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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Use of nanoindentation technique for a better understanding of the fracture toughness of Strombus gigas conch shell

In this work the nanochemical properties of the composite organomineral biomaterial constituting Strombus gigas conch shell are studied by means of dynamic mechanical analyses associated to nanoidentation technique. The measurements are performed on shell samples presenting different surface orientations relative to the growth axis of the conch shell. The influence of the organic component of the biomaterial on its nanomechanical properties is also investigated by studying fresh and dried S. gigas conch shells. Monocrystalline aragonite is used as a reference. For the understanding of nanochemical behaviour, special attention is paid to the pop in events observed on the load/displacement curves which results from nanofractures' initiation and propagation occuring during the load process. In order to better understand the mechanical properties systematic studies of the structure and morphology are performed using scanning electron microscopy, atomic force microscopy and X-ray diffractometry. The hardness and Young's modulus values measured on bio aragonite samples are close to those of the aragonite mineral standard. This surprising result shows that, H and E values are not related to the bio composition and lamellar structure of the bio aragonite. However, it was found that the organic layer and the micro architecture strongly influence the nanofracture initiation and propagation processes in the samples. Statistic study of the pop-in events can help to predict the macroscopic mechanical behaviour of the material. - Highlights: ► Nanomechanical properties of Strombus gigas conch shell ► Low influence of the crossed lamellar structure on H and E values at the nano scale ► Strong influence of the crossed lamellar on nanocracks initiation ► Correlation between mechanical behaviors at the macro and nano scales.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Pseudomorphic growth of InAs on misoriented GaAs for extending quantum cascade laser wavelength

The authors have studied the impact of epilayer strain on the deposition of InAs/GaAs on (100) and (111)B with 2° offset toward<2-1-1> surfaces. Consequences of a 7% lattice mismatch between these orientations in the form of three-dimensional growth are less apparent for (111)B with 2° offset toward<2-1-1> surfaces compared to (100). By exploring a range of molecular beam epitaxy process parameters for InAs/GaAs growth and utilizing scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to evaluate the quality of these strained layers, the authors develop empirical models that describe the influence of the process conditions in regards to surface roughness with >92% accuracy. The smoothest InAs/GaAs samples demonstrated average surface roughness of 0.08 nm for 10 μm{sup 2} areas, albeit at very low deposition rates. The authors have found the most important process conditions to be substrate temperature and deposition rate, leading us to believe that controlling diffusion length may be the key to reducing defects in severely strained structures. InGaAs/AlGaAs quantum cascade laser structures were also produced on (111)B with 2° offset toward<2-1-1> to take advantage of the piezoelectric effect, and the modified laser transitions due to these effects were observed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermally initiated disproportionation of manganese(II) bis(1-hydroxyethylidene)diphosphonate. Formation and properties of the lepidoid structure of manganese(II) (1-hydroxyethylidene)diphosphonate-2-hydroxyethaneaminium whiskers. Agronomical efficiency of the manganese(II) complex with (1-hydroxyethylidene)diphosphonic acid

The reaction of poorly soluble manganese(II) bis(1-hydroxyethylidene)diphosphonate tetrahydrate (Mn(H{sub 3}L){sub 2}•4H{sub 2}O) with 2-aminoethanol (H{sub 2}NCH{sub 2}CH{sub 2}OH) in an aqueous medium on heating to 70—80 оС causes the initial formation of soluble manganese(II) bis(1-hydroxyethylidene)diphosphonate tris(1-hydroxyethaneaminium) (Mn(H{sub 3}L)2• •3H{sub 2}NCH{sub 2}CH{sub 2}OH•4H{sub 2}O), which then disproportionates to slightly soluble manganese(II) (1-hydroxyethylidene)diphosphonate-2-hydroxyethaneaminium (MnH{sub 2}L•H{sub 2}NCH{sub 2}CH{sub 2}OH) and coordination polymer of 1-hydroxyethylidenediphosphonic acid with 2-aminoethanol containing no metal cations. In the course of the reaction, MnH{sub 2}L•H{sub 2}NCH{sub 2}CH{sub 2}OH precipitates as whiskers that are grouped into a leaf (lepidoid) structure. The latter was examined by IR spectroscopy, X-ray phase analysis, scanning electron microscopy, atomic force microscopy, optical microscopy, and thermal desorption of nitrogen. The starting and resulting manganese compounds refer to poorly soluble crystalline complexes. The presence of a 2-aminoethanol molecule in the final product leads to an increase in the solubility from 0.40 to 0.54 g in 100 mL of the solution. Poorly soluble MnH{sub 2}L•H{sub 2}NCH{sub 2}CH{sub 2}OH is easily converted to a soluble form by the treatment with 2-aminoethanol or 2-amino-2-(hydroxy- methyl)propane-1,3-diol (H{sub 2}NC(CH{sub 2}OH)3). The agronomical efficiency of a solution of the Mn(H{sub 3}L){sub 2}•3H{sub 2}NCH{sub 2}CH{sub 2}OH•4H{sub 2}O complex was studied on the cultures of white lupine Degas, spring wheat Ester, spring rape, and pea Stabil.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Controlling Domain Orientations in Thin Films of AB and ABA Block Copolymers

