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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Plant traits, productivity, biomass and soil properties from forest sites in the Pacific Northwest, 1999–2014

Plant trait measurements are needed for evaluating ecological responses to environmental conditions and for ecosystem process model development, parameterization, and testing. Here, we present a standardized dataset integrating measurements from projects conducted by the Terrestrial Ecosystem Research and Regional Analysis- Pacific Northwest (TERRA-PNW) research group between 1999 and 2014 across Oregon and Northern California, where measurements were collected for scaling and modeling regional terrestrial carbon processes with models such as Biome-BGC and the Community Land Model. The dataset contains measurements of specific leaf area, leaf longevity, leaf carbon and nitrogen for 35 tree and shrub species derived from more than 1,200 branch samples collected from over 200 forest plots, including several AmeriFlux sites. The dataset also contains plot-level measurements of forest composition, structure (e.g., tree biomass), and productivity, as well as measurements of soil structure (e.g., bulk density) and chemistry (e.g., carbon). Publically-archiving regional datasets of standardized, co-located, and geo-referenced plant trait measurements will advance the ability of earth system models to capture species-level climate sensitivity at regional to global scales.

09 BIOMASS FUELS↗
DOE OSTI2020

Understanding resistances in capacitive deionization devices

The desalination characteristics of capacitive deionization (CDI) are significantly impacted by the cell resistance. Here we apply electrochemical impedance spectroscopy (EIS) to analyze the resistive properties of a CDI device, which include EIS measurements on a complete assembled cell (in two wire mode) and EIS measurements with additional contacts to decouple electrode/electrolyte and contact impedances (four wire mode). These measurements shed light on the interface between current collector and electrode as well as the internal capacitive and resistive elements of the cell. With two-wire and four-wire EIS measurements, we find that the often observed high-frequency arc(s) in the impedance spectra can be due to contact effects and/or an internal ionic-transfer resistance that is locally in parallel with macropore wall capacitance. In some cases, the two associated arcs in the Nyquist plot are overlapping and present simultaneously, making their identification in the EIS spectra difficult unless both two-wire and four-wire measurements are made. Despite causing a large high-frequency arc in the Nyquist plot, we find that the apparent internal ionic-transfer resistance is negligible compared to the resistances of the electrode, separator, and external electronic components. Here, an investigation of the contact impedance between the electrode and current collector reveals a parallel RC arc that can grow over time if an improper material is used (e.g., titanium). In our system, the electrode ionic resistance dominates the total Ohmic power dissipation, which has implications for scale-up of CDI systems and future improvements of cell design.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Plot2Spectra: an automatic spectra extraction tool

Scientists cannot easily make use of numerical data encoded in plot images, such as of spectroscopy data, in scientific literature. Plot2Spectra was developed to use computer vision tools to automatically digitize plot images.

Jiang, Weixin↗
DOE OSTI2024

Influence of tritium exposure route on vegetation types at the Savannah River Site

Plant, soil, water, and other media from various locations at the Savannah River Site were measured for total tritium (T) content and T speciation to characterize T in these areas, as well as investigate its uptake behavior and the transport of T species in these media. This characterization included the isolation and measurement of T in tritiated water (HTO), and (when possible) exchangeable organic bound T (E-OBT) and non-exchangeable organic bound T (NE-OBT). Two areas of interest were investigated: (1) a holding pond with T-contaminated water and (2) open basins or streams with low to background levels of T. Water in the holding pond is used to irrigate forest plots in the local area as a T remediation approach. This study compares the analytical data for water, soil/sediment, plants, and lichens from these locations. Here, the results indicate that the behavior of T in plants from these areas can be a function of one or more of the following: seasonal precipitation, the plant's primary route of access to the T-contamination (such as water uptake through the root vs. shoot), plant physical location (relative to T-contaminated water sources), plant rooting depth, pond water level, and plant height above the ground. Total T concentrations were lowest in the un-irrigated forest plants, followed by irrigated forest plants, shallow rooting plants near the pond, deep rooting plants further from the pond, and then water-saturated plants. The OBT:HTO and NE-OBT:E-OBT ratios were always greater for plants from irrigated forest plots compared to those from the holding pond.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Characteristics of microdomains and microdomain patterns recorded by electron beam irradiation on Y-cut LiNbO{sub 3} crystals

