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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Synthesis and characterization of titanium-alloyed hematite thin films for photoelectrochemical water splitting

We have synthesized pure and Ti-alloyed hematite thin films on F doped SnO{sub 2} coated glass substrates by radio frequency magnetron co-sputtering of iron oxide and titanium targets in mixed Ar/O{sub 2} and mixed N{sub 2}/O{sub 2} ambient. We found that the hematite films deposited in the N{sub 2}/O{sub 2} ambient exhibit much poorer crystallinity than the films deposited in the Ar/O{sub 2} ambient. We determined that Ti alloying leads to increased electron carrier concentration and crystallinity, and reduced bandgaps. Moreover, Ti-alloyed hematite thin films exhibited improved photoelectrochemical performance as compared with the pure hematite films: The photocurrents were enhanced and the photocurrent onset shifted to less positive potentials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Performance and characterization of the prototype nm-scale spatial resolution scanning multilayer Laue lenses microscope

Synchrotron based x-ray microscopy established itself as a prominent tool for noninvasive investigations in many areas of science and technology. Many facilities around the world routinely achieve sub-micrometer resolution with a few instruments capable of imaging with the spatial resolution better than 100 nm. With an ongoing effort to push the 2D/3D resolution down to 10 nm in the hard x-ray regime both fabrication of the nano-focusing optics and stability of a microscope become extremely challenging. In this work we present our approach to overcome technical challenges on the path towards high spatial resolution hard x-ray microscopy and demonstrate the performance of a scanning fluorescence microscope equipped with the multilayer Laue lenses focusing optics.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Characterization of heat loads from mitigated and unmitigated vertical displacement events in DIII-D

Experiments have been conducted on the DIII-D tokamak to study the distribution and repeatability of heat loads and vessel currents resulting from vertical displacement events (VDEs). For unmitigated VDEs, the radiated power fraction appears to be of order 50%, with the remaining power dominantly conducted to the vessel walls. Shot-to-shot scatter in heat loads measured at one toroidal location is not large (<±50%), suggesting that toroidal asymmetries in conducted heat loads are not large. Conducted heat loads are clearly observed during the current quench (CQ) of both mitigated and unmitigated disruptions. Significant poloidal asymmetries in heat loads and radiated power are often observed in the experiments but are not yet understood. Energy dissipated resistively in the conducting walls during the CQ appears to be small (<5%). The mitigating effect of neon massive gas injection (MGI) as a function of MGI trigger delay has also been studied. Improved mitigation is observed as the MGI trigger delay is decreased. For sufficiently early MGI mitigation, close to 100% radiated energy and a reduction of roughly a factor 2 in vessel forces is achieved.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Laser assisted crystallization of ferromagnetic amorphous ribbons: A multimodal characterization and thermal model study

This paper focuses on laser-based de-vitrification of amorphous soft magnetic Fe-Si-B ribbons and its consequent influence on the magnetic properties. Laser processing resulted in a finer scale of crystallites due to rapid heating and cooling during laser annealing compared to conventional furnace annealing process. A significant increase in saturation magnetization is observed for laser-annealed ribbons compared to both as-received and furnace annealed samples coupled with an increase in coercivity compared to the as received samples. The combined effect of thermal histories and stresses developed during laser annealing results in the formation of nano-crystalline phase along the laser track. The phase evolution is studied by micro-XRD and TEM analysis. Solute partitioning and compositional variation within the phases are obtained by Local Electrode Atom probe analysis. The evolution of microstructure is rationalized using a Finite Element based heat transfer multi-physics model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Characterization of two different orientations of epitaxial niobium thin films grown on MgO(001) surfaces

Epitaxial Nb thin films deposited onto the same crystalline insulating surface can evolve in very different fashions depending on specific deposition conditions, thereby affecting their microstructure, surface morphology and superconducting properties. Here, we examine and compare the microstructure and ensuing surface morphology from two distinct Nb/MgO series each with its own epitaxial registry—namely Nb(001)/MgO(001) and Nb(110)/MgO(001)—leading to distinct surface anisotropy and we closely examine the dynamical scaling of the surface features during growth. We compare our findings with those in other metal/MgO epitaxial systems and for the first time, general scaling formalism is applied to analyze anisotropic surfaces exhibiting biaxial symmetry. Further, Power Spectral Density is applied to the specific problem of thin film growth and surface evolution to qualify the set of deposition conditions leading to smoother surfaces. We find good correlation between the surface morphology and microstructure of the various Nb films with superconducting properties such as their residual resistance ratio and lower critical field.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Some characterizations of quantum channel in infinite Hilbert spaces

We first show that for any quantum states ρ on H and σ on K there exists a quantum channel Φ such that Φ(ρ) = σ, where H and K are finite or infinite dimensional Hilbert spaces. Then we consider some conclusions for the quantum channel Φ such that Φ(ρ) = σ and Φ(I{sub H}) exists or Φ(I{sub H})=I{sub K}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

