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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 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Sulfur-induced structural motifs on copper and gold surfaces

The interaction of sulfur with copper and gold surfaces plays a fundamental role in important phenomena that include coarsening of surface nanostructures, and self-assembly of alkanethiols. Here, we identify and analyze unique sulfur-induced structural motifs observed on the low-index surfaces of these two metals. We seek out these structures in an effort to better understand the fundamental interactions between these metals and sulfur that lends to the stability and favorability of metal-sulfur complexes vs. chemisorbed atomic sulfur. The experimental observations presented here—made under identical conditions—together with extensive DFT analyses, allow comparisons and insights into factors that favor the existence of metal-sulfur complexes, vs. chemisorbed atomic sulfur, on metal terraces. We believe this data will be instrumental in better understanding the complex phenomena occurring between the surfaces of coinage metals and sulfur.

36 MATERIALS SCIENCE↗
DOE OSTI2017

On the transcritical mixing of fuels at diesel engine conditions

Whilst the physics of both classical evaporation and supercritical fluid mixing are reasonably well characterized and understood in isolation, little is known about the transition from one to the other in the context of liquid fuel systems. The lack of experimental data for microscopic droplets at realistic operating conditions impedes the development of phenomenological and numerical models. To address this issue we performed systematic measurements using high-speed long-distance microscopy, for three single-component fuels (n-heptane, n-dodecane, n-hexadecane), into gas at elevated temperatures (700–1200 K) and pressures (2–11 MPa). We describe these high-speed visualizations and the time evolution of the transition from liquid droplet to fuel vapour at the microscopic level. The measurements show that the classical atomization and vaporisation processes do shift to one where surface tension forces diminish with increasing pressure and temperature, but the transition to diffusive mixing does not occur instantaneously when the fuel enters the chamber. Rather, subcritical liquid structures exhibit surface tension in the near-nozzle region and then, after time surrounded by the hot ambient gas and fuel vapour, undergo a transition to a dense miscible fluid. Although there was clear evidence of surface tension and primary atomization for n-dodecane and n-hexadecane for a period of time at all the above conditions, n-heptane appeared to produce a supercritical fluid from the nozzle outlet when injected at the most elevated conditions (1200 K, 10 MPa). This demonstrates that the time taken by a droplet to transition to diffusive mixing depends on the pressure and temperature of the gas surrounding the droplet as well as the fuel properties. We summarise our observations into a phenomenological model which describes the morphological evolution and transition of microscopic droplets from classical evaporation through a transitional mixing regime and towards diffusive mixing, as a function of operating conditions. We provide criteria for these regime transitions as reduced pressure–temperature correlations, revealing the conditions where transcritical mixing is important to diesel fuel spray mixing.

02 PETROLEUM↗
DOE OSTI2016

Localized surface plasmon polariton resonance in holographically structured Al-doped ZnO

In this paper, we studied the localized surface plasmon polariton (SPP) resonance in hole arrays in transparent conducting aluminum-doped zinc oxide (AZO). CMOS-compatible fabrication process was demonstrated for the AZO devices. The localized SPP resonance was observed and confirmed by electromagnetic simulations. Using a standing wave model, the observed SPP was dominated by the standing-wave resonance along (1,1) direction in square lattices. This research lays the groundwork for a fabrication technique that can contribute to the core technology of future integrated photonics through its extension into tunable conductive materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe 3 GeTe 2

Here, magnetic force microscopy was used to observe the magnetic microstructure of Fe 3 GeTe 2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width D s = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization M s = 376 emu/cm 3 and the uniaxial magnetocrystalline anisotropy constant K u = 1.46 × 10 7 erg/cm 3 ), was used to determine the following micromagnetic parameters for Fe 3 GeTe 2 from phenomenological models: the domain wall energy γ w = 4.7 erg/cm 2 , the domain wall thickness δ w = 2.5 nm, the exchange stiffness constant A ex = 0.95 × 10 –7 erg/cm, the exchange length l ex = 2.3 nm, and the critical single domain particle diameter d c = 470 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Exploring the posterior surface of the large scale structure reconstruction

