Community action on FAIR data will fuel a revolution in materials research.

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Degeneration Behavior of Cu Nanowires under Carbon Dioxide Environment: An / Study.

Copper (Cu) is a catalyst broadly used in industry for hydrogenation of carbon dioxide, which has broad implications for environmental sustainability. An accurate understanding of the degeneration behavior of Cu catalysts under conditions is critical for uncovering the failure mechanism of catalysts and designing novel ones with optimized performance. Despite the widespread use of these materials, their failure mechanisms are not well understood because conventional characterization techniques lack the necessary time and spatial resolution to capture these complex behaviors.

Grain boundary formation through particle detachment during coarsening of nanoporous metals.

Grain boundary formation during coarsening of nanoporous gold (NPG) is investigated wherein a nanocrystalline structure can form by particles detaching and reattaching to the structure. MicroLaue and electron backscatter diffraction measurements demonstrate that an in-grain orientation spread develops as NPG is coarsened. The volume fraction of the NPG sample is near the limit of bicontinuity, at which simulations predict that a bicontinuous structure begins to fragment into independent particles during coarsening.

Quantifying Competitive Degradation Processes in Supported Nanocatalyst Systems.

The stability of supported metal nanoparticles determines the activity and lifetime of heterogeneous catalysts. Catalysts can destabilize through several thermodynamic and kinetic pathways, and the competition between these mechanisms complicates efforts to quantify and predict the overall evolution of supported nanoparticles in reactive environments. Pairing transmission electron microscopy with unsupervised machine learning, we quantify the destabilization of hundreds of supported Au nanoparticles in real-time to develop a model describing the observed particle evolution as a competition between evaporation and surface diffusion.

Reducing Time to Discovery: Materials and Molecular Modeling, Imaging, Informatics, and Integration.

Multiscale and multimodal imaging of material structures and properties provides solid ground on which materials theory and design can flourish. Recently, KAIST announced 10 flagship research fields, which include KAIST Materials Revolution: Materials and Molecular Modeling, Imaging, Informatics and Integration (M3I3). The M3I3 initiative aims to reduce the time for the discovery, design and development of materials based on elucidating multiscale processing-structure-property relationship and materials hierarchy, which are to be quantified and understood through a combination of machine learning and scientific insights.

Phase-field model of oxidation: Kinetics.

The kinetics of oxidation is examined using a phase-field model of electrochemistry when the oxide film is smaller than the Debye length. As a test of the model, the phase-field approach recovers the results of classical Wagner diffusion-controlled oxide growth when the interfacial mobility of the oxide-metal interface is large and the films are much thicker than the Debye length. However, for small interfacial mobilities, where the growth is reaction controlled, we find that the film increases in thickness linearly in time, and that the phase-field model naturally leads to an electrostatic overpotential at the interface that affects the prefactor of the linear growth law.

Surface deformations in dynamic thermocapillary convection under partial slip.

A prescribed, horizontal temperature gradient is imposed upon a horizontal liquid layer bounded from above by a deformable, liquid-gas interface and bounded from below by a partial-slip, rigid surface. A steady shear flow driven by thermocapillary motion emerges. This dynamic liquid layer is susceptible to the onset of oblique three-dimensional hydrothermal waves, purely two-dimensional hydrothermal waves, longitudinal traveling waves, and longitudinal rolls depending on the capillary number.

Phase Transformation Contributions to Heat Capacity and Impact on Thermal Diffusivity, Thermal Conductivity, and Thermoelectric Performance.

The accurate characterization of thermal conductivity κ, particularly at high temperature, is of paramount importance to many materials, thermoelectrics in particular. The ease and access of thermal diffusivity D measurements allows for the calculation of κ when the volumetric heat capacity, ρc , of the material is known. However, in the relation κ = ρc D, there is some confusion as to what value of c should be used in materials undergoing phase transformations.

