
Northeastern University1Show Abstract
We present results of a mesoscopic model of amorphous plasticity in which the material is subject to oscillatory shear. We show the existence of a threshold amplitude of the shear. Below this threshold amplitude, eventually all plasticity is exhausted and the material shows a fully elastic response under the periodic shear. The time necessary to reach this fully elastic state diverges as one approaches the critical amplitude. Above the critical amplitude we observe a hysteresis in the stress response. After several cycles the hysteresis reaches a steady state, showing that plasticity never vanishes above the threshold amplitude. Right above the critical amplitude, we observe a strong localization of plastic activity and a diffusive increase of strain and displacement fluctuations. Our results are in good agreement with several recent particle simulation observations.
11:15 AM - CM02.04.09
Topological Origin of Strain Induced Damage of Elastomers by Bond Breaking
Yikai Yin1,Nicolas Bertin1,Yanming Wang1,Zhenan Bao1,Wei Cai1
Stanford University1Show Abstract
Elastomers that can sustain large reversible strain are essential components for stretchable electronics, which enables novel wearable and biological applications. The stretchability and mechanical robustness of unfilled elastomers can be enhanced by adding breakable cross-links, which also causes stress-strain hysteresis indicating strain-induced damage in the elastomer network. However, it remains unclear whether the breaking of the cross-links follows a predictable pattern that can be used to understand the evolution of damage with strain. Through coarse-grained molecular dynamics simulations and topology analyses, we find that bond breaking events are controlled by the evolution of shortest paths between well-separated cross-linkers. We show that the average length of the shortest paths, which is both anisotropic and hysteretic with strain, is the microstructural parameter responsible for damage evolution. These findings provide an explicit connection between the microscopic molecular structures and the macroscopic mechanical behaviors of elastomers, thereby paving the way to the development of physics-based models of elastomers, and providing guidelines for the molecular design of mechanically robust soft materials.
11:30 AM - *CM02.04.10
Effects of Stress State on Flow and Fracture of Metallic Glasses
Case Western Reserve University1Show Abstract
The processing and subsequent mechanical behavior of a variety of commercially important materials are affected by the imposed stress state. An earlier review* has summarised the experimentally documented effects of superimposed pressure on deformation under quasi-static conditions, following the classic work of P.W. Bridgman at Harvard University. This will be used to put the effects of superimposed pressure on metallic glasses into perspective. It will be shown that the pressure response of a variety of materials exhibit distinct differences, including metallic glasses, and the potential reasons for these differences will be presented. If time permits, the relevance of such deformation and fracture studies to deformation processing will be overviewed.
*JJ Lewandowski and P Lowhaphandu, International Materials Reviews, 43(4), pp. 145-188, 1998.
CM02.05: Deformation of Glasses II
Tuesday PM, November 27, 2018
Hynes, Level 2, Room 200
1:30 PM - *CM02.05.01
A Study of Shear Band Broadening in Simulated Glasses
Michael Falk1,Darius Alix-Williams1
Johns Hopkins University1Show Abstract
Two models are proposed to predict the evolution of shear band width as a function of applied strain for simulated glasses mechanically deformed in simple shear. The first model arises from dimensional analysis and an assumption that band broadening is controlled by the strain rate inside the shear band. The second model describes the shear band as a pulled front propagating into an unsteady state, the dynamics of which are described using the effective temperature shear transformation zone (ET-STZ) theory. Both models are compared to three simulated systems: a two-dimensional binary Lennard-Jones glass, a Cu64Zr36 glass modeled using an embedded atom method (EAM) potential, and a Si glass modeled using the Stillinger-Weber potential. Shear bands form in all systems across a variety of quench rates. Depending on the case these bands either appear to broaden indefinitely or to saturate to a finite width. The shear band strain rate model appears to apply only when band growth is unconstrained, indicating the dominance of a single time scale in the early stages of band development. The front propagation model, which reduces to the other model in the early stages of band broadening, also applies to cases in which the band width saturates, suggesting that competition between the rate of shear-induced configurational disordering and thermal relaxation set a maximum width for shear bands in a variety of materials systems.
