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 lay