Domain orientations in thin films of lamellar copolymers are evaluated as a function of copolymer architecture, film thickness, and processing conditions. Two copolymer architectures are considered: An AB diblock of poly(styrene-b-methyl methacrylate) and an ABA triblock of poly(methyl methacrylate-b-styrene-b-methyl methacrylate). All films are cast on substrates that are energetically neutral with respect to the copolymer constituents. Film structures are evaluated with optical microscopy, atomic force microscopy, and grazing-incidence small-angle X-ray scattering. For AB diblock copolymers, the domain orientations are very sensitive to film thickness, annealing temperature, and imperfections in the 'neutral' substrate coating: Diblock domains are oriented perpendicular to the substrate when annealing temperature is elevated ({>=} 220 C) and defects in the substrate coating are minimized; otherwise, parallel or mixed parallel/perpendicular domain orientations are detected for most film thicknesses. For ABA triblock copolymers, the perpendicular domain orientation is stable for all the film thicknesses and processing conditions that were studied. The orientations of diblock and triblock copolymers are consistent with recent works that consider architectural effects when calculating the copolymer surface tension (Macromolecules 2006, 39, 9346 and Macromolecules 2010, 43, 1671). Significantly, the data demonstrate that triblocks are easier to process for applications in nanopatterning - in particular, when high-aspect-ratio nanostructures are required. However, both diblock and triblock films contain a high density of 'tilted' or bent domains, and these kinetically trapped defects should be minimized for most patterning applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Systematic Insight into Chloride Concentration, Applied Potential and Time Effect on the Passive Film of Cu-Zn-Ni Ternary Alloy in Alkaline Solution

The effects of chloride concentration, applied potential and time on the passive film of Cu-Zn-Ni ternary alloy in alkaline solution were systematically investigated using potentiodynamic and potentiostatic polarizations, electrochemical impedance spectroscopy, Mott–Schottky analysis, laser confocal microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. Results showed that the pitting potential decreased as a linear function of log(a{sub Cl{sup −}}), and the size of pits extended faster in the horizontal direction than in the vertical direction. The passive oxide film formed on Cu-Zn-Ni alloy mainly exhibited p-type semiconductor behavior, which was consistent with cuprous and nickel oxide, the main components in the film. The density of cation vacancy (approximately 10{sup 20}-10{sup 21} cm{sup −3}) increased with potentiostatic time but reduced by the increasing potentials. The kinetics of passive film growth followed a parabolic law D = m * t{sup n}, where m is a constant considered as the initial growth rate and n is the time exponent. Subsequent to the formation of a compact and coherent passive film at higher potential, it was hard for an ion to migrate or for an aggressive ion to penetrate, which indicated better corrosion resistance for passive film formed under higher potential.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis of layered double hydroxide nanosheets by coprecipitation using a T-type microchannel reactor

The synthesis of Mg{sub 2}Al–NO{sub 3} layered double hydroxide (LDH) nanosheets by coprecipitation using a T-type microchannel reactor is reported. Aqueous LDH nanosheet dispersions were obtained. The LDH nanosheets were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy and particle size analysis, and the transmittance and viscosity of LDH nanosheet dispersions were examined. The two-dimensional LDH nanosheets consisted of 1–2 brucite-like layers and were stable for ca. 16 h at room temperature. In addition, the co-assembly between LDH nanosheets and dodecyl sulfate (DS) anions was carried out, and a DS intercalated LDH nanohybrid was obtained. To the best of our knowledge, this is the first report of LDH nanosheets being directly prepared in bulk aqueous solution. This simple, cheap method can provide naked LDH nanosheets in high quantities, which can be used as building blocks for functional materials. - Graphical abstract: Layered double hydroxide (LDH) nanosheets were synthesized by coprecipitation using a T-type microchannel reactor, and could be used as basic building blocks for LDH-based functional materials. Display Omitted - Highlights: • LDH nanosheets were synthesized by coprecipitation using a T-type microchannel reactor. • Naked LDH nanosheets were dispersed in aqueous media. • LDH nanosheets can be used as building blocks for functional materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Structure and Anticorrosion, Friction, and Wear Characteristics of Pure Diamond-Like Carbon (DLC), Cr-DLC, and Cr-H-DLC Films on AZ91D Mg Alloy

