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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Se diffusion in CdTe thin films for photovoltaics

Manipulating CdSeTe bandgrading to enhance photocurrent and carrier lifetime is an essential part of high-performance CdTe photovoltaics (PVs). Here, we examine Se diffusion kinetics in single-crystal and polycrystalline CdTe during deposition, thermal annealing, and CdCl 2 treatments. Se distributions are determined by dynamic secondary-ion-mass spectroscopy and Auger electron spectroscopy depth profiling and coupled with electron backscatter diffraction images of the crystalline structure. Effective bulk and grain boundary diffusion coefficients are determined by analytical models and discussed in the context of processing and film morphology. Se is found to diffuse in CdTe at much higher rates during CdCl 2 treatments than with thermal processing alone. GB diffusion also occurs at a significantly faster rate than bulk diffusion. As a result of these two effects, the near interface bulk and GB Se diffusion during CdCl 2 treatments dominates the bandgrading profiles in CdTe PVs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1989

Alkoxysilane adsorption on metal oxide substrates

Reflection-absorption infrared and inelastic electron tunneling spectroscopies have been used to study adsorption of liquid phase mono-, di-, and trialkoxysilanes on evaporated Al and Cu substrates. Spectral evidence shows that substrate properties influence the chemical and physical nature of trialkoxysilane films and that silane functionality plays a role in molecular orientation. Results show that dialkoxysilane films contain structural gradients, with adsorption at the monomolecular level influenced by surface morphology, and with organofunctionality and dosing procedure affecting the formation of thicker films. Evidence is presented that monoalkoxysilanes react with alumina surfaces, and a broad, multipeaked band from 1600 to 1900/cm has been interpreted as characteristic of the silylated AlO(x)Pb interface.

Ramsier, R. D.↗
DOE OSTI2024

Plasma Surface Interactions: Predicting the Performance and Impact of Dynamic PFC Surfaces

The objective of this project is to develop, and integrate, high-performance simulation tools capable of predicting plasma-facing component (PFC) operating lifetime and the impact of the evolving surface morphology of tungsten-based PFCs on plasma contamination, including the dynamic recycling of fuel species and tritium retention, in future magnetic fusion devices. Establishing a fundamental physical understanding and developing predictive capabilities of plasma-surface interactions (PSI) requires simultaneously addressing complex and diverse physics occurring over a wide range of length (Angstroms to meters) and time (femtoseconds to years) scales, as well as integrating extensive physical processes across the plasma–surface interface. This requires development of not only detailed physics models and computational strategies at each scale, but also algorithms and methods to couple them effectively in a way that can be robustly validated. Deploying these tools requires the continued development and coupling of leadership-scale computational codes to describe the boundary plasma and the evolving PFC surface, as well as a host of simulations that bridge disparate scales to address complex physical and computational issues at the plasma–surface interface in multi-component materials systems for magnetic fusion energy development beyond ITER.

36 MATERIALS SCIENCE↗
NASA NTRS1996

The unusual X-ray collision morphology of NGC 4782/4783 (3C 278)

Deep Rosat high resolution imager (HRI) observations of the X-ray emitting gas associated with the colliding elliptical galaxy pair NGC 4782 and NGC 4783 reveals the gas distribution in a pair of close interacting ellipticals. The HRI image shows hot gas around each galaxy pair and a sheet of gas at the interaction interface between the two galaxies. The hot gas distributions do not peak at the optical centers of the galaxies, but are displaced in the same sense as the tidal distensions seen in the optical luminosity distributions.

Borne, Kirk↗
DOE OSTI2021

Monolayer Support Control and Precise Colloidal Nanocrystals Demonstrate Metal-Support Interactions in Heterogeneous Catalysts

We report that electronic and geometric interactions between active and support phases are critical in determining the activity of heterogeneous catalysts, but metal-support interactions are challenging to study. Here, it is demonstrated how the combination of the monolayer-controlled formation using atomic layer deposition (ALD) and colloidal nanocrystal synthesis methods leads to catalysts with sub-nanometer precision of active and support phases, thus allowing for the study of the metal-support inter-actions in detail. The use of this approach in developing a fundamental understanding of support effects in Pd-catalyzed methane combustion is demonstrated. Uniform Pd nanocrystals are deposited onto Al2O 3 /SiO 2 spherical supports prepared with control over morphology and Al 2 O 3 layer thicknesses ranging from sub-monolayer to a ≈4 nm thick uniform coating. Dramatic changes in catalytic activity depending on the coverage and structure of Al 2 O 3 situated at the Pd/Al 2 O 3 interface are observed, with even a single monolayer of alumina contributing an order of magnitude increase in reaction rate. By building the Pd/Al 2 O 3 interface up layer-by-layer and using uniform Pd nanocrystals, this work demonstrates the importance of controlled and tunable materials in determining metal-support interactions and catalyst activity.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ion transport in polymerized lyotropic liquid crystals containing ionic liquid