The large scale structure (LSS) of the universe is generated by the linear density gaussian modes, which are evolved into the observed nonlinear LSS. Given a set of data the posterior surface of the modes is convex in the linear regime, leading to a unique global maximum (MAP), but this is no longer guaranteed in the nonlinear regime. In this paper we investigate the nature of posterior surface using the recently developed MAP reconstruction method, with a simplified but realistic N-body simulation as the forward model. The reconstruction method uses optimization with analytic gradients from back-propagation through the simulation. For low noise cases we recover the initial conditions well into the nonlinear regime (k~ 1 h/Mpc) nearly perfectly. We show that the large scale modes can be recovered more precisely than the linear expectation, which we argue is a consequence of nonlinear mode coupling. For noise levels achievable with current and planned LSS surveys the reconstruction cannot recover very small scales due to noise. We see some evidence of non-convexity, specially for smaller scales where the non-injective nature of the mappings: several very different initial conditions leading to the same near perfect final data reconstruction. We investigate the nature of these phenomena further using a 1-d toy gravity model, where many well separated local maximas are found to have identical data likelihood but differ in the prior. We also show that in 1-d the prior favors some solutions over the true solution, though no clear evidence of these in 3-d. Our main conclusion is that on very small scales and for a very low noise the posterior surface is multi-modal and the global maximum may be unreachable with standard methods, while for realistic noise levels in the context of the current and next generation LSS surveys MAP optimization method is likely to be nearly optimal.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Surface Hydroxyls of Imogolite Nanotubes Drive Distinct Structures and Mobility Differentiation of Nanoconfined Water

Abstract Nanoconfined fluids, particularly water, govern subsurface geochemistry, yet the molecular-level mechanisms by which mineral surfaces dictate confined water structure and mobility remain poorly resolved. Here, we combine solution- and solid-state proton (1H) NMR spectroscopy, NMR relaxometry, modulated-gradient spin–echo (MGSE) NMR diffusometry, infrared spectroscopy, and molecular dynamics simulations to demonstrate that surface hydroxyls drive the structural and dynamic differentiation of water in imogolite nanotubes. In saturated suspensions, we observe the coexistence of distinct water 1H environments, each exhibiting significantly reduced mobility, which we attribute to strong interactions with the imogolite surfaces. As more mobile water is removed, long-range water diffusivity in the fibrous solid samples slows to 1.6 × 10–10 m2·s–1 while local fluctuations increase to 3.4 × 10–8 m2·s–1, indicating a significant increase in molecular restriction through surface interactions. Together, our experiments reveal three coexisting populations with varied structures and mobilities, all distinct from liquid bulk water. We resolve a persistent solid-like interfacial layer strongly bound to surface hydroxyls, characterized by an unusually short T2 (<1 ms), and a very close effective 1H–1H distance of ∼1.55 Å between water and the inner-surface silanol group. An inner-core population occupying the inner cavity exhibits an intermediate dynamic regime with restricted axial diffusion, while outer-surface water associated with aluminum hydroxyls retains relatively higher mobility. These results experimentally substantiate a hierarchy of water populations in imogolite and show how surface chemistry dictates the structures and dynamics of confined water.

Fleming, Xander B. [Earth and Environmental Scienc↗
DOE OSTI2018

Experimental and theoretical study of topology and electronic correlations in PuB 4

We synthesize single crystals of PuB 4 using an Al-flux technique. Single-crystal diffraction data provide structural parameters for first-principles density functional theory (DFT) calculations. By computing the density of states, the Z 2 topological invariant using the Wilson loop method, and the surface electronic structure from slab calculations, we find that PuB 4 is a nonmagnetic strong topological insulator with a band gap of 254 meV. Our magnetic susceptibility, heat capacity, and resistivity measurements are consistent with this analysis, albeit with a smaller gap of 35 meV. DFT plus dynamical mean-field theory calculations show that electronic correlations reduce the size of the band gap, and provide better agreement with the value determined by resistivity. Furthermore, these results demonstrate that PuB 4 is a promising actinide material to investigate the interplay of electronic correlations and nontrivial topology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ion–Electron Recombination and Heat Fluxes in High-Frequency Ion Thrusters

