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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 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Outstanding field emission properties of wet-processed titanium dioxide coated carbon nanotube based field emission devices

Field emission devices using a wet-processed composite cathode of carbon nanotube films coated with titanium dioxide exhibit outstanding field emission characteristics, including ultralow turn on field of 0.383 V μm{sup −1} and threshold field of 0.657 V μm{sup −1} corresponding with a very high field enhancement factor of 20 000, exceptional current stability, and excellent emission uniformity. The improved field emission properties are attributed to the enhanced edge effect simultaneously with the reduced screening effect, and the lowered work function of the composite cathode. In addition, the highly stable electron emission is found due to the presence of titanium dioxide nanoparticles on the carbon nanotubes, which prohibits the cathode from the influence of ions and free radical created in the emission process as well as residual oxygen gas in the device. The high-performance solution-processed composite cathode demonstrates great potential application in vacuum electronic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Preparation of graphene-Fe{sub 3}O{sub 4} nanocomposites using Fe{sup 3+} ion-containing magnetic ionic liquid

Graphene-Fe{sub 3}O{sub 4} (GN-Fe{sub 3}O{sub 4}) magnetic nanocomposites were prepared, GN-coated magnetic ionic liquid (MIL) as its precursors, which were used as both a magnetic resource and solvent. The method has proved to be valuable for the Fe{sub 3}O{sub 4} nanoparticles (NPs) well dispersed in the solution through strong interactions with GN, which are of interest because of their stability and chemical properties. In the process, strong interactions creates a condition for uniform dispersion in GN and [BMIm]FeCl{sub 4} (MIL) solution, and accelerate the formation of Fe{sub 3}O{sub 4} NPs. A transmission electron microscopy image has shown that the as-formed Fe{sub 3}O{sub 4} NPs with a diameter as small as 5–7 nm were deposited on GN sheets. Furthermore, the final material showed a superior properties than conventional method, which can be ascribed to the fact that [BMIm]FeCl{sub 4} plays a vital role in the process of producing small NPs size.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Recent progress in half-Heusler thermoelectric materials

Highlights: • Summarize the recent progress and advances in HH thermoelectric materials. • Preparing nanocomposites could reduce thermal conductivity. • Introducing enhance phonon scattering could further reduce the thermal conductivity. • Forming ternary systems to reducing the cost effectively. • The new class of HHs presents another opportunity to further optimize the HH system. - Abstract: Half-Heusler (HH) thermoelectric (TE) materials have been attracting extensive research interest over the last two decades, owing to their thermal stability, mechanical strength, and moderate ZT. This material system are potential candidates for medium to high temperature applications, which is close to the temperature range of most industrial waste heat sources. In this mini-review article, we briefly summarize the recent progress and advances in HH thermoelectric materials. Some effectively available approaches, such as HH nanocomposites to reduce thermal conductivity, using larger atomic mass and size differences to enhance phonon scattering to further reduce the thermal conductivity, forming ternary systems following the cost effective approach. In addition, new thermoelectric HH members are also discussed in this article, which points out that many new HH compounds may be possible for TE applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis and characterization of Mn doped ZnCdS core shell nanostructures QDs using a chemical precipitation route

With advancement in time, researchers has drawn great attention in the synthesis and characterization of mono dispersed alloyed nanocomposites of II-VI compounds. Ternary semiconductor alloyed ZnCdS quantum dots (QD’s) exhibit properties intermediate between those of ZnS and CdS. It shows high absorption coefficients, a composition tunable and size tunable band gap. Moreover, ZnCdS alloyed NC’s display unique composition dependent properties distinct from those of their bulk counterparts. The most striking feature of the alloyed NC’s nanocrystals is their unusual long time stability in emission wavelength. ZnCdS alloyed QD’s at room temperature has been synthesized using chemical precipitation method. Undoped and Mn{sup 2+} doped ZnCdS QDs have been synthesized and studied. UV-visible absorption spectrum shows absorbance in the visible region and photoluminescence (PL) emission spectra of the doped ZnCdS QD’s shows orange emission in comparison to weak blue emission from undoped QDs. The crystallite size is calculated from the XRD patterns. The experimental results indicate that this easy synthesis route would prove a versatile approach for the preparation of doped and undoped ZnCdS QD’s.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Pinch instability of a cylindrical couette flow in a nonuniform axial magnetic field

The paper addresses the linear stability to axisymmetric perturbations of an incompressible nonideal fluid between two rotating coaxial infinitely long cylinders in a nonuniform axial magnetic field. For conducting cylinders, the results for uniform and nonuniform magnetic fields are qualitatively identical. This is also observed for nonconducting cylinders in a magnetic field with a constant direction. Instability appears for nonconducting cylinders in a magnetic field with a varying direction, whose magnitude exceeds a certain critical value. This new instability also exists in the absence of rotation and, hence, is independent of its parameters. In addition, the critical magnetic field is independent of the magnetic Prandtl number, which facilitates experimental observation of the new instability.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Thermal property and assessment of biocompatibility of poly(lactic-co-glycolic) acid/graphene nanocomposites