Lattice Softening Significantly Reduces Thermal Conductivity and Leads to High Thermoelectric Efficiency.

The influence of micro/nanostructure on thermal conductivity is a topic of great scientific interest, particularly to thermoelectrics. The current understanding is that structural defects decrease thermal conductivity through phonon scattering where the phonon dispersion and speed of sound are assumed to remain constant. Experimental work on a PbTe model system is presented, which shows that the speed of sound linearly decreases with increased internal strain.

Capillary-driven elastic attraction between quantum dots.

We present a novel self-assembly route to align SiGe quantum dots. By a combination of theoretical analyses and experimental investigation, we show that epitaxial SiGe quantum dots can cluster in ordered closely packed assemblies, revealing an attractive phenomenon. We compute nucleation energy barriers, accounting for elastic effects between quantum dots through both elastic energy and strain-dependent surface energy.

PFHub: The Phase-Field Community Hub.

Scientific communities struggle with the challenge of effectively and efficiently sharing content and data. An online portal provides a valuable space for scientific communities to discuss challenges and collate scientific results. Examples of such portals include the Micromagnetic Modeling Group (μMAG [1]), the Interatomic Potentials Repository (IPR [2, 3]) and on a larger scale the NIH Genetic Sequence Database (GenBank [4]).

Self-Similarity and the Dynamics of Coarsening in Materials.

Two-phase mixtures, from metallic alloys to islands on surfaces, undergo coarsening wherein the total interfacial area of the system decreases with time. Theory predicts that during coarsening the average size-scale of a two-phase mixture increases with time as t when the two-phase mixture is self-similar, or time independent when scaled by a time-dependent length. Here, we explain why this temporal power law is so robustly observed even when the microstructure is not self-similar.

Nonequilibrium Solute Capture in Passivating Oxide Films.

We report experimental results on the composition and crystallography of oxides formed on NiCrMo alloys during both high-temperature oxidation and aqueous corrosion experiments. Detailed characterization using transmission electron microscopy and diffraction, aberration-corrected chemical analysis, and atom probe tomography shows unexpected combinations of composition and crystallography, far outside thermodynamic solubility limits. The results are explained using a theory for nonequilibrium solute capture that combines thermodynamic, kinetic, and density functional theory analyses.

Dynamics of Nanoscale Dendrite Formation in Solution Growth Revealed Through in Situ Liquid Cell Electron Microscopy.

Formation mechanisms of dendrite structures have been extensively explored theoretically, and many theoretical predictions have been validated for micro- or macroscale dendrites. However, it is challenging to determine whether classical dendrite growth theories are applicable at the nanoscale due to the lack of detailed information on the nanodendrite growth dynamics. Here, we study iron oxide nanodendrite formation using liquid cell transmission electron microscopy (TEM).

Quantitative characterization of high temperature oxidation using electron tomography and energy-dispersive X-ray spectroscopy.

We report quantitative characterization of the high temperature oxidation process by using electron tomography and energy-dispersive X-ray spectroscopy. As a proof of principle, we performed 3D imaging of the oxidation layer of a model system (MoSi) at nanoscale resolution with elemental specificity and probed the oxidation kinetics as a function of the oxidation time and the elevated temperature. Our tomographic reconstructions provide detailed 3D structural information of the surface oxidation layer of the MoSi system, revealing the evolution of oxidation behavior of MoSi from early stage to mature stage.

Evolution of NiO Island Size Distributions during the Oxidation of a Ni-5Cr Alloy: Experiment and Modeling.

The classic models of metal oxidation developed by Wagner and Cabrera and Mott presuppose the existence of a planar oxide film and develop expressions for the rate at which the film thickens. Missing from those models is a description of how that initially planar film forms. Using scanning tunneling microscopy, we study the growth of NiO islands on the (100) surface of a Ni-5Cr alloy during the oxidation regime where the initial planar film is formed as oxide islands.