2:00 PM - *CM02.05.02
Dynamic of Shear Bands Initiation in Metallic Glasses—Analysis of a Mg-Based Alloy Using Nano-Indentation
Centre National de la Recherche Scientifique1Show Abstract
Deformation in metallic glasses occurs by initiation and propagation of multiple thin shear bands. This mode is rather difficult to analyse since a single band propagates early and to a large extent in the specimen leading to catastrophic failure. Exception is for example in confined deformation tests. We used instrumented nano-indentations to perform series of independent experiments at room temperature on a Mg65Cu12.5Ni12.5(Ce75La25)10 metallic glass. Loading part of curves shows serrations which size and duration were measured using an automated procedure. To make analyses consistent, data were considered only in the domain with similar strain rates, in the range of 1 to 0.3 s-1. Times between successive serrations follow a normal distribution that suggests a random occurrence of serrations in the glass. It was then conjectured, that (i) serration occurs through activation of appropriate zone in the glass that should naturally scale with a multiple of an elementary domain size characterizing the deformation mechanism. (ii) As activated zones leading to serration are very few in the glass, the process should fit with rare event dynamics. Actually, serration sizes are well fitted by a Poisson distribution. The model predicts an elementary size which scale with that of the activation volume of 3 atoms, measured from nano-indentation creep tests at constant load in the same series of experiments (Thurieau et al, J. Appl. Phys. 2015). Dynamic of shear bands initiation is then analyzed using statistical approach based on the method proposed by Adam and Gibbs (J. Chem. Phys. 1965).
2:30 PM - CM02.05.03
Insight into Shear-Band Affected Zone in Metallic Glasses Through the Measurement of Magnetic Domains
Lai Quan Shen1,Wei Hua Wang1
Institute of Physics, Chinese Academy of Sciences1Show Abstract
Plastic deformation of metallic glasses (MGs) has long been considered to be confined in nanoscale shear band, which usually leads to catastrophic failure and limits their potential applications. Recently, it was found that an affected zone is also involved upon shear banding. Yet, due to technical limitations, the shear-band affected zone (SBAZ), which is critical for understanding shear banding and thus the design of ductile MGs, remains to be precisely identified. Here, by taking magneto-elastic coupling induced magnetic domains as a probe with sufficiently high sensitivity and spatial resolution, we unveil the structure of SBAZ in much more detail. We demonstrate that shear banding is composed of a nanoscale core surrounded by a micron-scale SBAZ with gradient in the strain field, and multiple shear bands interact through the superimposition of the SBAZs. There even exists super long-range gradual elastic stress field extending hundreds of micrometers away from the shear-band core. Our method and findings enable a visualized insight into SBAZ and provide a comprehensive picture on shear banding, which are important for elucidate the micro-mechanisms for plastic deformation of glasses.
2:45 PM - CM02.05.04
Understanding the Mechanisms of Amorphous Plasticity through Molecular Simulation
Penghui Cao1,Michael Short1,Sidney Yip1
Massachusetts Institute of Technology1Show Abstract
Using a meta-dynamics method of sampling activated state pathways we study two related plastic responses of a model metallic glass at experimental strain-rate levels beyond the reach of traditional molecular dynamics simulations. The problems are (1) discrete stress relaxation (slip avalanches) in the onset of yielding and subsequent strain evolution, and (2) stress effects on creep rate. In (1) we quantify the yielding response and the role of major and minor avalanches in sustaining serrated plastic deformation. In the case of deformation under a constant stress, problem (2), we demonstrate a nonlinear interplay between non-affine atomic displacement and cooperative shear transformation distortion of local atomic clusters that provides a molecular explanation of the familiar behavior of creep-rate upturn beyond a stress threshold, as well as a mechanism map delineating the effects of stress and temperature. Collectively these findings lead to an understanding of the elementary processes governing deformation and flow of disordered materials and the effects of thermal and stress activations.
3:30 PM - *CM02.05.05
Improving the Ductility of Metallic Glasses by Heterogeneities
Erich Schmid Institute of Materials Science, Austrian Academy of Sciences1,Montanuniversitaet Leoben2Show Abstract
Significant progress has been made in recent years in how to optimize processing conditions for glass formation, net-shape forming and property rejuvenation. However, the details of the correlation between composition, atomic structure, defects and thermo-mechanical treatments for structure modification and their impact on shear banding behavior and failure mechanisms for achieving macroscopic ductility are still not well-understood.
Recent work suggests that the intrinsic properties of metallic glasses and composites are strongly affected by the details of short- and medium-range order arrangements and their response to external fields like mechanical deformation or temperature cycling causing heterogeneous stress and strain variation on different length-scales.
