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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A Positive Low Cloud–Sea Surface Temperature Feedback in the East Asian Marginal Seas during El Niño Mature Winters and Their Following Spring

During the winter and subsequent spring of an El Niño year, the East Asian marginal sea (EAMS) exhibits positive sea surface temperature anomalies (SSTAs) and fewer low clouds, while the western North Pacific experiences negative SSTAs. In this study, we suggest that the positive SSTAs in EAMS are maintained by a positive low cloud–SST feedback. In neutral winters and springs, the EAMS is covered by low clouds, which have a cooling effect on surface temperatures. During an El Niño year, a western North Pacific anomalous anticyclone is established, and along its northwestern flank, there are favorable conditions for convergence of moisture and weaker surface latent heat flux over the EAMS. Once a positive SSTA has been established, a further reduction of turbulent mixing results in less low cloud and enhanced solar heating of the ocean mixed layer; this reinforces and maintains both the positive SSTA and the lack of low cloud via a positive feedback mechanism. Further, the concurrent increase of low cloud–SST feedback and anticyclone circulation strengths is evident in the coupled-model simulations from phase 6 of the Coupled Model Intercomparison Project. Furthermore, sensitivity experiments, performed with the atmospheric components of Community Earth System Model (CESM2), reveal that a positive SSTA helps to maintain the western North Pacific anomalous anticyclone. Four pacemaker-coupled experiments by CESM2, with sea surface temperature in the equatorial Pacific restored to the observational anomalies plus the model climatology and altered low cloud feedback over EAMS, suggest that the low cloud–SST feedback results in more than the maintenance of a positive SSTA over the EAMS: the positive feedback is also a previously overlooked mechanism for the maintenance of the western North Pacific anomalous anticyclone.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Divergent urbanization-induced impacts on global surface urban heat island trends since 1980s

Urbanization experiences different speeds and forms under diverse development stages across the globe. However, urbanization-induced impacts on long-term surface urban heat island intensity (I s ) trends across global cities and the regulators of such impacts remain understudied. Here we estimate interannual trends in daytime I s (i.e., urban-rural differences in surface temperatures) across 511 major cities for 1985 –2020 using annual averages calculated by using reconstructed land surface temperature data derived from more than >250,000 Landsat thermal images. Our study reveals that the global mean I s growth rate is 0.156 °C/decade. We further examine I s change associated with per 1% impervious land growth (denoted as ß) in each city throughout the research period and during different periods. The global mean ß is 0.018 ± 0.025 °C/% (mean ± 1 standard deviation) for the whole period, with greater values in humid than in arid climates; and the ß may change during different periods, e.g., it has more than tripled when urban impervious land exceeds 30%, indicating the spatiotemporally divergent impacts of urbanization on Is trends across global cities. The spatial variations in ß across global cities are well correlated with rural vegetation abundance and precipitation but not with urban population. Among these three factors, rural vegetation abundance possesses the greatest standardized regression coefficient of partial least-squares model, signifying the critical role of biome background in regulating ß. Furthermore, the finding implies that future urbanization over densely vegetated regions should be more carefully and strategically planned due to the greater urbanization-induced surface warming effect.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Preventing native oxide formation in niobium thin films through platinum encapsulation

Superconducting transmon qubits are a key technology in quantum computing, with niobium (Nb) widely used due to its favorable superconducting properties and compatibility with scalable fabrication. However, the performance of Nb-based qubits is hindered by two-level systems (TLS), which arise predominantly from native oxide layers at surfaces and interfaces. These oxides and suboxides form rapidly in air and contribute significantly to decoherence by introducing dielectric losses. While various mitigation strategies, including thermal-annealing, chemical-etching, and nitrogen plasma treatment, have been explored, many are challenging to integrate into large-scale manufacturing due to complexity and instability in ambient conditions. In this study, we investigate the structural, chemical, and superconducting properties of room-temperature sputtered Nb thin films grown on sapphire substrates. We focus on a surface protection strategy using noble metal encapsulation with platinum (Pt) to suppress oxides and reduce TLS-related losses. Structural and chemical characterization were performed using X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Superconducting properties were measured using a physical property measurement system. Results demonstrate that Pt encapsulation effectively suppresses surface oxidation and mitigates its detrimental impact on superconducting performance. In conclusion, this approach offers a promising path toward enhancing the coherence of Nb-based qubits while remaining compatible with scalable-fabrication processes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Application of community data to surface complexation modeling framework development: Iron oxide protolysis