Heat fluxes emitted from plasma to the surface of structural elements of high-frequency (HF) ion thrusters with perforated electrodes of the ion-optical system have been studied. Radiation fluxes formed during ion–electron recombination on surfaces in contact with plasma are considered taking into account their spatial distribution and partial reflection from surfaces. New expressions for the heat fluxes are obtained that should be used as boundary conditions in numerical models for the calculation of temperature fields in HF ion thrusters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electronic Properties and Fermi Surface for New Layered High-Temperature Superconductors CaAFe{sub 4}As{sub 4} (A = K, Rb, and Cs): FLAPW-GGA Calculations

Recently, new FeAs-based high-temperature superconductors CaAFe{sub 4}As{sub 4} (A = K, Rb, and Cs) with a layered tetragonal crystal structure were synthesized (T{sub C} ∼ 30 K). In this letter, we report for the first time the band structures, Fermi surface topology, total and partial densities of electronic states, and interatomic interactions for CaAFe{sub 4}As{sub 4} as estimated by means of the first-principle FLAPW-GGA calculations. The obtained data for CaAFe{sub 4}As{sub 4} phases are analyzed in comparison with each other and with other related FeAs systems. The interatomic bonding picture can be represented as a highly anisotropic mixture of metallic, covalent, and ionic contributions, which are realized inside Fe{sub 4}As{sub 4}-layered blocks and between these blocks and Ca, A atomic sheets. The Fermi surfaces of these systems have a multisheet character and are compiled of a large number of cylinders at the edges and in the central part of the Brillouin zone. It is established that the high-temperature superconductivity in CaAFe{sub 4}As{sub 4} compounds as in other related systems correlates well with such structure parameters as bond angles and anion height.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Structure of a Bacterial Cell Surface Decaheme Electron Conduit

Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves deca-heme cytochromes that are located on the bacterial cell surface at the termini of trans-outermembrane (OM) electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular inter-cytochrome electron exchange along ‘nanowire’ appendages. We present a 3.2 Å crystal structure of one of these deca-heme cytochromes, MtrF, that allows the spatial organization of the ten hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65 Å octa-heme chain transects the length of the protein and is bisected by a planar 45 Å tetra-heme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g. minerals), soluble substrates (e.g. flavins) and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Rotatable spin-polarized electron source for inverse-photoemission experiments

We present a ROtatable Spin-polarized Electron source (ROSE) for the use in spin- and angle-resolved inverse-photoemission (SR-IPE) experiments. A key feature of the ROSE is a variable direction of the transversal electron beam polarization. As a result, the inverse-photoemission experiment becomes sensitive to two orthogonal in-plane polarization directions, and, for nonnormal electron incidence, to the out-of-plane polarization component. We characterize the ROSE and test its performance on the basis of SR-IPE experiments. Measurements on magnetized Ni films on W(110) serve as a reference to demonstrate the variable spin sensitivity. Moreover, investigations of the unoccupied spin-dependent surface electronic structure of Tl/Si(111) highlight the capability to analyze complex phenomena like spin rotations in momentum space. Essentially, the ROSE opens the way to further studies on complex spin-dependent effects in the field of surface magnetism and spin-orbit interaction at surfaces.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Surface modification induced phase transformation and structure variation on the rapidly solidified recast layer of titanium

In this study, neodymium-doped yttrium orthovanadate (Nd:YVO{sub 4}) as a laser source with different scanning speeds was used on biomedical Ti surface. The microstructural and biological properties of laser-modified samples were investigated by means of optical microscope, electron microscope, X-ray diffraction, surface roughness instrument, contact angle and cell cytotoxicity assay. After laser modification, the rough volcano-like recast layer with micro-/nanoporous structure and wave-like recast layer with nanoporous structure were generated on the surfaces of laser-modified samples, respectively. It was also found out that, an α → (α + rutile-TiO{sub 2}) phase transition occurred on the recast layers of laser-modified samples. The Ti surface becomes hydrophilic at a high speed laser scanning. Moreover, the cell cytotoxicity assay demonstrated that laser-modified samples did not influence the cell adhesion and proliferation behaviors of osteoblast (MG-63) cell. The laser with 50 mm/s scanning speed induced formation of rough volcano-like recast layer accompanied with micro-/nanoporous structure, which can promote cell adhesion and proliferation of MG-63 cell on Ti surface. The results indicated that the laser treatment was a potential technology to enhance the biocompatibility for titanium. - Highlights: • Laser induced the formation of recast layer with micro-/nanoporous structure on Ti. • An α → (α + rutile-TiO{sub 2}) phase transition was observed within the recast layer. • The Ti surface becomes hydrophilic at a high speed laser scanning. • Laser-modified samples exhibit good biocompatibility to osteoblast (MG-63) cell.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Systematic Structure–Property Relationship Studies in Palladium-Catalyzed Methane Complete Combustion

