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  1. High-Temperature Ferroelectric Behavior of Al0.7Sc0.3N

    Drury, Daniel ; Yazawa, Keisuke ; Zakutayev, Andriy ; ... - Micromachines
    Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C.more » Polarization–electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high–temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study.« less

  2. “Top-Down” Li Deposition Pathway Enabled by an Asymmetric Design for Li Composite Electrode

    Yue, Xin-Yang ; Li, Xun-Lu ; Bao, Jian ; ... - Advanced Energy Materials
    Designing Li composite electrodes with host frameworks for accommodating Li metal has been considered to be an effective approach to suppress Li dendrites. Herein, an asymmetric design of a Mo net/Li metal film (MLF) composite electrode is developed by an inverted thermal infusion method. The asymmetric MLF electrode has a dense oxide passivated layer on the top side, a porous Mo net matrix on the back side, and active Li layer in between. The back side has a larger specific area and higher electric field than the top side, which contacts with the separator upon cycling, triggering the preferred Limore » deposition and stripping of the porous back side of the electrode far from the separator. The surface passivation layer on the top side of the electrode as an artificial solid electrolyte interphase ensures the stable contact with the electrolyte and separator. Meanwhile, the porous structure of the supporting Mo net provides enough space for accommodating the volume change during Li deposition and stripping. This asymmetry design enables a unique “top down” growth pathway for Li deposition in the MLF electrode, suppressing the dendrite growth effectively. In conclusion, the design strategy provides a new direction for high-energy dendrite-free Li metal anodes.« less

  3. Dissolution Kinetics of Epitaxial Cadmium Carbonate Overgrowths on Dolomite

    La Plante, Erika Callagon ; Lee, Sang Soo ; Eng, Peter J. ; ... - ACS Earth and Space Chemistry
    Thin films grown on mineral surfaces can immobilize toxic metals in natural systems, but the effects of epitaxy and film thickness on dissolution rates of the overgrowth are typically unknown. To explore these effects, otavite (CdCO3) films were grown on dolomite (104) surfaces from aqueous solutions containing [Cd] = [Ca] = [CO3] = 0.2 mM for 1–48 h and then dissolved in deionized water. Films of various thicknesses and strain states were obtained by varying the growth reaction time. Growth for up to 3 h produced strained thin films with Cd coverages of <4.3 ± 0.6 equivalent monolayers (ML) (correspondingmore » to a thickness of up to 17 Å), whereas reaction times of up to 48 h produced thicker films with as many as 114 ± 14 equivalent ML of Cd. Intrinsic dissolution rates were measured as a function of otavite film thickness by a combination of synchrotron X-ray fluorescence, specular X-ray reflectivity, and atomic force microscopy. As a result, the initial dissolution rates for unstrained films were comparable to those reported for synthetic otavite powders, whereas the thinnest films (<3.1 ± 1.1 ML) dissolved at a 50% slower rate, indicating that epitaxial strain effectively enhanced their stability. We discuss potential reasons for this difference.« less

  4. Nanoindentation of high-purity vapor deposited lithium films: The elastic modulus

    Herbert, Erik G. ; Hackney, Stephen A. ; Dudney, Nancy J. ; ... - Journal of Materials Research
    Nanoindentation has been used to measure the elastic modulus of 5 and 18 μm thick high-purity vapor deposited polycrystalline lithium films at 31 °C. Over indentation depths ranging from 150 to 1100 nm, the modulus is found to vary with film thickness from 9.8 GPa ± 11.9% to 8.2 GPa ± 14.5%. These results are well within the range of lithium's orientation dependent elastic modulus, which spans approximately 3.1 to 21.4 GPa. The measured values may also indicate (111) and (100) texture for the 5 and 18 μm thick films, respectively. The potential effects of pileup and surface contamination aremore » found to be negligible if any at all. Small but discernible changes in damping capability near the free surface may provide insight into the subsurface defect structure and the potential for localized heating. In conclusion, numerous experimental challenges are addressed and key metrics are used to validate the measured elastic modulus.« less

  5. Pore-scale water dynamics during drying and the impacts of structure and surface wettability

    Cruz, Brian C. ; Furrer, Jessica M. ; Guo, Yi-Syuan ; ... - Water Resources Research
    Plants and microbes secrete mucilage into soil during dry conditions, which can alter soil structure and increase contact angle. Structured soils exhibit a broad pore size distribution with many small and many large pores, and strong capillary forces in narrow pores can retain moisture in soil aggregates. Meanwhile, contact angle determines the water repellency of soils, which can result in suppressed evaporation rates. Although they are often studied independently, both structure and contact angle influence water movement, distribution, and retention in soils. Here drying experiments were conducted using soil micromodels patterned to emulate different aggregation states of a sandy loammore » soil. Micromodels were treated to exhibit contact angles representative of those in bulk soil (8.4° ± 1.9°) and the rhizosphere (65° ± 9.2°). Drying was simulated using a lattice Boltzmann single-component, multiphase model. In our experiments, micromodels with higher contact angle surfaces took 4 times longer to completely dry versus micromodels with lower contact angle surfaces. Microstructure influenced drying rate as a function of saturation and controlled the spatial distribution of moisture within micromodels. In conclusion, lattice Boltzmann simulations accurately predicted pore-scale moisture retention patterns within micromodels with different structures and contact angles.« less

