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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Structural Anisotropy of Amorphous Silicon Films Modified by Femtosecond Laser Pulses

It is demonstrated that the surface-relief orientation in the form of one-dimensional gratings with a period of 1.20 ± 0.02 μm formed under processing of hydrogenated-silicon films by femtosecond laser pulses (1.25 μm) with an energy density of 0.15 J/cm{sup 2} is determined by the direction of the polarization vector of the radiation and total laser exposure. Based on the results of the analysis of Raman spectra, the presence of a nanocrystalline phase of silicon with a volume fraction between 15 and 67% (depending on processing conditions) is detected. The observed processes of micro- and nanostructuring are caused by excitation of the surface plasmon–polaritons and nanocrystallization in the near-surface region in the field of high-power femtosecond laser pulses, respectively. In addition, formation of polymorph modifications of silicon Si-III and Si-XII under femtosecond laser processing with a number of pulses exceeding 500 is discovered. Anisotropy of the Raman signal for the above polymorph modifications is revealed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spectral Characteristics of Daily to Seasonal Ground Motion at the Piñon Flats Observatory from Coherence of Seismic Data

We investigate coherences of seismic data recorded during three years (2015–2017) at the Piñon Flats Observatory (PY) array and a collocated 148 m deep borehole station B084, along with oceanic data from a buoy southwest of the PY array. Seismic and barometric recordings at PY stations are analyzed with a multitaper spectral technique. The coherence of signals from seismic sources is >0.6 at 0.05–8 Hz between closely spaced (<65m) surface stations and decreases to ~0.2 in frequency bands in which the wavelengths are smaller than interstation distances. There are several local coherence increases at 1–8 Hz between nearby (<65 m) surface stations, whereas large coherence values between a surface and 148 m deep borehole stations are only present at the secondary microseism (~0.14 Hz). These points to significant modification of seismic recordings in the top crust, and those continual near-surface failures might produce shallow rapidly attenuating signals at surface stations. Incoherent local atmospheric effects induce incoherent seismic signals in low- and high-frequency ranges through different coupling mechanisms. Between 0.003 and 0.05 Hz, atmospheric loadings generate ground tilts that contaminate the two horizontal seismic recordings and decrease their coherence, whereas the vertical component is less affected. At 1–8 Hz, coupling of atmospheric pressure with surface structures transmits incoherent signals into the ground, degrading the seismic coherence in all three components. The two horizontal coherences show seasonal variations with extended coherent frequency bands in winter and spring, likely to be produced by seasonal variations in microseisms and local ground tilts. The coherences also contain high anomalies between 2 and 4 Hz resulting from anthropogenic activities. The results provide useful information on instrument characteristics and variations in the shallow crustal response to earthquakes, seasonal and ambient sources of seismic energy, along with atmospheric pressure–temperature changes and anthropogenic activities.

Geochemistry & Geophysics↗
DOE OSTI2017

Assessing Chemical Transformation of Reactive, Interfacial Thin Films Made of End-Tethered Poly(2-vinyl-4,4-dimethyl azlactone) (PVDMA) Chains

Designing thin films or surface scaffolds with an appropriate display of chemical functionality is useful for biomedical applications, sensing platforms, adhesives, and barrier coatings. Relationships between the structural characteristics of model thin films based on reactive poly(2-vinyl-4,4-dimethyl azlactone) (PVDMA) brushes and the amount and distribution of primary amines used to chemically functionalize these layers in situ are quantitatively detailed via neutron reflectometry and compared with results from ellipsometry. After functionalization, the PVDMA brush thickness increases as a result of the primary amines reacting with the azlactone rings. Both techniques show that the extent of functionalization by small-molecule amines depends on the size of the amine, the grafting density of brush chains, and their molecular weight. However, constrained analysis of neutron reflectivity data predicated on that technique’s sensitivity to isotopic substitution and its ability to resolve structure at the nanoscale shows that the extent of functionalization is not accurately represented by the average extent of functionalization determined from ellipsometric thickness: reactive modification is not uniform, even in modestly dense brushes, except when the penetrant is small. In addition, there appears to be a loss of PVDMA chains during functionalization, attributed to chain scission resulting from additional stretching brought about by functionalization. In conclusion, these findings provide unprecedented insight into the alteration of surface properties by reactive modification and broadly support efforts to produce tailored surfaces in which properties such as friction, colloidal stability, adhesion, wettability, and biocompatibility can be modulated in situ by chemical modification.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Nanosized low-temperature phases of titanium(IV) oxide with anatase and η-phase structures: composition, structure, and photocatalytic properties

