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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Controlled synthesis and formation mechanism of monodispersive lanthanum vanadate nanowires with monoclinic structure

Monodisperse LaVO{sub 4} nanowires with relatively high aspect ratio larger than 50 have been prepared by a one-step solvothermal synthesis. This method provides a simple, inexpensive, controllable and reproducible process to produce LaVO{sub 4} nanowires with an average diameter of 15 nm and a high aspect ratio. The as-synthesized products have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fast Fourier transform spectroscopy (FFT), indicative of a well-crystalline monoclinic structure and ascendant nanowire-morphology. The formation mechanism is suggested that oriented attachment plays a vital role in the growth of LaVO{sub 4} nanowires, which recommends a favorable route to fabricate similar morphological and structural nanometer materials. - Graphical abstract: The formation of LaVO{sub 4} nanowires is attributed to oriented attachment, a combination of nanocrystallites through their suitable surface planes, that is, with the same crystallographic orientations of [−120]. Highlights: ► Monodisperse LaVO{sub 4} nanowires with high aspect ratio have been prepared solvothermally without any templates. ► The morphology and structure of LaVO{sub 4} nanowires were characterized by XRD, SEM, TEM techniques. ► The formation mechanism of LaVO{sub 4} nanowires is suggested that oriented attachment plays a vital role.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Preparation and characterization of chitosan/Aloe Vera composite nanofibers generated by electrostatic spinning

Researches on the fabrication of nanostructured based membrane have attracted great attention amongst scientists due to their wide potential applications on medical application. In this work, Chitosan and Aloe Vera sol-gel solution were electrospun using 20 kV DC supply at room temperature. Morphological structure and functional group of nanofibers were characterized using field emission scanning electron microscopy (FESEM) and Fourier-transform infrared spectroscopy (FT-IR) respectively. The optimum parameter obtained at 90% concentration of acetic acid, 0.3 ml/h of solution flow rate and 10 cm distance of nozzle to collector. The fiber diameters were analyzed using the ImageJ software. Average diameters of the Chitosan/Aloe Vera composite nanofibers is 183nm in ranges of 140–260nm.

36 MATERIALS SCIENCE↗
DOE OSTI2021

SMC2021 Where to go in atomic world

'Graphene_CrSi.npy' contains a scanning transmission electron microscopy (STEM) movie from graphene monolayer. The movie is a sequence of atom-resolved images from the same sample region that undergoes chemical and structural transformations due to interaction with electron beam (which is used to perform imaging). 'topo_defects.npy' contains coordinates of some of the objects of interest (topological defects in graphene). It is a dictionary, where keys are frame numbers and values are xy coordinates. These objects are usually localized in relatively small areas of the image and we are interested in identifying them without having to scan an entire grid (which leads to fast degradation of the sample).

36 MATERIALS SCIENCE↗
DOE OSTI2014

Bio-compatibility, surface and chemical characterization of glow discharge plasma modified ZnO nanocomposite polycarbonate

Bio compatibility is an important issue for synthesis of biomedical devices, which can be tested by bioadoptability and creations of active site to enhance the bacterial/cell growth in biomedical devices. Hence a systematic study was carried out to characterize the effects of Nitrogen ion plasma for creations of active site in nano composite polymer membrane. Nano particles of ZnO are synthesized by chemical root, using solution casting nano composite polymeric membranes were prepared and treated with Nitrogen ion plasma. These membranes were characterized by different technique such as optical microscopy, SEM- Scanning electron microscope, optical transmittance, Fourier transform infrared spectroscopy. Then biocompatibility for membranes was tested by testing of bio-adoptability of membrane.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Direct-to-indirect electronic state transition in dynamically compressed GaAs quantum wells

Dynamic compression of GaAs quantum wells was achieved to examine the direct-to-indirect transition in a reduced dimension semiconductor structure under uniaxial strain conditions. Our results show that the transformation deviates significantly from the electronic structure predictions using bulk deformation potentials. This finding is attributed to the suppression of real-space type-II transitions by quantum state interactions due to the presence of large anisotropic strains.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1976

Lossy radial diffusion of relativistic Jovian electrons

The radial diffusion equation with synchrotron losses was solved by the Laplace transform method for near-equatorially mirroring relativistic electrons. The evolution of a power law distribution function was found and the characteristics of synchrotron burn-off are stated in terms of explicit parameters for an arbitrary diffusion coefficient. Emissivity from the radiation belts of Jupiter was studied. Asymptotic forms for the distribution in the strong synchrotron loss regime are provided.

