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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Electrical characteristics and thermal stability of HfO{sub 2} metal-oxide-semiconductor capacitors fabricated on clean reconstructed GaSb surfaces

HfO{sub 2}/GaSb interfaces fabricated by high-vacuum HfO{sub 2} deposition on clean reconstructed GaSb surfaces were examined to explore a thermally stable GaSb metal-oxide-semiconductor structure with low interface-state density (D{sub it}). Interface Sb-O bonds were electrically and thermally unstable, and post-metallization annealing at temperatures higher than 200 °C was required to stabilize the HfO{sub 2}/GaSb interfaces. However, the annealing led to large D{sub it} in the upper-half band gap. We propose that the decomposition products that are associated with elemental Sb atoms act as interface states, since a clear correlation between the D{sub it} and the Sb coverage on the initial GaSb surfaces was observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Cyclododecane as support material for clean and facile transfer of large-area few-layer graphene

The transfer of chemical vapor deposited graphene is a crucial process, which can affect the quality of the transferred films and compromise their application in devices. Finding a robust and intrinsically clean material capable of easing the transfer of graphene without interfering with its properties remains a challenge. We here propose the use of an organic compound, cyclododecane, as a transfer material. This material can be easily spin coated on graphene and assist the transfer, leaving no residues and requiring no further removal processes. The effectiveness of this transfer method for few-layer graphene on a large area was evaluated and confirmed by microscopy, Raman spectroscopy, x-ray photoemission spectroscopy, and four-point probe measurements. Schottky-barrier solar cells with few-layer graphene were fabricated on silicon wafers by using the cyclododecane transfer method and outperformed reference cells made by standard methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Epi-cleaning of Ge/GeSn heterostructures

We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100–300 °C range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structure determination of the clean (001) surface of strained Si on Si{sub 1−x}Ge{sub x}

The surface structure of the strained Si(001) (thickness of 20 nm) on Si{sub 1−x}Ge{sub x} (x = 0.1, 0.2, and 0.3) was studied by low-energy electron diffraction (LEED). LEED intensity-energy spectra of the 2 × 1 reconstructed clean surfaces showed a systematic change that indicates the lattice contraction along the [001] direction remains even at the surfaces. The atomic structures were quantitatively determined, and they were compared with the unstrained pristine Si. The differences in the atomic position almost follow the difference in the bulk lattice constant determined by X-ray diffraction measurements. The results indicate that the strain produced at the Si/Si{sub 1−x}Ge{sub x} interface remains unchanged up to the surface layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Unusually high critical current of clean P-doped BaFe{sub 2}As{sub 2} single crystalline thin film

Microstructurally clean, isovalently P-doped BaFe{sub 2}As{sub 2} (Ba-122) single crystalline thin films have been prepared on MgO (001) substrates by molecular beam epitaxy. These films show a superconducting transition temperature (T{sub c}) of over 30 K although P content is around 0.22, which is lower than the optimal one for single crystals (i.e., 0.33). The enhanced T{sub c} at this doping level is attributed to the in-plane tensile strain. The strained film shows high transport self-field critical current densities (J{sub c}) of over 6 MA/cm{sup 2} at 4.2 K, which are among the highest for Fe based superconductors (FeSCs). In-field J{sub c} exceeds 0.1 MA/cm{sup 2} at μ{sub 0}H=35 T for H‖ab and μ{sub 0}H=18 T for H‖c at 4.2 K, respectively, in spite of moderate upper critical fields compared to other FeSCs with similar T{sub c}. Structural investigations reveal no defects or misoriented grains pointing to strong pinning centers. We relate this unexpected high J{sub c} to a strong enhancement of the vortex core energy at optimal T{sub c}, driven by in-plane strain and doping. These unusually high J{sub c} make P-doped Ba-122 very favorable for high-field magnet applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces

We characterize niobium-based lateral Superconductor (S)–Normal metal (N)–Superconductor (SNS) weak links through low-temperature switching current measurements and tunnel spectroscopy. We fabricate the SNS devices in two separate lithography and deposition steps, combined with strong argon ion cleaning before the normal metal deposition in the last step. Our SNS weak link consists of high-quality sputtered Nb electrodes that have contacted with evaporated Cu. The two-step fabrication flow enables more flexibility in the choice of materials and pattern design. A comparison of the temperature-dependent equilibrium critical supercurrent with theoretical predictions indicates that the quality of the Nb-Cu interface is similar to that of evaporated Al-Cu weak links. We further demonstrate a hybrid magnetic flux sensor based on an Nb-Cu-Nb SNS junction, where the phase-dependent normal metal density of states is probed with an Al tunnel junction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Clean localization super-resolution microscopy for 3D biological imaging

We propose clean localization microscopy (a variant of fPALM) using a molecule filtering technique. Localization imaging involves acquiring a large number of images containing single molecule signatures followed by one-to-one mapping to render a super-resolution image. In principle, this process can be repeated for other z-planes to construct a 3D image. But, single molecules observed from off-focal planes result in false representation of their presence in the focal plane, resulting in incorrect quantification and analysis. We overcome this with a single molecule filtering technique that imposes constraints on the diffraction limited spot size of single molecules in the image plane. Calibration with sub-diffraction size beads puts a natural cutoff on the actual diffraction-limited size of single molecules in the focal plane. This helps in distinguishing beads present in the focal plane from those in the off-focal planes thereby providing an estimate of the single molecules in the focal plane. We study the distribution of actin (labeled with a photoactivatable CAGE 552 dye) in NIH 3T3 mouse fibroblast cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Beam cleaning of an incoherent laser via plasma Raman amplification