This study presents a comprehensive community data-driven surface complexation modeling framework for simulating potentiometric titration of mineral surfaces. Compiled community data for ferrihydrite, goethite, hematite, and magnetite are fit to produce representative protolysis constants that can reproduce potentiometric titration data collected from multiple literature sources. Using this framework, the impact of surface complexation model type and surface site density (SSD) on the fit quality and protolysis constants can be readily evaluated. For example, the non-electrostatic model yielded a poor data fit compared to diffuse double layer model and constant capacitance models due to the absence of known surface charge effects. Regardless of the choice of iron oxide mineral, pK a1 decreased with increasing SSD while the opposite tendency was observed for pK a2 . This newly developed framework demonstrates a method to reconcile community data-wide potentiometric titration data using Findable, Accessible, Interoperable, Reusable data principles to produce mineral protolysis constants that improve robustness of surface complexation models for applications in metal sorption and reactive transport modeling. The framework is readily expandable (as community data increase) and extensible (as the number of minerals increase). The framework provides a path forward for developing self-consistent, comprehensive, and updateable surface complexation databases for surface complexation and reactive transport modeling.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

CuPt and CuPtRu Nanostructures for Ammonia Oxidation Reaction

Liquid fuels, such as methanol, ethanol, and ammonia, are attractive alternative to hydrogen for fuel cells due to their lower costs for storage and distribution. However, lack of sufficiently active catalysts for their oxidation reactions is a roadblock. Our previous study found that Pt 3 Cu nanodendrites yielded higher activity and durability than Pt nanoparticles for methanol oxidation reaction (MOR) in acid. In this study, we synthesized two types of nanostructures of CuPt and CuPtRu catalysts via seed-mediated growth of Pt and Ru on Cu and tested their performance for ammonia oxidation reaction (AOR) in alkaline solution. Unlike for MOR, the nanodendrites do not promote AOR activity - CuPt performs similar to Pt and CuPtRu is less active than Pt. Interestingly, the AOR peak current is increased by 64% on CuPt nanowires and 330% on CuPtRu nanowires as compared to Pt nanoparticles. These results suggest that AOR prefers extended surface on long nanowires, distinctly differing from MOR. This can be contributed to two factors: NH 3 oxidization to N 2 involves dimerization of two N-containing intermediates to form the N-N bond and diffusion batters for adsorbed intermediates are generally lower on terrace than at low-coordination sites. This demonstrated strong effect of surface morphology will be further studied and utilized in developing advanced AOR nanocatalysts.

25 ENERGY STORAGE↗
DOE OSTI2017

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain‐relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN‐on‐Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack‐free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10 7 cm −2 achieved to date in GaN‐on‐Si is demonstrated. With these advances, the first vertical GaN metal–insulator–semiconductor field‐effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost‐effective high power device paradigm on an Si CMOS platform are demonstrated

Tanaka, Atsunori↗
DOE OSTI2017

Tuning the polar states of ferroelectric films via surface charges and flexoelectricity

In this work, using the self-consistent Landau-Ginzburg-Devonshire approach we simulate and analyze the spontaneous formation of the domain structure in thin ferroelectric films covered with the surface screening charge represented by the Bardeen-type surface states. Hence we consider the competition between the screening and the domain formation as alternative ways to reduce the electrostatic energy and reveal unusual peculiarities of distributions of polarization, electric and elastic fields conditioned by the surface screening length and the flexocoupling strength. We have established that the critical thickness of the film and its transition temperature to a paraelectric phase strongly depend on the Bardeen screening length, while the flexocoupling affects the polarization rotation and closure domain structure. Furthermore the flexocoupling induces ribbon-like nano-scale domains in the film depth far from the top open surface, which might be related to the enigmatic polar nanoregions in relaxor ferroelectrics. Thus the joint action of the surface screening (originating from e.g. the adsorption of ambient ions or surface states) and flexocoupling may remarkably modify polar and electromechanical properties of thin ferroelectric films.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Nucleation of Cu n ( n = 1–5) Clusters and Equilibrium Morphology of Cu Particles Supported on CeO 2 Surface: A Density Functional Theory Study

