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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Structure of a HAp/TiO{sub y} Nanocomposite Studied by Vibrational Spectroscopy Techniques

A hydroxyapatite/TiO{sub y} nanocomposite material has been studied by X-ray diffraction, infrared spectroscopy, and Raman spectroscopy. The results demonstrate that annealing at 400°C changes the valence state of the titanium and leads to the formation of [Ti(OH){sub 2}]{sup 2+} and [TiHPO{sub 4}]{sup 2+} surface groups and terminal carbonyls and partial heterovalent cation substitutions of Ti{sup 3+} and Ti{sup 4+} for Ca{sup 2+}. As the annealing temperature is raised to 600°C, surface groups disappear. The amount of inflowing oxygen is insufficient for the complete oxidation of TiO{sub 0.92} to TiO{sub 2} in hydroxyapatite/TiO{sub 0.92}. The result is the formation of an intermediate nanophase with the composition Ti{sub 4.5}O{sub 5}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Zinc Adsorption and Hydration Structures at Yttria-Stabilized Zirconia Surfaces

Zinc adsorption and interfacial hydration on yttria-stabilized zirconia (YSZ) surfaces in contact with aqueous zinc solutions at room temperature and neutral pH have been probed, with combined specular high-resolution X-ray reflectivity and element-specific (Zn) resonant anomalous X-ray reflectivity techniques. The total and partial zinc-Specific electron density profiles in the surface normal direction show the detailed interfacial hydration structures with zinc adsorption: Strongly depending on its crystallographic orientations, the YSZ (110) surface adsorbs zinc species only within adsorbed water layers above the terminal plane, while on (111) surface, zinc further-penetrates the substrate (below the terminal plane). Considering that both surfaces are enriched with oxygen vacancies and metal-depleted sites; on which chemisorbed water species are expected, the observed contrast indicates that specific zinc adsorption is controlled strongly by the intrinsic surface chemistry that results from orientation-dependent interfacial structures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Stoichiometry-dependent surface electronic structure of SrTiO3 films grown by hybrid molecular beam epitaxy

We investigate the surface electronic structure of SrTiO3 (STO) films grown by a hybrid molecular beam epitaxy that are both stoichiometric and nonstoichiometric by means of x-ray photoelectron spectroscopy and electron energy loss spectroscopy. Increasing the fraction of the surface that is terminated with an SrO layer is correlated with a decrease in the chemical potential whereby the valence band maximum moves closer to the Fermi level, but without a significant change in the bandgap. Inasmuch as SrO-terminated STO (001) has previously been shown to act as an electron scavenger in which carriers from the bulk are trapped, we argue that the high fraction of SrO in the terminal layer is what lowers the chemical potential in Sr-rich STO. Our experimental results provide important insights into various physical phenomena that can occur on STO (001) surfaces and their effect on bulk electronic properties.

Lee, Dooyong (ORCID:0000000175361677)↗
DOE OSTI2017

Surface structure of bulk 2H-MoS 2 (0001) and exfoliated suspended monolayer MoS 2 : A selected area low energy electron diffraction study

Here, we used selected area low energy electron diffraction intensity-voltage (μLEED-IV) analysis to investigate the surface structure of crystalline 2H molybdenum disulfide (MoS 2 ) and mechanically exfoliated and suspended monolayer MoS 2 . Our results show that the surface structure of bulk 2H-MoS 2 is distinct from its bulk and that it has a slightly smaller surface relaxation at 320 K than previously reported at 95 K. We concluded that suspended monolayer MoS 2 shows a large interlayer relaxation compared to the MoS 2 sandwich layer terminating the bulk surface. The Debye temperature of MoS 2 was concluded to be about 600 K, which agrees with a previous theoretical study. Our work has shown that the dynamical μLEED-IV analysis performed with a low energy electron microscope (LEEM) is a powerful technique for determination of the local atomic structures of currently extensively studied two-dimensional (2-D) materials.