Barbosa, D. D.↗
DOE OSTI2016

Coverage induced structural transformations of tetracene on Ag(110)

Self-assembly of tetracene on an anisotropic surface of Ag(110) has been investigated using scanning tunneling microscopy and low-energy electron diffraction. We observe multistage structural transformations of the self-assembled tetracene on Ag(110) as a function of molecular coverages, which are accompanied by the changes in molecular orientations. They are analyzed by a balance between multiple molecule-molecule and anisotropic substrate-molecule interactions.

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

Does a Free Electron Laser Exhibit Non-Standard Statistics? [Slides and Report]

The originally proposed work under this award sought to develop a theoretical basis for previous experimental observations in free-electron laser (FEL) physics involving certain non-classical effects in the light produced by these devices. A sound and valid theoretical interpretation of these experiments would represent a transformational understanding of free-electron lasers, and of electron-photon interactions in general. The specific objective of the completed work, as described in the attached progress report by Jeongwan Park, was to perform a detailed analysis of an experiment by Chen and Madey (Physical Review Letters; volume 86 number 26, 2001) concerning the purported sub-Poissonian photon statistics in an FEL. Since that published work contradicted FEL theory as presently understood, the purpose of the work under the present subcontract was to obtain a better understanding of the quantum nature of the FEL, to investigate the possibility of theoretical and experimental evidence for the non-standard photon statistics of the FEL, and to critically examine the experimental evidence through a re-evaluation of the data analysis of Chen and Madey. The results of this study showed that there were numerous experimental conditions under which the observed photon statistics could be explained by combining both the photon clustering property and the dead-time effect, and consequently, that the observed photon statistics in the Chen-Madey experiment did not require sub-Poissonian photon statistics for their explanation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

BENZENE FORMATION ON INTERSTELLAR ICY MANTLES CONTAINING PROPARGYL ALCOHOL

Propargyl alcohol (CHCCH{sub 2}OH) is a known stable isomer of the propenal (CH{sub 2}CHCHO) molecule that was reported to be present in the interstellar medium (ISM). At astrochemical conditions in the laboratory, icy layers of propargyl alcohol grown at 85 K were irradiated by 2 keV electrons and probed by a Fourier Transform InfraRed spectrometer in the mid-infrared (IR) region, 4000-500 cm{sup –1}. Propargyl alcohol ice under astrochemical conditions was studied for the first time; therefore, IR spectra of reported amorphous (85 K) and crystalline (180 K) propargyl alcohol ices can be used to detect its presence in the ISM. Moreover, our experiments clearly show benzene (C{sub 6}H{sub 6}) formation to be the major product from propargyl alcohol irradiation, confirming the role of propargyl radicals (C{sub 3}H{sub 3}) formed from propargyl alcohol dissociation that was long expected based on theoretical modeling to effectively synthesize C{sub 6}H{sub 6} in the interstellar icy mantles.

