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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Spectral characteristics of nanoamorphous phosphors obtained by evaporation of Sr{sub 2}Gd{sub 8}(SiO{sub 4}){sub 6}O{sub 2}: Eu polycrystals

Amorphous nanophosphors have been obtained for the first time by pulsed electron beam evaporation of targets from bulk polycrystalline phosphors of the composition Sr{sub 2}Gd{sub 8}(SiO{sub 4}){sub 6}O{sub 2}: Eu with oxyapatite structure. The processes of crystallization of amorphous nanopowder were studied using differential scanning calorimetry and termogravimetry (40−1400 °C). It was found that the Raman spectra of the samples are modified when the particles decrease from bulk to nanodimensional state. The spectral and luminescent characteristics of the phosphors in polycrystalline and nanoamorphous states have been examined. It was established that Eu{sup 3+} forms two types of optical centers. Unlike bulk phosphors, in the nanophosphors no Eu{sup 2+} ions are formed. The ratio of red to orange luminescence intensity for nanophosphors was found to increase as compared with bulk phosphors. This effect is due to disordering of nanoparticles. A resonant transfer of excitation energy from Gd{sup 3+} to Eu{sup 3+} ions was found in bulk and nanophosphors. Upon transition from polycrystalline to nanoamorphous state and laser excitation of phosphors, the luminescence intensity of Eu{sup 3+} ions increases approximately 10 times. This effect is explained in the framework of the configuration coordinates model. - Graphical abstract: Schematic configurational-coordinate diagram for Eu{sup 3+} ion in polycrystalline Sr{sub 2}Gd{sub 6.4}Eu{sub 1.6}Si{sub 6}O{sub 26−δ} and nanoamorphous phosphor. - Highlights: • Nanoamorphous phosphor is obtained by electron-beam evaporation of bulk silicate. • In nanoamorphous samples Raman spectra are modified intensity. • Nanofosfor luminescence by 10 times more intensively, than bulk phosphorus. • There is a transfer of energy of excitation from Gd{sup 3+} to Eu{sup 3+} in bulk- and nanophosphor.

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

Thermal evaporation and condensation synthesis of metallic Zn layered polyhedral microparticles

Highlights: Black-Right-Pointing-Pointer Zn polyhedral microparticles prepared by thermal evaporation and condensation route. Black-Right-Pointing-Pointer Vapour-solid process based growth model governs the formation of Zn microparticles. Black-Right-Pointing-Pointer A strong PL emission band is observed at 369 nm in UV region. Black-Right-Pointing-Pointer Radiative recombination of electrons in the s, p conduction band and the holes in the d bands causes this emission. -- Abstract: Metallic zinc layered polyhedral microparticles have been fabricated by thermal evaporation and condensation technique using zinc as precursor at 750 Degree-Sign C for 120 min and NH{sub 3} as a carrier gas. The zinc polyhedral microparticles with oblate spherical shape are observed to be 2-9 {mu}m in diameter along major axes and 1-7 {mu}m in thickness along minor axes. The structural, compositional and morphological characterizations were performed by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapour-solid (VS) mechanism based growth model has been proposed for the formation of Zn microparticles. Room temperature photoluminescence (PL) emission spectrum of the product exhibited a strong emission band at 369 nm attributed to the radiative recombination of electrons in the s, p conduction band near Fermi surface and the holes in the d bands generated by the optical excitation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Growth of copper indium sulphide films by thermal evaporation of mixtures of copper sulphide and indium sulphide powders

Graphical abstract: - Highlights: • CuInS{sub 2} films are prepared by resistively heating mixtures of CuS and In{sub 2}S{sub 3}. • As deposited films consist of Cu{sub 7}S{sub 4}, InS and In{sub 2}S{sub 3}. • These species react during vacuum annealing to produce CuInS{sub 2} films. • The films bear stoichiometric or Cu-rich composition. • Their electrical and optical features are conducive for photovoltaic applications. - Abstract: The physical evaporation of a 1:1 mixture of copper sulphide (CuS) and indium sulphide (In{sub 2}S{sub 3}) powders by resistive heating followed by the vacuum annealing of the resulting films at 723 K produces copper indium sulphide (CuInS{sub 2}) films with about 95% phase purity. Composed of sub-micron sized grains, the films bear stoichiometric or Cu-rich composition and are endowed with p-type conductivity, a band gap of about 1.5 eV and an absorption coefficient of about 4 × 10{sup 4} cm{sup −1} in visible region. Mechanistically, the formation of CuInS{sub 2} films takes place as a result of solid state reaction among Cu{sub 7}S{sub 4}, InS and In{sub 2}S{sub 3} in the condensed phase. These intermediate species are produced from the decomposition of CuInS{sub 2} formed in the evaporating mixture due to the reaction between CuS and In{sub 2}S{sub 3}, and excess CuS. Process simplicity and the absence of a sulphurisation step make this approach attractive for synthesising CuInS{sub 2} absorber layers for photovoltaic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

