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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Activating Layered Metal Oxide Nanomaterials via Structural Engineering as Biodegradable Nanoagents for Photothermal Cancer Therapy

Layered metal oxides including MoO 3 and WO 3 have been widely explored for biological applications owing to their excellent biocompatibility, low toxicity, and easy preparation. However, they normally exhibit weak or negligible near-infrared (NIR) absorption and thus are inefficient for photo-induced biomedical applications. Herein, the structural engineering of layered MoO 3 and WO 3 nanostructures is first reported to activate their NIR-II absorption for efficient photothermal cancer therapy in the NIR-II window. White-colored micrometre-long MoO 3 nanobelts are transformed into blue-colored short, thin, defective, interlayer gap-expanded MoO 3–x nanobelts with a strong NIR-II absorption via the simple lithium treatment. The blue MoO 3–x nanobelts exhibit a large extinction coefficient of 18.2 L g –1 cm –1 and high photothermal conversion efficiency of 46.9% at 1064 nm. After surface modification, the MoO 3–x nanobelts can be used as a robust nanoagent for photoacoustic imaging-guided photothermal therapy to achieve efficient cancer cell ablation and tumor eradication under irradiation by a 1064 nm laser. Importantly, the biodegradable MoO 3–x nanobelts can be rapidly degraded and excreted from body. We report the study highlights that the structural engineering of layered metal oxides is a powerful strategy to tune their properties and thus boost their performances in given applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electronic Structure of Double-Layer Epitaxial Graphene on SiC(0001) Modified by Gd Intercalation

In this work, we systematically study the effects of Gd adsorption and intercalation on the electronic band structure of double-layer epitaxial graphene on Si-terminated SiC(0001) by first-principles calculations. We show that Gd adsorption and intercalation exhibit strong effects on the coupling between the graphene layers and between the buffer layer and substrate. Different adsorption/intercalation geometries can result in very different electron band structures. The number of Dirac cones and the positions of the Dirac cones relative to the Fermi level can be effectively manipulated through controlling the Gd adsorption/intercalation geometries. Our calculations provide useful insights to guide the experimental design of graphene-based materials with desirable functionalities for applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

Fuselage Structure Response to Boundary Layer, Tonal Sound, and Jet Noise

Experiments have been conducted to study the response of curved aluminum and graphite-epoxy fuselage structures to flow and sound loads from turbulent boundary layer, tonal sound, and jet noise. Both structures were the same size. The aluminum structure was reinforced with tear stoppers, while the graphite-epoxy structure was not. The graphite-epoxy structure weighed half as much as the aluminum structure. Spatiotemporal intermittence and chaotic behavior of the structural response was observed, as jet noise and tonal sound interacted with the turbulent boundary layer. The fundamental tone distributed energy to other components via wave interaction with the turbulent boundary layer. The added broadband sound from the jet, with or without a shock, influenced the responses over a wider range of frequencies. Instantaneous spatial correlation indicates small localized spatiotemporal regions of convected waves, while uncorrelated patterns dominate the larger portion of the space. By modifying the geometry of the tear stoppers between panels and frame, the transmitted and reflected waves of the aluminum panels were significantly reduced. The response level of the graphite-epoxy structure was higher, but the noise transmitted was nearly equal to that of the aluminum structure. The fundamental shock mode is between 80 deg and 150 deg and the first harmonic is between 20 deg and 80 deg for the underexpanded supersonic jet impinging on the turbulent boundary layer influencing the structural response. The response of the graphite-epoxy structure due to the fundamental mode of the shock impingement was stabilized by an externally fixed oscillator.