  6. Tribology behavior on scratch tests: Effects of yield strength

    Feng, Biao - Friction
    In this paper, a three-dimensional (3D) scratch model is proposed to investigate the effects of yield strength of both coatings and substrates. With the help of combined Coulomb and plastic friction, the obtained results comprehensively interpret the experimental phenomena in most metals that with the growth of hardness after heat treatment the scratch friction coefficient (SFC) increases. This interpretation could not be done before. Scratch tests on the surface with or without the coating are discussed. Without the coating the SFC increases due to the decrease of the area with plastic slippage and/or the increase of friction stress during themore » increase of the yield strength in the material. With a softer substrate the friction stress decreases but the SFC increases, which is caused by the growth of the entire contact area and surface deformation. Conversely, with a stronger substrate the SFC decreases due to an intensified plastic slippage In conclusion, the obtained results pave a new way to understanding the effects of yield strength on scratch tests, interpret experimental phenomena, and should be helpful for an optimum design in experiments.« less

  7. Planetarium Show on Dark Matter

    Barnett, R. Michael - Nuclear and Particle Physics Proceedings
    We describe a new planetarium show about Dark Matter entitled “Phantom of the Universe”. When completed in late 2014, it will feature the exciting story of dark matter, from the Big Bang to its anticipated discovery at the Large Hadron Collider.

  8. Indentation-derived elastic modulus of multilayer thin films: Effect of unloading induced plasticity

    Jamison, Ryan Dale ; Shen, Yu -Lin - Journal of Materials Research
    Nanoindentation is useful for evaluating the mechanical properties, such as elastic modulus, of multilayer thin film materials. A fundamental assumption in the derivation of the elastic modulus from nanoindentation is that the unloading process is purely elastic. In this work, the validity of elastic assumption as it applies to multilayer thin films is studied using the finite element method. The elastic modulus and hardness from the model system are compared to experimental results to show validity of the model. Plastic strain is shown to increase in the multilayer system during the unloading process. Additionally, the indentation-derived modulus of a monolayermore » material shows no dependence on unloading plasticity while the modulus of the multilayer system is dependent on unloading-induced plasticity. Lastly, the cyclic behavior of the multilayer thin film is studied in relation to the influence of unloading-induced plasticity. Furthermore, it is found that several cycles are required to minimize unloading-induced plasticity.« less

  9. Thin liquid films in improved oil recovery from low-salinity brine

    Myint, Philip C. ; Firoozabadi, Abbas - Current Opinion in Colloid & Interface Science
    Low-salinity waterflooding is a relatively new method for improved oil recovery that has generated much interest. It is generally believed that low-salinity brine alters the wettability of oil reservoir rocks towards a wetting state that is optimal for recovery. The mechanism(s) by which the wettability alteration occurs is currently an unsettled issue. This study reviews recent studies on wettability alteration mechanisms that affect the interactions between the brine/oil and brine/rock interfaces of thin brine films that wet the surface of reservoir rocks. Of these mechanisms, we pay particular attention to double-layer expansion, which is closely tied to an increase inmore » the thickness and stability of the thin brine films. Our review examines studies on both sandstones and carbonate rocks. We conclude that the thin-brine-film mechanisms provide a good qualitative, though incomplete, picture of this very complicated problem. Finally, we give suggestions for future studies that may help provide a more quantitative and complete understanding of low-salinity waterflooding.« less

  10. Bayesian inference of substrate properties from film behavior

    Aggarwal, R. ; Demkowicz, M. J. ; Marzouk, Y. M. - Modelling and Simulation in Materials Science and Engineering
    We demonstrate that by observing the behavior of a film deposited on a substrate, certain features of the substrate may be inferred with quantified uncertainty using Bayesian methods. We carry out this demonstration on an illustrative film/substrate model where the substrate is a Gaussian random field and the film is a two-component mixture that obeys the Cahn–Hilliard equation. We construct a stochastic reduced order model to describe the film/substrate interaction and use it to infer substrate properties from film behavior. This quantitative inference strategy may be adapted to other film/substrate systems.
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