Highlights: • ITO nanowires were grown by e-beam evaporation method. • ITO nanowires growth done at low substrate temperature of 350 °C. • Nanowires growth was carried out without use of catalyst and reactive oxygen gas. • Nanowires growth proceeds via self catalytic VLS growth. • Grown nanowires have diameter 10–20 nm and length 1–4 μm long. • ITO nanowire films have shown good antireflection property. - Abstract: We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250–400 °C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (∼10–15 nm) and micron long ITO NWs growth was observed in a temperature window of 300–400 °C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300–400 °C have shown ∼2–6% reflection and ∼70–85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Electrochemical properties of Sn-based nanopowders synthesized by a pulsed wire evaporation method and effect of binder coating

Highlights: • Sn-based nanoparticles are fabricated by using the pulsed wire evaporation method. • The electrodes are prepared by mixing the graphene and coating the surface. • Coating the surface of electrode is used with brushing of simple and facile method. • The electrochemical measurements are performed with galvanostatic experiments. • The coating electrode maintains capacity nearly of 501 mAh g{sup −1} up to 100 cycles. - Abstract: Sn-based nanoparticles are prepared with the O{sub 2} concentrations in chamber of Ar atmosphere (by v/v) by using the pulsed wire evaporation (PWE) method. The prepared electrodes are only Sn-based powder electrode, its binder coating electrode and Sn-based powder/graphene nanocomposite electrode. Morphology and structure of the synthesized powders and electrodes are investigated with a field emission scanning electron microscope (FE-SEM) and an X-ray diffraction (XRD) analysis. The electrochemical measurements were performed with galvanostatic cycling experiments using a coin type cell of CR2032 (Ø20, T3.2 mm). The binder coating electrode is superior to others and maintains delithiation capacity nearly of 501 mAh g{sup −1} as 58.3% of first delithiation capacity at 0.2 C-rate up to 100 cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2016

An optimal thermal evaporation synthesis of c-axis oriented ZnO nanowires with excellent UV sensing and emission characteristics

Highlights: • c-Axis alignment of ZnO nanowires was optimized using self-seeding thermal evaporation method. • Influence of purified air on the morphology and optoelectronic properties were studied. • Nanowires grown under optimal conditions exhibit strong UV emission peak in PL spectrum. • Optimized growth condition establish nanowires of excellent UV sensing characteristics - Abstract: Well-aligned (c-axis oriented) ZnO nanowire arrays were successfully synthesized on Si (1 0 0) substrates through an optimized self-seeding thermal evaporation method. An open-ended chemical vapor deposition (CVD) setup was used in the experiment, with argon and purified air as reaction gases. Epitaxial growth of c-axis oriented ZnO nanowires was observed for 5 sccm flow rate of purified air, whereas Zn/Zn suboxide layers and multiple polycrystalline layers of ZnO were obtained for absence and excess of purified air, respectively. Ultraviolet (UV) sensing and emission properties of the as-grown ZnO nanostructures were investigated through the current–voltage (I–V) characteristics of the nanowires under UV (λ = 365 nm) illumination of 8 mW/cm{sup 2} and using photoluminescence spectra. Nanowires grown under optimum flow of air emitted four times higher intensity of 380 nm UV light as well as exhibited 34 times higher UV radiation sensitivity compared to that of other nanostructures synthesized in this study.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Large-scale uniform ZnO tetrapods on catalyst free glass substrate by thermal evaporation method

Highlights: • Investigate the growth of ZnO-Ts on glass substrate by thermal evaporation method. • Glass substrate without any catalyst or a seed layer. • The morphology was controlled by adjusting the temperature of the material and the substrate. • Glass substrate was placed vertically in the quartz tube. - Abstract: Here, we report for the first time the catalyst-free growth of large-scale uniform shape and size ZnO tetrapods on a glass substrate via thermal evaporation method. Three-dimensional networks of ZnO tetrapods have needle–wire junctions, an average leg length of 2.1–2.6 μm, and a diameter of 35–240 nm. The morphology and structure of ZnO tetrapods were investigated by controlling the preparation temperature of each of the Zn powder and the glass substrate under O{sub 2} and Ar gases. Studies were carried out on ZnO tetrapods using X-ray diffraction, field emission scanning electron microscopy, UV–vis spectrophotometer, and a photoluminescence. The results showed that the sample grow in the hexagonal wurtzite structure with preferentially oriented along (002) direction, good crystallinity and high transmittance. The band gap value is about 3.27 eV. Photoluminescence spectrum exhibits a very sharp peak at 378 nm and a weak broad green emission.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Cu-Ga-Se Thin Films Prepared by a Combination of Electrodeposition and Evaporation Techniques

