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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Molecular structure, morphology and growth mechanisms and rates of 5-hydroxymethyl furfural (HMF) derived humins

We apply ATR-FTIR spectroscopy, Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) experiments to investigate the molecular structure, morphology and growth mechanism of 5-hydroxymethyl furfural (HMF) derived humins as a function of HMF conversion. Our FTIR data support a reaction pathway in which humins form either through a ring opening mechanism and/or through substitution at the α or β position via nucleophilic attack. The addition of DMSO as a co-solvent leads to significant changes in the FTIR spectra of humins. We find that the nucleophilic attack pathway is suppressed in the presence of DMSO co-solvent and rationalizes the very small humin particles (~100 nm) observed in SEM images contrary to the large particles (with multimodal size distribution and largest particles of up to 3–4 μm) observed in neat water. DLS experiments under several reaction conditions further confirm the particle size distribution observed via SEM. A plausible reaction network for humin formation, which rationalizes qualitatively our experimental results as well as those reported in the literature, is also postulated.

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

Size‐Tunable Synthesis of Hollow Gold Nanospheres through Control of Reaction Temperature

Here, it is demonstrated that the size tunable hollow gold nanospheres (HGNs) of ≈24–122 nm in diameter can be facilely achieved by controlling a signal parameter, reaction temperature, in the synthesis. The varied particle sizes of HGNs result in highly tunable surface plasmon resonance (SPR) absorption in the entire visible to near infrared region of the spectrum, with maximum peak position from 565 to 850 nm when the reaction temperature is varied from 80 to 10 °C. The particle size and structural properties are determined using dynamic light scattering, transmission‐mode scanning electron microscopy, and high‐resolution transmission electron microscopy. The optical properties are characterized using UV–vis spectroscopy. A mechanism behind the temperature‐dependent HGN synthesis is explained by the thermodynamics of homogeneous nuclei formation of the cobalt scaffold. Discrete dipole approximation calculations are performed to simulate the SPR spectrum and provide insight into the relation between the SPR absorption and structural details of the HGNs. This study demonstrates a simple yet effective method based on temperature control for synthesizing produce size tunable HGNs with varying properties of interest for different applications.

Pu, Ying‐Chih↗
DOE OSTI2016

Silver photo-diffusion and photo-induced macroscopic surface deformation of Ge{sub 33}S{sub 67}/Ag/Si substrate

Ge-chalcogenide films show various photo-induced changes, and silver photo-diffusion is one of them which attracts lots of interest. In this paper, we report how silver and Ge-chalcogenide layers in Ge{sub 33}S{sub 67}/Ag/Si substrate stacks change under light exposure in the depth by measuring time-resolved neutron reflectivity. It was found from the measurement that Ag ions diffuse all over the matrix Ge{sub 33}S{sub 67} layer once Ag dissolves into the layer. We also found that the surface was macroscopically deformed by the extended light exposure. Its structural origin was investigated by a scanning electron microscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Heteroepitaxial growth and surface structure of L1 0 -MnGa(111) ultra-thin films on GaN(0001)

L1 0 -structured MnGa(111) ultra-thin films were heteroepitaxially grown on GaN(0001) under lightly Mn-rich conditions using molecular beam epitaxy. Room-temperature scanning tunneling microscopy (STM) investigations reveal smooth terraces and angular step edges, with the surface structure consisting primarily of a 2x2 reconstruction along with small patches of 1x2. Theoretical calculations were undertaken using density functional theory, and the simulated STM images were calculated using the Tersoff-Hamann approximation, demonstrating that a stoichiometric 1x2 and a Mn-rich 2x2 surface structure give the best agreement with the observed experimental images.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Hard x-ray scanning microscopy with coherent radiation: Beyond the resolution of conventional x-ray microscopes

We demonstrate x-ray scanning coherent diffraction microscopy (ptychography) with 10 nm spatial resolution, clearly exceeding the resolution limits of conventional hard x-ray microscopy. The spatial resolution in a ptychogram is shown to depend on the shape (structure factor) of a feature and can vary for different features in the object. In addition, the resolution and contrast are shown to increase with increasing coherent fluence. For an optimal ptychographic x-ray microscope, this implies a source with highest possible brilliance and an x-ray optic with a large numerical aperture to generate the optimal probe beam.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Plasmonic circular polarization analyzer formed by unidirectionally controlling surface plasmon propagation