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

Synthesis and Characterization of Er-Doped Nano ZnO Samples

Pure and erbium-doped ZnO nanoparticles (Zn{sub 1−x}Er{sub x}O), (0.00 ≤ x ≤ 0.10), were synthesized by wet chemical co-precipitation method. The structural, optical, and magnetic properties of the prepared samples were investigated using x-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), M-H magnetic hysteresis, and electron paramagnetic resonance (EPR). XRD studies exhibit the presence of a single ZnO wurtzite hexagonal crystal structure for 0.00 ≤ x ≤ 0.06. A secondary phase of Er{sub 2}O{sub 3} appears for x > 0.06. This means that the solubility limit for doping Zn{sup 2+} ions by Er{sup 3+} ions is about x = 0.06 under our preparations condition. The lattice parameter a is not affected by the Erbium doping. On the other hand, the lattice parameter c and the unit cell volume V increase with the increase of x up to x = 0.06. This is attributed to the larger ionic size of Er{sup 3+} ions (0.88 Å) compared to Zn{sup 2+} ions (0.74 Å). Both c and V decrease for x > 0.06. TEM micrographs indicate that the shape and the size of the ZnO nanoparticles are modified by changing the doping level of Er. The UV measurements point out that band gap energy E{sub g} decreases with the increase of x up to x = 0.06. Then, it increases for both x = 0.08 and 0.10. FTIR spectra confirm the presence of O–H and Zn–O stretching modes at 3451.963 and 428.901 cm{sup − 1}, respectively, in pure and doped ZnO samples. The Zn–O stretching mode shifts toward a lower wavenumber for x = 0.06 and toward a higher wavenumber for x = 0.10. M-H hysteresis analysis, at room temperature, reveals that the pure ZnO has a ferromagnetic signal combined with diamagnetic and paramagnetic contributions. This ferromagnetism is reduced for the doped samples up to x = 0.02, and an antiferromagnetic alignment appears for 0.04 ≤ x ≤ 0.10. The saturation magnetization (M{sub s}), the coercivity (H{sub c}), the retentivity (M{sub r}), the anisotropy constant (K{sub a}), and the magnetic moment (μ{sub m}) were estimated and discussed in terms of erbium doping for the different samples. EPR spectra for Zn{sub 1−x}Er{sub x}O were measured at room temperature in order to study the effect of Er substitution on the g value, resonance field (H{sub r}), peak to peak line width (ΔH{sub pp}) and spin–spin relaxation time constant (T{sub 2}).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Metal Ion Binding to the Amyloid β Monomer Studied by Native Top-Down FTICR Mass Spectrometry

Native top-down mass spectrometry is a fast, robust biophysical technique that can provide molecular-scale information on the interaction between proteins or peptides and ligands, including metal cations. Here we have analyzed complexes of the full-length amyloid β (1-42) monomer with a range of (patho)physiologically relevant metal cations using native Fourier transform ion cyclotron resonance mass spectrometry and three different fragmentation methods—collision-induced dissociation, electron capture dissociation, and infrared multiphoton dissociation—all yielding consistent results. Amyloid β is of particular interest as its oligomerization and aggregation are major events in the etiology of Alzheimer’s disease, and it is known that interactions between the peptide and bioavailable metal cations have the potential to significantly damage neurons. Those metals which exhibited the strongest binding to the peptide (Cu{sup 2+}, Co{sup 2+}, Ni{sup 2+}) all shared a very similar binding region containing two of the histidine residues near the N-terminus (His6, His13). Notably, Fe{sup 3+} bound to the peptide only when stabilized toward hydrolysis, aggregation, and precipitation by a chelating ligand, binding in the region between Ser8 and Gly25. We also identified two additional binding regions near the flexible, hydrophobic C-terminus, where other metals (Mg{sup 2+}, Ca{sup 2+}, Mn{sup 2+}, Na{sup +}, and K{sup +}) bound more weakly—one centered on Leu34, and one on Gly38. Unexpectedly, collisional activation of the complex formed between the peptide and [Co{sup III}(NH{sub 3}){sub 6}]{sup 3+} induced gas-phase reduction of the metal to Co{sup II}, allowing the peptide to fragment via radical-based dissociation pathways. This work demonstrates how native mass spectrometry can provide new insights into the interactions between amyloid β and metal cations. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Structure-property relation and Weibull analysis of calcium aluminate cement pastes

Highlights: • Weibull distribution analysis was conducted for calcium aluminate cement pastes with 52 wt% and 71 wt% of alumina contents. • Compressive strength ranged from 10 to 45 MPa. • The hydrated phases found showed diverse polymorphisms of Gibbsite (Nordstrandite, Bayerite, Hidrogarnet and Gehlenite). - Abstract: In this investigation calcium aluminate cement (CAC) pastes with 52 wt% and 71 wt% of alumina contents were fabricated and characterized with different techniques. Samples were made with 0.4 and 0.5 water to cement (W/C) ratios. Both the raw cement powders and their corresponding samples after hydration were characterized in their microstructure by scanning electron microscopy, X-ray diffraction (with Rietveld refinement), X-ray fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), density, and compression tests. With the compressive strength results, Weibull distribution analysis was conducted for 20 samples per composition. The higher compression strength obtained was about 45 MPa, which corresponds to samples with the higher W/C contents. The hydrated phases found showed diverse polymorphisms of Gibbsite (Nordstrandite, Bayerite, Hidrogarnet and Gehlenite).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chemical and physical transformations of carbon-based nanomaterials observed by liquid phase transmission electron microscopy