This talk explores the diversity that can be achieved in metallic glasses and composites considering structure changes, recovery and rejuvenation mechanisms when the materials are subjected to different casting conditions or thermo-mechanical cycling. The findings will be discussed with respect to short- and medium-range order modulation, local stress and strain states, defect generation and annihilation, and precipitation of secondary phases. The structure changes will be correlated with plastic deformability and failure mechanisms, and the effectiveness of composition tuning and thermo-mechanical processing for plasticity improvement will be discussed to derive guidelines for property optimization.
4:00 PM - *CM02.05.06
Spatial-Temporal Characterization of Shear Band in Bulk Metallic Glasses
Peter Liaw1,Xie Xie1,Yu Chieh Lo2,Tong Yang3,Junwei Qiao4,Gongyao Wang1,Shigenobu Ogata5,Hairong Qi1,Karin Dahmen6,Yanfei Gao1,3
University of Tennessee1,National Chiao Tung University2,Oak Ridge National Laboratory3,Taiyuan University of Technology4,Osaka University5,University of Illinois at Urbana-Champaign6Show Abstract
Recent research shows that temperature is an important factor for the shear-band operations in bulk metallic glasses (BMGs). Thus, the characterization of shear bands through thermal imaging provides a way tostudy BMG deformation. Based on recent reports and research progress, the present work develops a kinetic Monte Carlo (kMC) model to investigate and simulate the initiation and propagation of shear bands, which correlates well with the thermograph-imaging results. These findings are expected to reveal the hidden statistical characteristics during the BMG deformation and advance the basicunderstanding of the BMG deformation mechanism.
Acknowledgements: we would very much appreciate the supports from (1) the Department of Energy (DOE), Office of Fossil Energy, National Energy Technology Laboratory (DE-FE-0011194) with the program manager, Dr. J. Mullen, (2) the U.S. Army Research Office project (W911NF-13-1-0438) with the program managers, Dr. M. P. Bakas and Dr. D. M. Stepp, and (3) the support from the National Science Foundation (DMR-1611180) with the program directors, Drs G. Shiflet and D. Farkas.
4:30 PM - CM02.05.07
Local Yield Stress Analysis in Simulated 3D Glasses
Dihui Ruan1,Sylvain Patinet2,Michael Falk1
Johns Hopkins University1,ESPCI2Show Abstract
The ‘Local Yield Stress’ (LYS) method is applied to an atomistic model of as-quenched glasses by shearing local regions. By probing the structure in local shear modes, the LYS method measures the local yield stress as the incremental stress at the onset of a plastic instability. This method has been upgraded to a three-dimensional version with variations in orientations, rotations and triaxiality when locally deformed. This analysis is then utilized to identify the population of ‘Shear Transformation Zones’ (STZs), defined as local atomic clusters that rearrange cooperatively when the material is subjected to shear. These STZs are present in the as-quenched material structure. The population of STZs is correlated with the plastic events observed during a molecular dynamics simulation in which the glass is subjected to shear at the boundaries in order to assess the predictive capability and persistence of the derived STZ population while the material undergoes deformation.
4:45 PM - CM02.05.08
Atomic-Scale Homogeneous Plastic Flow of Bulk Metallic Glass
Jiaxin Yu1,2,Amit Datye2,Zheng Chen2,Chao Zhou2,Omur Dagdeviren2,Jan Schroers2,Udo Schwarz2,3
Southwest University of Science and Technology1,Yale University 2,Yale University3Show Abstract
The onset of yielding and the local plastic flow mechanism of bulk metallic glasses (BMGs) at room temperature have not been fully understood at atomic scale. Further reducing the stressed volumes of BMGs during mechanical testing can decrease the amount of activated shear transformation zones (STZs) under shear stress, which is expected to provide direct insight into the onset of plastic deformation and the material’s atomic-scale flow behavior. In this work, we employed thermoplastic forming to produce atomically flat Pt-based BMG surfaces, whose yield stress, the onset of yielding, and plastic flow at the atomic scale were subsequently studied using atomic force microscopy (AFM)-based nanoindentation. The experiments revealed a much higher yield stress compared to the value obtained by conventional nanoindentation testing, which indicates that the yield stress of BMG strongly depends on the stressed volume in the test, with a smaller stressed volume causing a higher yield stress. Differing from control experiments performed on Pt(111), the plastic flow of Pt-BMG is homogeneous, and no pop-in events are observed. Moreover, the plastic response of Pt-BMG does not exhibit any loading rate dependence, but needs a constant stress to sustain flow. These atomic-scale results are contrasted to the larger-scale model that explains plastic deformation of BMG as originating from the finite STZs activation.