A compact neutron spectrometer for characterizing inertial confinement fusion implosions at OMEGA and the NIF

A compact spectrometer for measurements of the primary deuterium-tritium neutron spectrum has been designed and implemented on the OMEGA laser facility [T. Boehly et al., Opt. Commun. 133, 495 (1997)]. This instrument uses the recoil spectrometry technique, where neutrons produced in an implosion elastically scatter protons in a plastic foil, which are subsequently detected by a proton spectrometer. This diagnostic is currently capable of measuring the yield to ∼±10% accuracy, and mean neutron energy to ∼±50 keV precision. As these compact spectrometers can be readily placed at several locations around an implosion, effects of residual fuel bulk flows during burn can be measured. Future improvements to reduce the neutron energy uncertainty to ±15−20 keV are discussed, which will enable measurements of fuel velocities to an accuracy of ∼±25−40 km/s.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Ellipsometric characterization and density-functional theory analysis of anisotropic optical properties of single-crystal α-SnS

We report on the anisotropic optical properties of single-crystal tin monosulfide (SnS). The components ε{sub a}, ε{sub b}, and ε{sub c} of the pseudodielectric-function tensor (ε)=(ε₁)+i(ε₂) spectra are taken from 0.73 to 6.45 eV by spectroscopic ellipsometry. The measured (ε) spectra are in a good agreement with the results of the calculated dielectric response from hybrid density functional theory. The (ε) spectra show the direct band-gap onset and a total of eight above-band-gap optical structures that are associated with the interband-transition critical points (CPs). We obtain accurate CP energies by fitting analytic CP expressions to second-energy-derivatives of the (ε) data. Their probable electronic origins and implications for photovoltaic applications are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Characterization of spatially resolved high resolution x-ray spectrometers for high energy density physics and light source experiments

A high resolution 1D imaging x-ray spectrometer concept comprising a spherically bent crystal and a 2D pixelated detector is being optimized for diagnostics of small sources such as high energy density physics (HEDP) and synchrotron radiation or x-ray free electron laser experiments. This instrument is used on tokamak experiments for Doppler measurements of ion temperature and plasma flow velocity profiles. Laboratory measurements demonstrate a resolving power, E/ΔE of order 10 000 and spatial resolution better than 10 μm. Initial tests of the high resolution instrument on HEDP plasmas are being performed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Time-resolved characterization and energy balance analysis of implosion core in shock-ignition experiments at OMEGA

Time-resolved temperature and density conditions in the core of shock-ignition implosions have been determined for the first time. The diagnostic method relies on the observation, with a streaked crystal spectrometer, of the signature of an Ar tracer added to the deuterium gas fill. The data analysis confirms the importance of the shell attenuation effect previously noted on time-integrated spectroscopic measurements of thick-wall targets [R. Florido et al., Phys. Rev. E 83, 066408 (2011)]. This effect must be taken into account in order to obtain reliable results. The extracted temperature and density time-histories are representative of the state of the core during the implosion deceleration and burning phases. As a consequence of the ignitor shock launched by the sharp intensity spike at the end of the laser pulse, observed average core electron temperature and mass density reach T ~ 1100 eV and ρ ~ 2 g/cm 3 ; then temperature drops to T ~ 920 eV while density rises to ρ ~ 3.4 g/cm 3 about the time of peak compression. Compared to 1D hydrodynamic simulations, the experiment shows similar maximum temperatures and smaller densities. Simulations do not reproduce all observations. Differences are noted in the heating dynamics driven by the ignitor shock and the optical depth time-history of the compressed shell. Time-histories of core conditions extracted from spectroscopy show that the implosion can be interpreted as a two-stage polytropic process. Furthermore, an energy balance analysis of implosion core suggests an increase in total energy greater than what 1D hydrodynamic simulations predict. This new methodology can be implemented in other ICF experiments to look into implosion dynamics and help to understand the underlying physics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Quantitative characterization of arc discharge as vacuum interface

An arc discharge with channel diameters of 3 mm and 6 mm and lengths between 30mm and 60mm was experimentally investigated for its potential to function as plasma window, i.e., interface vacuum regions of different pressures. In this study, electron temperature of the plasma channel measured spectroscopically varied in the range of 7000K to 15000K, increasing with discharge current while decreasing with gas flow rate. The plasma window had a slightly positive I-V characteristics over the whole range of investigated current 30A–70 A. Measurements of pressure separation capability, which were determined by input current, gas flow rate, discharge channel diameter, and length, were well explained by viscosity effect and “thermal-block” effect. The experimental results of global parameters including temperature, gas flow rate, and voltage had a good agreement with the simulation results calculated by an axis-symmetry Fluent-based magneto-hydrodynamic model.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Characterization of one-dimensional molecular chains of 4,4′-biphenyl diisocyanide on Au(111) by scanning tunneling microscopy