Maestrello, L.↗
DOE OSTI2019

Lattice Structure and Dynamics of Two-Layer Heterostructures of Barium–Strontium Titanate and Layered Bismuth Titanate of Various Thicknesses on a Magnesium Oxide Substrate

The lattice structure and dynamics of single-crystal Bi{sub 4}Ti{sub 3}O{sub 12} with a thickness from 4 to 430 nm on a (001)MgO substrate with a previously deposited Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} sublayer (4 nm) have been studied. The two-layer structures were prepared by radio-frequency sputtering of ceramic targets of the corresponding compositions. The X-ray diffraction studies performed at room temperature have shown that, in this heterostructure, axis c of the Bi{sub 4}Ti{sub 3}O{sub 12} unit cell is perpendicular to the substrate, and direction [100] has an angle of ±45° to the [100]MgO direction. At the thicknesses of Bi{sub 4}Ti{sub 3}O{sub 12} to ~40 nm, the film unit cell is compressed in the direction of a normal to the substrate plane and extended in the conjugate plane, and the sign of the deformation is changed at large thicknesses. It is found that the phonon mode frequency in the Bi{sub 4}Ti{sub 3}O{sub 12} film shift and additional peaks appear in the Raman spectra, which demonstrates an increase in the degree of monoclinic distortion of the film crystal structure as compared to the crystal structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Characterization and Optimization of GaN Cap Layers and SiN Cap Layers on AlGaN/GaN HEMT Structures Grown on 200 mm GaN on Silicon

We have studied capping layers for AlGaN‐based high electron mobility transistor (HEMT) structures, looking at different thicknesses of GaN, SiN, and GaN + SiN caps. SiN capping has no effect on the sheet resistance of the layers, as expected from a high quality amorphous passivation layer. GaN cap layers increase the sheet resistance whether combined with a SiN cap or not, a consequence of the polarisation charge present at the GaN/AlGaN interface. For both GaN and SiN caps on their own, we get excellent morphology from only 2 nm thickness, with no degradation for layers up to 10 nm thick. For GaN + SiN caps, we have a speckled morphology with lots of small holes, which transmission electron microscopy (TEM) analysis showed to be linked to holes created in the GaN layers before the deposition of SiN layers. We attribute this to the roughening effect of silane on GaN layers, known in the literature. Upon processing SiN capped and GaN + SiN capped layers into HEMT based heterojunction diode devices, the two have equivalent forward current, but GaN + SiN capping has greatly increased reverse current. We conclude that GaN + SiN is not an appropriate capping layer for AlGaN HEMT based diodes, compared with high quality in situ SiN passivation directly grown on the AlGaN.

Charles, Matthew↗
DOE OSTI2018

The Transfer of a Holographic Structure from Dihromated Gelatin Layers on a Polymethylmethacrylate Substrate

The possibility of the transfer of a holographic structure that was originally registered on layers of dichromated gelatin (DCG) onto a substrate material of polymethylmethacrylate (PMMA) has been shown. The use of a selective destructive effect of short-wave UV radiation with a wavelength that is less than 270 nm is the basis of the mechanism of formation of secondary relief-phase holographic structure on the surface of PMMA. The optimization of processing modes and selection of developing compositions which are based on isopropanol and methylisobutylketone (MIBK) have been carried out, which made it possible to create reliefphase holographic gratings with high diffraction efficiency (DE) of about 25% and the maximum depth of the surface relief of the order of 1 μm on the substrates of PMMA.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Self-Assembly of a Linear Alkylamine Bilayer around a Cu Nanocrystal: Molecular Dynamics

Copper nanocrystals are often grown with the help of alkylamine capping agents, which direct the nanocrystal shape. However, the role of these molecules is still unclear. We characterized the assembly of aqueous tetradecylamine (TDA) around a Cu nanocrystal and found that TDA exhibits a temperature-dependent bilayer structure. The bilayer involves an inner layer, in which TDA binds to Cu via the amine group and tends to orient the alkyl tail perpendicular to the surface, and an outer layer whose structure depends on temperature. At low temperatures, alkylamines in the inner layer form bundles with no apparent relation to the crystal facets. Alkylamines in the outer layer tend to orient their long axes perpendicular to the Cu surfaces, with interdigitation into the inner layer. At high temperatures, alkylamines in the inner layer lose their bundle structure, and outer-layer alkylamines tend to orient themselves tangential to the Cu surfaces, forming a “web” above inner-layer TDA. TDA exhibits a rapid interlayer exchange at typical synthesis temperatures, consistent with experiment. Here, the variety in the assemblies seen here and in other studies of alkanethiols around gold nanocrystals indicates a richness in the assemblies that can be achieved by modulating the interaction between the strongly binding end group and the surface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Long‐Term Structural Evolution of an Intercalated Layered Semiconductor