CM02.06: Poster Session II: Structure-Property Relations in Non-Crystalline Solids
Tuesday PM, November 27, 2018
Hynes, Level 1, Hall B
8:00 PM - CM02.06.01
Real-Time Observation of Thermally-Induced Structural Changes of Poly(Lactic Acid) Thin Film by Terahertz Spectroscopy
Madoka Nakamura1,Makoto Okano1,Shinichi Watanabe1
Keio University1Show Abstract
Polymeric materials exhibit intriguing temperature-dependent structural transitions, such as a glass transition at Tg, and a crystallization phase transition at Tc. Since some polymers have relatively low Tg and Tc, the structural change might occur during the productive processes. Since the structure of polymers affects their optical, electrical, and mechanical properties, it is important to characterize them in-situ during the productive processes. Recently, it has been demonstrated that the terahertz time-domain spectroscopy (THz-TDS) is a powerful tool to evaluate the structure of polymeric materials[1-5]. In contrast to the conventional methods such as X-ray diffraction, THz-TDS has some clear advantages: (i) Nondestructive and contactless inspection. (ii) Evaluation of Tg[1,3] (iii) Detection of both the amorphous and the crystalline phases. (iv) Prompt measurement within 1 ms. These features allow us to real-time monitor the structural change of the polymeric products. Here, we demonstrate a real-time sensitive monitoring of the thermally-induced structural changes of poly(lactic acid) (PLA) using THz-TDS. PLA is one of the most promising biodegradable polymers for industrial polymer products. Because the PLA has relatively low Tg (~60°C) and Tc (~120°C), its structure easily modified by the heating. Thus, the PLA is a suitable material for investigating the structural changes by the heating with the THz-TDS.
By real-time monitoring the terahertz optical responses of the PLA during the heating, the complicated temperature dependence of the complex dielectric function (ε=ε′+iε") of the PLA was observed. To clarify the structural change of the PLA, we focused on the spectral shape of ε′, especially the absolute value of the slope, |Δε′|, at 0.5-1.0 THz. We found two characteristic behaviors of |Δε′| regarding the structural changes of the PLA: (i) Existence of the inflection point at Tg. (ii) Drastic decrease around Tc. Our findings are well explained by the classical Lorentz oscillator model. The former behavior results from the broadening of the vibration mode due to the change in the free volume from the glass to the rubber states[1,3]. The latter one is attributed to the blueshift of the vibration mode accompanied by the phase transition from the amorphous to the crystalline phases[2,5]. Our novel analytical procedure that is based on the Lorentz oscillator model and utilizes |Δε′| as an indicator to evaluate the structure clearly reveals the structural change in the PLA compared with the previous reports [1-5]. Thus, we conclude that our method is promising for proving the structural change of polymeric materials in the productive processes.
 S. Wietzke et al., Opt. Express 17, 19006 (2009).
 N. Fuse et al., Jpn. J. Appl. Phys. 49, 102402 (2010).
 M. Komatsu et al., J. Appl. Phys. 117, 133102 (2015).
 H. Li et al., Polym. Test. 57, 52 (2017).
 H. Iwasaki et al., J. Phys. Chem. B 121, 6951 (2017).
8:00 PM - CM02.06.02
Beneficial Effects of Oxygen Addition on Glass Formation in a High-Entropy Bulk Metallic Glass
Di Cao1,Zhaoping Lu1,Yuan Wu1
University of Science and Technology Beijing1Show Abstract
Glass-forming ability (GFA) is one of critical scientific problems for the field of bulk metallic glass (BMGs), and how to facilitate glass formation is always a central yet important research theme for this field. Compared with conventional BMGs in the same alloy system, newly developed high-entropy BMGs (HE-BMG) usually show much enhanced thermal stability, but appreciably reduced GFA. In contrast to the conventional wisdom, we found that GFA of the Zr20Cu20Hf20Ti20Ni20 HE-BMG could be enhanced by oxygen microalloying. The underlying mechanism was explored from both thermodynamic and kinetic point of view, and our analysis indicates that the high packing density resulted from addition of small oxygen atoms is responsible for the beneficial effect of oxygen. The current findings not only shed new insights into understanding of glass formation, but also broaden the view for exploring new kinds of HE-BMGs with enhanced properties and low manufacturing costs.
