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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 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Photoemission spectroscopy study of the lanthanum lutetium oxide/silicon interface

Rare earth oxides are promising candidates for future integration into nano-electronics. A key property of these oxides is their ability to form silicates in order to replace the interfacial layer in Si-based complementary metal-oxide field effect transistors. In this work a detailed study of lanthanum lutetium oxide based gate stacks is presented. Special attention is given to the silicate formation at temperatures typical for CMOS processing. The experimental analysis is based on hard x-ray photoemission spectroscopy complemented by standard laboratory experiments as Rutherford backscattering spectrometry and high-resolution transmission electron microscopy. Homogenously distributed La silicate and Lu silicate at the Si interface are proven to form already during gate oxide deposition. During the thermal treatment Si atoms diffuse through the oxide layer towards the TiN metal gate. This mechanism is identified to be promoted via Lu-O bonds, whereby the diffusion of La was found to be less important.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Dynamic heterogeneity in the folding/unfolding transitions of FiP35

Molecular dynamics simulations have become an important tool in studying protein dynamics over the last few decades. Atomistic simulations on the order of micro- to milliseconds are becoming feasible and are used to study the state-of-the-art experiments in atomistic detail. Yet, analyzing the high-dimensional-long-temporal trajectory data is still a challenging task and sometimes leads to contradictory results depending on the analyses. To reveal the dynamic aspect of the trajectory, here we propose a simple approach which uses a time correlation function matrix and apply to the folding/unfolding trajectory of FiP35 WW domain [Shaw et al., Science 330, 341 (2010)]. The approach successfully characterizes the slowest mode corresponding to the folding/unfolding transitions and determines the free energy barrier indicating that FiP35 is not an incipient downhill folder. The transition dynamics analysis further reveals that the folding/unfolding transition is highly heterogeneous, e.g., the transition path time varies by ∼100 fold. We identify two misfolded states and show that the dynamic heterogeneity in the folding/unfolding transitions originates from the trajectory being trapped in the misfolded and half-folded intermediate states rather than the diffusion driven by a thermal noise. The current results help reconcile the conflicting interpretations of the folding mechanism and highlight the complexity in the folding dynamics. This further motivates the need to understand the transition dynamics beyond a simple free energy picture using simulations and single-molecule experiments.

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

Extending the diffusion approximation to the boundary using an integrated diffusion model

The widely used diffusion approximation is inaccurate to describe the transport behaviors near surfaces and interfaces. To solve such stochastic processes, an integro-differential equation, such as the Boltzmann transport equation (BTE), is typically required. In this work, we show that it is possible to keep the simplicity of the diffusion approximation by introducing a nonlocal source term and a spatially varying diffusion coefficient. We apply the proposed integrated diffusion model (IDM) to a benchmark problem of heat conduction across a thin film to demonstrate its feasibility. We also validate the model when boundary reflections and uniform internal heat generation are present.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thermoelectric transport coefficients in mono-layer MoS{sub 2} and WSe{sub 2}: Role of substrate, interface phonons, plasmon, and dynamic screening

The thermoelectric transport coefficients of electrons in two recently emerged transition metal di-chalcogenides (TMD), MoS{sub 2} and WSe{sub 2}, are calculated by solving Boltzmann transport equation using Rode's iterative technique in the diffusive transport regime and the coupled current (electrical and heat) equations. Scattering from remote phonons along with the hybridization of TMD plasmon with remote phonon modes and dynamic screening under linear polarization response are investigated in TMDs sitting on a dielectric environment. The transport coefficients are obtained for a varying range of temperature and doping density for three different types of substrates—SiO{sub 2}, Al{sub 2}O{sub 3}, and HfO{sub 2}. The Seebeck co-efficient for MoS{sub 2} and WSe{sub 2} is found to be higher than 3D semiconductors even with diffusive transport. The electronic thermal conductivity is found to be low, however, the thermoelectric figure of merit is limited by the high phonon thermal conductivity. It is found that judicious selection of a dielectric environment based on temperature of operation and carrier density is crucial to optimize the thermoelectric performance of TMD materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Developing a platform for Fresnel diffractive radiography with 1 μ m spatial resolution at the National Ignition Facility