Nanosized low-temperature modifications of titanium(IV) oxide with the anatase and η-phase (TiO{sub 2–x}•mH{sub 2}O) structures were prepared by the sulfate method (pH <3) and for the first time characterized by a complex of methods (X-ray diffractometry, scanning electron microscopy, IR spectroscopy, Raman spectroscopy, differential scanning calorimetry, low-temperature sorption capacity of samples to nitrogen, and differentiating dissolution). The physicochemical properties of the modifications were compared. Differences in compositions of the surface and volumes of the samples, compositions and structures of the phases (structure of η-phase is superstructure to anatase), and microstructure elements (sizes of crystallites, nanoparticles, and specific surface area; volume of nano- and ultrananopores) were revealed. The region of η-phase stability was found in the coordinates of temperature (T = 50–95 °C) and hydrolysis duration (τ = 10–80 min) and temperature (T≤200 °C) and annealing duration (τ <6 h). The distinctions in the thermal behavior of the nanosized anatase and η-phase were studied. The photocatalytic activity (PCA) is determined by the physicochemical characteristics of the samples and phases and also by the composition and structure of the decomposed substrate. In the case of difenoxazole, the PCA is affected by the compositions of the samples, phases, and surface (the presence of OH groups) and specific surface area, whereas the composition of the samples and specific surface area affect the PCA in the case of thiamethoxam.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Fabrication of Superhydrophobic Calcium Phosphate Coating on Mg-Zn-Ca alloy and Its Corrosion Resistance

A novel superhydrophobic calcium phosphate coating was prepared on a magnesium alloy substrate by a highly effective chemical conversion process and subsequent chemical modification. Different methods were employed to characterize the surface morphology and chemical composition as well as measure the wettability of the coating. It was demonstrated that the as-prepared superhydrophobic calcium phosphate coating has a typical three-level hierarchical structure consisted of micro-protrusions, submicro-lumps and nano-grains, conferring excellent superhydrophobicity with a water contact angle of 159°. The electrochemical measurements and appropriate equivalent circuit revealed that the corrosion-resistant performance of the superhydrophobic calcium phosphate coating was significantly improved as compared with that of the substrate, the corrosion potential of the superhydrophobic coating increases from −1.56 to −1.36 V, and its corrosion current density decreases from 1.29 × 10{sup −4} to 1.3 × 10{sup −6} A/cm{sup 2}. The anti-corrosion mechanism of the superhydrophobic coating was also discussed. It can be indicated that the corrosion inhibitive properties of the coating are in accordance with its hydrophobicity, which is owing to the presence of a protective layer of air trapped in the grooves of the coating surface to isolate the underlying materials from the external environment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Dip Coating Passivation of Crystalline Silicon by Lewis Acids

The reduction of carrier recombination processes by surface passivation is vital for highly efficient crystalline silicon (c-Si) solar cells and bulk wafer metrological characterization. In this paper, we report a dip coating passivation of silicon surfaces in ambient air and temperature with Nafion, achieving a champion effective carrier lifetime of 12 ms on high resistivity n-type c-Si, which is comparable to state-of-the-art passivation methods. Nafion is a nonreactive polymer with strong Lewis acidity, thus leading to the formation of a large density of fixed charges at silicon surface, 1-2 orders of magnitude higher than what is achievable with conventional thin-film passivation layers. Notably, Nafion passivates the c-Si surface only by the fixed charges without chemical modification of dangling bonds, which is fundamentally different from the common practice of combining chemical with field-effect passivation. This dip coating process is simple and robust, without the need for complex equipment or parameter optimization as there is no chemical reaction involved.