8:00 PM - CM02.06.04
Highly Processable Work-Hardenable Zr-Based Metallic Glass Composites Reinforced by Continuous TiNi Fiber
Jie Zhou1,Zhaoping Lu1,Yuan Wu1
University of Science and Technology Beijing1Show Abstract
Bulk metallic glasses (BMGs) have attracted considerable research activities because of their unique mechanical properties, such as high strength, large elastic limit and high hardness. However, room-temperature brittleness and strain-softening limited their structural applications. Up to now, it has been proved that enhanced plasticity and strong work-hardening ability could be achieved by introducing the concept of transformation-induced plasticity (TRIP) into Zr-based or Ti-based bulk metallic glass composites (BMGCs). Most currently developed TRIP-reinforced BMGCs are fabricated with in-situ formed second phase method, in which homogeneous formation of austenitic phase is a big challenge.
To producte work-hardenable BMGCs in a processable way, we designed a series of BMGC reinforced by introducing ex-situ continuous TiNi fibers, which can bring in martensitic transformation (MT) and TRIP effect and eventually leads to the combination of pronounced plasticity and considerable work-hardening ability under both quasi-static and dynamic compressive loading.
In this talk, preparation, microstructure characteristics, mechanical properties and deformation mechanism of BMGCs reinforced by TiNi fibers will be discussed.
8:00 PM - CM02.06.05
Combinatorial Temperature Resistance Sensors for the Analysis of Phase Transformations
Tan Lin Zhu1,Haitao Zhang1,Yong Xiang1,Joost Vlassak2
University of Electronic Science and Technology1,Harvard University2Show Abstract
In this work, we describe a sensor array that can effectively measure the resistance of thin films as a function of temperature and composition. The sensor is fabricated in very simple micro fabrication steps. Detailed FEM simulation indicates that the sensor has very high temperature uniformity, which leads to extreme sensitivity and thus the ability to detection of subtle structure change of materials. We have used the sensor to observe structural relaxation, the glass transition, and crystallization of PdSiCu metallic glasses. We also find that the ratio of the resistance of crystallized to as-deposited material is correlated with the glass-forming ability for both PdCuSi and NiZr-based alloys, potentially providing an avenue to the fast screening of good glass formers in complex material systems.
8:00 PM - CM02.06.06
How Alkaline and Earth-Alkaline Elements Can Change Role in Glasses and Melts? Implication for Nucleation Processes and Redox Change?
Daniel Neuville1,Maria Rita Cicconi1
Alkali and alkaline earth can behave as network modifier or as charge compensator of AlO4- in aluminosilicate glasses and melts. As a function of the role, density, molar volume, viscosity, liquidus and glass transition temperature and more generally, macroscopic properties, can change significantly. But how evaluate or prove this change of role? Recently, Helhen and Neuville (2014) have shown by comparing Raman in VV and VH polarization, that a new band appears in the VH Raman spectra when the role of Ca(Na, Mg) changes from charge compensator to network modifier. Furthermore, we have shown in the XANES spectra at the Ca K-edge, important differences in the Ca pre-edge peaks as a function of this same change of role. Similar behaviour were observed on the Calcium K-edge via XANES spectroscopy (Cicconi et al., 2016) and on the Na, via NMR (Le Losq et al., 2014). During this presentation, we plan to show some new results on XANES, Raman, NMR.
To conclude, by looking at the role of alkaline earth elements in glasses and melts, it is possible to have a better knowledge of the structure of glasses and melts, but also to better understand their influence on redox and nucleation processes.
Le Losq Ch., Neuville D.R., Florian P., G.S. Henderson and Massiot D. (2014) Geochimica Cosmochimica Acta, 126, 495-517.
Hehlen B. and Neuville D.R. (2015) The Journal of Physical Chemistry B. 119, 4093 4098.
Cicconi M.R., de Ligny D., Gallo T.M., Neuville D.R. (2016) American Mineralogist, 101, 1232-1236.