We present the results of investigations of planar domain patterns (isolated domains and domain gratings) fabricated by irradiation of the nonpolar Y-surface of LiNbO{sub 3} crystals by an electron beam (EB) incident normally onto the surface. The EB recorded domains were investigated using atomic force microscopy, confocal second harmonic generation microscopy, and chemical etching as an auxiliary method. The dependence of the domain characteristics on irradiation conditions (acceleration voltage U, EB current I, and irradiation time t{sub irr}) were determined. The length L{sub d} of both isolated domains and domain gratings along the polar axis Z grows linearly with t{sub irr} (at U, I = const) with no tending to saturation. The plots L{sub d}(t{sub irr}) obtained for U = 10 and 15 kV are practically identical, whereas the values of L{sub d} for U = 5 kV are essentially lower. The domain thickness T{sub d} along the Y-direction, i.e., the depth of the switched layer grows with acceleration voltage U. These results are discussed in terms of space-charge fields formation arising under EB irradiation of insulators. The linearity of L{sub d}(t{sub irr}) is accounted for by the frontal domain growth via the viscous friction law. The experimental dependence of T{sub d} on U supports the suggestion that the domain thickness is determined by the penetration depth R{sub e} of primary electrons, which in turn is governed by U. The difference in L{sub d}(t{sub irr}) plots for different U is accounted for by different electron emission σ. Indirect evidences of a defect structure modification in a thin surface layer with respect to the crystal bulk are obtained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Experimental investigation of quasiperiodic-chaotic-quasiperiodic-chaotic transition in a direct current magnetron sputtering plasma

Floating potential fluctuations from a direct current magnetron sputtering plasma have been analysed using time series analysis techniques like phase space plots, power spectra, frequency bifurcation plot, etc. The system exhibits quasiperiodic-chaotic-quasiperiodic-chaotic transitions as the discharge voltage was increased. The transitions of the fluctuations, quantified using the largest Lyapunov exponent, have been corroborated by Hurst exponent and the Shannon entropy. The Shannon entropy is high for quasiperiodic and low for chaotic oscillations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Structure and electronic properties of Cu nanoclusters supported on Mo{sub 2}C(001) and MoC(001) surfaces

The atomic structure and electronic properties of Cu{sub n} nanoclusters (n = 4, 6, 7, and 10) supported on cubic nonpolar δ-MoC(001) and orthorhombic C- or Mo-terminated polar β-Mo{sub 2} C(001) surfaces have been investigated by means of periodic density functional theory based calculations. The electronic properties have been analyzed by means of the density of states, Bader charges, and electron localization function plots. The Cu nanoparticles supported on β-Mo{sub 2} C(001), either Mo- or C-terminated, tend to present a two-dimensional structure whereas a three-dimensional geometry is preferred when supported on δ-MoC(001), indicating that the Mo:C ratio and the surface polarity play a key role determining the structure of supported clusters. Nevertheless, calculations also reveal important differences between the C- and Mo-terminated β-Mo{sub 2} C(001) supports to the point that supported Cu particles exhibit different charge states, which opens a way to control the reactivity of these potential catalysts.

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

Framework to predict optimal buffer layer pairing for thin film solar cell absorbers: A case study for tin sulfide/zinc oxysulfide