Intercalated molecules can dramatically modify the electronic band structure of layered semiconductors, significantly altering the optical properties of the material. In the layered monochalcogenide Gallium Telluride (GaTe), exposure to air induces a nearly 1 eV reduction of its band gap due to the interlayer diffusion and chemisorption of oxygen. The effect of oxygen chemisorption at the Te‐terminated surfaces on the structure of GaTe, however, is much less known. To better understand the structure–property relationship of intercalated GaTe, a systematic, long‐term, X‐ray diffraction study has been performed on GaTe exfoliated crystals exposed to ambient conditions. It is observed that the structural changes are not limited to a previously observed short‐term increase in lattice expansion. Over the course of months and even years after exfoliation, the oxygen adsorbates continue to modify the structure of GaTe, inducing significant disorder and grain reorientation. It is estimated that approximately one out of every two grains is slightly displaced by the intercalating oxygen, demonstrating a significant increase in grain mosaicity, while still maintaining the original {−2 0 1} out‐of‐plane texture. Correlating these structural transformations to observed changes in electrical and optical properties will enable capitalization of the use of adsorbates to engineer novel properties in these layered materials.

Chew, Annabel R.↗
DOE OSTI2019

Investigation into the Influence of a Buffer Layer of Nanoporous Silicon on the Atomic and Electronic Structure and Optical Properties of A{sup III}N/por-Si Heterostructures Grown by Plasma-Activated Molecular-Beam Epitaxy

The influence of using a buffer sublayer of nanoporous por-Si on the morphological, physical, and structural properties of nanocolumnar In{sub x}Ga{sub 1 –x}N structures fabricated by plasma-activated molecular-beam epitaxy on single-crystal Si(111) substrates is shown. Using a set of structural-spectroscopic analytical methods, the electronic structure of the grown heterostructures, morphology, and optical properties are investigated, and the interrelations between them are established. It is shown that the use of a por-Si sublayer makes it possible to attain a more uniform distribution of diameters of In{sub x}Ga{sub 1 –x}N nanocolumns and to increase the photoluminescence intensity of the latter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Methods for forming electrocatalyst structures and electrodes comprising same

Described herein are methods of forming an electrocatalyst structure on an electrode, comprising depositing a first layer on the electrode using atomic layer deposition (ALD), wherein the first layer comprises a plurality of discrete nanoparticles of a first electrocatalyst, and depositing one or more of a second layer on the first layer and the electrode using ALD, wherein the one or more second layer comprises a second electrocatalyst, wherein the first layer and the one or more second layers, collectively, form a multi-layer electrocatalyst structure on the electrode. Also described are electrodes having a multi-layer electrocatalyst structure. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.

Song, Xueyan↗
DOE OSTI2020

Aspects of the synthesis of thin film superconducting infinite-layer nickelates

The recent observation of superconductivity in Nd 0.8 Sr 0.2 NiO 2 calls for further investigation and optimization of the synthesis of this infinite-layer nickelate structure. Here, we present our current understanding of important aspects of the growth of the parent perovskite compound via pulsed laser deposition on SrTiO 3 (001) substrates and the subsequent topotactic reduction. We find that to achieve single-crystalline, single-phase superconducting Nd 0.8 Sr 0.2 NiO 2 , it is essential that the precursor perovskite Nd 0.8 Sr 0.2 NiO 3 thin film is stabilized with no visible impurity phases; in particular, a Ruddlesden–Popper-type secondary phase is often observed. We have further investigated the evolution of the soft-chemistry topotactic reduction conditions to realize full transformation to the infinite-layer structure with no film decomposition or formation of other phases. We find that capping the nickelate film with a subsequent SrTiO 3 layer provides an epitaxial template to the top region of the nickelate film, much like the substrate. Thus, for currently optimized growth conditions, we can stabilize superconducting single-phase Nd 0.8 Sr 0.2 NiO 2 (001) epitaxial thin films up to ~10 nm.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Structures Of Turbulent Boundary Layers

Report presents second part of two-part comprehensive study of coherent motions in, and structures of, turbulent boundary-layer flows. Study critically reviews current fragmented knowledge with view toward eventual unification and understanding of physical causes and statistical properties of turbulence phenomena.