Polymer-matrix nanocomposites based on Poly(lactic-co-glycolic) acid (PLGA) and Graphene platelets (GNPs) were studied. GNPs, nanomaterials with a 2D flat surface, were chosen with or without chemical modification in PLGA/GNP nanocomposites and their microstructure, thermal property, and their compatibility as scaffolds for cell growth were investigated. PLGA/GNP nanocomposites (0, 1, and 5 wt. % of GNPs) were prepared using a solution based technique. Transmission electron microscopy, X-ray diffraction, Differential scanning calorimeter, and Thermogravimetric analyzer were used to analyze morphology and thermal properties. This work demonstrated the role of GNPs flat surface to provide a favorable platform resulting in an enhanced PLGA crystallization. Functionalized GNPs suppress both the thermal stability and the crystallization of PLGA. Finally, to determine the potential usefulness of these scaffolds for biomedical applications, mammalian cells were cultured on various PLGA/GNP nanocomposites (0, 1, and 5 wt. % GNPs). 1 wt. % PLGA/GNP nanocomposites showed better biocompatibility for cell growth with/without graphenes functionalization compared to pure PLGA and 5 wt. % PLGA/GNP. The function of GNPs in PLGA/GNPs (1 wt. %) composites is to provide a stage for PLGA crystallization where cell growth is favored. These results provide strong evidence for a new class of materials that could be important for biomedical applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Electronic properties and carrier mobilities of 6,6,12-graphyne nanoribbons

Structures, stabilities, electronic properties and carrier mobilities of 6,6,12-graphyne nanoribbons (GyNRs) with armchair and zigzag edges are investigated using the self-consistent field crystal orbital method based on density functional theory. It is found that the 1D GyNRs are more stable than the 2D 6,6,12-graphyne sheet in the view of the Gibbs free energy. The stabilities of these GyNRs decrease as their widths increase. The calculated band structures show that all these GyNRs are semiconductors and that dependence of band gaps on the ribbon width is different from different types of the GyNRs. The carrier mobility was calculated based on the deformation theory and effective mass approach. It is found that the carrier mobilities of these GyNRs can reach the order of 10{sup 5} cm{sup 2} V {sup –1}s{sup –1} at room temperature and are comparable to those of graphene NRs. Moreover, change of the mobilities with change of the ribbon width is quite different from different types of the GyNRs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Particle-In-Cell (PIC) simulation of long-anode magnetron

Long Anode Magnetron (LAM) is a design scheme adopted to attain greater thermal stability and higher power levels for the conventional magnetrons. So a LAM for 5MW Power level at 2.858 GHz was ‘Virtual Prototyped’ using Admittance Matching field theory (AMT) andthen a PIC Study (Beam-wave interaction) was conducted using CST Particle Studio (CST-PS) which is explained in this paper. The convincing results thus obtained were – hot resonant frequency of 2.834 GHz. Output power of 5 MW at beam voltage of 58kV and applied magnetic field of 2200 Gauss with an overall efficiency of 45%. The simulated parameters values on comparison with the E2V LAM tube (M5028) were in good agreement which validates the feasibility of the design approach.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Structure, electronic and magnetic properties of Mn{sub n} (n=2-8) clusters: A DFT investigation

A detail studyon the stability, electronic and magnetic properties of Mn{sub n} (n=2-8) cluster series is performed under the utilization ofdensity functional theory (DFT). The binding energy (B.E.), HOMO-LUMO energy gap (HLG), chemical hardness (η), ionization potential (I.P.), electron affinity (E.A)and electronegativity (χ) of these clusters are predicted. We have also studied the magnetic moments associated with the stable cluster isomers. The lowest energy structures for each cluster sizes aredetermined with a systematic search imposing all possible initial magnetic configuration on the cluster. All the calculations are carried out using a popular GGA functional PBE as proposed by Pardew, Burke and Ernzerhof and implemented in the VASP program.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The effects of intrinsic noise on the behaviour of bistable cell regulatory systems under quasi-steady state conditions