This article addresses recent advances in liquid phase transmission electron microscopy (LPTEM) for studying nanoscale synthetic processes of carbon-based materials that are independent of the electron beam—those driven by nonradiolytic chemical or thermal reactions. In particular, we focus on chemical/physical formations and the assembly of nanostructures composed of organic monomers/polymers, peptides/DNA, and biominerals. The synthesis of carbon-based nanomaterials generally only occurs at specific conditions, which cannot be mimicked by aqueous solution radiolysis. Carbon-based structures themselves are also acutely sensitive to the damaging effects of the irradiating beam, which make studying their synthesis using LPTEM a unique challenge that is possible when beam effects can be quantifi ed and mitigated. With new direct sensing, high frame rate cameras, and advances in liquid-cell holder designs, combined with a growing understanding of irradiation effects and proper experimental controls, microscopists have been able to make strides in observing traditionally problematic carbon-based materials under conditions where synthesis can be controlled, and imaged free from beam effects, or with beam effects quantified and accounted for. These materials systems and LPTEM experimental techniques are discussed, focusing on nonradiolytic chemical and physical transformations relevant to materials synthesis.

Parent, Lucas R.↗
DOE OSTI2019

Magnetocaloric Effect in La{sub 0.67}Ba{sub 0.33}Mn{sub 0.95}Ni{sub 0.05}O{sub 3} Manganite Near Room Temperature

We report the structural, magnetic, and magnetocaloric properties of La{sub 0.67}Ba{sub 0.33}Mn{sub 0.95}Ni{sub 0.05}O{sub 3} (LBMNO) manganite, synthesized by sol-gel method. X-ray diffraction (XRD) analysis using Rietveld refinement showed that this sample crystallizes in the rhombohedral structure with R 3-bar c space group. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis were used to confirm the structure formation of the LBMNO material. The temperature dependent magnetization data revealed a transition from ferromagnetic (FM) to paramagnetic (PM) phase at T{sub C}= 308 K. Using Arrott plots, it was found that the transition is of a second order. From the measured magnetization data as a function of magnetic applied field, the magnetic entropy change (−ΔS{sub M}) and the relative cooling power RCP have been determined. In the vicinity of T{sub C} (−ΔS{sub M}) reached a maximum value of 2.15 J kg{sup − 1} K{sup − 1} and a large RCP value of about 299 J kg{sup − 1} under 5 T{sup − 1}. This magnetocaloric effect has been analyzed by considering the Landau theory of magnetic phase transition. Consequently, our sample can be considered a promising material in room-temperature magnetic refrigeration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Facile one-pot synthesis and characterization of nickel supported on hierarchically porous carbon

Highlights: • Novel, inexpensive, one-pot, synthesis method for Ni on hierarchically porous carbon. • Disappearance of surfactant mesopores seen with incorporation of nickel. • Distribution of Ni nanoparticles on the hierarchically porous carbon support was studied by SEM. • Nickel nanoparticles were dispersed on macropore walls and not within carbon. - Abstract: Described is a novel, facile route for the synthesis of nickel supported on hierarchically porous carbon (Ni/HPC) using a one-pot co-gelation sol–gel method. Ni/HPC with varying nickel loadings (0.5, 1, 2.5 and 5 wt% Ni) were synthesized and the materials characterized by nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) and Raman spectroscopies. The results show a three-dimensional network of disordered carbon with fine nickel nanoparticles of sizes ranging from 8 nm to 13 nm at 0.5 wt% Ni loading which gradually increased with increase in the Ni loading. The carbon structure was retained at the macropore level, but not at the mesoscale where the ordered mesopores were lost on nickel addition. The nickel nanoparticles were observed to grow on the surface of the ligaments. This may make them particularly suitable for low pressure Ni-catalyzed organic transformations e.g., hydrogenations, C–C coupling, C-heteroatom coupling, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Dynamics of Transformation from Platinum Icosahedral Nanoparticles to Larger FCC Crystal at Millisecond Time Resolution

