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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Evaluation of Zn-rich coatings for IMC reaction control in aluminum-magnesium dissimilar welds

Highlights: • Thermodynamic and diffusion simulations have estimated the Zn conc. required to change the IMC reaction in Al-Mg dissimilar welding. • The selected coating alloy was effective in changing the Al-Mg reaction path by forming τ-(Al,Zn){sub 49}Mg{sub 32} as a substitute for β-Al{sub 3}Mg{sub 2}. • Refill™ friction stir spot welds produced with the coating alloy exhibited a thinner reaction layer and an increase in lap shear strength. - Abstract: The dissimilar welding of Al to Mg is very challenging owing to the rapid formation of an intermetallic (IMC) reaction layer at the joint interface, typically comprised of the binary phases γ-Al{sub 12}Mg{sub 17} and β-Al{sub 3}Mg{sub 2}. A potential metallurgical solution has been explored that aimed to change the reaction path by using Al-Zn alloy coatings to promote alternative IMCs with a slower growth rate. To determine the optimum composition for the coating, combined CALPHAD thermodynamic calculations and diffusion simulations were used to estimate the minimum Zn concentration (20 at.%) required to suppress the formation of the faster growing Al{sub 3}Mg{sub 2} phase. This prediction was verified by both static diffusion and Refill™ friction stir spot welding (FSSW) experiments. In each case the selected coating alloy was effective in changing the Al-Mg reaction path by forming the τ-(Al,Zn){sub 49}Mg{sub 32} phase as a substitute for β-Al{sub 3}Mg{sub 2}. However, in static heat treatments there was no reduction in the IMC reaction layer thickness due to the new phase having similar growth kinetics to the β-Al{sub 3}Mg{sub 2} phase it replaced. Nevertheless, Refill™ friction stir spot welds prepared with the new AL-Zn coating alloy exhibited a thinner reaction layer and an increase in lap shear strength. This benefit was attributed to the Zn addition reducing the joint interface liquation temperature, which resulted in a lower peak weld temperature and less IMC reaction; although an increase in local eutectic melting limited the improvement observed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Site-specific spectroscopic measurement of spin and charge in (LuFeO3)m/(LuFe2O4)1 multiferroic superlattices

Abstract Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO 3 ) m /(LuFe 2 O 4 ) 1 superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe 2+ → Fe 3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe 2 O 4 layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.

36 MATERIALS SCIENCE↗
DOE OSTI2019

SnO 2 -Catalyzed Oxidation in High-Efficiency CdTe Solar Cells

Interfaces at the front of superstrate CdTe-based solar cells are critical to carrier transport, recombination, and device performance, yet determination of the chemical structure of these nanoscale regions has remained elusive. This is partly due to changes that occur at the front interfaces during high temperature growth and substantive changes occurring during postdeposition processing. In addition, these buried interfaces are extremely difficult to access in a way that preserves chemical information. In this work, we use a recently developed thermomechanical cleaving technique paired with X-ray photoelectron spectroscopy to probe oxidation states at the SnO 2 interface of CdTe solar cells. We show that the tin oxide front electrode promotes the formation of nanometer-scale oxides of tellurium and sulfur. Most oxidation occurs during CdCl 2 /O 2 activation. Surprisingly, we show that relatively low-temperature anneals (180-260 degrees C) used to diffuse and activate copper acceptors in a doping/back contact process also cause significant changes in oxidation at the front of the cell, providing a heretofore missing aspect of how back contact processes can modify device transport, recombination, and performance. Device performance is shown to correlate with the extent of tellurium and sulfur oxidation within this nanometer-scale region. Mechanisms responsible for these beneficial effects are proposed.