8:00 PM - CM02.06.07
Short Range Order in Fluorine Containing CaO-SiO2-CaF2 Glasses from NMR, Neutron Diffraction, and X-Ray Absorption Spectroscopy
Gavin Mountjoy1,Laura Swansbury1,2
University of Kent1,Morgan Advanced Materials2Show Abstract
The glass system CaO-SiO2-CaF2 has been studied to help elucidate the structure of more complex CaO-SiO2-P2O5-CaF2 fluorine-containing bioactive glasses. The CaO-SiO2-CaF2 glass series was synthesized and the glass transition temperature decreased linearly with increasing CaF2 concentrations. Compositional analysis revealed that fluorine losses occurred due to fluorine volatilisation during synthesis. The chemical shift positions in the 19F MAS-NMR spectra became more negative with increasing CaF2 concentrations, becoming more similar to that of pure CaF2. By studying the calcium environment using neutron diffraction and x-ray absorption spectroscopy at the Ca K-edge, reasonably consistent values for Ca-F and Ca-O nearest neighbour distances of approximately 2.3Å and 2.4Å (respectively) could be obtained. However, it was challenging to establish the coordination numbers and disorder in distances of such nearest neighbours.
8:00 PM - CM02.06.08
Structure-Property Relations in Amorphous Polymer Derived Ceramics for Electronic Applications
Mehrdad Abbasi1,Soohyun Im1,Jared Johnson1,Gabriel Calderon Ortiz1,Menglin Zhu1,Nathan Oyler2,Michelle Paquette2,Paul Rulis2,Ridwan Sakidja3,Jinwoo Hwang1
The Ohio State University1,University of Missouri – Kansas City2,Missouri State University3Show Abstract
We develop a novel methodology for accurate design and fabrication of complex disordered solids using a combination of advanced experimental and computational techniques. Complex disordered solids are non-crystalline materials for which the fundamental building blocks are typically molecules or molecule fragments, and therefore they have great potential for tunable structure and properties for various
applications. However, the complexity and high degree of freedom in their structure impose substantial challenges to the design and optimization of these materials. This presentation will focus on the structural characterization of polymer derived amorphous hydrogenated boron carbide thin films using 4-dimensional scanning transmission electron microscopy (4D-STEM). The 4-D STEM utilizes electron nanoprobes and the new-generation fast pixelated STEM detector, which records the diffraction patterns from individual nanoscale volumes of the material. The fluctuation and angular correlation analyses of the diffraction patterns can provide the unprecedented details of the structural heterogeneity, including the size, distribution, connection, and volume fraction of medium range ordering (MRO). We show that the MRO
in amorphous hydrogenated boron carbide can be comprised of the connection and networking of the icosahedral short-range clusters, and the MRO can directly affect the important physical and electrical properties of the films. Our finding is promising as it could greatly expand the breadth of materials-by-design approaches by flexibly tuning the structure of disordered materials to achieve desired properties.
8:00 PM - CM02.06.11
Amorphous Germanium Material Evaluation for Evanescent Wave Sensors for MWIR and LWIR Sensing Applications
Eveline Postelnicu1,Peter Su1,Danhao Ma1,Ruitao Wen1,Ruturaj Pujari1,Ryan Kosciolek1,Venita Boodhoo1,Ron Synowicki2,Jurgen Michel1,Lionel Kimerling1,Kazumi Wada1,Anuradha Agarwal1
Massachusetts Institute of Technology1,J.A. Woollam Company, Inc.2Show Abstract
Room temperature deposited amorphous germanium (Ge) material has been evaluated for evanescent sensing applications in the Midwave and Longwave infrared regions (MWIR and LWIR). The advantage of amorphous Ge is that it can be used to sense a wide variety of organic molecules for both biomedical and environmental sensing and its room temperature processing is very economically efficient. Thin films of amorphous Ge were obtained using various processing approaches: Sputter Deposition, Electron Beam Evaporation (E-beam), and Physical Vapor Deposition (or thermal evaporation). Films were characterized using X-Ray Diffraction (XRD), Fourier Transform InfraRed (FTIR) Spectroscopy, Wavelength-Dispersive (Electron) Spectroscopy (WDS), Hall Effect measurements, and Ellipsometry. It was shown that Electron Beam Evaporation yielded the purest material, with 96% Ge and 4% carbon contamination, while thermal evaporation showed only around 70% Ge and 30% of the film containing contaminants from the evaporation chamber. Ellipsometry performed on the amorphous Ge samples at a wavelength range of 1.5 to 15 microns showed that the index of refraction, n, of sputtered Ge had a lower range (2.9 – 3.4) than that of E-beam Ge (4 – 4.5). The extinction coefficients for both sputtered Ge and E-beam Ge are in a comparable range, 0 to 0.4, for the same measured wavelength range (1.5 to 15 microns), indicating low absorption losses within the material. X-Ray Diffraction confirmed the amorphous nature of the deposited Germanium. Waveguides utilizing this low loss amorphous Ge within a Si-CMOS-compatible platform will be presented.
