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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

TM surface wave diffraction by a truncated dielectric slab recessed in a perfectly conducting surface

The diffraction of a TM sub o surface wave by a terminated dielectric slab which is flush mounted in a perfectly conducting surface is studied. The incident surface wave gives rise to waves reflected and diffracted by the termination; these reflected and diffracted fields may be expressed in terms of the geometrical theory of diffraction by introducing surface wave reflection and diffraction coefficients which are associated with the termination. In this investigation, the surface wave reflection and diffraction coefficients have been deduced from a formally exact solution to this canonical problem. The solution is obtained by a combination of the generalized scattering matrix technique and function theoretic methods.

Pathak, P. H.↗
NASA NTRS1979

Surface wave diffraction by a truncated dielectric slab recessed in a perfectly conducting surface

The diffraction of a TM sub 0 surface wave by a terminated dielectric slab which is flush mounted in a perfectly conducting surface is studied. The incident surface wave gives rise to waves reflected and diffracted by the termination; these reflected and diffracted fields may be expressed in terms of the geometrical theory of diffraction by introducing surface wave reflection and diffraction coefficients which are associated with the termination. In this investigation the surface wave reflection and diffraction coefficients have been deduced from a formally exact solution to this canonical problem. The solution is obtained via a combination of the generalized scattering matrix technique and the Wiener-Hopf procedure. Expressions for the reflection and diffraction coefficients contain integrals which can be evaluated numerically.

Pathak, P. H.↗
DOE OSTI2025

Revealing the Origin and Nature of the Buried Metal‐Substrate Interface Layer in Ta/Sapphire Superconducting Films

Abstract Despite constituting a smaller fraction of the qubit's electromagnetic mode, surfaces and interfaces can exert significant influence as sources of high‐loss tangents, which brings forward the need to reveal properties of these extended defects and identify routes to their control. Here, we examine the structure and composition of the metal‐substrate interfacial layer that exists in Ta/sapphire‐based superconducting films. Synchrotron‐based X‐ray reflectivity measurements of Ta films, commonly used in these qubits, reveal an unexplored interface layer at the metal‐substrate interface. Scanning transmission electron microscopy and core‐level electron energy loss spectroscopy identified an intermixing layer (≈0.65 ± 0.05 nm) at the metal‐substrate interface containing Al, O, and Ta atoms. Density functional theory modeling reveals that the structure and properties of the Ta/sapphire heterojunctions are determined by the oxygen content on the sapphire surface prior to Ta deposition for two atomic terminations of sapphire. Using a multimodal approach, we gained deeper insights into the interface layer between the metal and substrate, which suggests that the orientation of deposited Ta films depend on the surface termination of sapphire. The observed elemental intermixing at the metal‐substrate interface influences the thermodynamic stability and electronic behavior of the film, which may also affect qubit performance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ligand induced shape transformation of thorium dioxide nanocrystals

Nanocrystals (NCs) with size and shape dependent properties are a thriving research field. Significant progress has been made in the controlled synthesis of NCs of stable elements in the past two decades; however, the knowledge of the NCs of actinide compounds has been considerably limited due the difficulties in handling them both experimentally and theoretically. Actinide compounds, especially actinide oxides, play a critical role in many stages of the nuclear fuel cycle. Recently, a non-aqueous surfactant assisted approach has been developed for the synthesis of actinide oxide NCs with different morphologies, but an understanding of its control factors is still missing to date. Herein we present a comprehensive study on the low index surfaces of thorium dioxide (ThO 2 ) and their interactions with relevant surfactant ligands using density functional calculations. A systematic picture on the thermodynamic stability of ThO 2 NCs of different sizes and shapes is obtained employing empirical models based on the calculated surface energies. It is found that bare ThO 2 NCs prefer the octahedral shape terminated by (111) surfaces. Oleic acid displays selective adsorption on the (110) surface, leading to the shape transformation from octahedrons to nanorods. Other ligands such as acetylacetone, oleylamine, and trioctylphosphine oxide do not modify the equilibrium shape of ThO 2 NCs. This research provides atomic level insights into the anisotropic growth of ThO2 NCs that was recently observed in experiments, and thus may contribute to the controlled synthesis of actinide oxide NCs with well-defined size and shape for future applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Analysis of the thermodynamic stability of ThO 2 and UO 2 surfaces in the presence of surfactant ligands