Cu-Ga-Se thin films were prepared using a combination of electrodeposition and evaporation techniques. A Cu-Se/Mo/glass precursor thin film was first prepared by galvanostatic electrodeposition. On top of this film three different thicknesses of Ga were deposited by evaporation. The Cu-Ga-Se thin films were formed by annealing the Ga/Cu-Se/Mo/glass thin film configuration in a tubular chamber with Se powder, at different temperatures. Thin films were characterized by X-ray diffraction (XRD), photocurrent spectroscopy (PS), inductively coupled plasma (ICP) analysis, and scanning electron microscopy (SEM). The detailed analysis from X-ray reveals that after annealing at 550 C the CuGaSe{sub 2} phase is formed when the thickness of Ga is 0.25 {mu}m, however at 0.5 {mu}m and 1.0 {mu}m Ga the formation of CuGa{sub 3}Se{sub 5} and CuGa{sub 5}Se{sub 8} phases is observed respectively. Band gap values were obtained using photocurrent spectroscopy.

14 SOLAR ENERGY↗
DOE OSTI2012

Co-Evaporated Cu2ZnSnSe4 Films and Devices

The use of vacuum co-evaporation to produce Cu2ZnSnSe4 photovoltaic devices with 9.15% total-area efficiency is described. These new results suggest that the early success of the atmospheric techniques for kesterite photovoltaics may be related to the ease with which one can control film composition and volatile phases, rather than a fundamental benefit of atmospheric conditions for film properties. The co-evaporation growth recipe is documented, as is the motivation for various features of the recipe. Characteristics of the resulting kesterite films and devices are shown in scanning electron micrographs, including photoluminescence, current-voltage, and quantum efficiency. Current-voltage curves demonstrate low series resistance without the light-dark cross-over seen in many devices in the literature. Band gap indicated by quantum efficiency and photoluminescence is roughly consistent with that expected from first principles calculation.

14 SOLAR ENERGY↗
DOE OSTI2021

Modeled Emission of Hydroxyl and Ozone Reactivity from Evaporation of Fragrance Mixtures

Volatile chemical products (VCPs) account for increasing fractions of organic carbon emitted to the atmosphere, particularly in urban areas. Fragrances are potentially reactive components that are added to many VCPs. To better constrain these emissions, 11 commercially available liquid fragrance mixtures were characterized for their composition and their evaporation modeled. Here, emissions of mass, hydroxyl reactivity, and ozone reactivity were estimated by modeling under four different scenarios. Fragrance compounds were generally less than one-half the mass of fragrance mixtures, with the balance comprised of solvents and plasticizers and unresolved mass thought to be dominated by plasticizers. The results showed that terpenes and terpenoids account for nearly all of the emitted mass and reactivity while only comprising ~10% w/w on average of the liquid fragrance mixtures. Most of the reactivity is emitted within hours, with ozone reactivity evolving more rapidly than OH reactivity and comprised almost entirely of terpenes. Limonene, a common fragrance constituent, dominates the reactivity of emitted carbon. Generally, 20–40% of the potential hydroxyl reactivity contained in the fragrance mixture does not evaporate on time scales sufficient to have an impact on local or regional air quality.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Evaporation and Molecular Beam Scattering from a Flat Liquid Jet

An experimental setup for molecular beam scattering from flat liquid sheets has been developed, with the goal of studying reactions at gas–liquid interfaces for volatile liquids. Specifically, a crossed molecular beam instrument that can measure angular and translational energy distributions of scattered products has been adapted for liquid jet scattering. A microfluidic chip is used to create a stable flat liquid sheet inside vacuum from which scattering occurs, and both evaporation and scattering from this sheet are characterized using a rotatable mass spectrometer that can measure product time-of-flight distributions. This article describes the instrument and reports on the first measurements of evaporation of dodecane and Ne from a Ne-doped dodecane flat jet, as well as scattering of Ne from a flat jet of pure dodecane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Simultaneous multiparticle emissions in hot nuclei evaporation process

This work presents a new mechanism for the evaporation with simultaneous particles emission mechanism in the evaporation chain as new channels opened to high excitation energy regime of the compound nucleus. The probability of multiple simultaneous emissions is determined based on phase space approach. A Monte Carlo simulation is employed to compute the final average yield of emitted particles after the decay chain. The neutron, proton, alpha and fission yields are obtained and compared to the conventional calculation with sequential simple particles emission and the relevance of the different channels in competition is also analyzed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Direct synthesis of Cu{sub 2}O-RGO nanocomposite on Cu foil by thermal evaporation method and its field emission study