We analyse the effect of intrinsic fluctuations on the properties of bistable stochastic systems with time scale separation operating under quasi-steady state conditions. We first formulate a stochastic generalisation of the quasi-steady state approximation based on the semi-classical approximation of the partial differential equation for the generating function associated with the chemical master equation. Such approximation proceeds by optimising an action functional whose associated set of Euler-Lagrange (Hamilton) equations provides the most likely fluctuation path. We show that, under appropriate conditions granting time scale separation, the Hamiltonian can be re-scaled so that the set of Hamilton equations splits up into slow and fast variables, whereby the quasi-steady state approximation can be applied. We analyse two particular examples of systems whose mean-field limit has been shown to exhibit bi-stability: an enzyme-catalysed system of two mutually inhibitory proteins and a gene regulatory circuit with self-activation. Our theory establishes that the number of molecules of the conserved species is order parameters whose variation regulates bistable behaviour in the associated systems beyond the predictions of the mean-field theory. This prediction is fully confirmed by direct numerical simulations using the stochastic simulation algorithm. This result allows us to propose strategies whereby, by varying the number of molecules of the three conserved chemical species, cell properties associated to bistable behaviour (phenotype, cell-cycle status, etc.) can be controlled.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tailoring the dipole properties in dielectric polymers to realize high energy density with high breakdown strength and low dielectric loss

High energy density polymer materials are desirable for a broad range of modern power electronic systems. Here, we report the development of a new class of polymer dielectrics based on polyurea and polythiourea, which possess high thermal stability. By increasing the dipole density, the dielectric constant of meta-phenylene polyurea and methylene polythiourea can be increased to 5.7, compared with aromatic polyurea and aromatic polythiourea, which have a dielectric constant in the range of 4.1–4.3. The random dipoles with high dipolar moment and amorphous structure of these polyurea and polythiourea based polymers provide strong scattering to the charge carriers, resulting in low losses even at high electric fields. Consequently, this new class of polymers exhibit a linear dielectric response to the highest field measured (>700 MV/m) with a high breakdown strength, achieving high energy density (>13 J/cm{sup 3}) with high efficiency (>90%)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Recent breakthroughs on C-2U: Norman’s legacy

Conventional field-reversed configurations (FRC) face notable stability and confinement concerns, which can be ameliorated by introducing and maintaining a significant fast ion population in the system. This is the conjecture first introduced by Norman Rostoker multiple decades ago and adopted as the central design tenet in Tri Alpha Energy’s advanced beam driven FRC concept. In fact, studying the physics of such neutral beam (NB) driven FRCs over the past decade, considerable improvements were made in confinement and stability. Next to NB injection, the addition of axially streaming plasma guns, magnetic end plugs, as well as advanced surface conditioning lead to dramatic reductions in turbulence driven losses and greatly improved stability. In turn, fast ion confinement improved significantly and allowed for the build-up of a dominant fast particle population. This recently led to the breakthrough of sustaining an advanced beam driven FRC, thereby demonstrating successful maintenance of trapped magnetic flux, plasma dimensions and total pressure inventory for times much longer than all characteristic system time scales and only limited by hardware and electric supply constraints.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Neutron scattering study on cathode LiMn{sub 2}O{sub 4} and solid electrolyte 5(Li{sub 2}O)(P{sub 2}O{sub 5})

Neutron scattering is very important technique in order to investigate the energy storage materials such as lithium-ion battery. The unique advantages, neutron can see the light atoms such as Hydrogen, Lithium, and Oxygen, where those elements are negligible by other corresponding X-ray method. On the other hand, the energy storage materials, such as lithium ion battery is very important for the application in the electric vehicles, electronic devices or home appliances. The battery contains electrodes (anode and cathode), and the electrolyte materials. There are many challenging to improve the existing lithium ion battery materials, in order to increase their life time, cyclic ability and also its stability. One of the most scientific challenging is to investigate the crystal structure of both electrode and electrolyte, such as cathodes LiCoO{sub 2}, LiMn{sub 2}O{sub 4} and LiFePO{sub 4}, and solid electrolyte Li{sub 3}PO{sub 4}. Since all those battery materials contain Lithium ions and Oxygen, the used of neutron scattering techniques to study their structure and related properties are very important and indispensable. This article will review some works of investigating electrodes and electrolytes, LiMn{sub 2}O{sub 4} and 5(Li{sub 2}O)(P{sub 2}O{sub 5}), by using a high resolution powder diffraction (HRPD) at the multipurpose research reactor, RSG-Sywabessy of the National Nuclear Energy Agency (BATAN), Indonesia.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structural stability and electronic properties of low-index surfaces of SnS

Thin film photovoltaic cells are increasingly important for cost-effective solar energy harvesting. Layered SnS is a promising absorber material due to its high optical absorption in the visible and good doping characteristics. We use first-principles calculations based on density functional theory to study structures of low-index surfaces of SnS using stoichiometric and oxygen-containing structural models, in order to elucidate their possible effect on the efficiency of the photovoltaic device. We find that the surface energy is minimized for the surface with orientation parallel to the layer stacking direction. Compared to stoichiometric surfaces, the oxygen-containing surfaces exhibit fewer electronic states near the band gap. This reduction of near-gap surface states by oxygen should reduce recombination losses at grain boundaries and interfaces of the SnS absorber, and should be beneficial to the efficiency of the solar cell.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Significant electrical control of amorphous oxide thin film transistors by an ultrathin Ti surface polarity modifier