An x-ray Fresnel diffractive radiography platform was designed for use at the National Ignition Facility. It will enable measurements of micron-scale changes in the density gradients across an interface between isochorically heated warm dense matter materials, the evolution of which is driven primarily through thermal conductivity and mutual diffusion. Here we use 4.75 keV Ti K-shell x-ray emission to heat a 1000 μm diameter plastic cylinder, with a central 30 μm diameter channel filled with liquid D 2 , up to 8 eV. This leads to a cylindrical implosion of the liquid D 2 column, compressing it to ~2.3 g/cm 3 . After pressure equilibration, the location of the D 2 /plastic interface remains steady for several nanoseconds, which enables us to track density gradient changes across the material interface with high precision. For radiography, we use Cu He- α x rays at 8.3 keV. Using a slit aperture of only 1 μm width increases the spatial coherence of the source, giving rise to significant diffraction features in the radiography signal, in addition to the refraction enhancement, which further increases its sensitivity to density scale length changes at the D 2 /plastic interface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Resonant interactions involving local vibrational modes in crystals

When an impurity with a light mass is inserted into a crystal, it can undergo a high-frequency oscillation referred to as a local vibrational mode (LVM). A Fermi resonance may occur between the LVM and lower-frequency modes of the defect. The LVM may also interact with phonons or the electromagnetic field. Understanding these interactions can help model and control diffusion, defect reactions, and thermal conductivity. LVMs have been probed in semiconductors using pressure and alloying as experimental parameters, resulting in anticrossing between localized and extended vibrational modes. Furthermore, these types of vibrational interactions could play an important role in the stability and thermal properties of organic–inorganic hybrid semiconductors. The coupling between an LVM and electromagnetic wave yields an “LVM polariton,” an excitation that has significant vibrational and electric-field amplitudes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Physical nature of the [S II]-bright shell nebulae N70 and N185

N70 and N185 are two large (≥100 pc in diameter) shell nebulae in the Large Magellanic Cloud (LMC). Their high [S II]/Hα ratios rival those of supernova remnants (SNRs), but they are not confirmed as SNRs. To study their physical nature, we have obtained XMM-Newton X-ray observations and high-dispersion long-slit echelle spectroscopic observations of these two nebulae. The X-ray spectra of both nebulae can be well interpreted with an optically thin thermal (∼0.2 keV) plasma with the average LMC abundance in a collisional ionization equilibrium. N70 encompasses the OB association LH114. Although N70 has a modest expansion velocity and essentially thermal radio emission, its diffuse X-ray luminosity (∼6.1 × 10{sup 35} erg s{sup –1}) is higher than that from a quiescent superbubble with N70's density, size, and expansion velocity; thus, N70 is most likely a superbubble that is recently energized by an interior SNR. N185 does not contain any known OB association, and its X-ray luminosity is an order of magnitude lower than expected if it is a quiescent superbubble. N185 has nonthermal radio emission and has high-velocity material expanding at nearly 200 km s{sup –1}, similar to many known SNRs in the LMC. Its X-ray luminosity (∼1.9 × 10{sup 35} erg s{sup –1}) is also consistent with that of an evolved SNR. We therefore suggest that N185 is energized by a recent supernova.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Amorphization and siliconization of silicon carbide as a first wall material