To limit further rising levels in methane emissions from stationary and mobile sources and to enable promising technologies based on methane, the development of efficient combustion catalysts that completely oxidize CH 4 to CO 2 and H 2 O at low temperatures in the presence of high steam concentrations is required. Palladium is widely considered as one of the most promising materials for this reaction, and a better understanding of the factors affecting its activity and stability is crucial to design even more improved catalysts that efficiently utilize this precious metal. Here we report a study of the effect of three important variables (particle size, support, and reaction conditions including water) on the activity of supported Pd catalysts. We use uniform palladium nanocrystals as catalyst precursors to prepare a library of well-defined catalysts to systematically describe structure–property relationships with help from theory and in situ X-ray absorption spectroscopy. With this approach, we confirm that PdO is the most active phase and that small differences in reaction rates as a function of size are likely due to variations in the surface crystal structure. We further demonstrate that the support exerts a limited influence on the PdO activity, with inert (SiO 2 ), acidic (Al 2 O 3 ), and redox-active (Ce 0.8 Zr 0.2 O 2 ) supports providing similar rates, while basic (MgO) supports show remarkably lower activity. Finally, we show that the introduction of steam leads to a considerable decrease in rates that is due to coverage effects, rather than structural and/or phase changes. Altogether, the data suggest that to further increase the activity and stability of Pd-based catalysts for methane combustion, increasing the surface area of supported PdO phases while avoiding strong adsorption of water on the catalytic surfaces is required. Furthermore, this study clarifies contrasting reports in the literature about the active phase and stability of Pd-based materials for methane combustion.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of transport mechanism on the coarsening of bicontinuous structures: A comparison between bulk and surface diffusion

Here, coarsening of bicontinuous microstructures is observed in a variety of systems, such as nanoporous metals and mixtures that have undergone spinodal decomposition. To better understand the morphological evolution of these structures during coarsening, we compare the morphologies resulting from two different coarsening mechanisms, surface and bulk diffusion. We perform phase-field simulations of coarsening via each mechanism in a two-phase mixture at nominal volume fractions of 50%-50% and 36%-64%, and the simulated structures are characterized in terms of topology (genus density), the interfacial shape distribution, structure factor, and autocorrelations of phase and mean curvature. We observe self-similar evolution of morphology and topology and agreement with the expected power laws for dynamic scaling, in which the characteristic length scale increases over time proportionally to t 1/4 for surface diffusion and t 1/3 for bulk diffusion. While we observe the expected difference in the coarsening kinetics, we find that differences in self-similar morphology due to coarsening mechanism are relatively small, although typically they are larger at 36% volume fraction than at 50% volume fraction. In particular, we find that bicontinuous structures coarsened via surface diffusion have lower scaled genus densities than structures coarsened via bulk diffusion. We also compare the self-similar morphologies to those in literature and to two model bicontinuous structures, namely, constant-mean-curvature surfaces based on the Schoen G minimal surface and random leveled-wave structures. The average scaled mean curvatures of these model structures agree reasonably with those of the coarsened structures at both 36% and 50%, but we find substantial disagreements in the scaled genus densities and the standard deviations of mean curvature.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pd overlayer on Oxygen pre-covered Graphene/Ru(0001): Thermal Stability

