Search

Abstract: Interfaces and the movement of atoms within an interface play a crucial role in determining the processing and properties of virtually all materials. However, the nature of interfaces in solids is highly complex and it has been an ongoing challenge to link material performance with the internal interface structure and related atomic transport mechanisms. Interface complexions offer a missing link to help solve this universal problem. We have theoretically predicted the existence of multiple interface complexions by thermodynamics, but the present work represents the most comprehensive characterization and proof of their existence in a real material system. An interface complexion can be considered as a separate phase, which can be made to transform into different complexions (phases) with vastly different properties by chemistry and heat treatment, thereby enabling the engineering control of material properties on a level not previously realizable. As such, complexions offer a solution to outstanding fundamental scientific mysteries, such as the origin of abnormal grain growth in inorganic materials, a problem which leading researchers in the field have struggled to explain for the past 50 years. It is also described how interface complexions will likely have widespread impact across all branches of material science and related disciplines. [Copyright &y& Elsevier]

Abstract: A diffuse-interface model for interfaces in multi-component systems with energetic contributions from chemistry, defects, structure, orientation, electrostatics and gradients is proposed. The energy minimizing profiles of planar grain boundaries in the pseudo-binary SiO2–SiN4/3 system are calculated in the SiN4/3-rich single-phase field. Intergranular films are found to be stable below the eutectic temperature. Evidence of first-order grain boundary order–disorder transitions is found in misorientation and chemical potential space. Interface transitions predicted with the model can be plotted on equilibrium phase diagrams to produce “interfacial phase diagrams.” These could be a tool for designing processing routes to optimize bulk, polycrystalline material properties through control of grain boundary characteristics. [Copyright &y& Elsevier]

We propose a theoretical framework to derive thermodynamically consistent equilibrium equations and kinetic driving forces to describe the time evolution for electrically and magnetically active materials. This procedure starts from the combined statement of the first and second laws of thermodynamics, naturally incorporates Maxwell’s equations, and accommodates the description of continuous phase transformations for conserved and non-conserved order parameters. The kinetics of conserved and non-conserved ordered parameters are introduced, the adequate gradient flow is identified, thus the appropriate kinetics (e.g., Allen–Cahn, Cahn–Hilliard) are derived. Example applications of this theory include the electromechanical fields of piezoelectric materials and the wave equation in the limit of chemically homogeneous solids. Moreover, we derive a thermodynamically consistent set of partial differential equations which describe the transport of charged species in conductive, non-polarizable, magnetizable solids, and in polarizable, electrically insulating, non-magnetizable solids. [Copyright &y& Elsevier]

A stability analysis of phase separation of charged species by spinodal decomposition is presented. The charge effects introduce a short wave number cutoff for linear perturbations about the homogeneous, neutral solution. Phase field calculations using a semi-implicit spectral method support this conclusion. This suggests that coarsening is limited in ionic solid systems that are unstable with respect to charged-phase separation. [Copyright &y& Elsevier]

Dewetting is a well-known degradation mechanism for thin films at elevated temperatures. It is driven by surface energy minimization and occurs while the film is solid. The dewetting process is characterized by the formation of holes, retracting edges, and the formation of thickened rims on retracting edges. In anisotropic single-crystal thin films, holes are initially faceted. It is often observed that the corners of the holes retract faster than the edges of the hole, leading to dendritic or star-shaped holes. This so-called "corner instability" is one of the defining morphological characteristics of the dewetting process, and an understanding of this instability may lead to new film patterning techniques. In this work, we present a study of the growth of natural and patterned initially square holes in single-crystal Ni thin films on MgO substrates. A characteristic structure near the corners of the holes was observed, and a model for the growth of faceted holes was developed based on these observations. Despite its simplicity, the model reproduces the observed phenomenology and is in quantitative agreement with experiments. The model reveals that the corner instability arises from a redistribution of mass to create a new hole perimeter, which can only be created at the corner. The consequence is that the corner reaches a steady-state constant retraction rate while mass accumulation at the rims causes their retraction rate to continuously decrease. [ABSTRACT FROM AUTHOR]