An outstanding challenge in the development of novel functional materials for optoelectronic devices is identifying suitable charge-carrier contact layers. Herein, we simulate the photovoltaic device performance of various n-type contact material pairings with tin(II) sulfide (SnS), a p-type absorber. The performance of the contacting material, and resulting device efficiency, depend most strongly on two variables: conduction band offset between absorber and contact layer, and doping concentration within the contact layer. By generating a 2D contour plot of device efficiency as a function of these two variables, we create a performance-space plot for contacting layers on a given absorber material. For a simulated high-lifetime SnS absorber, this 2D performance-space illustrates two maxima, one local and one global. The local maximum occurs over a wide range of contact-layer doping concentrations (below 10{sup 16 }cm{sup −3}), but only a narrow range of conduction band offsets (0 to −0.1 eV), and is highly sensitive to interface recombination. This first maximum is ideal for early-stage absorber research because it is more robust to low bulk-minority-carrier lifetime and pinholes (shunts), enabling device efficiencies approaching half the Shockley-Queisser limit, greater than 16%. The global maximum is achieved with contact-layer doping concentrations greater than 10{sup 18 }cm{sup −3}, but for a wider range of band offsets (−0.1 to 0.2 eV), and is insensitive to interface recombination. This second maximum is ideal for high-quality films because it is more robust to interface recombination, enabling device efficiencies approaching the Shockley-Queisser limit, greater than 20%. Band offset measurements using X-ray photoelectron spectroscopy and carrier concentration approximated from resistivity measurements are used to characterize the zinc oxysulfide contacting layers in recent record-efficiency SnS devices. Simulations representative of these present-day devices suggest that record efficiency SnS devices are optimized for the second local maximum, due to low absorber lifetime and relatively well passivated interfaces. By employing contact layers with higher carrier concentrations and lower electron affinities, a higher efficiency ceiling can be enabled.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Temperature dependent dielectric and conductivity studies of polyvinyl alcohol-ZnO nanocomposite films by impedance spectroscopy

Dielectric and conductivity behaviors of nano ZnO doped polyvinyl alcohol (PVA) composites for various concentrations of dopant were investigated using impedance spectroscopy for a wide range of temperatures (303 K–423 K) and frequencies (5 Hz–30 MHZ). The dielectric properties of host polymer matrix have been improved by the addition of nano ZnO and are found to be highly temperature dependent. Anomalous dielectric behavior was observed in the frequency range of 2.5 MHz–5 MHz. Increase in dielectric permittivity and dielectric loss was observed with respect to temperature. The Cole-Cole plot could be modeled by low resistance regions in a high resistance matrix and the lowest resistance was observed for the 10 mol. % films. The imaginary part of the electric modulus showed asymmetric peaks with the relaxation following Debye nature below and non-Debye nature above the peaks. The ac conductivity is found to obey Jonscher's power law, whereas the variation of dc conductivity with temperature was found to follow Arrhenius behavior. Two different activation energy values were obtained from Arrhenius plot indicating that two conduction mechanisms are involved in the composite films. Fitting the ac conductivity data to Jonscher's law indicates that large polaron assisted tunneling is the most likely conduction mechanism in the composites. Maximum conductivity is observed at 423 K for all the samples and it is optimum for 10 mol. % ZnO doped PVA composite film. Significant increase in dc and ac conductivities in these composite films makes them a potential candidate for application in electronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo{sub 2}O{sub 5.5+δ} thin films

Single-crystalline epitaxial thin films of PrBaCo{sub 2}O{sub 5.5+δ} (PrBCO) were prepared, and their resistance R(t) under a switching flow of oxidizing and reducing gases were measured as a function of the gas flow time t in the temperature range of 200–800 °C. During the oxidation cycle under O{sub 2}, the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co{sup 2+}/Co{sup 3+} → Co{sup 3+} and Co{sup 3+} → Co{sup 3+}/Co{sup 4+}, that the Co atoms of PrBCO undergo. Each oscillation consists of two peaks, with larger and smaller peaks representing the oxygen/hydrogen diffusion through the (BaO)(CoO{sub 2})(PrO)(CoO{sub 2}) layers of PrBCO via the oxygen-vacancy-exchange mechanism. This finding paves a significant avenue for cathode materials operating in low-temperature solid-oxide-fuel-cell devices and for chemical sensors with wide range of operating temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Temperature varying photoconductivity of GeSn alloys grown by chemical vapor deposition with Sn concentrations from 4% to 11%