The understanding and prediction of silicon carbide (SiC) material evolution exposed to SOL plasma conditions is of prime interest because SiC represents a promising main chamber wall plasma-facing material for next-step fusion devices (low hydrogenic diffusion, good mechanical and thermal properties under neutron irradiation). Gross and net Si erosion rates from SiC surfaces in contact with a well-diagnosed L-mode plasma in the DIII-D tokamak have been simulated and the surface concentrations of impurities have been tracked as a function of time. Coupled simulation of surface model and impurity transport demonstrates amorphization of crystalline SiC exposed to L-mode plasma due to the accumulation of displacement damages under ion irradiation. This affects the lifetime of SiC plasma facing components. Surface evolution is tightly coupled to impurity transport in the plasma and therefore needs to be integrated with impurity transport simulations to effectively predict Si erosion rates and sub-surface concentrations as a function of time. The simulation workflow couples a semi-analytical surface model to the impurity transport code GITR. The surface model is a homogeneous mixed-material model that tracks physical & chemical sputtering and reflection of impurities. Gross erosion is primarily influenced by the background plasma parameters and redeposition patterns are mainly influenced by the prompt redeposition due to the gyro-orbits of impurity ions. Although crystalline form of SiC is preferable for fusion wall applications because of resistance to neutron irradiation, this work indicates that crystalline SiC will undergo amorphization under D plasma contact with implications of higher sputtering and fuel retention. These results direct us to explore the effects of amorphization on crystalline SiC and further the physics basis of SiC usage as first wall material for fusion environments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Effective dissipation rate in a Liouvillian-graph picture of high-temperature quantum hydrodynamics

At high temperature, generic strongly interacting spin systems are expected to display hydrodynamics: local transport of conserved quantities, governed by classical partial differential equations like the diffusion equation. I argue that the emergence of this dissipative long-wavelength dynamics from the system's unitary microscopic dynamics is controlled by the structure of the Liouvillian graph of the system's Hamiltonian, that is, the graph induced on Pauli strings by commutation with that Hamiltonian. The Liouvillian graph decomposes naturally into subgraphs of Pauli strings of constant diameter, and the coherent dynamics of these subgraphs determines the rate at which operator weight spreads to long operators. In conclusion, this argument provides a quantitative theory of the emergence of a dissipative effective dynamics from unitary microscopic dynamics; it also leads to an effective model with Hilbert space dimension linear in system size and exponential in the UV cutoff for diffusion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Transport coefficients of the quark-gluon plasma at the critical point and across the first-order line

A bottom-up Einstein-Maxwell-dilaton holographic model is used to compute, for the first time, the behavior of several transport coefficients of the hot and baryon-rich strongly coupled quark-gluon plasma at the critical point and also across the first-order phase transition line in the phase diagram. The observables under study are the shear and bulk viscosities, the baryon and thermal conductivities, the baryon diffusion, the jet quenching parameter $\hat{q}$, as well as the heavy-quark drag force and the Langevin diffusion coefficients. These calculations provide a phenomenologically promising estimate for these coefficients, given that our model quantitatively reproduces lattice QCD thermodynamics results, both at zero and finite baryon density, besides naturally incorporating the nearly perfect fluidity of the quark-gluon plasma. Here we find that the diffusion of baryon charge, and also the shear and bulk viscosities, are suppressed with increasing baryon density, indicating that the medium becomes even closer to perfect fluidity at large densities. On the other hand, the jet quenching parameter and the heavy-quark momentum diffusion are enhanced with increasing density. The observables display a discontinuity gap when crossing the first-order phase transition line, while developing an infinite slope at the critical point. The transition temperatures associated with different transport coefficients differ in the crossover region but are found to converge at the critical point.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Ionic transport in high-energy-density matter

Ionic transport coefficients for dense plasmas have been numerically computed using an effective Boltzmann approach. Here, we developed a simplified effective potential approach that yields accurate fits for all of the relevant cross sections and collision integrals. These results have been validated with molecular-dynamics simulations for self-diffusion, interdiffusion, viscosity, and thermal conductivity. Molecular dynamics has also been used to examine the underlying assumptions of the Boltzmann approach through a categorization of behaviors of the velocity autocorrelation function in the Yukawa phase diagram. By using a velocity-dependent screening model, we examine the role of dynamical screening in transport. Implications of these results for Coulomb logarithm approaches are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Dimensionless parameters for cloudy Rayleigh-Bénard convection: Supersaturation, Damköhler, and Nusselt numbers