14 SOLAR ENERGY↗
DOE OSTI2017

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplay of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Interleukin-13-induced MUC5AC expression is regulated by a PI3K–NFAT3 pathway in mouse tracheal epithelial cells

Highlights: • IL-13 specifically induced NFAT3 activation in mouse tracheal epithelial cells. • CsA and LY294002 significantly blocked IL-13-induced MUC5AC production. • The PI3K–NFAT3 pathway is positively involved in IL-13-induced MUC5AC production. - Abstract: Interleukin-13 (IL-13) plays a critical role in asthma mucus overproduction, while the mechanisms underlying this process are not fully elucidated. Previous studies showed that nuclear factor of activated T cells (NFAT) is involved in the pathogenesis of asthma, but whether it can directly regulate IL-13-induced mucus (particularly MUC5AC) production is still not clear. Here we showed that IL-13 specifically induced NFAT3 activation through promoting its dephosphorylation in air–liquid interface (ALI) cultures of mouse tracheal epithelial cells (mTECs). Furthermore, both Cyclosporin A (CsA, a specific NFAT inhibitor) and LY294002 (a Phosphoinositide 3-kinase (PI3K) inhibitor) significantly blocked IL-13-induced MUC5AC mRNA and protein production through the inhibition of NFAT3 activity. We also confirmed that CsA could not influence the forkhead Box A2 (Foxa2) and mouse calcium dependent chloride channel 3 (mClca3) expression in IL-13-induced MUC5AC production, which both are known to be important in IL-13-stimulated mucus expression. Our study is the first to demonstrate that the PI3K–NFAT3 pathway is positively involved in IL-13-induced mucus production, and provided novel insights into the molecular mechanism of asthma mucus hypersecretion.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Atomistic to continuum modeling of solidification microstructures

We summarize recent advances in modeling of solidification microstructures using computational methods that bridge atomistic to continuum scales. We first discuss progress in atomistic modeling of equilibrium and non-equilibrium solid–liquid interface properties influencing microstructure formation, as well as interface coalescence phenomena influencing the late stages of solidification. The latter is relevant in the context of hot tearing reviewed in the article by M. Rappaz in this issue. We then discuss progress to model microstructures on a continuum scale using phase-field methods. We focus on selected examples in which modeling of 3D cellular and dendritic microstructures has been directly linked to experimental observations. Finally, we discuss a recently introduced coarse-grained dendritic needle network approach to simulate the formation of well-developed dendritic microstructures. The approach reliably bridges the well-separated scales traditionally simulated by phase-field and grain structure models, hence opening new avenues for quantitative modeling of complex intra- and inter-grain dynamical interactions on a grain scale.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tailoring MgZnO/CdSeTe Interfaces for Photovoltaics

Mg x Zn 1-x O (MZO) shows great promise to replace CdS as a buffer layer in CdTe-based solar cells. It is more transparent, and the MZO bandgap and electron density can be tuned, thus providing flexibility in controlling the conduction band offsets and recombination rates between transparent conductive oxide/MZO and MZO/CdSeTe interfaces. Integrating this material into solar cell devices has been frustrated by the common observation of abnormal current-voltage curves. Simulations indicate that this anomalous behavior can be attributed to front interface barrier effects. Experiments demonstrate that this common MZO interface problem can be resolved experimentally by surface preparation, preheat steps, and removing oxygen during absorber deposition and CdCl 2 treatment. Oxygen during the cell fabrication process is likely to alter MZO properties and MZO/CdSeTe band alignment. After addressing these interface issues and modest optimization, devices with high short-circuit density of 29 mA/cm 2 and efficiency above 16% are demonstrated.

14 SOLAR ENERGY↗
DOE OSTI2016

The C 1s core level spectroscopy of carbon atoms at the surface SiC/Si(111)-4° layer and Cs/SiC/Si(111)-4° interface