Analyzing the polarization of a circularly polarized light is a critical issue. We have fabricated a spiral nano-structure on the Au film by using focused ion beam etching technique. The fabricated structure can be used as a plasmonic circular polarization analyzer. By designing the relative orientation of two nano-apertures in the spiral structural unit, the propagation direction of the surface plasmon polaritons excited by circularly polarized light of opposite handedness can be controlled. Therefore, the spiral structure could be used to accurately determine the helicity of the excited circularly polarized light. Based on the results of scanning near-field optical microscopy, the obtained circular polarization extinction ratio of this structure was above 500. This structure can be used for a flexible detecting size and a very wide spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Two-Step Thermoresponsive Ultrafiltration Membranes from Polymerization of Lyotropic Liquid Crystals

Here, in this study, we present the fabrication of a two-step thermoresponsive ultrafiltration (UF) membrane through polymerization of a lyotropic liquid crystal (LLC). A mixture of commercially available Pluronic F 127 block copolymer, water (containing ammonium persulfate as the initiator), and polymerizable oil (n-butyl acrylate/ethylene glycol dimethacrylate) is used to create an LLC with a lamellar structure, as characterized by cross-polarized light microscopy and atomic force microscopy. Differential scanning calorimetry is employed to evaluate the thermoresponsive behavior of the polymerized LLC (polyLLC). Two-step thermoresponsiveness (~35 and ~50 °C) of the polyLLC is observed due to the lower critical solution temperature (LCST) of F 127 and melting of the crystalline structure of the polyethylene oxide (PEO) chains of the F 127 surfactant. In the next step, the obtained mesophase is cast on a nonwoven polyester support sheet followed by thermal polymerization. The hydration capacity, water flux, water flux recovery after fouling, and molecular weight cutoff (MWCO) of the obtained membrane are evaluated at different temperatures to examine its thermoresponsiveness. The experimental results reveal that the UF membrane has a reversible thermoresponsive behavior at the LCST and PEO melting of polyLLC. Additionally, the cleaning efficiency of the fouled membrane can be enhanced by using its thermoresponsive behavior, resulting in an extended lifetime of the product. Furthermore, the MWCO of the membrane can be altered with temperature due to the pore size change with temperature stimulus.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Titanium Alloys Thin Sheet Welding with the Use of Concentrated Solar Energy

The present study deals with the welding of titanium alloys thin sheets 1.3 mm thick, with the use of concentrated solar energy. The experimental part of the work took place at a medium size solar furnace at the installation of the Centre National de la Recherche Scientifique, at Odeillo, in Southern France, where similar and dissimilar defect-free welds of titanium Grades 4 and 6 were achieved, in the butt joint configuration. After the determination of the appropriate welding conditions, the optimum welded structures were examined and characterized microstructurally, by means of light optical microscopy, scanning electron microscopy, and microhardness testing. In addition, test pieces extracted from the weldments were tested under uniaxial tensile loading aiming to the estimation of the strength and the ductility of the joint. The analysis of the experimental results and the recorded data led to the basic concluding remarks which demonstrate increased hardness distribution inside the fusion area and severe loss of ductility, but adequate yield and tensile strength of the welds.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Main Directions of Recent Works on Al-Zn-Based Alloys for Foundry Engineering

The composition and structural modification of high-aluminum zinc alloys and high-zinc aluminum alloys influence their wear properties and structural stability. The work described has been aimed at improving properties of the sand-cast Al-Zn-based foundry alloys, particularly their ductility and dimensional stability, by melt inoculation and/or change of chemical composition. In a series of studies, high-aluminum Zn-(25-26) wt.% Al-(1-2.5) wt.% Cu and high-zinc Al-(27-30) wt.% Zn-(1.5-2.5) wt.% Cu alloys have been doped with different levels of added Ti and Mn. The alloys’ structure and mechanical properties have been studied using scanning electron microscopy (SEM), light microscopy (LM), dilatometry and pin-on-disk wear measurements. A small addition of Ti introduced with Zn-4Ti master alloy leads to significant grain refinement of the high-aluminum zinc alloys. A small addition of Ti introduced with Al-3Ti-0.15C master alloy leads to significant grain refinement of the high-zinc aluminum alloys. In the ternary alloys, partially replacing Cu with Ti and/or Mn allows dimensional changes to be reduced while preserving good wear properties.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Polythiophene-block-polyfluorene and Polythiophene-blockpoly(fluorene-co-benzothiadiazole): Insights into the Self-Assembly of All-Conjugated Block Copolymers