In this work, we investigate the effect of morphology and segmental dynamics on ion transport in polymerized lyotropic liquid crystals (polyLLCs) containing 1-butyl-3-methylimidazolium tetrafluoroborate as ionic liquid (IL). We demonstrate that two important factors, which affect ion conduction in polyLLCs, are grain size and chain density at the interface. The polyLLC with large grain size (70 nm) shows significant reduction in ion conductivity (one order of magnitude) compared to its homopolymer/IL mixture. However, the polyLLC with small grain size (20 nm) has little difference in ion conductivity compared to its homopolymer/IL mixture. It is observed that decreasing the chain density enhances the interaction of IL with polymer chains and consequently slows the relaxation of polymer chains. Finally, in addition, comparing the dynamics of polymer chains in mixtures of homopolymer/IL and templated LLC mesophases shows that the confinement in LLC structure prolongs the relaxation of polymer chains.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Elucidating the impact of stress states on grain boundary passivation in Ni-5Cr using the Rhines pack method

The oxidation behavior of a Ni–5Cr (at.%) alloy was evaluated at 420 ° C using the Rhines pack method and simultaneous tensile and compressive stress states via a miniature four-point bending fixture. At this moderate temperature, grain boundaries dominate mass transport and the resulting oxidation response. Oxidation produced approximately 1μ⁢m-wide protective Cr 2 O 3 films capping some grain boundaries and penetrative, intergranular Cr-rich oxides at other grain boundaries. Externally applied tensile and compressive stress during oxidation increased the prevalence of Cr 2 O 3 cap formation compared to no applied stress, with tensile stress resulting in more Cr 2 O 3 caps than compressive stress. The observed oxide cap morphology was similar across all test conditions. Regions under compressive stress showed an order of magnitude greater Cr depletion depth along the grain boundary. Chromium nitrides (CrN), likely from N contamination of the Rhines pack cell, were observed both at the oxide–metal interface and intergranularly within the alloy. Collectively these results demonstrate that applied stress promotes localized protective oxide cap formation over grain boundaries, with compressive stress additionally promoting deeper Cr depletion. Furthermore the experimental approach helped separate out the effects of stress on local oxide formation and grain boundary passivation.

4 point bend↗
DOE OSTI2018

Effects of in-process cryocooling on metallurgical and mechanical properties of friction stir processed Al7075 alloy

Highlights: • For in-process cryocooling (IPC) during FSP, an efficient cooling fixture was designed & fabricated. • FSP of Al7075 alloy with IPC setup suppressed precipitate coarsening as well as grain growth. • Nanosize η′ precipitates (20–30 nm) in IPC condition increased work hardening capacity & strength. • Simultaneous improvement in ductility & strength occurred for sample FSPed with IPC. - Abstract: Friction stir processing (FSP) of heat treatable aluminum alloys is reported to deteriorate strength and hardness properties in spite of huge grain size refinement. The improvement in strength due to the grain size refinement after FSP could not be able to offset the reduction in strength due to coarsening or dissolution of the strengthening precipitate(s). To overcome this, the present work investigates an effective way of heat rejection from the FSP zone to control the precipitate evolution besides the grain size refinement during FSP of Al7075 alloy. The FSP was carried out with standardized process parameters (i.e. 720 rpm, 65 mm/min traverse speed) under two different cooling environments: (i) at normal air cooling and (ii) by rushing a chilled mixture (−30 °C) of liquid nitrogen and methanol through the bottom of the backing plate. Microstructural evolution was examined through optical, scanning and transmission electron microscopy and electron backscatter diffraction to confirm the grain size and morphology of precipitate(s) formed. The in-process cryocooling during the FSP led to 65 and 72% improvement in the Vickers hardness and tensile strength, respectively, in comparison to the solutionized base metal. The results have been analyzed in terms of precipitate interface characteristics and its strengthening effect, Hall–Petch strengthening due to grain size reduction and tradeoff between them.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Partial Solvation of Lithium Ions Enhances Conductivity in a Nanophase-Separated Polymer Electrolyte