Photoemission studies of the electronic structure of the Cs/nano-SiC/Si(111)-4° nanointerface are for the first time carried out with the use of synchrotron radiation in the photon energy range 120–450 eV. The in situ experiments are conducted in the case of submonolayer Cs coating of the surface of an epitaxial SiC layer grown on the vicinal surface Si(111)-4° by a new method of substrate-atom substitution. Modification of the valence-band spectra and the C 1s and Si 2p core levels is studied. The appearance of Cs-induced surface states, with binding energies of 1.2 and 7.4 eV, and a sharp change in the spectrum of the C 1s core level with the appearance of two additional modes are found. The evolution of the spectra shows that the Cs/nano-SiC/Si(111)-4° interface is formed due to charge transfer from Cs adatoms to surface atoms at terraces and steps of the vicinal surface. It is found that the structure of the C layer is nontrivial and involves energetically different carbon states.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Autonomic Materials for Smarter, Safer, Longer-Lasting Batteries (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum)

"Autonomic Materials for Smarter, Safer, Longer-Lasting Batteries" was submitted by the Center for Electrochemical Energy Science (CEES) to the "Life at the Frontiers of Energy Research" video contest at the 2011 Science for Our Nation's Energy Future: Energy Frontier Research Centers (EFRCs) Summit and Forum. Twenty-six EFRCs created short videos to highlight their mission and their work. CEES, an EFRC directed by Michael Thackery at Argonne National Laboratory is a partnership of scientists from four institutions: ANL (lead), Northwestern University, Purdue University, and the University of Illinois at Urbana-Champaign. The Office of Basic Energy Sciences in the U.S. Department of Energy's Office of Science established the 46 Energy Frontier Research Centers (EFRCs) in 2009. These collaboratively-organized centers conduct fundamental research focused on 'grand challenges' and use-inspired 'basic research needs' recently identified in major strategic planning efforts by the scientific community. The overall purpose is to accelerate scientific progress toward meeting the nation's critical energy challenges. The mission of the Center for Electrochemical Energy Science (CEES) is "to create a robust fundamental understanding of the phenomena that control the reactivity of electrified oxide interfaces, films and materials relevant to lithium-ion battery chemistries". Research topics are: electrical energy storage, batteries, battery electrodes, electrolytes, adaptive materials, interfacial characterization, matter by design; novel materials synthesis, charge transport, and defect tolerant materials.

25 ENERGY STORAGE↗
DOE OSTI2012

Performance improvement of P3HT/TiO{sub 2} coaxial heterojunction polymer solar cells by introducing a CdS interface modifier

Coaxial heterojunction polymer solar cells consisting of vertical aligned crystalline TiO{sub 2} nanotube arrays transferred onto FTO-coated glass and ordered interpenetrating poly(3-hexylthiophene-2,5-diyl) (P3HT) have been fabricated through interface sensitization of CdS quantum dots on TiO{sub 2} nanotube walls. The performances of structurally identical polymer solar cells with and without CdS quantum dots sensitization were investigated and compared. The sensitized P3HT/CdS-TiO{sub 2} cell demonstrated an open-circuit photovoltage of 0.72 V and a short-circuit current of 8.29 mA/cm{sup 2} while the P3HT/TiO{sub 2} cell was 0.41 V and 5.64 mA/cm{sup 2}. The efficiency of this sensitized cell represents a more than four-fold improvement compared to the non-sensitized cell. By probing the charge transport characteristics at interfaces and the mechanism of photoelectric conversion, it is found the moderately interfacial CdS QDs plays the role of assisting charge separation and suppression of back recombination at interfaces, which accounts for the observed enhanced J{sub sc} and V{sub oc} in photovoltaic performance. - Graphical abstract: Schematic illustration of the Au/P3HT/CdS-TiO{sub 2}/FTO coaxial heterojunction polymer solar cell and its photovoltaic property compared with Au/P3HT/TiO{sub 2}/FTO cell. Highlights: Black-Right-Pointing-Pointer CdS QDs sensitized P3HT/TiO{sub 2} solid coaxial heterojunction solar cells are fabricated. Black-Right-Pointing-Pointer The V{sub oc} of such sensitized polymer solar cell reaches the value as high as 0.72 V. Black-Right-Pointing-Pointer 4.5 times higher PCE obtains as compared with the non-sensitized cell. Black-Right-Pointing-Pointer The dominate roles of CdS QDs sensitization on the PCE enhancement are investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Solvation Environment and Interface Dynamics of Li 2 B 12 H 12 and Li 2 B 12 F 12 Electrolytes Uncovered by Theory and Operando Optical and FTIR Spectroelectrochemistry