[Display omitted] The infiltration of a non-wetting liquid, such as molten metal, into a porous solid, such as a ceramic preform, is influenced by the wetting angle of the liquid on the solid. The link between local wetting and the minimum pressure required for initiation of infiltration or the pressure required for full preform infiltration can deviate strongly from what one would expect on the basis of elementary thermodynamic considerations or simple geometrical models. In this work, we explain the trends observed in experimental studies of pressure infiltration of molten metal into ceramic preforms by means of a percolation model, in which the pores themselves are given a simple geometric shape. This gives a simple yet rich and realistic treatment of the infiltration process. Specifically, the pop-through pressure necessary to traverse a throat between two neighboring circular (2D) or spherical (3D) pores can easily be calculated and incorporated in a 3D network model of many pores produced by generating a packing of slightly overlapping circles or spheres. The resulting pore structure defines a bond percolation network that agrees overall both with predictions of percolation theory and observations from experiment, and which can be extended to address a range of other aspects of multi-phase flow through porous media. [ABSTRACT FROM AUTHOR]

The theoretical reflectance spectrum of a one-dimensional photonic crystal with large amounts of interfacial roughness has been calculated using a previously proposed method, and compared to the actual experimental reflectivity of the structure. The photonic crystal was fabricated using a simple and fast method involving the holographic exposure of a liquid crystal/photosensitive prepolymer syrup via the self-interference patterns from two laser beams. The calculated reflectance spectrum for this structure matched the experimental one extremely well, giving very similar reflectivity peak positions and intensities. Slight discrepancies between the two reflectance spectra are attributed to either small variations in the microstructure of the reflection grating beyond that which is captured in the transmission electron micrograph, or the dispersion of the polymer which was not taken into account. These results serve as experimental verification of the theory for rough photonic crystals reported previously. [ABSTRACT FROM AUTHOR]

Li deposition is observed and measured on a solid electrolyte in the vicinity of a metallic current collector. Four types of ion-conducting, inorganic solid electrolytes are tested: Amorphous 70/30 mol% Li2S-P2S5, polycrystalline β-Li3PS4, and polycrystalline and single-crystalline Li6La3ZrTaO12 garnet. The nature of lithium plating depends on the proximity of the current collector to defects such as surface cracks and on the current density. Lithium plating penetrates/infiltrates at defects, but only above a critical current density. Eventually, infiltration results in a short circuit between the current collector and the Li-source (anode). These results do not depend on the electrolytes shear modulus and are thus not consistent with the Monroe-Newman model for 'dendrites.' The observations suggest that Li-plating in pre-existing flaws produces crack-tip stresses which drive crack propagation, and an electrochemomechanical model of plating-induced Li infiltration is proposed. Lithium short-circuits through solid electrolytes occurs through a fundamentally different process than through liquid electrolytes. The onset of Li infiltration depends on solid-state electrolyte surface morphology, in particular the defect size and density. [ABSTRACT FROM AUTHOR]

Ga-catalyzed growth of GaAs nanowires on Si is a candidate process for achieving seamless III/V integration on IV. In this framework, the nature of silicon's surface oxide is known to have a strong influence on nanowire growth and orientation and therefore important for GaAs nanowire technologies. We show that the chemistry and morphology of the silicon oxide film controls liquid Ga nucleation position and shape; these determine GaAs nanowire growth morphology. We calculate the energies of formation of Ga droplets as a function of their volume and the oxide composition in several nucleation configurations. The lowest energy Ga droplet shapes are then correlated to the orientation of nanowires with respect to the substrate. This work provides the understanding and the tools to control nanowire morphology in self-assembly and pattern growth. [ABSTRACT FROM AUTHOR]