In this work, a facile one step thermal evaporation method for deposition of Cu{sub 2}O nanoparticles on RGO sheets to form Cu{sub 2}O-RGO nanocomposite is discussed. To the best of our knowledge, this is the first report on Cu{sub 2}O-RGO nanocomposite, directly grown on Cu foil by a simple thermal evaporation route. The as –prepared nanocomposite exhibits well dispersed Cu{sub 2}O nanoparticles distributed all over the graphene sheet. Field emission properties of the nanocomposite were investigated at a base pressure of 1*10{sup −8} torr. The turn on field, required to draw emission current density of 0.1µA/cm2, was found to be 3.8V/µm with a maximum emission current density of 80 µA/cm2 at an applied field of 6.8 V/µm. Moreover, the nanocomposite shows fairly good emission stability without significant degradation of emission current. The FE results seem to be encouraging, indicative of potential candidature of the Cu{sub 2}O-RGO nanocomposite emitter as an electron source for practical applications in vacuum nanoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Realization of PbS thin films by reactive evaporation technique for possible opto-electronic applications

Stoichiometric Lead sulphide (PbS) thin films were successfully prepared on glass substrates by reactive evaporation technique. Elemental evaporation of lead and sulphur taken in different sources onto substrates held at temperature of 400±5K employed in the present study. The structural as well as compositional studies compromises compound formation. Electrical transport properties and optical co-efficient were evaluated from appropriate characterization techniques.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Investigation on thermal evaporated CH{sub 3}NH{sub 3}PbI{sub 3} thin films

CH{sub 3}NH{sub 3}I, PbI{sub 2} and CH{sub 3}NH{sub 3}PbI{sub 3} films were fabricated by evaporation and characterized with X-ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD). The XPS results indicate that the PbI{sub 2} and CH{sub 3}NH{sub 3}PbI{sub 3} films are more uniform and stable than the CH{sub 3}NH{sub 3}I film. The atomic ratio of the CH{sub 3}NH{sub 3}I, PbI{sub 2} and CH{sub 3}NH{sub 3}PbI{sub 3} films are C:N:I=1.00:1.01:0.70, Pb:I= 1.00:1.91 and C: N: Pb: I = 1.29:1.07:1.00:2.94, respectively. The atomic ratio of CH{sub 3}NH{sub 3}PbI{sub 3} is very close to that of the ideal perovskite. Small angle x-ray diffraction results demonstrate that the as evaporated CH{sub 3}NH{sub 3}PbI{sub 3} film is crystalline. The valence band maximum (VBM) and work function (WF) of the CH{sub 3}NH{sub 3}PbI{sub 3} film are about 0.85eV and 4.86eV, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Spin-pump-induced spin transport in a thermally evaporated pentacene film

We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni{sub 80}Fe{sub 20} tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni{sub 80}Fe{sub 20}, which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Preparation of Cu{sub 2}ZnSnSe{sub 4} solar cells by low-temperature co-evaporation and following selenization

Cu{sub 2}ZnSnSe{sub 4} (CZTSe) thin films are prepared by a two-step method which involves co-evaporation of Cu, Zn, Sn, and Se on molybdenum-coated soda-lime glass at low substrate temperature and a following selenization. Solar cells with efficiencies of up to 6.5% can be achieved. The influence of the selenium deposition rates during co-evaporation and the nitrogen pressure during selenization on the properties of the CZTSe films are investigated. It is found that these two parameters can significantly affect the morphology and crystallinity of the CZTSe films. The possible reasons for the experimental results are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Super-Maxwellian helium evaporation from pure and salty water

Helium atoms evaporate from pure water and salty solutions in super-Maxwellian speed distributions, as observed experimentally and modeled theoretically. The experiments are performed by monitoring the velocities of dissolved He atoms that evaporate from microjets of pure water at 252 K and 4–8.5 molal LiCl and LiBr at 232–252 K. The average He atom energies exceed the flux-weighted Maxwell-Boltzmann average of 2RT by 30% for pure water and 70% for 8.5m LiBr. Classical molecular dynamics simulations closely reproduce the observed speed distributions and provide microscopic insight into the forces that eject the He atoms from solution. Comparisons of the density profile and He kinetic energies across the water-vacuum interface indicate that the He atoms are accelerated by He–water collisions within the top 1-2 layers of the liquid. We also find that the average He atom kinetic energy scales with the free energy of solvation of this sparingly soluble gas. This free-energy difference reflects the steeply decreasing potential of mean force on the He atoms in the interfacial region, whose gradient is the repulsive force that tends to expel the atoms. The accompanying sharp decrease in water density suppresses the He–water collisions that would otherwise maintain a Maxwell-Boltzmann distribution, allowing the He atom to escape at high energies. Helium is especially affected by this reduction in collisions because its weak interactions make energy transfer inefficient.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