Robinson, Stephen K.↗
DOE OSTI2020

Probing Thermal Stability of Li-Ion Battery Ni-Rich Layered Oxide Cathodes by means of Operando Gas Analysis and Neutron Diffraction

Thermal stability is a crucial parameter that must be considered within the overall performance metrics of Ni-rich layered oxide cathodes. While the intrinsic structural stability of the cathode materials under thermal conditions is important, it is also critical to consider their reaction with electrolytes. In this study, operando gas analysis, ex situ neutron diffraction, and differential scanning calorimetry were combined to give a broader picture of the thermal stability of Ni-rich NMC cathodes. Li 1– x Ni 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) composite materials with four different states of charge were investigated with and without the presence of an electrolyte. It has been found that electrolyte can greatly accelerate both the structural and thermal decomposition of the cathode materials. A higher state of charge will also make cathode materials more susceptible to thermal shock. Without an electrolyte, O 2 release inducing a structural change from layered to rock salt was the major observation during thermal runaway. However, all samples retained some levels of layered structure after annealing up to 300 °C without the electrolyte. In comparison, almost all the O3-type layered phase transformed to the rock-salt phase for the cathode materials heated with the electrolyte at the same experimental conditions. Moreover, the amount of CO 2 increased by nearly two orders of magnitude when annealing cathode materials with electrolyte in operando gas analysis experiments. More delithiated NMC811 samples released larger amounts of CO 2 at earlier onset temperatures, resonating well with the differential scanning calorimetry (DSC) results showing that more delithiated samples release more heat during thermal shock.

25 ENERGY STORAGE↗
NASA NTRS1992

Sensitivity of the structure of untripped mixing layers to small changes in initial conditions

An experimental study was conducted concerning the influence of small changes in initial conditions on the near- and far-field evolution of the three-dimensional structure of a plan mixing layer. A two-stream mixing layer with a velocity ratio of 0.6 was generated with the initial boundary layers on the splitter plate laminar and was nominally two-dimensional. The initial conditions were changed slightly by interchanging the high- and low-speed sides of the wind tunnel, while maintaining the same velocities, and hence velocity ratio. This resulted in small changes in the initial boundary layer properties, and the perturbations present in the boundary layers were interchanged between the high- and low-speed sides for the two cases. The results indicate that, even with this relatively minor change in initial conditions, the near-field regions of the two cases differ significantly. The peak Reynolds stress levels in the near-field differ by up to 100 percent, and this is attributed to a difference in the location of the initial spanwise vortex roll-up. In addition, the positions and shapes of the individual streamwise vortical structures differ for the two cases, although the overall structures differ for the two cases, although the overall qualitative description of these structures is comparable. The subsequent reorganization and decay of the streamwise vortical structures is very similar for the two cases. As a result, in the far field, both mixing layers achieve similar structure, yielding comparable growth rates, Reynolds stress, distribution, and spectral content.

Plesniak, M. W.↗
DOE OSTI2018

Atomic-layer-resolved composition and electronic structure of the cuprate B i 2 S r 2 CaC u 2 O 8 + δ from soft x-ray standing-wave photoemission

A major remaining challenge in the superconducting cuprates is the unambiguous differentiation of the composition and electronic structure of the CuO 2 layers and those of the intermediate layers. The large c axis for these materials permits employing soft x-ray (930.3 eV) standing wave (SW) excitation in photoemission that yields atomic layer-by-layer depth resolution of these properties. Applying SW photoemission to Bi 2 Sr 2 CaCu 2 O 8+δ yields the depth distribution of atomic composition and the layer-resolved densities of states. We detect significant Ca presence in the SrO layers and oxygen bonding to three different cations. The layer-resolved valence electronic structure is found to be strongly influenced by the atomic supermodulation structure, as determined by comparison to density functional theory calculations, by Ca-Sr intermixing, and by correlation effects associated with the Cu 3 d -3 d Coulomb interaction, further clarifying the complex interactions in this prototypical cuprate. Here, measurements of this type for other quasi-two-dimensional materials with large c represent a promising future direction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Mild Hydrothermal Crystal Growth of Two Luminescing Uranyl Phosphates Exhibiting an Autunite-Type Sheet Structure

