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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

High hole concentration in p-type AlGaN by indium-surfactant-assisted Mg-delta doping

High hole concentration was achieved in Mg-doped Al{sub x}Ga{sub 1−x}N (x ∼ 0.4) by using indium-surfactant-assisted delta doping method. A maximum carrier concentration of 4.75 × 10{sup 18 }cm{sup −3} was obtained, which is three times higher than that of the conventionally delta-doped sample. Sheet resistivity as low as 2.46 × 10{sup 4} Ω/sq was realized, benefiting from the high hole concentration (p). Analysis results show that the Mg incorporation is effectively enhanced, while the compensation ratio and acceptor activation energy (E{sub A}) are significantly reduced by using In surfactant. It was also found that the In surfactant may induce stronger valence-band modulation, contributing to the decrease of E{sub A} and the increase of p.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Hall effect measurements on thermoelectric Ca{sub 3}Co{sub 4}O{sub 9}: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

The Hall coefficient R{sub H} and electrical conductivity of misfit calcium cobalt oxide (Ca{sub 2}CoO{sub 3−δ}){sub q}(CoO{sub 2}) (CCO) were measured at room temperature for different oxygen vacancy concentrations δ. Based on these and numerous previous results, it is shown that the charge carrier concentrations n obtained by the classical formula R{sub H} = 1/ne are between 3 and 6 × 10{sup 20} cm{sup −3} and thereby much lower than those derived by other experimental techniques and fail to explain the observed electric properties of CCO. We show that the experimental results are well described using an earlier proposed t–J-model for strongly correlated electrons on a triangular lattice. The hopping parameter t for CCO was found to be ≈ −20 K and the charge carrier concentration of fully oxidized CCO to be 5.7 × 10{sup 21} cm{sup −3} (0.41 hole type carriers per formula unit), in agreement with other experimental techniques.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Hydrogen concentration and electric field dependent on electronic properties of germanene

Electronic properties of the pristine/hydrogenated germanene are investigated by means of first principles calculations. Our calculation shows interesting results where the electronic properties of the hydrogenated germanene exhibit semiconductor with a direct band gap. It is interesting because pristine germanene (germanium analogue to graphene) has semi-metal properties with zero band gap. We also obtained that the band gap of hydrogenated germanene was influenced by the hydrogen (H) concentration, it is decreasing non-linearly as the H concentration decreased. As 100 percent concentration of H applied on top and bottom layer of germanene, the band gap is 1.41 eV. The pairing of the p{sub z}-orbital of Ge with the s-orbital of H gave contribution to the band gap of hydrogenated germanene. External electrical field is also can be applied to open the band gap. The band gap increasing linearly when the external electrical field increased on pristine germanene. The external electrical field no longer effect the band gap when it applied to the hydrogenated germanene.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Dependence of aggregation behavior on concentration in triblock copolymer solutions: The effect of chain architecture

Using the self-consistent field lattice technique, the effects of concentration and hydrophobic middle block length (where the chain length remains constant) on aggregation behavior are studied in amphiphilic symmetric triblock copolymer solutions. The heat capacity peak for the unimer-micelle transition and the distribution peaks for the different degrees of aggregation for micelles and small aggregates (submicelles) are calculated. Analysis of the conducted computer simulations shows that the transition broadness dependence on concentration is determined by the hydrophobic middle block length, and this dependence is distinctly different when the length of the hydrophobic middle block changes. Different size for small aggregates simultaneously appear in the transition region. As temperature decreases, the number of different size small aggregates for the large hydrophobic middle block length first ascends and then descends in aggregation degree order. These results indicate that any transition broadness change with concentration is related to the mechanism of fragmentation and fusion. These results are helpful for interpreting the aggregation process of amphiphilic copolymers at equilibrium.

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

Effect of pulsed corona discharge voltage and feed gas flow rate on dissolved ozone concentration

Ozonization is one of the methods extensively used for water purification and degradation of organic materials. Ozone (O{sub 3}) is recognized as a powerful oxidizing agent. Due to its strong oxidability and better environmental friendless, ozone increasing being used in domestic and industrial applications. Current technology in ozone production utilizes several techniques (corona discharge, ultra violet radiation and electrolysis). This experiment aimed to evaluating effect of voltage and gas flow rate on ozone production with corona discharge. The system consists of two net-type stainless steel electrode placed in a dielectric barrier. Three pulsed voltage (20, 30, 40 KV) and flow rate (5, 10, 15 L/min) were prepare for operation variable at high frequency (3.7 kHz) with AC pulsed power supply. The dissolved ozone concentration depends on the applied high-voltage level, gas flow rate and the discharge exposure duration. The ozone concentration increases with decreasing gas flow rate. Dissolved ozone concentrations greater than 200 ppm can be obtained with a minimum voltage 40 kV.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of variable cerium concentration on photoluminescence behaviour in ZrO{sub 2} phosphor synthesized by combustion synthesis method