In steady-state Rayleigh-Bénard convection, heat is transported by turbulent thermal convection from the bottom, hot surface to the top, cold surface, leading to a height-independent sensible heat flux. When water vapor is present and cloud formation occurs, there is also an additional latent heat flux. Heat transport in cloudy Rayleigh-Bénard convection depends on turbulent flow as well as the microphysical state of the clouds: specifically, whether substantial supersaturations exist and whether cloud liquid water is removed through sedimentation/precipitation. In this article we bridge between the Rayleigh-Bénard convection literature and the atmospheric literature. We express the governing equations for cloudy convection in dimensionless form, thereby explicitly identifying the governing parameters relevant to the cloudy case, including Schmidt, Damköhler, supersaturation, and sedimentation numbers. We further connect to the atmospheric literature by obtaining a Nusselt number (dimensionless heat flux) for a cloud-convection system, directly from the conservation equations for temperature and water vapor. This flux has the same form as that identified by Zhang et al. [L. Zhang, K. L. Chong, and K.-Q. Xia, J. Fluid Mech. 874, 1041 (2019)] for convection with water vapor, but is extended to the cloudy case. For equal thermal and water vapor diffusivities, the flux corresponds to the widely used atmospheric quantities equivalent temperature and moist static energy. Using large eddy simulation (LES) of an idealized cloudy Rayleigh-Bénard convection system with fixed boundary conditions, we find that the equivalent heat flux (Nusselt number) is only weakly dependent on the microphysical details of the system, such as liquid water mixing ratio and cloud droplet number concentration. Finally, from the results, we show the vertical profiles of sensible and latent heat fluxes depend on the liquid water content, whereas the equivalent heat flux remains a constant throughout the height of the chamber.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

High-Throughput In-Line Deposition of Silicon Oxide for Polycrystalline Silicon Passivating Contacts

Polycrystalline silicon passivating contacts rely on an ultrathin (1–2 nm) silicon oxide layer to minimize recombination at the wafer/oxide interface and regulate dopant diffusion. Traditionally formed by thermal or chemical oxidation, this oxide is herein replaced by silicon oxide deposited via aerosol impact-driven assembly (AIDA), enabling high wafer-per-hour throughput and precise thickness control. In this study, we show that AIDA coatings conformally cover planar or textured substrates and achieve a SiO x /poly-Si(n) structure with an implied open-circuit voltage (iV oc = 726 mV) and contact saturation current density (J 0 = 8.8 fA/cm 2 ). Furthermore, annealing AIDA SiO x films at elevated temperatures desorbs hydroxyl groups while the stoichiometry transitions toward SiO 2 , improving passivation quality. Together, these results highlight AIDA’s potential for scalable, high-throughput manufacturing of advanced passivating contacts, offering a cost-effective alternative to conventional low-pressure chemical vapor deposition and plasma-enhanced chemical vapor deposition-based silicon and oxide processes.

TOPcon↗
DOE OSTI2024

Multiple origins of extra electron diffractions in fcc metals

Diffuse intensities in the electron diffraction patterns of concentrated face-centered cubic solid solutions have been widely attributed to chemical short-range order, although this connection has been recently questioned. This article explores the many nonordering origins of commonly reported features using a combination of experimental electron microscopy and multislice diffraction simulations, which suggest that diffuse intensities largely represent thermal and static displacement scattering. A number of observations may reflect additional contributions from planar defects, surface terminations incommensurate with bulk periodicity, or weaker dynamical effects.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Verification and Validation of Two Hydrodynamic Methods for Simulations of High Energy Density Physics Problems