Pseudomorphic GeSn layers with Sn atomic percentages between 4.5% and 11.3% were grown by chemical vapor deposition using digermane and SnCl{sub 4} precursors on Ge virtual substrates grown on Si. The layers were characterized by x-ray diffraction rocking curves and reciprocal space maps. Photoconductive devices were fabricated, and the dark current was found to increase with Sn concentration. The responsivity of the photoconductors was measured at a wavelength of 1.55 μm using calibrated laser illumination at room temperature and a maximum value of 2.7 mA/W was measured for a 4.5% Sn device. Moreover, the responsivity for higher Sn concentration was found to increase with decreasing temperature. Spectral photoconductivity was measured using Fourier transform infrared spectroscopy. The photoconductive absorption edge continually increased in wavelength with increasing tin percentage, out to approximately 2.4 μm for an 11.3% Sn device. The direct band gap was extracted using Tauc plots and was fit to a bandgap model accounting for layer strain and Sn concentration. This direct bandgap was attributed to absorption from the heavy-hole band to the conduction band. Higher energy absorption was also observed, which was thought to be likely from absorption in the light-hole band. The band gaps for these alloys were plotted as a function of temperature. These experiments show the promise of GeSn alloys for CMOS compatible short wave infrared detectors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Ghost fringe removal techniques using Lissajous data presentation

A VISAR (Velocity Interferometer System for Any Reflector) is a Dopplervelocity interferometer which is an important optical diagnostic in shockwave experiments at the national laboratories, used to measureequation of state(EOS) of materials under extreme conditions. Unwanted reflection of laser light from target windows can produce an additional component to the VISAR fringe record that can distort and obscure the true velocity signal. When accurately removing this so-called ghost artifact component is essential for achieving high accuracy EOSmeasurements, especially when the true light signal is only weakly reflected from the shock front. Independent of the choice of algorithm for processing the raw data into a complex fringe signal, we have found it beneficial to plot this signal as a Lissajous and seek the proper center of this path, even under time varying intensity which can shift the perceived center. Moreover, the ghost contribution is then solved by a simple translation in the complex plane that recenters the Lissajous path. For continuous velocity histories, we find that plotting the fringe magnitude vs nonfringing intensity and optimizing linearity is an invaluable tool for determining accurate ghost offsets. For discontinuous velocity histories, we have developed graphically inspired methods which relate the results of two VISARs having different velocity per fringe proportionalities or assumptions of constant fringe magnitude to find the ghost offset. The technique can also remove window reflection artifacts in generic interferometers, such as in the metrology of surfaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A method for determining average damage depth of sawn crystalline silicon wafers

The depth of surface damage (or simply, damage) in crystalline silicon wafers, caused by wire sawing of ingots, is determined by performing a series of minority carrier lifetime (MCLT) measurements. Samples are sequentially etched to remove thin layers from each surface and MCLT is measured after each etch step. The thickness-removed (δt) at which the lifetime reaches a peak value corresponds to the damage depth. This technique also allows the damage to be quantified in terms of effective surface recombination velocity (S eff ). To accomplish this, the MCLT data are converted into an S eff vs δt plot, which represents a quantitative distribution of the degree of damage within the surface layer. We describe a wafer preparation procedure to attain reproducible etching and MCLT measurement results. We also describe important characteristics of an etchant used for controllably removing thin layers from the wafer surfaces. Lastly, some typical results showing changes in the MCLT vs δt plots for different cutting parameters are given.

14 SOLAR ENERGY↗
DOE OSTI2016

Temperature dependent x-ray diffraction and dielectric studies of multiferroic GaFeO{sub 3}

Polycrystalline GaFeO{sub 3} (GFO) samples were synthesized by sol-gel method. The structural and dielectric properties of GaFeO{sub 3} ceramic have been investigated by a combination of XRD and permittivity measurement. The X-ray diffraction spectra shows single phase orthorhombically distorted perovskite structure with Pc2{sub 1}n symmetry over a wide range of temperature 300 K to 600 K, with no evidence of any phase transition. Refined lattice parameters (a, b, c and V) increases with increasing temperature. Temperature dependent dielectric properties were investigated in the frequency range from 100Hz–5MHz. Impedance spectroscopy study on the sample showed that the dielectric constant and ac conductivity with frequency increases on increasing the temperature. Cole-Cole plots suggest that the response from grain is dominant at low temperature whereas grain boundary response overcomes as temperature increases. The relaxation activation energy (calculated from Cole-Cole plots) value is found to be 0.32 eV for the grain boundary. We believe that the oxygen ion vacancies play an important role in conduction processes at higher temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of sintering treatment on structural and magnetic properties of Ni{sub 0.5}Co{sub 0.5}Fe{sub 2}O{sub 4} ferrites