Nanocrystals (NCs) with size and shape dependent properties are a thriving research field. Remarkable progress has been made in the controlled synthesis of NCs of stable elements in the past two decades; however, the knowledge of the NCs of actinide compounds has been considerably limited due the difficulties in handling them both experimentally and theoretically. Actinide compounds, especially actinide oxides, play a critical role in many stages of the nuclear fuel cycle. Recently, a non-aqueous surfactant assisted approach has been developed for the synthesis of actinide oxide NCs with different morphologies, but an understanding of its control factors is still missing to date. Herein we present a comprehensive study on the low index surfaces of thorium dioxide (ThO 2 ) and their interactions with relevant surfactant ligands using density functional calculations. A systematic picture on the thermodynamic stability of ThO 2 NCs of different sizes and shapes is obtained employing empirical models based on the calculated surface energies. It is found that bare ThO 2 NCs prefer the octahedral shape terminated by (111) surfaces. Oleic acid displays selective adsorption on the (110) surface, leading to the shape transformation from octahedrons to nanorods. Other ligands such as acetylacetone, oleylamine, and trioctylphosphine oxide do not modify the equilibrium shape of ThO 2 NCs. This work provides atomic level insights into the anisotropic growth of ThO 2 NCs that was recently observed in experiments, and thus may contribute to the controlled synthesis of actinide oxide NCs with well-defined size and shape for future applications.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

First-Principles Thermodynamics Study of Spinel MgAl 2 O 4 Surface Stability

The surface stability of all possible terminations for three low-index (111, 110, 100) structures of the spinel MgAl2O4 has been studied using first-principles based thermodynamic approach. The surface Gibbs free energy results indicate that the 100_AlO2 termination is the most stable surface structure under ultra-high vacuum at T=1100 K regardless of Al-poor or Al-rich environment. With increasing oxygen pressure, the 111_O2(Al) termination becomes the most stable surface in the Al-rich environment. The oxygen vacancy formation is thermodynamically favorable over the 100_AlO2, 111_O2(Al) and the (111) structure with Mg/O connected terminations. On the basis of surface Gibbs free energies for both perfect and defective surface terminations, the 100_AlO2 and 111_O2(Al) are the most dominant surfaces in Al-rich environment under atmospheric condition. This is also consistent with our previously reported experimental observation. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computing time was granted by the National Energy Research Scientific Computing Center (NERSC). Part of computing time was also granted by a scientific theme user proposal in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington.

ab initio calculation↗
NASA NTRS2009

Flight Deck Display Technologies for 4DT and Surface Equivalent Visual Operations

NASA research is focused on flight deck display technologies that may significantly enhance situation awareness, enable new operating concepts, and reduce the potential for incidents/accidents for terminal area and surface operations. The display technologies include surface map, head-up, and head-worn displays; 4DT guidance algorithms; synthetic and enhanced vision technologies; and terminal maneuvering area traffic conflict detection and alerting systems. This work is critical to ensure that the flight deck interface technologies and the role of the human participants can support the full realization of the Next Generation Air Transportation System (NextGen) and its novel operating concepts.

Prinzel, Lawrence J., III↗
DOE OSTI2016

Role of porosity on the stiffness and stability of (001) surface of the nanogranular C–S–H gel

We present here a nanoscale modeling of the bulk and surface states of the nanogranular Calcium Silicate Hydrate (C–S–H) gel. Regarding the mechanical properties as well as porosity, we identify two main phases: a ductile one, for a porosity from 12.4% to 27% and a brittle phase for a porosity lower than 12.4% or higher than 27%. Particularly, our calculations show that 20% of gel porosity gives a better structural stability to C–S–H and a higher stiffness. Besides, we have explored the (001) surface of C–S–H gel at the nanoscale level and have proved that more water on the surface will stabilize thermodynamically the nanostructure. This means that adsorbed H{sub 2}O molecules lead to the coexistence of Si–OH and Ca–OH groups on the surface. The calcium-terminated plane is a polar and unstable surface, and will either reconstruct to neutralize the dipole moment or adsorb ions to remove it. Our results also show that the (001) surface of low density C–S–H tends to be more stable than the surface of high density phase since the obtained surface energy decreases with increasing gel porosity.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Apparatus for measuring semiconductor device resistance

A test structure is described for enabling the accurate measurement of the resistance characteristics of a semiconductor material and includes one or more pairs of electrical terminals disposed on the surface of the material to enable measurements of the resistance encountered by currents passed between the terminals. A pair of terminals includes a first terminal extending in a closed path, such as a circle, around a second terminal, so that all currents flowing between the terminals flow along a region of known width and length. Two or more pairs of concentric terminals can be utilized, wherein the ratio of radii of each pair of terminals is the same as the ratio for all other pairs of terminals, to facilitate the calculation of the contact resistance between each terminal and the semiconductor surface, as well as the calculation of the resistance of the semiconductor material apart from the effect of the terminal to semiconductor contact resistances.