In this study, we demonstrate that a multiblock lithium-ion-conducting polymer can be swollen with ethylene carbonate solvent to increase the conductivity relative to the dry polymer material by nearly 4 orders of magnitude. This increase is due to the partial solvation of lithium ions by ethylene carbonate, which leads to Li + diffusion along the solvent–polymer interface. This differs from the vehicular transport mechanism for lithium ions in pure solvent. We use a combination of broadband dielectric spectroscopy, X-ray scattering, and all-atom molecular dynamics simulations to probe the effect of the solvent on the polymer morphology and to elucidate the mechanism of lithium ion transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Materials characterization: Can artificial intelligence be used to address reproducibility challenges?

Material characterization techniques are widely used to characterize the physical and chemical properties of materials at the nanoscale and, thus, play central roles in material scientific discoveries. However, the large and complex datasets generated by these techniques often require significant human effort to interpret and extract meaningful physicochemical insights. Artificial intelligence (AI) techniques such as machine learning (ML) have the potential to improve the efficiency and accuracy of surface analysis by automating data analysis and interpretation. In this perspective paper, we review the current role of AI in surface analysis and discuss its future potential to accelerate discoveries in surface science, materials science, and interface science. We highlight several applications where AI has already been used to analyze surface analysis data, including the identification of crystal structures from XRD data, analysis of XPS spectra for surface composition, and the interpretation of TEM and SEM images for particle morphology and size. We also discuss the challenges and opportunities associated with the integration of AI into surface analysis workflows. These include the need for large and diverse datasets for training ML models, the importance of feature selection and representation, and the potential for ML to enable new insights and discoveries by identifying patterns and relationships in complex datasets. Most importantly, AI analyzed data must not just find the best mathematical description of the data, but it must find the most physical and chemically meaningful results. In addition, the need for reproducibility in scientific research has become increasingly important in recent years. The advancement of AI, including both conventional and the increasing popular deep learning, is showing promise in addressing those challenges by enabling the execution and verification of scientific progress. By training models on large experimental datasets and providing automated analysis and data interpretation, AI can help to ensure that scientific results are reproducible and reliable. Although integration of knowledge and AI models must be considered for the transparency and interpretability of models, the incorporation of AI into the data collection and processing workflow will significantly enhance the efficiency and accuracy of various surface analysis techniques and deepen our understanding at an accelerated pace.

Materials Science↗
NASA NTRS2002

Surface Processes of Faceted Growth

Atomic force microscopy and high precision optical interferometry allow to analyze the processes that are in the core of our present understanding of faceted crystal growth. Some of these processes will be reviewed. Recent experiments suggest that the Gibbs-Thomson Law (GTL) may not be applicable to the weakly fluctuating strongly polygonized steps, with low kink density. Propagation rate of a straight short step segment changes with the segment length much steeper than predicted by GTL. If the step fluctuations are still well developed, the typical transition length may be determined just by the radius of rounded comers of the polygonized step. If fluctuations do not have enough time to develop, the kinetic effects may be essential. Indeed, 'communications' between comers of a short straight step segment may occur and, thus, the GTL may be implemented only via kink exchange. E.g., dissolutions of this short segment at macroscopic equilibrium occurs as follows: The kinks are split from one comer as a result of fluctuations, and annihilate with kinks of the opposite sign generated by another comer. Similarly, an exchange via chain of kinks on a rough step is the mechanism to implement the GT Law. If there is a supersaturation with respect to a large crystal, the kinks not only diffuse along the step, but move back the generating comers. This 'wind' prevents communication between the comers and places upper limit supersaturation only below which GTL is applicable. Steps replace kinks in the 3D case, though, of course, another dimensionality brings about another physics. Another specific problem to think about is if fluctuations are always fast enough to provide enough kinks for linear dependence of step rate on supersaturation. Increasing azimuthal polygonization of growth hillocks is a sign of insufficient fluctuation rate. Morphological stability of vicinal faces is usually considered on the basis of mutually parallel steps. Azimuthal anisotropy and interlacing of step bunches inducing the well known bunch splitting is another challenge. Among other challenging problems are: existence of surface diffusion on the crystal/so1ution interface, step interaction in solutions, achievement of step flow modes from liquids, impurity effects. New phenomena essential in biomacromolecular crystallization is another interesting area.