Present paper reports synthesis and characterization of trivalent cerium (Ce{sup 3+}) doped zirconium dioxide (ZrO{sub 2}) phosphors. Effect of variable concentration of cerium on photoluminescence (PL) is studied. Samples were prepared by combustion synthesis technique which is suitable for less time taking techniques also for large scale production for phosphors. Starting material used for sample preparation are Zr(NO{sub 3}){sub 3} and Ce(NO{sub 3}){sub 3} and urea used as a fuel. All prepared phosphor with variable concentration of Ce{sup 3+} (0.1 to 2mol%) was studied by photoluminescence analysis it is found that the excitation spectra of prepared phosphor shows broad excitation centred at 390nm. The excitation spectra with variable concentration of Ce{sup 3+} show strong peaks at 447nm. Spectrophotometric determinations of peaks are evaluated by Commission Internationale de I’Eclairage technique. Using this phosphor, the desired CIE values including emissions throughout the violet (390 nm) and blue (427 nm) of the spectra were achieved. Efficient blue light emitting diodes were fabricated using Ce{sup 3+} doped phosphor based on near ultraviolet (NUV) excited LED lights.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Role of salt concentration in blend polymer for energy storage conversion devices

Solid Polymer Electrolytes (SPE) are materials of considerable interest worldwide, which serves dual purpose of electrolyte and separator between electrode compartments in renewable energy conversion/storage devices such as; high energy density batteries, electrochromic display devices, and supercapacitors. Polymer blend electrolytes are prepared for various concentration of salt (Ö/Li) with the constant ratio (0.5 gm) of each PEO and PAN polymers (blend polymer) using solution casting technique. Solid polymeric ionic conductor as a separator is the ultimate substitute to eliminate the drawback related to liquid and gel polymer ionic conductors. In the present work, solid polymer electrolyte film consisting of PEO, PAN and LiPF{sub 6} are examined for various concentration of lithium salt by keeping PEO/PAN blend ratio as a constant with a view to optimize the dominant salt concentration which could give the maximum conductivity at ambient temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Impact of dopant concentrations on emitter formation with spin on dopant source in n-type crystalline silicon solar cells

Use of a suitable dopant source for emitter formation is an essential requirement in n-type crystalline silicon solar cells. Boron spin on dopant source, used as alternative to mostly used BBr{sub 3} liquid source, can yield an emitter with less diffusion induced defects under controlled conditions. Different concentrations of commercially available spin on dopant source is used and optimized in this work for sheet resistance values of the emitter ranging from 30 Ω/□ to 70 Ω/□ with emitter doping concentrations suitable for ohmic contacts. The dopant concentrations diluted with different ratios improves the carrier lifetime and thus improves the emitter performance. Hence use of suitable dopant source is essential in forming emitters in n-type crystalline silicon solar cells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electrical properties of tin-doped zinc oxide nanostructures doped at different dopant concentrations

This project has been focused on the electrical and optical properties respectively on the effect of Tin doped zinc oxide (ZnO) thin films at different dopant concentrations. These thin films were doped with different Sn dopant concentrations at 1 at%, 2 at%, 3 at%, 4 at% and 5 at% was selected as the parameter to optimize the thin films quality while the annealing temperature is fixed 500 °C. Sn doped ZnO solutions were deposited onto the glass substrates using sol-gel spin coating method. This project was involved with three phases, which are thin films preparation, deposition and characterization. The thin films were characterized using Current Voltage (I-V) measurement and ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometer (Perkin Elmer Lambda 750) for electrical properties and optical properties. The electrical properties show that the resistivity is the lowest at 4 at% Sn doping concentration with the value 3.08 × 10{sup 3} Ωcm{sup −1}. The absorption coefficient spectrum obtained shows all films exhibit very low absorption in the visible (400-800 nm) and near infrared (NIR) (>800 nm) range but exhibit high absorption in the UV range.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Six-Junction Concentrator Solar Cells