Matzen, W. J.↗
NASA NTRS1979

ALSEP termination report

The Apollo Lunar Surface Experiments Package (ALSEP) final report was prepared when support operations were terminated September 30, 1977, and NASA discontinued the receiving and processing of scientific data transmitted from equipment deployed on the lunar surface. The ALSEP experiments (Apollo 11 to Apollo 17) are described and pertinent operational history is given for each experiment. The ALSEP data processing and distribution are described together with an extensive discussion on archiving. Engineering closeout tests and results are given, and the status and configuration of the experiments at termination are documented. Significant science findings are summarized by selected investigators. Significant operational data and recommendations are also included.

Bates, J. R.↗
NASA NTRS1972

Near-terminator photography, part R

The advantages resulting from the use of near-terminator photography in lunar surface investigations are discussed. It is pointed out that, under near-terminator conditions, small changes in slope produce greater contrast changes than at high sun elevation angles. This desirable phenomenon is confirmed by an examination of the near-terminator photography taken during the Apollo 15 mission. Many of the photographs obtained show lunar surface areas within a few degrees of the terminator and are therefore of significant geologic interest. In addition, many geologic features stand out in a distinct manner not normal in conventional lunar photography, thus providing additional data on the surface morphology and the configuration of a large number of lunar surface structures.

Head, J. W.↗
DOE OSTI2024

Scanning tunneling microscopy study of epitaxial Fe 3 GeTe 2 monolayers on Bi 2 Te 3

Abstract Introducing magnetism to the surface state of topological insulators, such as Bi 2 Te 3 , can lead to a variety of interesting phenomena. We use scanning tunneling microscopy (STM) to study a single quintuple layer (QL) of the van der Waals magnet Fe 3 GeTe 2 (FGT) that is grown on Bi 2 Te 3 via molecular beam epitaxy. STM topographic images show that the FGT grows as free-standing islands on Bi 2 Te 3 and outwards from Bi 2 Te 3 steps. Atomic resolution imaging shows triangular lattices of 390 ± 10 pm for FGT and 430 ± 10 pm for Bi 2 Te 3 , consistent with the respective bulk crystals. A moiré pattern is observed on FGT regions with a periodicity of 4.3 ± 0.4 nm that can be attributed solely to this lattice mismatch and thus indicates zero rotational misalignment. While most of the surface is covered by a single QL of the FGT, there are small double QL regions, as well as regions with distinct chemical terminations due to an incomplete QL. The most common partial QL surface termination is the FeGe layer, in which the top two atomic layers are missing. This termination has a distinctive electronic structure and a 3 x 3 R 30 ∘ reconstruction overlaid on the moiré pattern in STM images. Magnetic circular dichroism measurements confirm these thin FGT films are ferromagnetic withT C ∼190 K.

Materials Science↗
DOE OSTI2018

Synthesis and properties of carbosilane dendrimers with perfluorohexyl groups in the outer layer of the molecular structure

Branched perfluorohydrosiloxane with CF{sub 3}CF{sub 2}CF{sub 2}C(CF{sub 3}){sub 2}(CH{sub 2}){sub 3} groups at the silicon atom was synthesized by a sequence of chemical reactions. The resulting compound was used as a modifying agent for carbosilane dendrimers of the 3rd and 6th generations. Dendrimers with perfluorohexyl terminal groups in surface layer are characterized by a complex of physicochemical methods. It is demonstrated that due to the branching of perfluoroalkyl terminal groups, obtained carbosilane dendrimers are soluble in organic and inorganic media. Differences in the solubility of small and large dendrimers are caused by the formation of the outer fluoride shell of different densities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Quantum Confinement and Decoherence Effect on Excited Electron Transfer at the Semiconductor–Molecule Interface: A First-Principles Dynamics Study

Excited electron dynamics at the semiconductor–molecule interface play a vital role in many solar energy conversion applications and beyond. First-principles dynamics simulation is used to study how excited electron dynamics in a type-II semiconductor–molecule interface is affected when the surface of a bulk semiconductor is replaced with that of a quantum dot. In particular, the interface between the hydrogen-terminated silicon(111) surface and a simple organic molecule is investigated. Quantum confinement was found to significantly slow down the excited electron relaxation and the interfacial transfer of the excited electron. Additionally, the role of decoherence was examined. The decoherence affects the dynamics much more significantly for the interface with the quantum dot, while the bulk surface case is affected only marginally by it. Finally, compared to the excited electron relaxation within the quantum dot, the decoherence effect was found to slow down the interfacial transfer from the quantum dot to the molecule by more than an order of magnitude, exhibiting a significant quantum Zeno effect.