This study evaluated the protection against corrosion and wear afforded to AZ91D Mg alloy by coatings of hydrogen-free and low-Cr-doped hydrogenated diamond-like carbon (DLC) films. The microstructure and corrosion resistance were evaluated using scanning electron microscopy, atomic force microscopy, Raman spectroscopy, polarization curves, and neutral salt spraying tests. Wear tests were performed to investigate the friction and wear behaviors of the samples against 9Cr18 in humid air, deionized water, and 3.5 wt.% NaCl solution using a reciprocating sliding test in the ball-on-disk mode. The results showed that the more compact Cr-H-DLC film improved the corrosion resistance of the Mg alloy, whereas the Cr-DLC film accelerated the corrosion in the 3.5 wt.% NaCl solution. All Mg alloy samples coated with DLC films exhibited low coefficient of friction (COF) values and smaller wear volumes compared with those of bare substrate in air, water, or NaCl solution. The Cr-DLC film presented the lowest COF and wear rate in air, but the worst corrosion protection in air and NaCl solution, whereas the converse was found for the Cr-H-DLC film. Unfortunately, all coated samples showed limited protection ability because of pore defects in the films, high galvanic potential between the substrate and the buffer layer or film, and high electrical conductivity, which caused severe tribocorrosion of the Mg alloy during the wear tests in NaCl solution. The corrosion protection ability of DLC films is key to the wear resistance protection of Mg alloys in water or NaCl solution.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High performance unipolar inverters by utilizing organic field-effect transistors with ultraviolet/ozone treated polystyrene dielectric

High performance unipolar inverters based on a significant variation of threshold voltage (V{sub th}) of organic field-effect transistors (OFETs), which was realized by introducing UV/ozone (UVO) treatment to polystyrene (PS) dielectric, were fabricated. A controllable V{sub th} shift of more than 10 V was obtained in the OFETs by adjusting the UVO treating time, and the unipolar inverters exhibited inverting voltage near 1/2 driving voltage and a noise margin of more than 70% of ideal value. From the analysis of scanning electron microscopy, atom force microscopy, and X-ray photoelectron spectroscopy, the dramatic controllable V{sub th} of OFETs, which played a key role in high performance unipolar inverters, was attributed to the newly generated oxygen functional groups in the PS dielectric induced by UVO treatment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of trimethylaluminum predoses on the growth morphology, film-substrate interface, and microstructure of MOCVD-grown AlN on (1 1 1)Si

Aluminum nitride (AlN) was deposited on (1 1 1) silicon by metalorganic chemical vapor deposition after varied trimethylaluminum “predoses”. Growth morphologies, film-substrate interfaces, and film microstructures were examined using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. In samples grown with predoses, lateral growth was observed over faceted “patches” formed during the predose. Three-dimensional growth was observed to seed from small islands on the surface of these patches and eventually overgrow them. The three-dimensional growth mode was similar to that observed when AlN was grown without a predose, resulting in similar morphologies in all films, regardless of predose, after the islands coalesced. The AlN-silicon interface was found to be predominantly amorphous when no predose was used. However, narrow regions were observed over which the film was in atomic registry with the substrate. This indicates AlN nucleates in epitaxy with the substrate and amorphous silicon nitride forms between nucleation sites due to ammonia exposure. Films grown with predoses had structurally abrupt interfaces, suggesting aluminum within the observed patch features inhibits the reaction between ammonia and silicon at the onset of growth. A structure distinct from both wurtzite AlN and diamond cubic silicon was observed at the substrate interface in films grown with a predose, consistent with either zinc blende AlN or a strained Si/Al alloy. A mosaic microstructure was observed in all films, grown with or without predoses, which consisted of sub-boundaries formed by clusters of threading dislocations. Finally, threading dislocations, separated by hundreds of nanometers, were found to be tilted along common directions, providing evidence for a dislocation bending mechanism possibly enhanced by the predose.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Elastomeric Nanocomposite with Solvent‐Free, One Step, In Situ Shear Exfoliation of Graphite to Graphene