Instabilities in rapid directional solidification under weak flow.

We examine a rapidly solidifying binary alloy under directional solidification with nonequilibrium interfacial thermodynamics viz. the segregation coefficient and the liquidus slope are speed dependent and attachment-kinetic effects are present. Both of these effects alone give rise to (steady) cellular instabilities, mode S, and a pulsatile instability, mode P.

Catalyst-particle configurations: From nanowires to carbon nanotubes.

Surface-energy minimization is used to study capillary effects that determine the stable configurations of (liquid or solid) particles atop tubes or wires. The results give allowable ranges for the volume (V_{c}) of the particles as a function of the inner and outer radii of the tubes, R_{I} and R_{o}, respectively. When R_{I}/R_{o}=0, the object is a nanowire.

Modeling of the growth of GaAs-AlGaAs core-shell nanowires.

Heterostructured GaAs-AlGaAs core-shell nanowires with have attracted much attention because of their significant advantages and great potential for creating high performance nanophotonics and nanoelectronics. The spontaneous formation of Al-rich stripes along certain crystallographic directions and quantum dots near the apexes of the shell are observed in AlGaAs shells. Controlling the formation of these core-shell heterostructures remains challenging.

Phase-field-crystal model for ordered crystals.

We describe a general method to model multicomponent ordered crystals using the phase-field-crystal (PFC) formalism. As a test case, a generic B2 compound is investigated. We are able to produce a line of either first-order or second-order order-disorder phase transitions, features that have not been incorporated in existing PFC approaches.

The mechanism of eutectic growth in highly anisotropic materials.

In the past 50 years, there has been increasing interest-both theoretically and experimentally-in the problem of pattern formation of a moving boundary, such as a solidification front. One example of pattern formation is that of irregular eutectic solidification, in which the solid-liquid interface is non-isothermal and the interphase spacing varies in ways that are poorly understood. Here, we identify the growth mode of irregular eutectics, using reconstructions from four-dimensional (that is, time and space resolved) X-ray microtomography.

In Situ Graphene Growth Dynamics on Polycrystalline Catalyst Foils.

The dynamics of graphene growth on polycrystalline Pt foils during chemical vapor deposition (CVD) are investigated using in situ scanning electron microscopy and complementary structural characterization of the catalyst with electron backscatter diffraction. A general growth model is outlined that considers precursor dissociation, mass transport, and attachment to the edge of a growing domain. We thereby analyze graphene growth dynamics at different length scales and reveal that the rate-limiting step varies throughout the process and across different regions of the catalyst surface, including different facets of an individual graphene domain.

Twin-mediated crystal growth: an enigma resolved.

During crystal growth, faceted interfaces may be perturbed by defects, leading to a rich variety of polycrystalline growth forms. One such defect is the coherent Σ3 {111} twin boundary, which is widely known to catalyze crystal growth. These defects have a profound effect on the properties of many materials: for example, electron-hole recombination rates strongly depend on the character of the twin boundaries in polycrystalline Si photovoltaic cells.

Integrated approach to the data processing of four-dimensional datasets from phase-contrast x-ray tomography.

Phase contrast X-ray tomography (PCT) enables the study of systems consisting of elements with similar atomic numbers. Processing datasets acquired using PCT is nontrivial because of the low-pass characteristics of the commonly used single-image phase retrieval algorithm. In this study, we introduce an image processing methodology that simultaneously utilizes both phase and attenuation components of an image obtained at a single detector distance.

Twin plane re-entrant mechanism for catalytic nanowire growth.

A twin-plane based nanowire growth mechanism is established using Au catalyzed Ge nanowire growth as a model system. Video-rate lattice-resolved environmental transmission electron microscopy shows a convex, V-shaped liquid catalyst-nanowire growth interface for a ⟨112⟩ growth direction that is composed of two Ge {111} planes that meet at a twin boundary. Unlike bulk crystals, the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center.