charge transfer↗
DOE OSTI2018

Laser-driven hydrothermal processing: a new, efficient technique to effect separation of silica from other oxides for analysis

We report on what appeared to be an unstudied regime of laser-matter interactions, when modest-intensity, modest-fluence laser pulses struck weakly-absorbing, silica-rich material that was submerged in water: material was efficiently removed from the surface and colorless particles were left behind, decorating crater's surface. One explanation for this color loss was a transient dissolution of the material, due to the pressure and temperature pulse caused by the laser absorption and thermally-driven expansion of the material. Yet, other explanations were possible. Here, we have studied this process with laser intensity and fluence so low that no crater was formed, when a sample of natural quartzite rock was submerged in deionized water and illuminated with 40 MW cm –2 , 527 nm laser pulses. After one hundred laser pulses, the treated surface of the originally colored quartzite was colorless. We cut the quartzite in cross section and examined the colorless material on the surface with x-ray fluorescence. We report that the transition element Fe was found to be significantly depleted in this colorless layer, while Si was not. This bolsters the hypothesis that the laser exposure led to a transient hydrothermal dissolution of the material, followed by a recrystallization process of the SiO 2 that preferentially released iron oxides into the submerging water.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Lightweight bipolar storage battery

An apparatus [10] is disclosed for a lightweight bipolar battery of the end-plate cell stack design. Current flow through a bipolar cell stack [12] is collected by a pair of copper end-plates [16a,16b] and transferred edgewise out of the battery by a pair of lightweight, low resistance copper terminals [28a,28b]. The copper terminals parallel the surface of a corresponding copper end-plate [16a,16b] to maximize battery throughput. The bipolar cell stack [12], copper end-plates [16a,16b] and copper terminals [28a,28b] are rigidly sandwiched between a pair of nonconductive rigid end-plates [20] having a lightweight fiber honeycomb core which eliminates distortion of individual plates within the bipolar cell stack due to internal pressures. Insulating foam [30] is injected into the fiber honeycomb core to reduce heat transfer into and out of the bipolar cell stack and to maintain uniform cell performance. A sealed battery enclosure [ 22] exposes a pair of terminal ends [26a,26b] for connection with an external circuit.

Rowlette, John J.↗
DOE OSTI2020

Robust A -Type Order and Spin-Flop Transition on the Surface of the Antiferromagnetic Topological Insulator MnBi 2 Te 4

Here, we present microscopic evidence of the persistence of uniaxial A-type antiferromagnetic order to the surface layers of MnBi 2 Te 4 single crystals using magnetic force microscopy. Our results reveal termination-dependent magnetic contrast across both surface step edges and domain walls, which can be screened by thin layers of soft magnetism. The robust surface A-type order is further corroborated by the observation of termination-dependent surface spin-flop transitions, which have been theoretically proposed decades ago. Our results not only provide key ingredients for understanding the electronic properties of the antiferromagnetic topological insulator MnBi 2 Te 4 , but also open a new paradigm for exploring intrinsic surface metamagnetic transitions in natural antiferromagnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Modeling Electron Injection at Semiconductor–Molecule Interfaces using First-Principles Dynamics Simulation: Effects of Nonadiabatic Coupling, Self-energy, and Surface Models

Excited electron transfer across semiconductor–molecule heterogeneous interfaces is central to various future electronic and optoelectronic devices. At the same time, first-principles modeling of such dynamical processes remains as a great challenge in theoretical chemistry and condensed matter physics for developing better understanding at the molecular scale. Excited electron transfer from a molecule to semiconductor surface is a particularly difficult case to model accurately, because the initial state of such an electron injection process often lies deep within the dense manifold of the conduction band states in the semiconductor. Nonadiabatic couplings and energy level alignments at such interfaces as well as the finite size error of the surface model all play important roles in numerical modeling of electron injection via first-principles theory. Here, using representative interfaces between a well-defined hydrogen-terminated Si(111) surface and series of covalently adsorbed conjugated molecules, we investigate the extent to which these theoretical and numerical considerations influence the description of electron injection at the semiconductor–molecule interface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