A 3D verification and validation suite of test problems is presented and used to evaluate hydrodynamic methods within a radiation hydrodynamics code, xRAGE. These test problems exercise different levels of complexity, building towards ICF problems which in addition to hydrodynamics also include three temperature plasma physics, thermal conduction, and radiation diffusion. Among the problems in the test suite are the Kidder ball problem, the Verney shell problem, and a 5-material compression problem, which exercise different purely hydrodynamic methods implemented within xRAGE. There is excellent agreement between 2D and 3D XRAGE simulation results and between the xRAGE results and the benchmark solutions. Two 3D ICF test problems are also presented, based on an OMEGA direct drive capsule experiment and on a NIF indirect drive capsule experiment. It is demonstrated that the newer unsplit hydrodynamic method in xRAGE produces more vorticity relative to the older default method. For the indirect drive capsule, the 3D simulations are in reasonable agreement with the experimental values of ion temperature and neutron production.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

TMAP7

TMAP7 was developed by the Fusion Safety Program at INL primarily as a safety analysis code, to analyze tritium retention and loss in fusion reactor structures and systems during normal operation and accident conditions. TMAP7 solves one-dimensional thermal- and mass-diffusive transport and trapping equations for transport through structures, across the interface between enclosures and structures, and zero dimensional fluid transport between enclosures.

Humrickhouse, PaulW.↗
DOE OSTI2021

TMAP4

TMAP4 was developed by the Fusion Safety Program at INL primarily as a safety analysis code, to analyze tritium retention and loss in fusion reactor structures and systems during normal operation and accident conditions. TMAP4 solves one-dimensional thermal- and mass-diffusive transport and trapping equations for transport through structures, across the interface between enclosures and structures, and zero dimensional fluid transport between enclosures.

Humrickhouse, PaulW.↗
DOE OSTI2017

Identification and Characterization of Thermal Fluid Phenomena Associated with Selected Operating/Accident Scenarios in Modular High Temperature Gas-cooled Reactors

Dominant phenomena are identified and characterized for the loss-of-forced-convection (LOFC) scenario, the depressurized loss-of-forced-convection (DLOFC) scenario, and the moisture ingress scenario with relief valves available scenario. These scenarios are considered for the modular high temperature gas-cooled reactor (MHTGR) baseline design—with both a prismatic core and a pebble-bed core. The objectives of this effort, described in the above paragraph, were achieved by following a methodology identified by the U.S. Nuclear Regulatory Commission (NRC) and recommended in their Regulatory Guide 1.203. The methodology employed is described. For the above scenarios, baseline phenomena identification and ranking tables (PIRTs) generated by a NRC-sponsored effort in 2008 for the LOFC and DLOFC scenarios and a baseline PIRT generated by a Department of Energy-sponsored effort in 2011 by their Next Generation Nuclear Plant (NGNP) Moisture Ingress Assessment Committee were used to identify the dominant phenomena and existing levels-of-knowledge. Ten dominant phenomena (with only medium or low levels-of-knowledge) were identified for the LOFC and DLOFC scenarios including: (1) Inlet plenum stratification and plumes, (2) core coolant flow distribution, (3) radiant heat transfer from the top of the core to the upper vessel head, (4) reactor cavity air circulation and heat transfer, (5) reactor cavity cooling system behavior, (6) decay heat distributions, (7) core effective thermal conductivity, (8) molecular diffusion in air ingress DLOFC, (9) duct exchange flow, (10) phenomena that affect cavity gas composition for air-ingress. Five dominant phenomena, with high levels of knowledge, were identified for the moisture-ingress scenario with relief valves available including: (1) flow through break, (2) moisture level in the primary, (3) transport to moisture monitor, (4) moisture monitor instrument response, and (5) heat removal by shutdown cooling system. These phenomena are discussed and characterized. A listing of experiments—both completed and ongoing—is given with a view toward including data useful for further more detailed examination of the dominant phenomena listed in the previous paragraph. Note that only data for the LOFC and DLOFC scenarios are listed—since the moisture ingress scenario with relief valves available –have been identified as having adequate levels-of-knowledge by the PIRT committee. Finally, a preliminary computational fluid dynamics (CFD) calculation of inlet plenum stratification and plumes is described. Techniques employed for this calculation are typical for preliminary scoping calculations performed to validate numeric tools.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