Flowable suspensions that conduct both electrons and ions can enable the use of energy-dense electroactive species in flow batteries [M. Duduta et al., Adv. Energy Mater. , 1 , 511 (2011); Z. Li et al., Phys. Chem. Chem. Phys. , 15 , 15,833 (2013); F. Fan et al., Nano Lett. , 14 , 2210 (2014)]. In comparison with conventional flow batteries where electrochemical reactions are confined to a fixed current-collector region, electronically conductive flow electrodes permit electrochemical reactions to extend outside of the physical confines of the stack. We have measured and modeled how mixed-conduction enables an electroactive zone (EAZ, in which electrochemical reactions occur) that is of greater spatial extent than current collectors, the extension being termed side zone, SZ. Electrochemical reactions in SZs can reduce coulombic and energetic efficiency. Here we show that for realistic suspension properties and operating conditions, the added inefficiency is small in practice, and can be further mitigated by using appropriate operating conditions and/or materials choices. For the specific example of a non-aqueous Li 4 Ti 5 O 12 suspension, we show that EAZ extension contributes less than 1% additional efficiency loss at C/10 rates for current collectors greater than 20 mm long. [ABSTRACT FROM AUTHOR]

Abstract: A Li4Ti5O12–Li0.29La0.57TiO3–Ag electrode composite was fabricated via sintering the corresponding powder mixture. The process achieved a final relative density of 97% the theoretical. Relatively thick, ∼100μm, electrodes were fabricated to enhance the energy density relatively to the traditional solid-state thin film battery electrodes. The sintered electrode composite delivered full capacity in the first discharge at C/40 discharge rate. Full capacity utilization resulted from the 3D percolated network of both solid electrolyte and metal, which provide paths for ionic and electronic transport, respectively. The electrodes retained 85% of the theoretical capacity after 10 cycles at C/40 discharge rate. The tensile strength and the Young''s modulus of the sintered electrode composite are the highest reported values to date, and are at least an order of magnitude higher than the corresponding value of traditional tapecast “composite electrodes”. The results demonstrate the concept of utilizing thick all-solid electrodes for high-strength batteries, which might be used as multifunctional structural and energy storage materials. [Copyright &y& Elsevier]

Abstract: Oppositely charged colloidal particles in suspension undergo rapid coagulation in the absence of any repulsive component in the interaction potential. With an added steric component serving as the repulsive force it is possible to order oppositely charged particles, which are also weakly charged, in solution. However given the novel features obtainable for an ordered structure from strong oppositely charged particles it becomes imperative to gain a full understanding of methods that can order these particles. Here we report a simple and rapid layer-by-layer method to order strongly and oppositely charged particles. Although this method is in principle scalable to order multiple layers of oppositely charged particles, herein we report ordering of one layer of positively charged particles onto a substrate made of negatively charged particles. This method utilizes a non-ionic surfactant to induce a steric repulsive force between particles and involves spin-coating to disperse and order particles on a very short time scale. The ordered structure obtained through this process is verified as the structure with one of the lowest interaction energies. [Copyright &y& Elsevier]

Fragmentation of substance abuse treatment represents a major barrier to effective treatment for individuals with cooccurring substance abuse and mental and physical health disorders. Linkages of substance abuse treatment organizations with primary care and mental health agencies are widely considered to be a feasible way to integrate services. In this study, we analyzed information collected from a national sample of 62 outpatient substance abuse treatment units (OSATs) to understand the extent of services linkages in these organizations and to identify facilitators and barriers to service linkages. Results showed that OSATs had limited service linkages with primary care and mental health providers. The cited barriers to linkages included clients' financial problems, managed care restrictions, and limited organizational capacity. Onsite service provision was implemented in some OSATs. The pattern of service linkages in OSATs appeared to reflect the health needs of substance abuse clients. [ABSTRACT FROM AUTHOR]