Atomic motion at grain boundaries is essential to microstructure development, growth and stability of catalysts and other nanostructured materials. However, boundary atomic motion is often too fast to observe in a conventional transmission electron microscope (TEM) and too slow for ultrafast electron microscopy. Here, we report on the entire transformation process of strained Pt icosahedral nanoparticles (ICNPs) into larger FCC crystals, captured at 2.5 ms time resolution using a fast electron camera. Results show slow diffusive dislocation motion at nm/s inside ICNPs and fast surface transformation at μm/s. By characterizing nanoparticle strain, we show that the fast transformation is driven by inhomogeneous surface stress. And interaction with pre-existing defects led to the slowdown of the transformation front inside the nanoparticles. Particle coalescence, assisted by oxygen-induced surface migration at T ≥ 300°C, also played a critical role. Furthermore by studying transformation in the Pt ICNPs at high time and spatial resolution, we obtain critical insights into the transformation mechanisms in strained Pt nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Oxygen Atom Transfer Reactions of Colloidal Metal Oxide Nanoparticles

Redox transformations at metal oxide (MO x )/solution interfaces are broadly important, and oxygen atom transfer (OAT) is one of the simplest and most fundamental examples of such reactivity. OAT is a two-electron transfer process, well-known in gas/solid reactions and catalysis. However, OAT is rarely directly observed at oxide/water interfaces, whose redox reactions are typically proposed to occur in one-electron steps. Reported here are stoichiometric OAT reactions of organic molecules with aqueous colloidal titanium dioxide and iridium oxide nanoparticles (TiO 2 and IrO x NPs). Me 2 SO (DMSO) oxidizes reduced TiO 2 NPs with the formation of Me 2 S, and IrO x NPs transfer O atoms to a water-soluble phosphine and a thioether. The reaction stoichiometries were established and the chemical mechanisms were probed using typical solution spectroscopic techniques, exploiting the high surface areas and transparency of the colloids. Furthermore, these OAT reactions, including a catalytic example, utilize the ability of the individual NPs to accumulate many electrons and/or holes. Observing OAT reactions of two different materials, in opposite directions, is a step toward harnessing oxide nanoparticles for valuable multi-electron and multi-hole transformations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

An alternative solid-state method to prepare pyrochlore-free KTaO{sub 3} at low temperature

Perovskite-type KTaO{sub 3} powder was synthesized by an alternative solid-state method at low temperature. Stoichiometric ammonium tantalum hydroxide, K{sub 2}C{sub 2}O{sub 4} and KF were mixed in water and then dried at room temperature. The crude product was formed by calcining the dried mixture at different temperatures. Pyrochlore-free KTaO{sub 3} powder was successfully synthesized after treating the crude product with water. KF plays an important role to inhibit the formation of pyrochlore K{sub 2}Ta{sub 2}O{sub 6} during the calcination process of ammonium tantalum hydroxide/K{sub 2}C{sub 2}O{sub 4}/KF mixture. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, UV-vis diffuse reflectance (UV-vis) spectroscopy and thermogravimetric (TG) analysis were used to characterize the precursor compound and as-prepared samples. XRD results show that pyrochlore-free KTaO{sub 3} powder can be obtained at 600 deg. C. SEM results reveal that the as-prepared products are agglomerated and each of the agglomerations consists of many small grains with 10-30 nm in diameter. - Graphical abstract: Pyrochlore-free KTaO{sub 3} powder was prepared at 600 deg. C using tantalum hydroxide/K{sub 2}C{sub 2}O{sub 4}/KF raw materials. Pyrochlore K{sub 2}Ta{sub 2}O{sub 6} and perovskite KTaO{sub 3} coexist at 600 deg. C using tantalum hydroxide/K{sub 2}C{sub 2}O{sub 4} raw materials. Highlights: > In-situ degradation of TaO{sub x}(OH){sub 5-x}(NH{sub 4}){sub x}, K{sub 2}C{sub 2}O{sub 4} and KF promotes the reaction. > Synthesis of KTaO{sub 3} displayed a two-step reaction path with the intermediate formation of K{sub 2}TaO{sub 3}F. > Formation of intermediate K{sub 2}TaO{sub 3}F benefits to prepare pyrochlore-free KTaO{sub 3} at low temperature. > Pyrochlore-free KTaO{sub 3} is prepared at 600 deg. C, which is the lowest temperature reported so far by hard chemistry method. > Synthetic method is a facile, rapid, low price and environment friendly route.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