A graphene nanoflake (GNF)‐enhanced elastomeric nanocomposite (G‐EMC) is fabricated following an innovative, cost‐effective, single‐step, in situ shear exfoliation (ISE) method from low‐cost bulk material, graphite, where uniform mixing happens simultaneously within the elastomer matrix. Electron microscopy, atomic force microscopy, and photo‐induced force microscopy results show good dispersion of GNFs with exfoliation to a few layers and uniform distribution in the elastomer matrix. X‐ray photoelectron spectroscopy analysis shows less than 1% oxygen‐containing functional groups/impurity, enhanced bonding through the formation of edge sites as fracture occurs across the GNF basal plane, and pi‐pi interactions with newly exfoliated planar basal plane surfaces of the GNFs. Raman spectroscopy results confirm the formation of GNFs with only a few layers of graphene formed by the ISE process. Fabricated 10 wt.% G‐EMC nanocomposites show a 400%–500% increase in strength and fracture toughness. And 35 wt.% G‐EMCs provide an electrical conductivity of 25.64 S m −1 and a sensor gauge factor of 45. The resulting intrinsic piezo resistivity of the fabricated nanocomposite has been exploited to fabricate a multi‐functional wired and wireless sensor for detecting different body movements, speech, human vital functions, solvents, and biomolecules.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A revisit to atomic layer deposition of zinc oxide using diethylzinc and water as precursors

Nanophase zinc oxide (ZnO) has been widely studied as an important multifunctional material in many applications. Atomic layer deposition (ALD) is a unique thin-film synthesis technique, featuring its extreme uniformity, unrivaled conformal coverage, low deposition temperature, and precise controllability. Using diethylzinc (DEZ) and water as precursors, ALD has been reported previously for growing nanophase ZnO thin films. However, the growth characteristics and the resultant ZnO crystallinity have not been well characterized and understood. To this end, we revisited the ALD process of ZnO using DEZ and water. Through employing a suite of advanced characterization techniques, we systematically addressed the growth characteristics, morphological changes, and the crystallinity evolution of ZnO along with growth temperature in the range of 30-250 °C. The growth characteristics of the ALD ZnO films were investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy, atomic force microscopy, and synchrotron-based X-ray reflectivity. The crystallinity of the ALD ZnO films was determined using synchrotron-based X-ray diffraction and high-resolution transmission electron microscopy. In addition, through further analyzing QCM data, we proposed the adsorption-limited surface reaction for ALD ZnO growth with the temperature-dependent number of -OH surface group reacting with one DEZ molecule. Furthermore, this study contributes to offer new and deep insights on the fundamental ALD process of ZnO.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Properties of Nb3Sn films fabricated by magnetron sputtering from a single target

Superconducting Nb3Sn films were fabricated on sapphire and fine grain Nb substrates by magnetron sputtering from a single stoichiometric Nb3Sn target. The structural, morphological and superconducting properties of the films annealed for 24 h at temperatures of 800-1000 {\deg}C were investigated. The effect of the annealing time at 1000 {\deg}C was examined for 1, 12, and 24 h. The film properties were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. The DC superconducting properties of the films were characterized by a four-point probe measurement down to cryogenic temperatures. The RF surface resistance of films was measured over a temperature range of 6-23 K using a 7.4 GHz sapphire-loaded Nb cavity. As-deposited Nb3Sn films on sapphire had a superconducting critical temperature of 17.21 K, which improved to 17.83 K when the film was annealed at 800 {\deg}C for 24 h. For the films annealed at 1000 {\deg}C, the surface Sn content was reduced to ~11.3 % for an annealing time of 12 h and to ~4.1 % for an annealing time of 24 h. The Raman spectra of the films confirmed the microstructural evolution after annealing. The RF superconducting critical temperature of the as-deposited Nb3Sn films on Nb was 16.02 K, which increased to 17.44 K when the film was annealed at 800 {\deg}C for 24 h.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structural and superconducting properties of Nb 3 Sn films grown by multilayer sequential magnetron sputtering

Nb 3 Sn thin films are fabricated by sequential sputtering followed by annealing at 850–1200°C in vacuum. The effects of the annealing temperature and time on the formation of Nb 3 Sn were examined. The film crystal structure, morphology, surface topography and composition were distinguished by X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and energy dispersive X-ray spectroscopy analysis. The superconducting properties of the films were characterized by measuring the surface resistivity by the four-point probe method. The highest critical temperature T c = 17.86 K was observed for the Nb 3 Sn films annealed at 950°C for 3 h. When the films were annealed above 1000°C for 3 h, Sn evaporation resulted in a Nb-rich film, degrading the superconducting performance. Annealing at 1200°C for 3 h resulted in evaporation of Sn leaving less than 1% Sn on the surface, as detected by energy dispersive spectroscopy, and for that film a T c of 7.9 K was observed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Properties of vapor-deposited and solution-processed targets for laser-driven inertial confinement fusion experiments

Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter, wall thickness, wall-thickness uniformity, and presence of surface features. Of these, restrictions on the size and number of defects (bumps and depressions) on the surface are the most challenging. The properties of targets that are made using vapor-deposition and solution-based microencapsulation techniques are reviewed. Targets were characterized using confocal microscopy, bright- and dark-field microscopy, atomic force microscopy, electron microscopy, and interferometry. Each technique has merits and limitations, and a combination of these techniques is necessary to adequately characterize a target. The main limitation with the glow-discharge polymerization (GDP) method for making targets is that it produces hundreds of domes with a lateral dimension of 0.7–2 μm. Polishing these targets reduces the size of some but not all domes, but it adds scratches and grooves to the surface. Solution-made polystyrene shells lack the dome features of GDP targets but have hundreds of submicrometer-size voids throughout the wall of the target; a few of these voids can be as large as ∼12 μm at the surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Key mechanistic features of swelling and blistering of helium-ion-irradiated tungsten

In this study, helium-ion-induced swelling and blistering of single-crystal tungsten is investigated using a Helium Ion Microscope for site-specific dose-controlled irradiation (at 25 keV) with analysis by Helium Ion Microscopy, Atomic Force Microscopy and Transmission Electron Microscopy (cross-sectioning by Focused Ion Beam milling). We show that the blister cavity forms at a depth close to the simulated helium peak and that nanobubbles coalesce to form nanocracks within the envelope of the ion stopping range, swelling the blister shell. These results provide the first direct experimental evidence for the interbubble fracture mechanism proposed in the framework of the gas pressure model for blister formation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Morphological study of borosilicate glass surface irradiated by heavy ions

Borosilicate glass is a candidate material for radiation waste formation and other optical applications in various fields. To understand the radiation effect of borosilicate glass, heavy ion (Ar q+ , Kr q+ and Xe q+ ) irradiations were used to simulate the alpha and recoiled nuclei irradiations in this study. The surface morphology of glass has been compared to ion irradiation doses and ion energies. The surface topography evolution of irradiated samples is characterized by optical microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). Micro-bumps are observed on the sample surface after irradiationwith 5 MeV Xe q+ over 5 × 10 13 ions·cm -2 . The size and density of the bumps increaseswith increasing irradiation dose. At a lowdose, bumps are on the nanometer (nm) scale and rather rare.While the dose is higher than 9 × 10 15 ions·cm -2 , the size of bumps is on the scale of a few microns, and the density is saturated. However, the height of the bumps increases froma fewnmto over 150nmwith further irradiation. The distribution of micro-bumps is nearly homogeneous. The bumps are condensed and swell up, and there is no crystallized structure according to the TEMdiffraction pattern. Elementmigration and concentrations are observedwith SIMS imaging. The arrayed micro-bumps are a new finding, and they might be used to change the surface properties. Bump formation is caused by phase separation, and volume swelling is induced by ion irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Control of Peptide Amphiphile Supramolecular Nanostructures by Isosteric Replacements

Supramolecular nanostructures with tunable properties can have applications in medicine, pharmacy, and biotechnology. In this work, we show that the self-assembly behavior of peptide amphiphiles (PAs) can be effectively tuned by replacing the carboxylic acids exposed to the aqueous media with isosteres, functionalities that share key physical or chemical properties with another chemical group. Transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering studies indicated that the nanostructure’s morphologies are responsive to the ionization states of the side chains, which are related to their pK a values. Circular dichroism studies revealed the effect of the isosteres on the internal arrangement of the nanostructures. The interactions between diverse surfaces and the nanostructures and the effect of salt concentration and temperature were assessed to further understand the properties of these self-assembled systems. These results indicate that isosteric replacements allow the pH control of supramolecular morphology by manipulating the pK a of the charged groups located on the nanostructure’s surface. Theoretical studies were performed to understand the morphological transitions that the nanostructures underwent in response to pH changes, suggesting that the transitions result from alterations in the Coulomb forces between PA molecules. Furthermore, this work provides a strategy for designing biomaterials that can maintain or change behaviors based on the pH differences found within cells and tissues.

36 MATERIALS SCIENCE↗