In this work, we evaluated two closo-borate salts (Li 2 B 12 H 12 and Li 2 B 12 F 12 ) in propylene carbonate from theoretical and experimental perspectives to understand how the coordination environment influences their spectroscopic and electrochemical properties. The coordination environments of the closo-borate salts were modeled via density functional theory (DFT) and molecular dynamics (MD). Vibrational spectra calculated from the predicted coordination environments are in agreement with experimentally measured steady-state FTIR data. This theoretical investigation also suggested that Li 2 B 12 F 12 would possess a higher ionic conductivity than Li 2 B 12 H 12 , which was corroborated experimentally. Additionally, an electrochemical cell was designed and fabricated that enabled operando optical and FTIR spectroelectrochemical (OP-IR-SEC) measurements. This allowed for the simultaneous measurement of the relative changes of species at a lithium electrode-liquid electrolyte interface and the visualization of lithium plating at the electrode surface. This technique could provide new chemical insights and potentially link optical changes at the electrode–electrolyte interface to specific chemical species in similar electrochemical systems. The Li 2 B 12 F 12 electrolyte was found to have a higher thermal stability, which may find utility in applications for batteries that are subject to high-temperature conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Numerical simulation of seawater intrusion to coastal aquifers and brine water/freshwater interaction in south coast of Laizhou Bay, China

Seawater intrusion and brine water/freshwater interaction have significantly affected agriculture, industry and public water supply at Laizhou Bay, Shandong Province, China. A two-dimensional SEAWAT model is developed to simulate the seawater intrusion to coastal aquifers and brine water/fresh water interaction in the south of Laizhou Bay. This model is applied to predict the seawater intrusion and brine water/freshwater interface development in the coming years. The model profile is perpendicular to the coastal line with two interfaces, freshwater-saline water interface near the shore and inland brine water-saline water-seawater interface. The hydrogeological parameters in the SEAWAT-2000 model are calibrated by the head and salinity measurements. The precipitation infiltration coefficient, boundary conditions and thicknesses of aquifers are studied in a sensitivity analysis. The predicted results indicate that equivalent freshwater head in shallow freshwater-saline water area will decline 2.0 m by the end of the forecasting period, caused by groundwater over-pumping for farmland irrigation. The groundwater head in the brine-saline water area will also decrease about 1.8 m by the end of forecasting period, caused by excessive brine mining. Salinity decreases below 105 g/L in the brine area, but increases in other areas and contaminates fresh groundwater resources.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Structural and subband changes at the LaAlO{sub 3}/SrTiO{sub 3} interface investigated by two-dimensional correlation spectroscopy

The interplay among many ground states in correlated electron materials, especially at the LaAlO{sub 3}/SrTiO{sub 3} interface is central in deeply understanding the physical characteristics and improving further applications of these materials. Here, we use two-dimensional infrared correlation spectroscopy to study the influence of magnetic fields and temperature on the mid-infrared spectral responsivity of the interface. The magnetic field plays the main role at temperatures below the transition temperature, T{sub C}. Two additional spectral peaks were identified at wavelengths of 2800 nm and 3400 nm, when compared with our prior studies. All of these response bands are related to the spin-orbit coupling effect and crystal structure changes. Detailed structural and subband changes in the interface are also investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Silicon Nanomembranes with Hybrid Crystal Orientations and Strain States