In the present work, the interactions between Cun (n=1~4) clusters and three low-index structural CeO2 (111, 110, 100) surfaces were investigated using density functional theory calculations. The atomic Cu prefers to aggregate into large clusters on the CeO2(111) surface while it is unfavorable on both CeO2(110) and CeO2(100) surfaces. Once the planar Cu4-p cluster is formed, it would convert into the 3D tetrahedral Cu4-t cluster on CeO2(110) and CeO2(111) surfaces, i.e., 2D to 3D transition growth is thermodynamically favorable and kinetically feasible on CeO2(110) and CeO2(111) surfaces. The effects of ceria support structure on the morphology of the large Cu nanoparticle was examined using calculated adhesion and interfacial energies of periodic Cu(khl)/CeO2 model systems. The calculated macroscopic contact angles (? > 100?) of various model systems suggest that the supported Cu nanoparticle is in bad wetting condition. Finally, the morphologies of large Cu nanoparticles on different CeO2 surfaces were predicted using Wulff-Kaichew construction principle.

Cu/CeO2 catalyst, Adsorption and nucleation, DFT c↗
DOE OSTI2017

Photothermal Infrared Radiometry in Experimental Studies of the Pyroelectric Properties of Bulk Materials

A simple and efficient method for determining the pyrolelectric coefficients of ferroelectric and pyroelectric bulk materials by taking into account the heat exchange of a sample with the environment is proposed on the basis of the radiometric registration of the variation dynamics of the temperature of the surface when it is exposed to laser radiation in the form of a temporal step.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Reflectance determination of optical spectral emissivity of metal surfaces at ambient conditions

Optical pyrometry requires knowledge of both spectral radiance and spectral emissivity to accurately measure temperature. No reliable compendium of spectral emissivity data currently exists for common metals in the optical and near-infrared spectral regions where pyrometry is typically performed. In this paper, we measure the spectral reflectivity of numerous common metals, with known surface finishes, between 400 and 1100 nm. The measurements are carried out under ambient conditions, near 300 K at an atmospheric pressure of ~0.78 bar. We then calculate the emissivity as a function of the wavelength for each sample. We define and use the illumination and collection geometries most practical for applying these measurements to radiometric thermometry. We also examine the effect of surface finish upon the relative spectral emissivity of a given material and find qualitative guidelines for predicting the increase in emissivity with increasing surface roughness. Finally, these measurements can both improve the accuracy and precision of optical pyrometry and provide the necessary reference value for converting emerging diagnostic measurements of relative spectral emissivity under extreme dynamic conditions into absolute dynamic spectral emissivity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Transition of Blast Furnace Slag from Silicate Based to Aluminate Based: Density and Surface Tension

The effects of the Al{sub 2}O{sub 3} concentration and Al{sub 2}O{sub 3}/SiO{sub 2} ratio on the density and surface tension of molten aluminosilicate CaO-SiO{sub 2}-Al{sub 2}O{sub 3}-9 mass pct MgO-1 mass pct TiO{sub 2} slag were investigated at temperatures from 1723 K to 1823 K (1450 °C to 1550 °C) using the Archimedean method and the maximum bubble pressure (MBP) technique, respectively. The mechanism of the changes in density and surface tension with composition was analyzed from the viewpoint of the degree of polymerization in the structure and the types of oxygen species in the melts. At a fixed CaO/SiO{sub 2} ratio of 1.20, the density decreased with increasing Al{sub 2}O{sub 3} content up to 25 mass pct, subsequently increasing. Increasing the Al{sub 2}O{sub 3}/SiO{sub 2} ratio from 0.47 to 0.92 caused an increase in the density at a fixed CaO content, and the density decreased slightly when the Al{sub 2}O{sub 3}/SiO{sub 2} ratio was greater than 0.92. Based on the structural information, the density decreased when the Al{sub 2}O{sub 3} content enhanced the network structure and increased when the (Q{sub 2} + Q{sub 3})/(Q{sub 0} + Q{sub 1}) ratio and structural complexity decreased. The surface tension increased with increasing Al{sub 2}O{sub 3} content and Al{sub 2}O{sub 3}/SiO{sub 2} ratio. On the one hand, the surface-active component of SiO{sub 2} decreased; on the other hand, the concentration of [AlO{sub 4}]{sup 5−} tetrahedra and metal cations that act as charge compensators increased at the melt surface. A model based on the anionic and cationic radii and the Butler equation was employed to predict the surface tension, and an iso-surface tension diagram was obtained at 1773 K (1500 °C).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ethane Dehydrogenation on Single and Dual Centers of Ga-modified γ-Al 2 O 3