Two new layered uranyl phosphate compounds, K(UO 2 )PO 4 (H 2 O) 3 and Na(UO 2 )PO 4 (H 2 O) 1.52 , crystallizing in an autunite-type sheet structure, were successfully synthesized as both single-crystals and polycrystalline powders under mild hydrothermal conditions. The compound K(UO 2 )PO 4 (H 2 O) 3 crystallizes in the tetragonal crystal system with the space group P4/ncc, exhibiting lattice parameters of a = b = 6.99320(7) Å and c = 17.8389(3) Å. Similarly, Na(UO 2 )PO 4 (H 2 O) 1.52 also crystallizes in the tetragonal crystal system, however, in the space group P4/nmm and exhibits lattice parameters of a = b = 6.9787 Å and c = 8.6303(17) Å. Both compounds adopt layered structures, a characteristic feature of uranyl phosphates, and exhibit intense green fluorescence typical for uranyl-containing materials. As a result, the infrared spectroscopy, photoluminescence, and scintillation properties of these compounds were investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Convective structure of the planetary boundary layer of the ocean during gale

The structure of the Planetary Boundary Layer (PBL) was measured, using an airborne lidar, over the Atlantic Ocean during several intensive observation periods of the Genesis of Atlantic Lows Experiment (GALE). Primary emphasis is on the understanding of the convective structure within the PBL during cold air outbreaks. Cold outbreaks generally occur in between the development of coastal storms; and behind a cold front sweeping down from Canada out across the Atlantic. As the cold dry air moves over the relatively warm ocean, it is heated and moistened. The transfer of latent and sensible heat during these events accounts for most of the heat transfer between the ocean and atmosphere during winter. Moistening of the PBL during these eventsis believed to be an important factor in determining the strength of development of the storm system which follows. In general, the more PBL moisture available as latent heat the higher the probability the storm will intensify. The major mechanism for vertical mixing of heat and mositure within the PBL is cellular convection. Knowlede of the organization and structure of the convection is important for understanding the process.

Melfi, S. H.↗
DOE OSTI2019

Chemical and Structural Diversity of Hybrid Layered Double Perovskite Halides

Hybrid halide double perovskites are a class of compounds attracting growing interest due to their richness of structure and property. Two-dimensional (2D) derivatives of hybrid double perovskites are formed by the incorporation of organic spacer cations into three-dimensional (3D) double perovskites. Here, we report a series of seven new layered double perovskite halides with propylammonium (PA), octylammonium (OCA), and 1,4-butyldiammonium (BDA) cations. The general formulas of the compounds are A m M I M III X 8 (single-layered Ruddlesden–Popper type with m = 4 and A = PA or OCA, and single-layered Dion–Jacobson type with m = 2 and A = BDA, M I = Ag, M III = In or Bi, X = Cl or Br) and PA 2 Cs M I M III Br 7 (bilayered, with M I = Ag, M III = In or Bi). These families of compounds demonstrate significant versatility, with tunable layer thickness, the ability to vary the interlayer spacing, and the ability to selectively tune the band gap by varying the M I and M III cations along with the halide anions. The band gap of the single-layered materials varies from 2.41 eV for PA 4 AgBiBr 8 to 3.96 eV for PA 4 AgInCl 8 . Photoluminescent emission spectra of the layered double perovskites at low-temperature (100 K) are reported, and density functional theory electronic structure calculations are presented to understand the nature of the band gap evolution. The development of new structural and compositions in layered double perovskite halides enhances the understanding of structure–property relations in this important family.

36 MATERIALS SCIENCE↗