8:00 PM - CM02.06.12
Structural Variation of (Hydrogenated) Amorphous Silicon with Density—A Classical Monte Carlo Study
David Strubbe1,Enrique Guerrero1
University of California, Merced1Show Abstract
We present computational generation of hydrogenated (a-Si:H) and non-hydrogenated (a-Si) amorphous silicon structures for use in studying the electronic properties of thin-film solar cells, such as "heterojunction with intrinsic thin-layer" (HIT) cells with a-Si:H and c-Si layers. We generate structures using the Wooten-Winer-Weaire (WWW) classical-potential Monte Carlo method using our CHASSM (Computational Hydrogenated Amorphous Semiconductor Structure Maker) code, which implements a WWW scheme that can take into account Si-H bonds. We create structures of various densities and study the effect on structural parameters including bond lengths, bond angles, dihedral angles, and radial distribution functions. Abrupt transitions occur at certain critical densities (different depending on hydrogen content) which suggest crossover between different types of amorphous structures, perhaps even diffferent phases. We investigate mechanical and spectroscopic consequences of these changes. At low densities, voids form, which are likely to constitute defects limiting carrier mobilities and may be implicated in light-induced degradation (the Staebler-Wronski effect). We mathematically characterize the voids using Voronoi polyhedra and persistent homology. We show some refinements of the Monte Carlo randomization process needed to avoid ending in crystalline structures or a class of unphysical excessively coordinated structures.
8:00 PM - CM02.06.13
Insight into the Mechanism of Damage Initiation and Fracture of Conductive Polyurethane Nanocomposites
Dhriti Nepal5,Spencer Hawkins1,Evan Sullivan2,Alireza Sarvestani3,4,Hilmar Koerner5
Universal Technology Corporation1,University of Kentucky2,Ohio University3,Mercer University4,Air Force Research Laboratory5Show Abstract
Polyurethane (PU) is a functional copolymer whose properties bridge the gap between rubber and thermoplastics. Their excellent physical properties, such as flexibility and abrasion resistance along with their high temperature plasticity have made them an ideal structural material for application in aerospace structures, automobiles, electro-machinery vocation, etc. In an attempt to promote the formation of a conductive network within PU, we have developed an experimental technique to decorate carbon nanofibers (CNFs) with silver (Ag) nanoparticles and subsequently blended them with PU. Introduction of a small amount of CNF (coated with Ag) into the PU matrix produced a conductive nanocomposite with higher stiffness and strength compared to that of pure PU but substantially reduced the fracture toughness of the material. Here, we present a systematic and comprehensive study to understand the mechanism of damage nucleation and fracture evolution in Ag-CNF-PU nanocomposites. By mapping the surface of samples using AFM-IR, the onset of damage was monitored prior to realization of plastic deformation during in situ tensile testing. Coupled with the results of DMA analysis, we concluded that strain induced crystallization in PU and polymer debonding from CNF surface are the most detrimental mechanisms that control the fracture toughness of PU nanocomposites. These conclusions were used to develop a model that predicts the mechanical behavior of PU nanocomposites at finite deformations.
8:00 PM - CM02.06.14
Mechanical Behavior of Highly Rejuvenated Bulk Metallic Glasses
Yi Li1,Jie Pan1
Institute of Metal Research, Chinese Academy of Sciences1Show Abstract
Rejuvenation of metallic glasses, bringing them to higher-energy states, is of interest in improving their plasticity. However, how to achieve significant flow and rejuvenation throughout a deformed metallic glass remains challenging, and the mechanical behavior of the highly rejuvenated bulk metallic glasses is unexplored. In this presentation, we will reveal the significant improvement in compressive plasticity in a Zr-based bulk metallic glass (BMG) by structural rejuvenation, which is in stark