14 SOLAR ENERGY↗
DOE OSTI2024

Application of the AI2 Climate Emulator to E3SMv2's Global Atmosphere Model, With a Focus on Precipitation Fidelity

Abstract Can the current successes of global machine learning‐based weather simulators be generalized beyond 2‐week forecasts to stable and accurate multiyear runs? The recently developed AI2 Climate Emulator (ACE) suggests this is feasible, based upon 10‐year simulations with a network trained on output from a physics‐based global atmosphere model using a grid spacing of approximately 110 km and forced by a repeating annual cycle of sea‐surface temperature. Here we show that ACE, without modification, can be trained to emulate another major atmospheric model, EAMv2, run at a comparable grid spacing for at least 10 years with similarly small climate biases—a prerequisite to wider applicability. With an analysis that combines multiple temporal, spatial, and frequency domain perspectives, we show that ACE faithfully represents the spatiotemporal structure of EAMv2 precipitation and related variables. Finally, we show that a pretrained ACE network is able to adapt to a new global climate model simulation data set with 10 fewer training steps than when starting from random initialization, all while still maintaining low levels of climate bias. Further analysis of these fine‐tuning experiments reveal ACE's intriguing ability to interpolate between distinct global climate models.

Duncan, James P. C.↗
DOE OSTI2013

Effect of post-deposition treatment on energy conversion efficiency of nanostructured CdS/Cu{sub 2}S thin films

In the present manuscript we report about synthesis of nanostructured CdS/Cu{sub 2}S thin films by economically viable soft chemical route and effect of post deposition treatments such as annealing in air and swift heavy ion irradiation on solar energy conversion efficiency of the heterojunction device. These as grown, annealed and irradiated thin films are characterized for structural, morphological, optical and I-V properties. X-ray diffraction pattern (XRD) represents structural as well as crystallite modifications, atomic force microscopy (AFM) shows improvement in surface appearance of the materials. The solar energy conversion efficiency calculated from I-V exhibited increase in conversion efficiency i. e. 0.09, 0.24 and 0.48 % for as grown, annealed and SHI irradiated thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Note: Real time optical sensing of alpha-radiation emitting radioactive aerosols based on solid state nuclear track detector

A sensitive radioactive aerosols sensor has been designed and developed. Its design guidance is based on the need for a low operational cost and reliable measurements to provide daily aerosol monitoring. The exposure of diethylene-glycol bis (allylcarbonate) to radiation causes modification of its physico-chemical properties like surface roughness and reflectance. In the present study, optical sensor based on the reflectance measurement has been developed with an aim to monitor real time presence of alpha radioactive aerosols emitted from thorium nitrate hydrate. The results shows that the fabricated sensor can detect 0.0157 kBq to 0.1572 kBq of radio activity by radioactive aerosols generated from (Th(NO{sub 3}){sub 4} ⋅ 5H{sub 2}O) at 0.1 ml/min flow rate. The proposed instrument will be helpful to monitor radioactive aerosols in/around a nuclear facility, building construction sites, mines, and granite polishing factories.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Use of protein cross-linking and radiolytic footprinting to elucidate PsbP and PsbQ interactions within higher plant Photosystem II

We used protein cross-linking and radiolytic footprinting coupled with high-resolution mass spectrometry to examine the structure of PsbP and PsbQ when they are bound to Photosystem II, in this paper. In its bound state, the N-terminal 15-amino-acid residue domain of PsbP, which is unresolved in current crystal structures, interacts with domains in the C terminus of the protein. These interactions may serve to stabilize the structure of the N terminus and may facilitate PsbP binding and function. These interactions place strong structural constraints on the organization of PsbP when associated with the Photosystem II complex. Additionally, amino acid residues in the structurally unresolved loop 3A domain of PsbP ( 90 K– 107 V), 93 Y and 96 K, are in close proximity (≤11.4 Å) to the N-terminal 1E residue of PsbQ. Our findings are the first, to our knowledge, to identify a putative region of interaction between these two components. Cross-linked domains within PsbQ were also identified, indicating that two PsbQ molecules can interact in higher plants in a manner similar to that observed by Liu et al. [(2014) Proc Natl Acad Sci 111(12):4638–4643] in cyanobacterial Photosystem II. Furthermore, this interaction is consistent with either intra-Photosystem II dimer or inter-Photosystem II dimer models in higher plants. Finally, OH• produced by synchrotron radiolysis of water was used to oxidatively modify surface residues on PsbP and PsbQ. Finally, domains on the surface of both protein subunits were resistant to modification, indicating that they were shielded from water and appear to define buried regions that are in contact with other Photosystem II components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Direct radiative effect by multicomponent aerosol over China