Density-functional theory calculations and microkinetic analysis are used to investigate the efficacy of Ga-modified γ-Al 2 O 3 (110) surfaces for the catalytic dehydrogenation of ethane and elucidate the synergy between Ga and Al sites. The model surfaces are modified by either Ga grafting or doping. We consider and analyze numerous active sites and rank them using microkinetic analysis. The kinetic parameters obtained from microkinetic modelling are compared with experimental values for ethane dehydrogenation over Ga 2 O 3 -Al 2 O 3 mixed oxides prepared by co-precipitation. The dominant reaction pathway proceeds via heterolytic C-H bond dissociation to a surface proton and a metal-carbanion intermediate that undergoes β-hydride elimination. We find that grafted Ga sites are catalytically inactive. In contrast, Ga-doped sites exhibit fivefold enhancement in catalytic activity when compared to the sites on pristine Al 2 O 3 , owed to the synergy between neighboring AlIII and GaIV sites. Furthermore, we model and investigate the effect of surface hydroxylation, demonstrate how surface water interferes with the aforementioned synergy between AlIII and GaIV sites and discuss the implications for the catalytic activity of the modified surfaces. Here, an increase in the partial pressure of H 2 O significantly increases the apparent activation energies of dehydrogenation and interestingly changes the most active site.

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

Multimodel Surface Temperature Responses to Removal of U.S. Sulfur Dioxide Emissions

Abstract Three Earth System models are used to derive surface temperature responses to removal of U.S. anthropogenic SO 2 emissions. Using multicentury perturbation runs with and without U.S. anthropogenic SO 2 emissions, the local and remote surface temperature changes are estimated. In spite of a temperature drift in the control and large internal variability, 200 year simulations yield statistically significant regional surface temperature responses to the removal of U.S. SO 2 emissions. Both local and remote surface temperature changes occur in all models, and the patterns of changes are similar between models for northern hemisphere land regions. We find a global average temperature sensitivity to U.S. SO 2 emissions of 0.0055 K per Tg(SO 2 ) per year with a range of (0.0036, 0.0078). We examine global and regional responses in SO 4 burdens, aerosol optical depths (AODs), and effective radiative forcing (ERF). While changes in AOD and ERF are concentrated near the source region (United States), the temperature response is spread over the northern hemisphere with amplification of the temperature increase toward the Arctic. In all models, we find a significant response of dust concentrations, which affects the AOD but has no obvious effect on surface temperature. Temperature sensitivity to the ERF of U.S. SO 2 emissions is found to differ from the models' sensitivity to radiative forcing of doubled CO 2 .

Conley, A. J.↗
DOE OSTI2022

Measurements of multiple heat flux components at the divertor target by using surface eroding thermocouples (invited)

The Surface Eroding Thermocouple (SETC) is a robust diagnostic utilized in DIII-D to provide fast, edge-localized modes (ELMs) resolved heat flux measurements, in particular in geometric regions that are too shadowed for traditional infrared thermography. In order to further investigate the power dissipation in the divertor region, a combination of flush-mounted and recessed SETCs was developed to assess the effect on surface heating from non-charged particles at the divertor target. Utilizing the Divertor Materials Evaluation System sample exposure platform, the first demonstration of the feasibility of using this new method to distinguish between the heat flux from charged particles and that from neutrals and radiative heating was achieved. This paper details the process of using the combination of flush SETCs and recessed SETCs to measure the multiple heat flux components at the divertor target and further discusses how to determine two important ratios, α (ratio of heat flux from charged particles deposit on recessed SETC to that deposit on flush SETC) and β (ratio of heat flux from non-charged particles deposit on recessed SETC to that deposit on flush SETC), in the estimation of the heat flux from non-charged particle sources. Using a time dependent ratio α, it was found that ~50% of the total incident heat flux is attributable to the non-charged particles in the fully detached open divertor in DIII-D. Finally, the new application of similar SETC diagnostics in the Small Angle Slot divertor with a V-like configuration and partial tungsten coated surface (SAS-VW) is also introduced.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