2-D material↗
DOE OSTI2017

Superconducting cable connections and methods

Superconducting cable connector structures include a terminal body (or other structure) onto which the tapes from the superconducting cable extend. The terminal body (or other structure) has a diameter that is sufficiently larger than the diameter of the former of the superconducting cable, so that the tapes spread out over the outer surface of the terminal body. As a result, gaps are formed between tapes on the terminal body (or other structure). Those gaps are filled with solder (or other suitable flowable conductive material), to provide a current path of relatively high conductivity in the radial direction. Other connector structures omit the terminal body.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Scanning tunneling microscopy study of the antiferromagnetic topological insulator MnBi 2 Se 4

Topological insulators with intrinsic magnetic ordering such as MnBi 2 Se 4 have been predicted to host many exotic topological phenomena including dissipationless edge states and magnetoelectric effects. Here we use scanning tunneling microscopy to study the surface of MnBi 2 Se 4 epitaxial thin films. Large scale topographic images show steps between van der Waals layers and screw dislocations. While we find the Se-termination predominant on the surface, areas attributed to Bi-termination are found at the edges of small islands in as-grown films, or in larger areas upon removal of surface capping. Here, we compare these terminations through an analysis of step heights, atomic resolution images and tunneling spectroscopy. Tunneling spectra on the Se-termination reveals semiconducting behavior, with an apparent bandgap of >0.18eV that depends on the tip height. In contrast, tunneling spectra of the Bi-termination appears gapless, which could be an indication of dangling bond states on the surface. In both cases, a hexagonal 3.9Å lattice is observed that is consistent with the expected crystal structure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2014

Grid-Free 2D Plasma Simulations of the Complex Interaction Between the Solar Wind and Small, Near-Earth Asteroids

We present results from a new grid-free 2D plasma simulation code applied to a small, unmagnetized body immersed in the streaming solar wind plasma. The body was purposely modeled as an irregular shape in order to examine photoemission and solar wind plasma flow in high detail on the dayside, night-side, terminator and surface-depressed 'pocket' regions. Our objective is to examine the overall morphology of the various plasma interaction regions that form around a small body like a small near-Earth asteroid (NEA). We find that the object obstructs the solar wind flow and creates a trailing wake region downstream, which involves the interplay between surface charging and ambipolar plasma expansion. Photoemission is modeled as a steady outflow of electrons from illuminated portions of the surface, and under direct illumination the surface forms a non-monotonic or ''double-sheath'' electric potential upstream of the body, which is important for understanding trajectories and equilibria of lofted dust grains in the presence of a complex asteroid geometry. The largest electric fields are found at the terminators, where ambipolar plasma expansion in the body-sized night-side wake merges seamlessly with the thin photoelectric sheath on the dayside. The pocket regions are found to be especially complex, with nearby sunlit regions of positive potential electrically connected to unlit negative potentials and forming adjacent natural electric dipoles. For objects near the surface, we find electrical dissipation times (through collection of local environmental solar wind currents) that vary over at least 5 orders of magnitude: from 39 Micro(s) inside the near-surface photoelectron cloud under direct sunlight to less than 1 s inside the particle-depleted night-side wake and shadowed pocket regions

Asteroids↗
DOE OSTI2021

Chemistry of Titanium Deposition Precursors for Area-Selective Deposition of Functionalized Silicon [Posters]

Area-selective atomic layer deposition (AS-ALD) is an appealing bottom-up fabrication technique that can produce atomic-scale device features, overcoming challenges in current industrial techniques such as edge alignment errors. TiCI 4 is a common thermal ALD precursor for Ti0 2 thin films, which are appealing candidates for DRAM capacitors due to their excellent dielectric constants. Hydrogen and chlorine termination passivate the Si surface, allowing for selective deposition of TiCI 4 onto HO-terminated areas. However, selectivity loss occurs after several ALD cycles. Ti oxide nucleates onto surface defects on Cl- and H-Si resists. Previously, the use of H-Si as an ALD resist has been studied extensively, but less work has focused on chemical forces driving nucleation, especially for Cl-Si. Here, formation of defect nuclei was investigated with selectivity loss during Ti0 2 ALD with TiCI 4 and water on the (100) and (111) crystal surfaces of hydrogenated, chlorinated, and oxidized Si.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