The morphology and electronic structure of vapor deposited 4,4′-biphenyldiisocyanide (BPDI) on a Au(111) surface were investigated using variable-temperature scanning tunneling microscopy. When deposited at room temperature, BPDI molecules form one-dimensional molecular chains similar to that recently observed for the structurally related 1,4-phenyl diisocyanide (PDI). Compared to PDI, the longer periodicity for the BPDI molecular chains is consistent with the addition of a second phenyl ring and supports a structural model in which the BPDI molecules lie parallel to the surface and interconnected by Au-adatoms. The molecular chains are mostly aligned along the [11{sup -}0] direction of the Au(111) substrate, but exhibit frequent changes in angle that are consistent with directions between fcc and hcp three-fold hollow sites. Dispersion-corrected density functional theory calculations for one-dimensional chains of BPDI molecules bound end-to-end via their isocyanide groups to Au-adatoms reproduce the observed periodicity of the chains and show that this morphology is energetically favored over upright binding with one free —NC group. The spatially resolved conductance (dI/dV) map for BPDI on Au(111) exhibits a feature centered at −0.67 eV below the Fermi level which are delocalized along the chain with maxima at the Au-adatom and biphenyl positions. This occupied resonant feature is close to that previously observed for the PDI in both photoemission and conductance measurements and is attributed to an occupied interfacial state resulting from BPDI-Au interactions.

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

Characterization of the temperature dependence of the thermoreflectance coefficient for conductive thin films

We describe a novel approach for calibration of the thermoreflectance coefficient, ideally suited for measurements in a vacuum thermostat, and present the high temperature thermoreflectance coefficients for several metals commonly encountered in electronic devices: gold, platinum, and aluminum. The effect of passivation on these metals is also examined, and we demonstrate the signal to noise ratio of a thermoreflectance measurement can be improved with informed selection of the dielectric layer thickness. Furthermore, the thermo-optic coefficients of the metals are extracted over a wide temperature range. The results presented here can be utilized in the optimization of experimental configurations for high temperature thermoreflectance imaging.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Characterization of Lorenz number with Seebeck coefficient measurement

In analyzing zT improvements due to lattice thermal conductivity (κ{sub L}) reduction, electrical conductivity (σ) and total thermal conductivity (κ{sub Total}) are often used to estimate the electronic component of the thermal conductivity (κ{sub E}) and in turn κ{sub L} from κ{sub L} = ∼ κ{sub Total} − LσT. The Wiedemann-Franz law, κ{sub E} = LσT, where L is Lorenz number, is widely used to estimate κ{sub E} from σ measurements. It is a common practice to treat L as a universal factor with 2.44 × 10{sup −8} WΩK{sup −2} (degenerate limit). However, significant deviations from the degenerate limit (approximately 40% or more for Kane bands) are known to occur for non-degenerate semiconductors where L converges to 1.5 × 10{sup −8} WΩK{sup −2} for acoustic phonon scattering. The decrease in L is correlated with an increase in thermopower (absolute value of Seebeck coefficient (S)). Thus, a first order correction to the degenerate limit of L can be based on the measured thermopower, |S|, independent of temperature or doping. We propose the equation: L=1.5+exp[−(|S|)/(116) ] (where L is in 10{sup −8} WΩK{sup −2} and S in μV/K) as a satisfactory approximation for L. This equation is accurate within 5% for single parabolic band/acoustic phonon scattering assumption and within 20% for PbSe, PbS, PbTe, Si{sub 0.8}Ge{sub 0.2} where more complexity is introduced, such as non-parabolic Kane bands, multiple bands, and/or alternate scattering mechanisms. The use of this equation for L rather than a constant value (when detailed band structure and scattering mechanism is not known) will significantly improve the estimation of lattice thermal conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Multidimensional characterization of stochastic dynamical systems based on multiple perturbations and measurements

Generalized nonlinear response theory is presented for stochastic dynamical systems. Experiments in which multiple measurements of dynamical quantities are used along with multiple perturbations of parameters of dynamical systems are described by generalized response functions (GRFs). These constitute a new type of multidimensional measures of stochastic dynamics either in the time or the frequency domains. Closed expressions for GRFs in stochastic dynamical systems are derived and compared with numerical non-equilibrium simulations. Several types of perturbations are considered: impulsive and periodic perturbations of temperature and impulsive perturbations of coordinates. The present approach can be used to study various types of stochastic processes ranging from single-molecule conformational dynamics to chemical kinetics of finite-size reactors such as biocells.

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

Experimental characterization of a transition from collisionless to collisional interaction between head-on-merging supersonic plasma jets

We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques

We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