Chernov, A.↗
DOE OSTI2020

Low-temperature and high-rate-charging lithium metal batteries enabled by an electrochemically active monolayer-regulated interface

Stable operation of rechargeable lithium (Li)-based batteries at low temperatures is vital for cold-climate applications but is plagued with dendritic Li plating and unstable solid-electrolyte interphase (SEI). Here we report high-performance Li-metal batteries under low-temperature and high-rate-charging conditions. This is realized by utilizing a self-assembled monolayer of electrochemically active molecules on current collectors that regulates the nanostructure and composition of SEI and deposition morphology of Li metal anodes. A multilayer SEI containing a LiF-rich inner phase and amorphous outer layer effectively seals the Li surface in contrast to the conventional impassive SEI at low temperatures. As a result, galvanic Li corrosion and self-discharge were suppressed; stable Li deposition was realized from -60º to 45ºC; and a Li|LiCoO 2 cell with a capacity of 2.0 mAh cm -2 displayed a 200-cycle life at -15ºC with a recharge time of 45 minutes.

25 ENERGY STORAGE↗
DOE OSTI2022

Composition‐Conditioning Agent for Doped Spiro‐OMeTAD to Realize Highly Efficient and Stable Perovskite Solar Cells

Abstract The doped Spiro‐OMeTAD hole transport layer (HTL) formed using the lithium bis(trifluoromethane) sulfonimide salt and 4‐tert‐butylpyridine with phenethylammonium iodide surface treatment on a perovskite film has continuously dominated the record power conversion efficiencies (PCEs) of perovskite solar cells (pero‐SCs). However, unstable HTL compositions and iodide salts can cause severe device degradation. In this study, an HTL composition‐conditioning agent (CCA), Spiro‐BD‐2OEG, is designed, which contains a Spiro‐OMeTAD‐like backbone, functional pyridine units, and oligo (ethylene glycol) chains. This finely designed CCA presents good miscibility with Spiro‐OMeTAD and its dopants and acts as a conditioning agent through weak bond interactions. As a result, the CCA‐regulated HTL shows a pinhole‐free and smooth morphology with enhanced Spiro‐OMeTAD ordering and improves dopant stability. In addition, the gradient‐distributed CCA in the HTL can narrow the energy level offset with the valence band of the perovskite. The resultant pero‐SCs exhibit an excellent PCE of 24.19% without any interface treatment and weak size dependence. A remarkable PCE of 22.63% is obtained even for a 1.004‐cm 2 device. Importantly, the strategy shows good universality and significantly promotes the long‐term stability of the pero‐SCs based on the classical doped Spiro‐OMeTAD.

Chemistry↗
DOE OSTI2018

Multicompartment Polymeric Nanoreactors for Non-Orthogonal Cascade Catalysis

Spatial confinement of multiple catalysts presents an effective strategy for performing sequential or tandem chemical transformations in a one-pot reaction. These methods may be used to catalyze numerous reactions in conditions that are otherwise incompatible between catalyst and solvent, different catalysts, or reagents. Appropriate site isolation or support structure design would lead to significant advantages in atom economy, purification, and costs and the development of the interface between a catalyst and its confined microenvironment is paramount for realizing the next-generation of nanoreactors. Polymer scaffolds can create tailor-made microenvironments resulting in catalyst compartmentalization. Through the optimization of a number of variables such as size, solubility, functionality, and morphology of the nanoreactor, catalyst activity and selectivity can be tuned. In this Feature Article, we introduce design principles and early strategies for polymer supports for catalyst site-isolation and discuss current strategies towards multi-compartment polymer nanoreactors for non-orthogonal cascade catalysis. We conclude by outlining future design trends in this burgeoning field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Reduced Graphene Oxide–Cadmium Zinc Sulfide Nanocomposite with Controlled Band Gap for Large-Area Thin-Film Optoelectronic Device Application