THE SURFACE DENSITY PROFILE OF THE GALACTIC DISK FROM THE TERMINAL VELOCITY CURVE

The mass distribution of the Galactic disk is constructed from the terminal velocity curve and the mass discrepancy–acceleration relation. Mass models numerically quantifying the detailed surface density profiles are tabulated. For R{sub 0} = 8 kpc, the models have stellar mass 5 < M{sub *} < 6 × 10{sup 10} M{sub ⊙}, scale length 2.0 ≤ R{sub d} ≤ 2.9 kpc, LSR circular velocity 222 ≤ Θ{sub 0} ≤ 233 km s{sup −1}, and solar circle stellar surface density 34 ≤ Σ{sub d}(R{sub 0}) ≤ 61 M{sub ⊙} pc{sup −2}. The present interarm location of the solar neighborhood may have a somewhat lower stellar surface density than average for the solar circle. The Milky Way appears to be a normal spiral galaxy that obeys scaling relations like the Tully–Fisher relation, the size–mass relation, and the disk maximality–surface brightness relation. The stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles in the terminal velocity curve correspond to known spiral features (e.g., the Centaurus arm is a ∼50% overdensity). The rotation curve switches between positive and negative over scales of hundreds of parsecs. The rms amplitude 〈|dV/dR|{sup 2}〉{sup 1/2}≈14 km s{sup −1} kpc{sup −1}, implying that commonly neglected terms in the Jeans equations may be nonnegligible. The spherically averaged local dark matter density is ρ{sub 0,DM} ≈ 0.009 M{sub ⊙} pc{sup −3} (0.34 GeV cm{sup −3}). Adiabatic compression of the dark matter halo may help reconcile the Milky Way with the c–V{sub 200} relation expected in ΛCDM while also helping to mitigate the too-big-to-fail problem, but it remains difficult to reconcile the inner bulge/bar-dominated region with a cuspy halo. We note that NGC 3521 is a near twin to the Milky Way, having a similar luminosity, scale length, and rotation curve.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Enhancement of perfluoropolyether boundary lubrication performance: I. Preliminary results

A ball bearing simulator operating under starved conditions was used to evaluate the boundary lubrication performance of a perfluoropolyether (PFPE) Krytox 143 AB. Several approaches to enhance boundary lubrication were studied. These included: (1) soluble boundary additives, (2) bearing surface modifications, (3) 'run-in' surface films, and (4) ceramic bearing components. In addition, results were compared with two non-perfluorinated liquid lubricant formulations. Based on these preliminary tests, the following tentative conclusions can be made: (1) substantial improvements in boundary lubrication performance were observed with a beta-diketone boundary additive and a tricresyl phosphate (TCP) liquid surface pretreatment; (2) the use of rough Si3N4 balls (Ra = 40 micro-in) also provided substantial improvement but with concomitant abrasive wear; (3) marginal improvements were seen with two boundary additives (a phosphine and a phosphatriazine) and a neat (100%) fluid (a carboxylic acid terminated PFPE); and surface pretreatments with a synthetic hydrocarbon, a PTFE coating, and TiC coated 440C and smooth Si3N4 balls (R(sub a) less than 1 micro-in); and (4) two non-PFPE lubricant formulations (a PAO and a synthetic hydrocarbon) yielded substantial improvements.

Jones, W. R., Jr.↗
DOE OSTI2024

Untangling charge-order dependent bulk states from surface effects in a topological kagome metal ScV 6 Sn 6

Kagome metals with charge density wave (CDW) order exhibit a broad spectrum of intriguing quantum phenomena. The recent discovery of the novel kagome CDW compound ScV 6 Sn 6 has spurred significant interest. However, understanding the interplay between CDW and the bulk electronic structure has been obscured by a profusion of surface states and terminations in this quantum material. Here, in this study, we employ photoemission spectroscopy and potassium dosing to elucidate the complete bulk band structure of ScV 6 Sn 6 , revealing multiple van Hove singularities near the Fermi level. We surprisingly discover a robust spin-polarized topological Dirac surface resonance state at the M point within the twofold van Hove singularities. Assisted by first-principles calculations, the temperature dependence of the k z -resolved angle-resolved photoemission spectroscopy spectrum provides unequivocal evidence for the proposed $\sqrt{3}$×$\sqrt{3}$×3 charge order over other candidates. Our work not only enhances the understanding of the CDW-dependent bulk and surface states in ScV 6 Sn 6 , but also establishes an essential foundation for potential manipulation of the CDW order in kagome materials.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Lunar ion energy spectra and surface potential