We report on six-junction inverted metamorphic (6J IMM) solar cells developed for concentrator applications. Monolithic III-V structures are grown by metal organic vapor phase epitaxy with junction bandgaps of 2.06, 1.70, 1.40, 1.16, 0.94, and 0.70 eV. The top three junctions are lattice-matched to the GaAs substrate, but the bottom three junctions use three consecutive metamorphic compositionally graded buffers to transition the lattice constant to GaxIn1-xAs compositions with the previously listed bandgaps. Performance of 6J IMM devices at one-sun AM1.5 Direct conditions gives VOC = 5.301 V, JSC = 8.05 mA/cm2, fill factor=83.9%, and efficiency=35.8%. Promising operation at high concentration is achieved but the spectrum was not controlled to AM1.5D. Tunnel junctions do not limit until at least several hundred suns. High concentration performance appears to be limited by internal heterojunction barriers created by zinc diffusion that decreases the fill factor. The properties of each junction within the 6J IMM have been separately characterized through electroluminescence and luminescent coupling measurements.

14 SOLAR ENERGY↗
DOE OSTI2023

Ion concentration ratio measurements of ion beams generated by a commercial microwave electron cyclotron resonance plasma source

A commercially available electron cyclotron resonance (ECR) plasma source (GenII Plasma Source, tectra GmbH) is widely used for surface processing. This plasma source is compatible with ultrahigh vacuum systems, and its working pressure is relatively low, around 10 –6 –10 –4 Torr even without differential pumping. Here, we report ion flux concentration ratios for each ion species in an ion beam from this source, as measured by a mass/energy analyzer that is a combination of a quadrupole mass spectrometer, an electrostatic energy analyzer, and focusing ion optics. In this study, the examined beams were those arising from plasmas produced from feed gases of H 2 , D 2 , N 2 , O 2 , Ar, and dry air over a range of input power and working pressures. H 2 (D 2 ) plasmas are widely used for nuclear fusion applications and, hence, the ion concentration ratios of H + , H 2 + , and H 3 + reported here will be useful information for research that applies this plasma source to well-controlled plasma-material interaction studies. Ion energy distributions, stability of operation, and impurity concentrations were also assessed for each of the plasma species investigated.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Measurements of water molecule isotopomer concentrations in a discharge of inert gas with addition of H{sub 2}O and D{sub 2} vapours by the method of external-cavity diode laser spectroscopy

Discharge plasma in inert gases with added water vapours and deuterium is studied by using the optimised diode laser spectroscopy with an external cavity. Formation of a spectrally dense grid of cavity transverse mode eigenfrequencies allows one to determine the parameters of Doppler broadening for absorption lines, a kinetic temperature of molecules, and their statistical sums. By using these parameters and the value of an absorption coefficient, correlations of concentrations are found for H{sub 2}O and HDO isotopomers at various ratios of plasma-forming gas components. An important contribution of initial gas molecules adsorbed on walls into the formation of plasma composition is stressed. It is found that the ratio of H{sub 2}O and HDO concentrations is the same at various ratios of H{sub 2}O and D{sub 2} concentrations in plasma-forming gases and is constant during the discharge burning process. (laser applications and other topics in quantum electronics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

CLASH: The concentration-mass relation of galaxy clusters

We present a new determination of the concentration–mass (c–M) relation for galaxy clusters based on our comprehensive lensing analysis of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble (CLASH). Our sample spans a redshift range between 0.19 and 0.89. We combine weak-lensing constraints from the Hubble Space Telescope (HST) and from ground-based wide-field data with strong lensing constraints from HST. The results are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids. Our derivation of Navarro–Frenk–White parameters yields virial masses between 0.53×10{sup 15} M{sub ⊙}/h and 1.76×10{sup 15} M{sub ⊙}/h and the halo concentrations are distributed around c{sub 200c}∼3.7 with a 1σ significant negative slope with cluster mass. We find an excellent 4% agreement in the median ratio of our measured concentrations for each cluster and the respective expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology. The simulations are analyzed in two dimensions to account for possible biases in the lensing reconstructions due to projection effects. The theoretical c–M relation from our X-ray selected set of simulated clusters and the c–M relation derived directly from the CLASH data agree at the 90% confidence level.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Impact of temperature and concentration on flow behaviour of reconstituted lactose and protein–rich dairy powders

To help with designing the drying process, this study investigated the flow behaviour of lactose and protein-rich reconstituted dairy powders at 25°C and 50°C. Lactose-rich samples, 50% dried whey (DW) and 60% whey protein concentrate (WPC35) did not follow the Herschel–Bulkley model because of presence of lactose crystals. Reconstituted 50% skim milk powder (SMP) and protein-rich dairy powders exhibited shear-thinning behaviour (n < 0.3). With increasing concentration, whey protein concentrate/isolate (WPC80/WPI) and micellar casein concentrate high-solid dispersions exhibited more shear-thinning behaviour (n < 0.4). Furthermore, understanding shear-thinning behaviour of lactose-rich and protein-rich reconstituted dairy powders will provide basis for optimising drying parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Linking the Dynamic Response of the Carbon Dioxide-Concentrating Mechanism to Carbon Assimilation Behavior in Fremyella diplosiphon