The direct radiative effect (DRE) of multiple aerosol species (sulfate, nitrate, ammonium, black carbon (BC), organic carbon (OC), and mineral aerosol) and their spatiotemporal variations over China were investigated using a fully coupled meteorology–chemistry model (WRF-Chem) for the entire year of 2006. We made modifications to improve model performance, including updating land surface parameters, improving the calculation of transition metal-catalyzed oxidation of SO 2 , and adding in heterogeneous reactions between mineral aerosol and acid gases. The modified model well reproduced the magnitude, seasonal pattern, and spatial distribution of the measured meteorological conditions, concentrations of PM 10 and its components, and aerosol optical depth (AOD). A diagnostic iteration method was used to estimate the overall DRE of aerosols and contributions from different components. At the land surface, all kinds of aerosol species reduced the incident net radiation flux with a total DRE of 10.2 W m -2 over China. Aerosols significantly warm the atmosphere with the national mean DRE of +10.8 W m -2 . BC was the leading radiative-heating component (+8.7 W m -2 ), followed by mineral aerosol (+1.1 W m -2 ). At the top of the atmosphere (TOA), BC introduced the largest radiative perturbation (+4.5 W m -2 ), followed by sulfate (-1.4 W m -2 ). The overall perturbation of aerosols on radiation transfer is quite small over China, demonstrating the counterbalancing effect between scattering and adsorbing aerosols. Aerosol DRE at the TOA had distinct seasonality, generally with a summer maximum and winter minimum, mainly determined by mass loadings, hygroscopic growth, and incident radiation flux.

Huang, Xin↗
DOE OSTI2015

The Transfer of Improved Cavity Processing Protocols to Industry for LCLS-II: N-Doping and Electropolishing

Based on the R&D efforts of colleagues at FNAL, Cornell, and JLab, the LCLS-II project adopted a modification to the rather standard niobium SRF cavity surface processing protocol that incorporates a high temperature diffusion doping with nitrogen gas. This change was motivated by the resulting higher Q0 and the prospect of significantly lower cryogenic heat load for LCLS-II. JLab is responsible for managing the cavity procurement for the LCLS-II project. The first phase of the procurement action is to transfer the nitrogen-doping protocol to the industrial vendors. We also seek to exploit improvements in understanding of the niobium electropolishing process as part of the production processing of the TESLA-style LCLS-II cavities. We report on the technology transfer activities and progress toward the envisaged performance demonstration of vendor-processed cavities.

Reece, Charles E.↗
DOE OSTI2013

High order spatial expansion for the method of characteristics applied to 3-D geometries

The method of characteristics is an efficient and flexible technique to solve the neutron transport equation and has been extensively used in two-dimensional calculations because it permits to deal with complex geometries. However, because of a very fast increase in storage requirements and number of floating operations, its direct application to three-dimensional routine transport calculations it is not still possible. In this work we introduce and analyze several modifications aimed to reduce memory requirements and to diminish the computing burden. We explore high-order spatial approximation, the use of intermediary trajectory-dependent flux expansions and the possibility of dynamic trajectory reconstruction from local tracking for typed subdomains. (authors)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Deposition-Dependent Coverage and Performance of Phosphonic Acid Interface Modifiers in Halide Perovskite Optoelectronics