The acceleration model for lunar ions and the resulting ionosphere dynamics are reviewed briefly. An application is made to lunar atmosphere trapped in the surface fines, and the enhancement in the Ar-40/Ar-36 ratio in samples from the Apennine Front compared to the adjacent mare is calculated to be about 2.0. The predicted lunar ion energy spectra is shown and found to agree well with Suprathermal Ion Detector measurements; from this spectra, the neutral atmosphere scale height can be studied and the neutral atmosphere number density is found to be 100,000 to 300,000 per cu cm at the sunrise and sunset terminators. The lunar surface potential is calculated and is found to be several volts positive over much of the sunlit face of the moon but to go tens of volts negative at the terminator.

Manka, R. H.↗
DOE OSTI2019

Evidence for non-electrostatic interactions between a pyrophosphate-functionalized uranyl peroxide nanocluster and iron (hydr)oxide minerals

We report the terminal oxygen atoms of the pyrophosphate groups in the uranyl peroxide nanocluster U 24 Pp 12 ([(UO 2 ) 24 (O 2 ) 24 (P 2 O 7 ) 12 ] 48- ) are not fully satisfied by bond valence considerations and can become protonated. This functionality could allow for specific interactions with mineral surfaces, as opposed to the electrostatically-driven interactions observed between non-functionalized uranyl peroxide nanoclusters and mineral surfaces. The sorption of U 24 Pp 12 to goethite and hematite was studied using batch sorption experiments as a function of U 24 Pp 12 concentration, mineral concentration, and pH. A suite of spectroscopic techniques, scanning electron microscopy, and electrophoretic mobility measurements were used to examine the minerals before and after reaction with U 24 Pp 12 , leading to a proposed conceptual model for U 24 Pp 12 interactions with goethite. The governing rate laws were determined and compared to those previously determined for a non-functionalized uranyl peroxide nanocluster. The rate of uranyl peroxide nanocluster sorption depends on the charge density and functionalized component of the uranyl peroxide cage. Electrophoretic mobility and attenuated total reflectance Fourier transform infrared spectroscopy analyses show that an inner-sphere complex forms between the U 24 Pp 12 cluster and the goethite surface through the terminal pyrophosphate groups, leading to a proposed conceptual model in which U 24 Pp 12 interacts with the triply-coordinated reactive sites on the (110) plane of goethite. Finally, these results demonstrate that the behavior of U 24 Pp 12 at the iron (hydr)oxide-water interface is unique relative to interactions of the uranyl ion and non-functionalized uranyl peroxide nanoclusters.

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

Quantum chemical calculations to determine partitioning coefficients for HgCl 2 on iron-oxide aerosols

Gas-to-particle phase partitioning controls the pathways for oxidized mercury deposition from the atmosphere to the Earth's surface. The propensity of oxidized mercury species to transition between these two phases is described by the partitioning coefficient (K p ). Experimental measurements of K p values for HgCl 2 in the presence of atmospheric aerosols are difficult and time-consuming. Quantum chemical calculations, therefore, offer a promising opportunity to efficiently estimate partitioning coefficients for HgCl 2 on relevant aerosols. In this study, density functional theory (DFT) calculations are used to predict K p values for HgCl 2 on relevant iron-oxide surfaces. The model is first verified using a NaCl(100) surface, showing good agreement between the calculated (2.8) and experimental (29–43) dimensionless partitioning coefficients at room temperature. Then, the methodology is applied to six atmospherically relevant terminations of α-Fe 2 O 3 (0001): OH-Fe-R, (OH) 3 -Fe-R, (OH) 3 -R, O-Fe-R, Fe-O 3 -R, and O 3 -R (where R denotes bulk ordering). The OH-Fe-R termination is predicted to be the most stable under typical atmospheric conditions, and on this surface termination, a dimensionless HgCl 2 K p value of 5.2 x 10 3 at 295 K indicates a strong preference for the particle phase. Here this work demonstrates DFT as a promising approach to obtain partitioning coefficients, which can lead to improved models for the transport of mercury, as well as for other atmospheric pollutant species, through and between the anthroposphere and troposphere.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Effect of surface segregation on the oxidation resistance of Cu 3 Pt ( 100 )