Two sets of Ni{sub 0.5}Co{sub 0.5}Fe{sub 2}O{sub 4} ferrites were synthesized using sol-gel method. Both the samples were heat treated at different temperatures. The effect of sintering treatment analyzed on structural and magnetic properties. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used for structural analysis. Alternating gradient magnetometer (AGM) is used for magnetic measurements. In structural analysis, grains size is calculated using Debye - Scherrer’s formula and Williamson-Hall (W-H) plot. From both the techniques, grain size is found nearly same and increased in size with increase sintering temperature. Increased particle size is confirmed from SEM micrographs. Strain value is calculated from intercept of W-H plot. In both the samples, compressive strain in nature is found. Magnetic properties were also varying under different heat treatment. The change in magnetic properties with change in structural change at different sintering treatment is discussed in this report.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural and impedance studies of LiNi{sub 0.5}Mn{sub 1.5}O{sub 4} synthesized by sol-gel method

LiNi{sub 0.5}Mn{sub 1.5}O{sub 4} is synthesized by sol-gel method by using succinic acid as chelating agent. X-ray diffraction pattern confirms the material is spinel cubic structure with Fd3m space group. Impedance spectroscopy analysis of spinel LiNi{sub 0.5}Mn{sub 1.5}O{sub 4} was performed under a wide frequency and temperature range of 50 Hz to 5 MHz and 303 K to 783 K respectively. The hopping of the electrons, ionic conductivity and activation energy were analyzed from the relaxation frequency of the imaginary impedance (Z”). The activation energy E{sub a} is calculated from the Arrhenius plots and it is found to be 0.3713 eV, which indicates the existence of oxygen vacancy in the material. Nyquist plot indicates the presence of grain effect in the material and suppression in the grain effect is observed with increasing temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Oscillating plasma bubble and its associated nonlinear studies in presence of low magnetic field

Oscillating plasma bubbles have been created around a cylindrical mesh grid of 75% optical transparency in a DC plasma system with a low magnetic field. Plasma bubbles are created by developing ion density gradient around a cylindrical grid of 20 cm in diameter and 25 cm in height, inserted into the plasma. Relaxation and contraction of the plasma bubbles in the presence of external conditions, such as magnetic field and pressure, have been studied. A Langmuir probe has been used to detect the plasma floating potential fluctuations at different imposed experimental conditions. Nonlinear behavior of the system has been characterized by adopting nonlinear techniques such as Fast Fourier Transform, Phase Space Plot, and Recurrence Plot. It shows that the system creates highly nonlinear phenomena associated with the plasma bubble under the imposed experimental conditions. A theoretical and numerical model has also been developed to satisfy the observed experimental analysis. Moreover, observations are extended further to study the growth of instability associated with the plasma bubbles. The intention of the present work is to correlate the findings about plasma bubbles and their related instability with the one existing in the equatorial F-region of the ionosphere.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Visualizing dispersive features in 2D image via minimum gradient method

Here, we developed a minimum gradient based method to track ridge features in a 2D image plot, which is a typical data representation in many momentum resolved spectroscopy experiments. Through both analytic formulation and numerical simulation, we compare this new method with existing DC (distribution curve) based and higher order derivative based analyses. We find that the new method has good noise resilience and enhanced contrast especially for weak intensity features and meanwhile preserves the quantitative local maxima information from the raw image. An algorithm is proposed to extract 1D ridge dispersion from the 2D image plot, whose quantitative application to angle-resolved photoemission spectroscopy measurements on high temperature superconductors is demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