ABSTRACT Cyanobacteria use a carbon dioxide (CO 2 )-concentrating mechanism (CCM) that enhances their carbon fixation efficiency and is regulated by many environmental factors that impact photosynthesis, including carbon availability, light levels, and nutrient access. Efforts to connect the regulation of the CCM by these factors to functional effects on carbon assimilation rates have been complicated by the aqueous nature of cyanobacteria. Here, we describe the use of cyanobacteria in a semiwet state on glass fiber filtration discs—cyanobacterial discs—to establish dynamic carbon assimilation behavior using gas exchange analysis. In combination with quantitative PCR (qPCR) and transmission electron microscopy (TEM) analyses, we linked the regulation of CCM components to corresponding carbon assimilation behavior in the freshwater, filamentous cyanobacterium Fremyella diplosiphon . Inorganic carbon (C i ) levels, light quantity, and light quality have all been shown to influence carbon assimilation behavior in F. diplosiphon . Our results suggest a biphasic model of cyanobacterial carbon fixation. While behavior at low levels of CO 2 is driven mainly by the C i uptake ability of the cyanobacterium, at higher CO 2 levels, carbon assimilation behavior is multifaceted and depends on C i availability, carboxysome morphology, linear electron flow, and cell shape. Carbon response curves (CRCs) generated via gas exchange analysis enable rapid examination of CO 2 assimilation behavior in cyanobacteria and can be used for cells grown under distinct conditions to provide insight into how CO 2 assimilation correlates with the regulation of critical cellular functions, such as the environmental control of the CCM and downstream photosynthetic capacity. IMPORTANCE Environmental regulation of photosynthesis in cyanobacteria enhances organismal fitness, light capture, and associated carbon fixation under dynamic conditions. Concentration of carbon dioxide (CO 2 ) near the carbon-fixing enzyme RubisCO occurs via the CO 2 -concentrating mechanism (CCM). The CCM is also tuned in response to carbon availability, light quality or levels, or nutrient access—cues that also impact photosynthesis. We adapted dynamic gas exchange methods generally used with plants to investigate environmental regulation of the CCM and carbon fixation capacity using glass fiber-filtered cells of the cyanobacterium Fremyella diplosiphon . We describe a breakthrough in measuring real-time carbon uptake and associated assimilation capacity for cells grown in distinct conditions (i.e., light quality, light quantity, or carbon status). These measurements demonstrate that the CCM modulates carbon uptake and assimilation under low-C i conditions and that light-dependent regulation of pigmentation, cell shape, and downstream stages of carbon fixation are critical for tuning carbon uptake and assimilation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Ellipsoidal concentrators for laboratory X-ray sources: Analytical approach for optimization

Extremely low intensity of most existing laboratory X-ray sources ({lambda} {approx} 0.01-10 nm) calls for the development of collimating and concentrating optics, which allow to increase significantly the radiation power on the sample surface. The problem of optimizing concentrator parameters is analytically solved in this study. This solution allows one to determine (without any auxiliary calculations) the maximum possible efficiency of a concentrator at any wavelength and analyze the dependence of its efficiency on the source size, wavelength, the source-sample distance, etc.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Temperature, Time, Concentration, Annealing, and Substrates on ZnO Nanorod Arrays Growth by Hydrothermal Process on Hot Plate

Well aligned 1D ZnO nanostructures are important for optoelectronic and nanoscale electronic devices. In this report, 1D ZnO nanorods were synthesized by very simple, low cost, low temperature hydrothermal process. An effect of concentration, growth time, growth temperature, seed layer annealing, and seed layer thickness was investigated. The synthesized ZnO nanorods were characterized by scanning and transmission electron microscopies, X-ray diffraction, Raman and ultraviolet–visible spectroscopies. Growth parameters were found to influence strongly on the morphology, orientation, diameter, length, and density of the ZnO nanorod arrays. The growth temperature 80–90°C, seed layer annealing at 300–400°C, growth time 3 h, 0.025 M precursor concentration, and 0.2–0.3 M seed layer solution concentrations are more favorable conditions for better orientation and excellent crystallinity of the ZnO nanorods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