All-conjugated block copolymers have significant potential for solution-processed optoelectronic applications, in particular those relying on a p/n junction. Herein, we report the synthesis and structure of all-conjugated diblock copolymers poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene) and poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene-co-benzothiadiazole) in thin films and in the bulk. The diblock copolymers are prepared using a combination of Grignard metathesis polymerization and Suzuki polycondensation and characterized with NMR spectroscopy, size-exclusion chromatography, multiangle laser light scattering, and UV/vis spectroscopy. Structure in thin films and in the bulk is characterized using differential scanning calorimetry, X-ray diffraction, small-angle X-ray scattering, and atomic force microscopy. Diblock copolymer thin films self-assemble into a crystalline nanostructure with some long-range order after extended solvent annealing, and X-ray scattering measurements show that powder samples exhibit crystallinity throughout the bulk. By temperature dependent X-ray scattering measurements, we find that diblock copolymers self-assemble into crystalline nanowires with phase segregated block copolymer domains. These measurements show all-conjugated diblock copolymers may be useful for achieving solution-processed active layers in organic photovoltaics and light-emitting diodes with optimized structural and photophysical characteristics.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Research on the effect of crystal structures on W-TiO{sub 2} nanotube array photoelectrodes by theoretical and experimental methods

W-doped/undoped TiO{sub 2} nanotube array (TNAs) photoelectrodes with different nanostructures were successfully fabricated using the anodization method. Their morphology and characteristics were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and ultra violet/visible light diffuse reflectance spectra (UV/vis/DRS). Their electronic structure and optical properties were studied by means of first-principle. Photocatalytic (PC) performance of W-TNAs photoelectrodes with different crystal structures was evaluated using the decomposition rates of Rhodamine B (Rh.B) under xenon light illumination. The results demonstrated that W substituting Ti broadened the width of conduction band (CB) and valence band (VB) of anatase and rutile TiO{sub 2}, reduced the band gap of rutile TiO{sub 2} and even caused its red-shift. W incorporated into TNAs photoelectrodes extended light absorption threshold and enhanced its utilization of solar light and PC activity, particularly, the PC performance of W-TNAs photoelectrodes with mixed crystal and rutile crystal structure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Visible-light photoconductivity of Zn1-xCoxO and its dependence on Co2+ concentration

Many metal oxides investigated for solar photocatalysis or photoelectrochemistry have band gaps that are too wide to absorb a sufficient portion of the solar spectrum. Doping with impurity ions has been extensively explored as a strategy to sensitize such oxides to visible light, but the electronic structures of the resulting materials are frequently complex and poorly understood. Here, we report a detailed photoconductivity investigation of the wide-gap II-VI semiconductor ZnO doped with Co2+ (Zn1-xCoxO), which responds to visible light in photoelectrochemical and photoconductivity experiments and thus represents a well-defined model system for understanding dopant-sensitized oxides. Variable-temperature scanning photoconductivity measurements have been performed on high-structural-quality Zn1-xCoxO epitaxial films to examine the relationship between dopant concentration (x) and visible-light photoconductivity, with particular focus on mid-gap d-d photoactivity. Excitation into the intense 4T1(P) d-d band at ~2.0 eV (620 nm) leads to Co2+/3+ ionization with a quantum efficiency that increases with decreasing cobalt concentration and increasing sample temperature. Both spontaneous and thermally assisted ionization from the Co2+ d-d excited state are found to become less effective as x is increased, attributed to an increasing conduction-band-edge potential. These trends counter the increasing light absorption with increasing x, explaining the experimental maximum in external photon-to-current conversion efficiencies at values well below the solid solubility of Co2+ in ZnO.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Experimental evaluation of direct current magnetron sputtered and high-power impulse magnetron sputtered Cr coatings on SiC for light water reactor applications

Two types of physical vapor deposition Cr coatings were deposited on chemical vapor deposited SiC coupons using conventional direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) to mitigate the corrosion of SiC, an advanced fuel and structural material in light water nuclear reactor cores. Coating microstructure was characterized using scanning electron microscopy and scanning transmission election microscopy. X-ray diffraction analysis was conducted for phase identification and qualitative analysis of residual stresses. The mechanical integrity of the coatings was evaluated using scratch testing, micro-indentation, and nano-indentation tests. Additionally, the microstructure of the DCMS coating consisted of fine columnar grains with nanoscale intercolumnar channels, while the HiPIMS microstructure was denser and free of any columnar defects. The DCMS coating showed a small tensile residual stress, while the HiPIMS coating was under compressive stress. Both types of coatings showed good mechanical integrity in terms of ductility and adhesion to the substrate. Corrosion performance of the coatings was assessed with a 30-day high temperature water autoclave test. Both types of coatings formed a protective Cr 2 O 3 surface layer 20-30 nm thick during the autoclave test. In the DCMS coating, the columnar defects provided permeation pathways for water penetration resulting in oxide formation in the intercolumnar regions in the interior of the coating. Overall, both types of Cr coatings offer promise for the mitigation of hydrothermal corrosion of SiC in light water reactor operating environments.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Efficient linear phase contrast in scanning transmission electron microscopy with matched illumination and detector interferometry