Alloying element segregation often occurs under a reactive environment but its interplay with the subsequent surface oxidation of the alloy remains unclear. Using synchrotron-based ambient-pressure x-ray photoelectron spectroscopy, we dynamically monitor the surface segregation in Cu 3 Pt(100) in response to temperature and oxygen gas. Vacuum annealing leads to surface segregation of Cu along with the enrichment of Pt in the subsurface region. Upon switching to the O 2 atmosphere, dissociative chemisorption of oxygen does not change the surface segregation profile from that under the vacuum annealing condition. A stepwise increase in the oxygen pressure results in the transformation pathway of Cu → Cu 2 O → CuO, in which the selective oxidation of Cu gives rise to further accumulation of Pt underneath the oxide/alloy interface that hinders the supply of Cu from the bulk to the oxide/alloy interface, thereby leading to the termination of the surface oxidation after the Cu 2 O → CuO conversion is completed. This differs from the transformation pathway of Cu → Cu 2 O → Cu 2 O/CuO for the oxidation of pure Cu and Cu-Au alloys, in which the oxidation of Cu continues and the Cu 2 O/CuO bilayer growth is constantly maintained. Furthermore, these key differences provide useful insight into alloy design for controlling the surface properties such as corrosion resistance and catalytic performance of Cu base alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2020

SiO 2 Is Wasted Space in Single-Nanometer-Scale Silicon Nanoparticle-Based Composite Anodes for Li-Ion Electrochemical Energy Storage

The electrode processing conditions of silicon-based composite anodes play a pivotal role in the resulting interfacial chemical speciation and, thus, the electrochemical cycling behavior of the electrode. Systematically investigating how small chemical changes to the surface of the silicon nanoparticle (NP) affect larger, electrode-level properties is a strategy that will inform design principles to maximize electrode energy density and extend electrode lifetime. Here, we incorporate silicon nanoparticles (NPs) with an average diameter of 5.5 nm synthesized from the gas phase through a nonthermal plasma method into composite anode half-cell coin cells. We perform chemistry to functionalize the native hydride-terminated silicon NP surface with N-methylpyrrolidone (NMP) to improve slurry properties and reduce the silicon reactivity prior to composite electrode fabrication. We construct composite electrodes from these silicon NPs and observe an 86% capacity retention over 100 cycles at a rate of C/5, with an initial silicon specific capacity of 2600 mAh/g. We expose the same Si NPs to water that completely oxidizes these small-diameter NPs to SiO 2 and find that the SiO 2 NPs in the same electrode configuration exhibit no obvious lithium alloying capacity in the electrochemical potential range of lithium silicide alloy formation. As this result stands in contrast to existing literature, we provide a discussion on the origin of the discrepancies.

25 ENERGY STORAGE↗
DOE OSTI2017

Acetylene and Ethylene Adsorption on a β-Mo 2 C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Mo 2 C catalysts are widely used in hydrogenation reactions; however, the role of the C and Mo terminations in these catalysts is not clear. Understanding the binding of adsorbates is key for explaining the activity of Mo 2 C. The adsorption of acetylene and ethylene, probe molecules representing alkynes and olefins, respectively, was studied in this paper on a β-Mo 2 C(100) surface with C and Mo terminations using calculations based on periodic density functional theory. Moreover, the role of the C/Mo molar ratio was investigated to compare the catalytic potential of cubic (δ-MoC) and orthorhombic (β-Mo 2 C) surfaces. The geometry and electronic properties of the clean δ-MoC(001) and β-Mo 2 C(100) surfaces have a strong influence on the binding of unsaturated hydrocarbons. The adsorption of ethylene is weaker than that of acetylene on the surfaces of the cubic and orthorhombic systems; adsorption of the hydrocarbons was stronger on β-Mo 2 C(100) than on δ-MoC(001). The C termination in β-Mo 2 C(100) actively participates in both acetylene and ethylene adsorption and is not merely a spectator. Finally, the results of this work suggest that the β-Mo 2 C(100)-C surface could be the one responsible for the catalytic activity during the hydrogenation of unsaturated C≡C and C=C bonds, while the Mo-terminated surface could be poisoned or transformed by the strong adsorption of C and CH x fragments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