Nanoparticle assembly is a material synthesis strategy that enables precise control of nanoscale structural features. Concepts from traditional crystal growth research have been tremendously useful in predicting and programming the unit cell symmetries of these assemblies, as their thermodynamically favored structures are often identical to atomic crystal analogues. However, these analogies have not yielded similar levels of influence in programming crystallite shapes, which are a consequence of both the thermodynamics and kinetics of crystal growth. Here, we demonstrate kinetic control of the colloidal crystal shape using nanoparticle building blocks that rapidly assemble over a broad range of concentrations, thereby producing well-defined crystal habits with symmetrically oriented dendritic protrusions and providing insight into the crystals' morphological evolution. Counterintuitively, these nonequilibrium crystal shapes actually become more common for colloidal crystals synthesized closer to equilibrium growth conditions. This deviation from typical crystal growth processes observed in atomic or molecular crystals is shown to be a function of the drastically different time scales of atomic and colloidal mass transport. Moreover, the particles are spherical with isotropic ligand grafts, and these kinetic crystal habits are achieved without the need for specifically shaped particle building blocks or external templating or shape-directing agents. Thus, this work provides generalizable design principles to expand the morphological diversity of nanoparticle superlattice crystal habits beyond the anhedral or equilibrium polyhedral shapes synthesized to date. Finally, we use this insight to synthesize crystallite shapes that have never before been observed, demonstrating the ability to both predict and program kinetically controlled superlattice morphologies.

The need for higher energy density rechargeable batteries has generated interest in metallic electrodes paired with solid electrolytes. However, impedance growth at the Li metal-solid electrolyte interface due to void formation during cycling at practical current densities and areal capacities, e.g., greater than 0.5 mA cm -2 and 1.5 mAh cm -2 respectively, remains a significant barrier. Here, we show that introducing a wetting interfacial film of Na-K liquid between the Li metal and the Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 (LLZTO) solid electrolyte permits reversible stripping and plating of up to 150 μm of Li (30 mAh cm -2 ), approximately 10 times the areal capacity of today's lithium-ion batteries, at current densities above 0.5 mA cm -2 and stack pressures below 75 kPa, all with minimal changes in cell impedance. We further show that this increase in the accessible areal capacity at high stripping current densities is due to the presence of Na-K liquid at the Li stripping interface; this performance improvement is not enabled in the absence of the Na-K liquid. This design approach holds promise for overcoming interfacial stability issues that have heretofore limited the performance of solid-state metal batteries.

The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase-transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase under anchoring-driven planar alignment leads to the assembly of individual nanometer-sized particles into arrays of micrometer-sized agglomerates, whose size and characteristic spacing can be tuned by varying the cooling rate. Phase field simulations coupling the conserved and nonconserved order parameters exhibit a similar evolution of the morphology as the experimental observations. This fully reversible process offers control over structural order on the microscopic level and is an interesting model system for the programmable and reconfigurable patterning of nanocomposites with access to micrometer-sized periodicities.

Single-crystal nanowires are of broad interest for applications in nanotechnology. However, such wires are subject to both the Rayleigh-Plateau instability and an ovulation process that are expected to lead to their break up into particle arrays. Single crystal Ru nanowires were fabricated with axes lying along different crystallographic orientations. Wires bound by equilibrium facets along their length did not break up through either a Rayleigh-Plateau or ovulation process, while wires with other orientations broke up through a combination of both. Mechanistic insight is provided using a level-set simulation that accounts for strongly anisotropic surface energies, providing a framework for design of morphologically stable nanostructures.

Here, we present a two-step annealing procedure to imprint nanofeatures on SiO 2 starting from metallic microfeatures. The first annealing transforms the microfeatures into gold nanoparticles and the second imprints these nanoparticles into the SiO 2 layer with nanometric control. The resulting nanohole arrays show a high ensemble uniformity. As a potential application, the nanohole mask is used as a selective mask for the Ga self-assisted growth of GaAs nanowires (NWs). Thus, for the first time, a successful implementation of nano-self-imprinting that links high-throughput microlithography with bottom-up NW growth is shown. The beneficial hole morphology of the SiO 2 mask promotes high Ga droplet contact angles with the silicon substrate and the formation of single droplets in the mask holes. This droplet predeposition configuration enables a high vertical yield of NWs. Thus, this article describes a new protocol to grow NW devices that combines simultaneously nanosized holes and parallel processing.