In this work, we study the effect of various deposition methods for phosphonic acid interface modifiers commonly pursued as self-assembled monolayers in high-performance metal halide perovskite photovoltaics and light-emitting diodes. We compare the deposition of (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid onto indium tin oxide (ITO) bottom contacts by varying three parameters: the method of deposition, specifically spin coating or prolonged dip coating; ITO surface treatment via HCl/FeCl3 etching; and use in combination with a second modifier, 1,6-hexylenediphosphonic acid. We demonstrate that varying these modification protocols can impact time-resolved photoluminescence carrier lifetimes and quasi-Fermi level splitting of perovskite films deposited onto the phosphonic acid-modified ITO. Ultraviolet photoelectron spectroscopy shows an increase in the effective work function after phosphonic acid modification and clear evidence for photoemission from carbazole functional groups at the ITO surface. We used X-ray photoelectron spectroscopy to probe differences in phosphonic acid coverage on the metal oxide contact and show that perovskite samples grown on ITO with the highest phosphonic acid coverage exhibit the longest carrier lifetimes. Finally, we establish that device performance follows these same trends. These results indicate that the reactivity, heterogeneity, and composition of the bottom contact help to control recombination rates and therefore power conversion efficiencies. ITO etching, prolonged deposition times for phosphonic acids via dip coating, and the use of a secondary, more hydrophilic bisphosphonic acid all contribute to improvements in surface coverage, carrier lifetime, and device efficiency. Furthermore, these improvements each have a positive impact, and we achieve the best results when all three strategies are implemented.

contact engineering↗
DOE OSTI2018

The Temperature and Structure Dependence of Surface Tension of CaO-SiO{sub 2}-Na{sub 2}O-CaF{sub 2} Mold Fluxes

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO{sub 2}-Na{sub 2}O-CaF{sub 2} mold-flux melts with different CaO/SiO{sub 2} mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO{sub 2} mass ratios, and agreed with the modification of melt structure. When the CaO/SiO{sub 2} mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO{sub 2} mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

36 MATERIALS SCIENCE↗
DOE OSTI2013

On the connection between continental-scale land surface processes and the tropical climate in a coupled ocean-atmosphere-land system

The impact of global tropical climate to perturbations in land surface processes (LSP) are evaluated using perturbations given by different LSP representations of continental-scale in a global climate model that includes atmosphere-ocean interactions. One representation is a simple land scheme, which specifies climatological albedos and soil moisture availability. The other representation is the more comprehensive Simplified Simple Biosphere Model, which allows for interactive soil moisture and vegetation biophysical processes. The results demonstrate that LSP processes such as interactive soil moisture and vegetation biophysical processes have strong impacts on the seasonal mean states and seasonal cycles of global precipitation, clouds, and surface air temperature. The impact is especially significant over the tropical Pacific. To explore the mechanisms for such impact, different LSP representations are confined to selected continental-scale regions where strong interactions of climate-vegetation biophysical processes are present. We find that the largest impact is mainly from LSP perturbations over the tropical African continent. The impact is through anomalous convective heating in tropical Africa due to changes in the surface heat fluxes, which in turn affect basinwide teleconnections in the Pacific through equatorial wave dynamics. The modifications in the equatorial Pacific climate are further enhanced by strong air-sea coupling between surface wind stress and upwelling, as well as effect of ocean memory. Our results further suggest that correct representations of land surface processes, land use change and the associated changes in the deep convection over tropical Africa are crucial to reducing the uncertainty when performing future climate projections under different climate change scenarios.

Ma, Hsi-Yen↗
DOE OSTI2021

Modification of the Coordination Environment of Active Sites on MoC for High-Efficiency CH 4 Production

Modulating the coordination environment of active sites on catalyst surfaces is crucial to developing effective catalysts and controlling catalysis, but it is highly challenging. Guided by our first-principles calculations, we experimentally accomplish the modification of the coordination environment of active sites on MoC nanoparticle surfaces by anchoring pyridinic N atom rings of holey graphene on Mo atoms. The rings produce electrostatic forces that enable the tuning of the Mo sites' affinity to reaction intermediates, which passivates Mo hollow sites, activates Mo top sites and reduces the over-adsorption of OH on the Mo active sites, as predicted by the calculations. The atomic-level modification is well confirmed by atomic-resolution imaging, high-resolution electron tomography, synchrotron soft X-ray spectroscopy and operando electrochemical infrared spectroscopy. Consequently, the Faradaic efficiency for CO 2 reduction to CH 4 is enhanced from 16% to 89%, a record high efficiency so far, in aqueous electrolyte. Meantime, it also exhibits a negligible activity loss over 50 h.

77 NANOSCIENCE AND NANOTECHNOLOGY↗