A Subgrid Approach for Modeling Microtopography Effects on Overland Flow: Modeling Archive

This Modeling Archive is in support of an NGEE Arctic publication. A new subgrid model was implemented in the Advanced Terrestrial simulator (ATS) to capture micro-topography effects on surface flow. Model evaluation was performed on disparate landscapes including: 1) seven individual ice-wedge polygons and a cluster of ice-wedge polygons from Barrow Alaska, 2) hummocky microtopography from Spruce field site in Minnesota, 3) synthetic rills, and 4) synthetic multGaussian realizations. Results of the subgrid model are compared to benchmark (fine-scale) and null hypothesis (model ignoring microtopography). Our finding confirms that the effects of small-scale spatial heterogeneities can be captured in the coarsened models. The dataset contains variety of files including meshes, input files, and subgrid parameters required to run the simulations. Python scripts (jupyter notebooks) for post-processing and files for geometric analyses are also included. More details are provided in file "simulations_info", which has been provided in both .docx and .pdf formats. This dataset is a zip file.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research.The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska.Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

The CARMENES search for exoplanets around M dwarfs: Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines

In this paper, we present precise photospheric parameters of 282 M dwarfs determined from fitting the most recent version of PHOENIX models to high-resolution CARMENES spectra in the visible (0.52–0.96 μ m) and NIR wavelength range (0.96–1.71 μ m). With its aim to search for habitable planets around M dwarfs, several planets of different masses have been detected. The characterization of the target sample is important for the ability to derive and constrain the physical properties of any planetary systems that are detected. As a continuation of previous work in this context, we derived the fundamental stellar parameters effective temperature, surface gravity, and metallicity of the CARMENES M-dwarf targets from PHOENIX model fits using a χ 2 method. We calculated updated PHOENIX stellar atmosphere models that include a new equation of state to especially account for spectral features of low-temperature stellar atmospheres as well as new atomic and molecular line lists. We show the importance of selecting magnetically insensitive lines for fitting to avoid effects of stellar activity in the line profiles. For the first time, we directly compare stellar parameters derived from multiwavelength range spectra, simultaneously observed for the same star. In comparison with literature values we show that fundamental parameters derived from visible spectra and visible and NIR spectra combined are in better agreement than those derived from the same spectra in the NIR alone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Focused ion beam milling of polycrystalline diamond

Focused ion beam (FIB) technology has a large potential for precise milling of ultrahard materials such as diamond. However, studies of the sputtering of diamond with ion species and energies relevant to the FIB technology are scarce. Here, we report a systematic study of the sputtering of polycrystalline diamond surfaces with ion beams in a wide range of ion energies (2 - 30 keV), incident beam angles (0 - 80°), and ion masses (N, O, Ar, and Xe). Results show that the sputter yield is relatively insensitive to ion energy but strongly depends on the ion species and incident beam angles. Bombardment with O ions results in sputter yields that are significantly larger than ballistic predictions due to chemical etching effects. Characteristic surface ripples develop for oblique beam incidence angle irradiation. The critical beam tilt angle for the onset of ripple formation and the wavelength of the ripples depend on ion species and energies. Ripples appear to suppress ion reflection at high beam tilt angles and, hence, a peak in the sputter yield angular dependence. In conclusion, these results have direct implications for the development of process parameter maps for high-precision ion-beam milling of diamond.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Modifying the Structure of Multiwalled Carbon Nanotubes with Continuous and Pulsed Ion Beams

Changes in the local atomic and electronic structure and the chemical state of the surface of multiwalled carbon nanotubes (MWCNTs) irradiated with continuous and pulsed ion beams are studied using transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy. It is demonstrated that changes in the structure and the chemical state of MWCNTs under continuous irradiation with argon ions are attributable to the radiation-induced defect formation. When a pulsed carbon–proton beam is used, thermal effects exert a considerable influence on the structure of carbon nanotubes. The obtained results suggest that continuous and pulsed ion beams are suitable for targeted functionalization of physical and chemical properties of MWCNTs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