Liquid droplets sitting on nanowire (NW) tips constitute the starting point of the vapor-liquid-solid method of NW growth. Shape and volume of the droplet have been linked to a variety of growth phenomena ranging from the modification of growth direction, NW orientation, crystal phase, and even polarity. In this work we focus on numerical and theoretical analysis of the stability of liquid droplets on NW tips, explaining the peculiarity of this condition with respect to the wetting of planar surfaces. We highlight the role of droplet pinning at the tip in engineering the contact angle. Experimental results on the characteristics of In droplets of variable volume sitting on the tips or side facets of InAs NWs are also provided. This work contributes to the fundamental understanding of the nature of droplets contact angle at the tip of NWs and to the improvement of the engineering of such nanostructures.

Diffusion-induced phase transitions typically change the lattice symmetry of the host material. In battery electrodes, for example, Li ions (diffusing species) are inserted between layers in a crystalline electrode material (host). This diffusion induces lattice distortions and defect formations in the electrode. The structural changes to the lattice symmetry affect the host material's properties. Here, we propose a 2D theoretical framework that couples a Cahn-Hilliard (CH) model, which describes the composition field of a diffusing species, with a phase-field crystal (PFC) model, which describes the host-material lattice symmetry. We couple the two continuum models via coordinate transformation coefficients. We introduce the transformation coefficients in the PFC method to describe affine lattice deformations. These transformation coefficients are modeled as functions of the composition field. Using this coupled approach, we explore the effects of coarse-grained lattice symmetry and distortions on a diffusion-induced phase transition process. In this paper, we demonstrate the working of the CH-PFC model through three representative examples: First, we describe base cases with hexagonal and square symmetries for two composition fields. Next, we illustrate how the CH-PFC method interpolates lattice symmetry across a diffuse phase boundary. Finally, we compute a Cahn-Hilliard type of diffusion and model the accompanying changes to lattice symmetry during a phase transition process.

The kinetics of Li2 S electrodeposition onto carbon in lithium-sulfur batteries are characterized. Electrodeposition is found to be dominated by a 2D nucleation and growth process with rate constants that depend strongly on the electrolyte solvent. Nucleation is found to require a greater overpotential than growth, which results in a morphology that is dependent on the discharge rate., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, we present atomistic simulations and theoretical analyses that reveal a capillary instability that is intrinsic to wetting geometries characteristic of the vapor-liquid-solid mechanism for nanowire growth. The analysis establishes a transition between axisymmetric and tilted wetting configurations that occurs when the triple line geometry satisfies Young's force-balance condition. The intrinsic nature of the instability is anticipated to be linked to the phenomenon of nanowire kinking in response to changes in environmental conditions, such that the current results may have broad implications for the design of experimental strategies for controlled growth of crystalline nanowires with complex geometries.

An aqueous Li-ion flow cell using suspension-based flow electrodes based on the LiTi2(PO4)3-LiFePO4 couple is demonstrated. Unlike conventional flow batteries, the semi-solid approach utilizes fluid electrodes that are electronically conductive. A model of simultaneous advection and electrochemical transport is developed and used to separate flow-induced losses from those due to underlying side reactions. The importance of plug flow to achieving high energy efficiency in flow batteries utilizing highly non-Newtonian flow electrodes is emphasized.

We present a phase-field model to study the morphological transitions of surfactant micelles in supersaturated dilute solution. Simulations reveal that multiply connected micellar structure can be produced by interface branching instability of a growing micelle at relatively large supersaturation and intermediate spontaneous curvatures. Two branching mechanisms, i.e., a disk-to-cylinder shape transition and a tip bifurcation process, are identified for disklike and cylindrical micelles, respectively. We propose that dynamic branching at the micelle growth front provides an important kinetic pathway for the formation of branched wormlike micelles that are observed in many surfactant systems.

: Although treatment of co-occurring behavioral and physical health problems could be facilitated by the linkages between health care providers, it is uncertain how such inter-agency linkages are affected by managed care. We used a sample of 167 service linkages to examine the effects of managed care arrangements on inter-agency communication, coordination, and perceived effectiveness. These linkages were identified based on interviews with 62 outpatient substance abuse treatment units in 2000. Results indicate that frequency of communication and inter-agency coordination are positively related to several managed care arrangements and may moderate the relationships between managed care arrangements and perceived effectiveness.