The behaviors of metal atoms on graphene and graphene oxide are quite important since the composite materials consisting of graphene and transition metal(s) can be employed in numerous technological applications. Despite that the great importance of metal particles on graphene or graphene oxide substrates, fundamental studies of the physical and chemical properties of metal clusters on graphene or graphene oxide are still needed. In this study, in order to elucidate the properties of metal on graphene (GR) and oxygen-precovered graphene (O-GR), the systems consisting of Pd deposited either on to pristine graphene or oxygen-precovered graphene layers have been investigated. The oxygen-precovered graphene was prepared by hot filament method under oxygen atmosphere. Exposure of the graphene layer to atomic oxygen resulted in both intercalation of oxygen between the graphene layer and the Ru(0001) substrate and functionalization of the graphene layer (mainly epoxide formation). Pd deposited onto the oxidized graphene layer interacted strongly with the intercalated oxygen, resulting in intercalation of some of the deposited Pd even at lower temperature than we have seen for Pd on pristine graphene. At the low coverage of 0.25 MLE, Pd mainly formed large planar domains (spreading of Pd on the oxidized graphene layer) and intercalated between the graphene layer and the Ru substrate at lower temperature due to the interaction between Pd and intercalated oxygen. At higher temperatures, both systems experience the same phenomenon, i.e., the intercalation of all of palladium between the graphene layer and Ru substrate. The intercalated Pd desorbed from the substrate at temperatures >1100 K. At higher Pd coverages, some of the Pd intercalated between the GR and the Ru substrate, while small Pd particles spread on the surface. The structure of the Pd overlayer after the 800 K annealing cycle seems to be very different from that observed at 300 K. The Pd that was present in small clusters spread out on the graphene surface due to the interaction with the intercalated Pd layer through the graphene layer. This interaction stabilized the Pd and even after 1000 K annealing the metal film was stable. After even higher temperature annealing all the Pd intercalated, and then desorbed above 1100 K. The graphene layer preserved its perfect structure (i.e., continuity) without any damage after the intercalation and desorption of Pd. We gratefully acknowledge the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division for the support of this work. The research described in this article was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute under contract number DE-AC05-76RL01830. CWY gratefully acknowledges the support of this work by the Sungshin Women’s University Research Grant of 2015.

Yi, Cheol-Woo W.↗
DOE OSTI2019

Demonstration and analysis of a 600 V, 10 A, 4H-SiC lateral single RESURF MOSFET for power ICs applications

This paper reports the demonstration of a 600 V 4H-SiC lateral MOSFET with a large current handling capability (10 A). To achieve a high breakdown voltage in a lateral architecture, a REduced SURface Field (RESURF) structure was implemented to alleviate surface electric field crowding. A single RESURF (P-top) design on an N-drift on a 6-in. N+ substrate demonstrated a voltage supporting capability of 120 V/ μ m, resulting in a breakdown voltage of 600 V. The total width of 198 mm for the interdigitated gate fingers was designed to accomplish the high current capability. It turned out that, for relatively low voltage SiC lateral MOSFETs (<600 V), more focus needs to be placed on achieving a low channel, contact, metal, and JFET region resistance than a low drift layer resistance to further improve the on-resistance. Device design, fabrication, and electrical characterization of the proposed 600 V, 10 A, 4H-SiC lateral single RESURF MOSFETs are discussed in this paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

High-Resolution Spore Coat Architecture and Assembly of Bacillus Spores

Elucidating the molecular architecture of bacterial and cellular surfaces and its structural dynamics is essential to understanding mechanisms of pathogenesis, immune response, physicochemical interactions, environmental resistance, and provide the means for identifying spore formulation and processing attributes. I will discuss the application of in vitro atomic force microscopy (AFM) for studies of high-resolution coat architecture and assembly of several Bacillus spore species. We have demonstrated that bacterial spore coat structures are phylogenetically and growth medium determined. We have proposed that strikingly different species-dependent coat structures of bacterial spore species are a consequence of sporulation media-dependent nucleation and crystallization mechanisms that regulate the assembly of the outer spore coat. Spore coat layers were found to exhibit screw dislocations and two-dimensional nuclei typically observed on inorganic and macromolecular crystals. This presents the first case of non-mineral crystal growth patterns being revealed for a biological organism, which provides an unexpected example of nature exploiting fundamental materials science mechanisms for the morphogenetic control of biological ultrastructures. We have discovered and validated, distinctive formulation-specific high-resolution structural spore coat and dimensional signatures of B. anthracis spores (Sterne strain) grown in different formulation condition. We further demonstrated that measurement of the dimensional characteristics of B. anthracis spores provides formulation classification and sample matching with high sensitivity and specificity. I will present data on the development of an AFM-based immunolabeling technique for the proteomic mapping of macromolecular structures on the B. anthracis surfaces. These studies demonstrate that AFM can probe microbial surface architecture, environmental dynamics and the life cycle of bacterial and cellular systems at near-molecular resolution under physiological conditions.

59 BASIC BIOLOGICAL SCIENCES↗