Herein, we report the one pot single step solvothermal synthesis of reduced grapheme oxide–cadmium zinc sulfide (RGO–Cd{sub 0.5}Zn{sub 0.5}S) composite. The reduction in graphene oxide (GO), synthesis of Cd{sub 0.5}Zn{sub 0.5}S (mentioned as CdZnS in the text) nanorod and decoration of CdZnS nanorods onto RGO sheet were done simultaneously. The structural, morphological and optical properties were studied thoroughly by different techniques, such as XRD, TEM, UV–Vis and PL. The PL intensity of CdZnS nanorods quenches significantly after the attachment of RGO, which confirms photoinduced charge transformation from CdZnS nanorods to RGO sheet through the interface of RGO–CdZnS. An excellent photocurrent generation in RGO–CdZnS thin-film device has been observed under simulated solar light irradiation. The photocurrent as well as photosensitivity increases linearly with the solar light intensity for all the composites. Our study establishes that the synergistic effect of RGO and CdZnS in the composite is capable of getting promising applications in the field of optoelectronic devising.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Oxidation kinetics and microstructure evolution of high Mn stainless-steel alloy in CO 2 at 700 °C

Oxidation kinetics and scale formation were examined in 21–2N Stainless Steel alloys in a CO 2 environment at 700 °C. Several characterization techniques were used to identify the morphology, crystallographic structure, and chemical composition of the oxide scale formation during exposures up to 1925 h. High manganese content played an important role in homogenous oxide scale formation of Mn 3 O 4 and MnCr 2 O 4 at the scale/gas and scale/alloy interfaces and as an FCC stabilizer in the alloy. Depletion of Mn resulted in an FCC to BCC phase transformation at the scale/alloy interface. No carburization was observed, indicating that the oxide layer is preventing carbon uptake.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Decoupling Li out-diffusion and surface diffusion in the lithiation-assisted epitaxial growth of lithium tungstate

Lithiation-assisted epitaxy offers a flexible and robust approach for synthesizing high-quality Li-containing materials and interfaces with precise control. Here, in this study, we use lithium tungstate (Li x WO 3+x/2 , where x = 0 to 2) as a model system to investigate the intertwined effects of Li out-diffusion-induced compositional changes and surface-diffusion-induced morphological changes. By systematically varying synthesis and processing conditions, we uncover their impact on lithium tungstate film formation. Comprehensive characterizations, including X-ray diffraction, atomic force microscopy, X-ray photoemission spectroscopy and time-of-flight secondary ion mass spectrometry, reveal that low-temperature growth (< 300 °C) followed by high-temperature annealing yields continuous lithium tungstate films with significantly reduced surface roughness. In contrast, high-temperature deposition (≥ 300 °C) accelerates surface diffusion and Li out-diffusion, leading to island formation. Furthermore, in situ scanning transmission electron microscopy demonstrates the beam sensitivity of Li 2 WO 4 and reveals a phase transition from Li 2 WO 4 to LiWO 3.5 under prolonged electron beam exposure. These findings deepen our understanding of how to control composition and morphology of Li-containing films, providing valuable insights for the design and integration of energy materials.

Shi, Jueli [Pacific Northwest National Laboratory ↗
DOE OSTI2022

Microstructural pattern formation during liquid metal dealloying: Phase-field simulations and theoretical analyses

In recent years, liquid metal dealloying has emerged as a promising material processing method to generate micro- and nanoscale bicontinuous or porous structures. Most previous studies focused on the experimental characterization of the dealloying process and on the properties of the dealloyed materials, leaving the theoretical study incomplete to fully understand the fundamental mechanisms of the liquid metal dealloying process. In this paper, we use theoretical models and phase-field simulations to clarify the kinetics and pattern formation during liquid metal dealloying. Our investigation starts from a theoretical analysis of the 1D dissolution of a binary precursor alloy, which reveals that the 1D dissolution process involves two regimes. In the first regime, due to the low solubility of one of the elements in the melt, it accumulates at the solid-liquid interface, which reduces the dissolution kinetics. In the second regime, the interface kinetics reaches a stationary regime where both elements of the precursor alloy dissolve into the melt. Previous works revealed that in the early dealloying stage, the dealloying front is destabilized by an interfacial spinodal decomposition, which triggers the formation of interconnected ligaments. Here we extend this line of work by proposing a linear stability analysis able to predict the initial length scale of the ligaments formed in the initial stage of the dealloying. Combining this analysis with the 1D dissolution model proposed here enables us to better understand the initial conditions (composition of the precursor alloy and the melt) leading to a planar dissolution without interface destabilization. Finally, we report a strong influence of solid-state diffusion on dealloying. Although the solid-state diffusivity is four to five orders of magnitude smaller than in the liquid phase, it is found to affect both dissolution kinetics and ligament morphologies.

36 MATERIALS SCIENCE↗