We demonstrate an enhanced electrical stability through a Ti oxide (TiO{sub x}) layer on the amorphous InGaZnO (a-IGZO) back-channel; this layer acts as a surface polarity modifier. Ultrathin Ti deposited on the a-IGZO existed as a TiO{sub x} thin film, resulting in oxygen cross-binding with a-IGZO surface. The electrical properties of a-IGZO thin film transistors (TFTs) with TiO{sub x} depend on the surface polarity change and electronic band structure evolution. This result indicates that TiO{sub x} on the back-channel serves as not only a passivation layer protecting the channel from ambient molecules or process variables but also a control layer of TFT device parameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

First-principles study on stability of transition metal solutes in aluminum by analyzing the underlying forces

Although there have been some investigations on behaviors of solutes in metals under strain, the underlying mechanism of how strain changes the stability of a solute is still unknown. To gain such knowledge, first-principles calculations are performed on substitution energy of transition metal solutes in fcc Al host under rhombohedral strain (RS). Our results show that under RS, substitution energy decreases linearly with the increase of outermost d radius r{sub d} of the solute due to Pauli repulsion. The screened Coulomb interaction increases or decreases the substitution energy of a solute on condition that its Pauling electronegativity scale ϕ{sub P} is less or greater than that of Al under RS. This paper verifies a linear relation of substitution energy change versus r{sub d} and ϕ{sub P} under RS, which might be instructive for composition design of long life alloys serving in high stress condition.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Thermodynamic, Raman and electrical switching studies on Si{sub 15}Te{sub 85-x}Ag{sub x} (4 {<=} x {<=} 20) glasses

We have investigated thermal properties of bulk Si{sub 15}Te{sub 85-x}Ag{sub x} (4 {<=} x {<=} 20) glasses in detail, through alternating differential scanning calorimetry experiments. The composition dependence of thermal parameters reveal the signatures of rigidity percolation and chemical threshold at compositions x = 12 and x = 19, respectively. The stability and glass forming ability of these glasses have also been determined using the data obtained from different thermodynamic quantities and it is found that the Si{sub 15}Te{sub 85-x}Ag{sub x} glasses in the region 12 {<=} x {<=} 17 are more stable when compared to other glasses of the same series. Further, the blueshift observed in Raman spectroscopy investigations, in the composition range 12 {<=} x {<=} 13, support the occurrence of stiffness threshold in this composition range. All Si{sub 15}Te{sub 85-x}Ag{sub x} (4 {<=} x {<=} 20) glasses are found to exhibit memory type switching (for sample thickness 0.25 mm) in the input current range 3-9 mA. The effect of rigidity percolation and chemical thresholds on switching voltages are observed at x = 12 and 19, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Three luminescent d{sup 10} metal coordination polymers assembled from a semirigid V-shaped ligand with high selective detecting of Cu{sup 2+} ion and nitrobenzene

Three 2D luminescent coordination polymers with helical frameworks, [ZnL{sub 2}]{sub n} (1) and ([ML{sub 2}]·(H{sub 2}O)){sub n} (M=Zn (2), Cd (3)) (HL=4-((2-methyl-1 H-imidazol-1-yl)methyl)benzoic acid), have been assembled under hydro(solvo)thermal conditions. Complex 1 is in chiral space group and displays a rare 2D→2D 2-fold parallel interpenetrated layer network with two types of chiral double helixes. Interestingly, the single crystal structure analyses indicate the coexistence of enantiomers la and 1b in one pot, while the bulk crystallization of 1 are racemic mixtures based on the CD measurement. 2 and 3 are isostructural, in the structure, there are two kinds of 2D chiral helical-layers which stack in an -ABAB- sequence leading to the overall structure are mesomer and achiral. All compounds display intense luminescence in solid state at room temperature with high chemical and thermal stability. More importantly, 1 has been successfully applied in the detection of Cu{sup 2+} ions in aqueous media and nitrobenzene and the probable detecting mechanism was also discussed. - Graphical abstract: Three luminescent d{sup 10} metal coordination polymers with helical-layer based on 4-((2-methyl-1H-imidazol-1-yl)methyl)benzoic acid have been obtained. Compound 1 shows high selective detecting for Cu{sup 2+} ion in aqueous and nitrobenzene. - Highlights: • Three coordination polymers with chiral helical-layer have been obtained. • 1 Can luminescent detect Cu{sup 2+} ion in aqueous media and nitrobenzene. • Racemic mixture or mesomer compounds can be obtained by controlling the reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