The ability to image light elements in soft matter at atomic resolution enables unprecedented insight into the structure and properties of molecular heterostructures and beam-sensitive nanomaterials. In this study, we introduce a scanning transmission electron microscopy technique combining a pre-specimen phase plate designed to produce a probe with structured phase with a high-speed direct electron detector to generate nearly linear contrast images with high efficiency. We demonstrate this method by using both experiment and simulation to simultaneously image the atomic-scale structure of weakly scattering amorphous carbon and strongly scattering gold nanoparticles. Our method demonstrates strong contrast for both materials, making it a promising candidate for structural determination of heterogeneous soft/hard matter samples even at low electron doses comparable to traditional phase-contrast transmission electron microscopy. Ultimately, simulated images demonstrate the extension of this technique to the challenging problem of structural determination of biological material at the surface of inorganic crystals.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Isotope effects in molecular structures and electronic properties of liquid water via deep potential molecular dynamics based on the SCAN functional

Here, Feynman path-integral deep potential molecular dynamics (PI-DPMD) calculations have been employed to study both light (H 2 O) and heavy water (D 2 O) within the isothermalisobaric ensemble. In particular, the deep neural network is trained based on ab initio data obtained from the strongly constrained and appropriately normed (SCAN) exchange-correlation functional. Because of the lighter mass of hydrogen than deuteron, the properties of light water are more influenced by nuclear quantum effect than those of heavy water. Clear isotope effects are observed and analyzed in terms of hydrogen-bond structure and electronic properties of water that are closely associated with experimental observables. The molecular structures of both liquid H 2 O and D 2 O agree well with the data extracted from scattering experiments. The delicate isotope effects on radial distribution functions and angular distribution functions are well reproduced as well. Our approach demonstrates that deep neural network combined with SCAN functional based ab initio molecular dynamics provides an accurate theoretical tool for modeling water and its isotope effects.

36 MATERIALS SCIENCE↗
DOE OSTI2018

3D microstructure reconstruction of casting aluminum alloy based on serial block-face scanning electron microscopy

In this work, the inner microstructure of aluminum-silicon casting alloy was experimentally investigated to reveal the spatial morphology and phase distribution. Its industrial use is as a light-weight structural material. As a powerful three-dimensional (3D) imaging tool at the nano-scale, the serial block-face scanning electron microscopy (SBFSEM) was employed to investigate the specimens. After being 3D reconstructed, the images were visualized to identify preference for several specific intermetallics by quantitative analysis. It was found that these phases have certain relationships in spatial distribution and differences in spatial shapes. In conclusion, the spatial distribution of cracks was studied to understand their propagation and growth.

3D microstructure reconstruction↗
DOE OSTI2019

Nanosized carriers for hydrophobic compounds based on mesoporous silica: synthesis and adsorption properties

MCM-41 type mesoporous silica particles were obtained using a template method in an alkaline medium and cetyltrimethylammonium bromide as a matrix. The structural and adsorption characteristics of the mesoporous material were studied by dynamic light scattering, scanning electron microscopy, low-temperature adsorption—desorption of nitrogen, IR spectroscopy, and simultaneous thermal analysis. It was shown that the obtained mesoporous material possesses high porosity with the specific pore volume in excess of 1 cm{sup 3} g{sup −1}. It was established that the size of silica particles does not exceed 200 nm, which is a value acceptable for the penetration of drugs through cell membranes. The optimal compositions of aqueous dispersions of MCM-41 with minimal sedimentation processes were determined. A drug (indomethacin) was encapsulated into the silica pores using the precipitation method at various temperatures (40 and 60 °C), the quantitative parameters of loading efficiency were calculated. The infl uence of temperature on the encapsulation ability was demonstrated.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Interdomain region in single-crystal lithium niobate bimorph actuators produced by light annealing

The interdomain region of a bidomain strucrture formed in 127°-cut lithium niobate single crystals using light annealing has been studied by optical and scanning probe microscopies. A periodic subdomain structure on the 180° macrodomain wall is visualized by piezoresponse force microscopy. The piezoresponse signal (polarization) is shown to be a power-law function of the domain width with an exponent n = 0.53.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