Methods to integrate different crystal orientations, strain states, and compositions of semiconductors in planar and preferably flexible configurations may enable nontraditional sensing-, stimulating-, or communication-device applications. Here, we combine crystalline-silicon nanomembranes, patterning, membrane transfer, and epitaxial growth to demonstrate planar arrays of different orientations and strain states of Si in a single membrane, which is then readily transferable to other substrates, including flexible supports. As examples, regions of Si(001) and Si(110) or strained Si(110) are combined to form a multicomponent, single substrate with high-quality narrow interfaces. We perform extensive structural characterization of all interfaces and measure charge-carrier mobilities in different regions of a 2D quilt. The method is readily extendable to include varying compositions or different classes of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Metastable fcc-Fe film epitaxially grown on Cu(100) single-crystal underlayer

Fe film of 40 nm thickness is prepared on fcc-Cu(100) single-crystal underlayer at room temperature by ultra-high vacuum molecular beam epitaxy. The film growth and the detailed structure are investigated by reflection high-energy electron diffraction, cross-sectional high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). An Fe single-crystal with metastable fcc structure nucleates on the underlayer. The HR-TEM shows that fcc lattice is formed from the Fe/Cu interface up to the film surface. A large number of misfit dislocations are introduced around the Fe/Cu interface due to an accommodation of lattice mismatch. Dislocations exist up to the film near surface. The lattice constant is estimated by XRD to be a = 0.3607 nm. The film shows a ferromagnetic property, which reflects the property of fcc-Fe crystal with high-spin ferromagnetic state.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ionic charging by local imbalance at interfaces in hybrid lead halide perovskites

Identification of specific operating mechanisms becomes particularly challenging when mixed ionic-electronic conductors are used in optoelectronic devices. Ionic effects in perovskite solar cells are believed to distort operation curves and possess serious doubts about their long term stability. Current hysteresis and switchable photovoltaic characteristics have been connected to the kinetics of ion migration. However, the nature of the specific ionic mechanism (or mechanisms) able to explain the operation distortions is still poorly understood. It is observed here that the local rearrangement of ions at the electrode interfaces gives rise to commonly observed capacitive effects. Charging transients in response to step voltage stimuli using thick CH{sub 3}NH{sub 3}PbI{sub 3} samples show two main polarization processes and reveal the structure of the ionic double-layer at the interface with the non-reacting contacts. It is observed that ionic charging, with a typical response time of 10 s, is a local effect confined in the vicinity of the electrode, which entails absence of net mobile ionic concentration (space-charge) in the material bulk.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Unveiling interfaces between In-rich and Ga-rich GaInP vertical slabs of laterally composition modulated structures

Here, we report changes at the interface between Ga-rich/In-rich GaInP vertical slabs in laterally composition modulated (LCM) GaInP as a function of the V/III ratio. The photoluminescence exhibits satellite peaks, indicating that the parasitic potential between the GaInP vertical slabs disappears as the V/III ratio decreases. However, a high V/III ratio leads to an abrupt interface, increasing the parasitic potential because of the phosphorus-amount-dependent diffusion of group-III atoms during growth. These results suggest that the V/III ratio is an important parameter that must be wisely chosen in designing optoelectronic devices incorporating LCM structure.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Two Independent Histidines One in Human Prolactin and One in Its Receptor Are Critical for pH-dependent Receptor Recognition and Activation

Human prolactin (hPRL), a member of the family of hematopoietic cytokines, functions as both an endocrine hormone and autocrine/paracrine growth factor. We have previously demonstrated that recognition of the hPRL-receptor depends strongly on solution acidity over the physiologic range from pH 6 to pH 8. The hPRL-receptor binding interface contains four histidines whose protonation is hypothesized to regulate pH-dependent receptor recognition. Here, we systematically dissect its molecular origin by characterizing the consequences of His to Ala mutations on pH-dependent receptor binding kinetics, site-specific histidine protonation, and high resolution structures of the intermolecular interface. Thermodynamic modeling of the pH dependence to receptor binding affinity reveals large changes in site-specific protonation constants for a majority of interface histidines upon complexation. Removal of individual His imidazoles reduces these perturbations in protonation constants, which is most likely explained by the introduction of solvent-filled, buried cavities in the crystallographic structures without inducing significant conformational rearrangements.

59 BASIC BIOLOGICAL SCIENCES↗