We show that backward Raman amplification in plasma can efficiently compress a temporally incoherent pump laser into an intense coherent amplified seed pulse, provided that the correlation time of the pump is longer than the inverse plasma frequency. One analytical theory for Raman amplification using pump beams with different correlation functions is developed and compared to numerical calculations and particle-in-cell simulations. Since incoherence on scales shorter than the instability growth time suppresses spontaneous noise amplification, we point out a broad regime where quasi-coherent sources may be used as efficient low-noise Raman amplification pumps. As the amplified seed is coherent, Raman amplification provides an additional a beam-cleaning mechanism for removing incoherence. At near-infrared wavelengths, finite coherence times as short as 50 fs allow amplification with only minor losses in efficiency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Technology progress and clean vehicle policies on fleet turnover and equity: insights from household vehicle fleet micro-simulations with $\text{ATLAS}$

This paper documents the design and application of ATLAS (Automobile and Technology Lifecycle-Based ASsignment), a comprehensive household vehicle transaction and technology adoption micro-simulator in the San Francisco Bay Area. ATLAS evolves the fleet mix of individual households by simulating the vehicle transaction and choice decisions in response to co-evolving demographics, land use, and vehicle technology simulations. While most existing literature has focused on the aggregate clean vehicle uptake, this paper differentiates distributional effects and decomposes the underlying mechanisms across heterogeneous sub-populations of households. Using scenarios and sensitivity simulations that vary vehicle technology and policy assumptions, we find that Zero Emission Vehicles (ZEVs) penetrate into higher income groups at a faster rate than into lower income groups, which is intuitive and aligns with expectations. Interestingly, the relative income disparity in ZEV ownership shrinks over time across all scenarios, with a ZEV mandate coupled with declining battery cost leading to the greatest reduction in disparity of ZEV ownership by 2050. Federal, state, and local financial incentives influence the redistribution of ZEV uptake across income groups and contribute to narrowing income disparity. Vehicle transaction frequency and new versus used market dynamics are found to be important factors contributing to the income disparity.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2014

Evidence for ubiquitous high-equivalent-width nebular emission in z ∼ 7 galaxies: toward a clean measurement of the specific star-formation rate using a sample of bright, magnified galaxies

Growing observational evidence indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z ∼ 5-7 galaxies. This line emission makes z ∼ 5-7 galaxies appear more massive, with lower specific star-formation rates (sSFRs). However, corrections for this line emission have been difficult to perform reliably because of huge uncertainties on the strength of such emission at z ≳ 5.5. In this paper, we present the most direct observational evidence thus far for ubiquitous high-equivalent-width (EW) [O III] + Hβ line emission in Lyman-break galaxies at z ∼ 7, and we present a strategy for an improved measurement of the sSFR at z ∼ 7. We accomplish this through the selection of bright galaxies in the narrow redshift window z ∼ 6.6-7.0 where the Spitzer/Infrared Array Camera (IRAC) 4.5 μm flux provides a clean measurement of the stellar continuum light, in contrast with the 3.6 μm flux, which is contaminated by the prominent [O III] + Hβ lines. To ensure a high signal-to-noise ratio for our IRAC flux measurements, we consider only the brightest (H {sub 160} < 26 mag) magnified galaxies we have identified behind galaxy clusters. It is remarkable that the mean rest-frame optical color for our bright seven-source sample is very blue, [3.6]-[4.5] = –0.9 ± 0.3. Such blue colors cannot be explained by the stellar continuum light and require that the rest-frame EW of [O III] + Hβ is greater than 637 Å for the average source. The four bluest sources from our seven-source sample require an even more extreme EW of 1582 Å. We can also set a robust lower limit of ≳ 4 Gyr{sup –1} on the sSFR of our sample based on the mean spectral energy distribution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Experimental testing of additively manufactured embedded fiber optic smart devices for clean energy applications

Abstract An additively manufactured prototype smart device was created to investigate in-flow temperature distributions using embedded high-definition fiber optic sensors within a component for clean energy systems. The devices were created using Ultrasonic Additive Manufacturing to create a unique embedded pathway within a flow conditioner for the high-definition fiber optic sensors to be placed within. The fibers used allowed for temperature measurements to be taken every 0.65 mm along the fiber. The high-resolution fibers were thermally calibrated enable the 2D reconstruction of the temperature profile in the flow path of the structure. This is due to the temperature-related strain response of the material and strain measurements of the fibers. Hot airflow testing of these devices showed the ability to identify localized temperature differences in the flow. The observed strain response within the smart device had higher strain concentrations in the thicker web regions than in the thinner web regions. These higher strain regions resulted in higher uncertainties for the temperature responses. Further calibration is needed to improve the accuracy of the smart devices, specifically within the inner web structures of a flow straightening component. Further investigations of the devices within flow showed the temperature sensing to be independent of the effects of flow velocity. The devices were able to distinguish temperature differences within single and two-phase flow and showed local sensitivity to the temperature changes with the identification of hot and cold spots. The presented results showed the viability of the smart device for obtaining detailed temperature distributions using common industrial components. Eventually, the goal for these smart devices will be to withstand higher temperature and pressure environments such as those experienced in nuclear, fusion, and concentrated solar energy systems.

Donlan, Connor F. (ORCID:0000000223317882)↗
DOE OSTI2022

$\mathrm{BUDDI}$-$\mathrm{MaNGA}$ $\mathrm{I}$: A statistical sample of cleanly decomposed bulge and disc spectra

Many galaxies display clear bulges and discs, and understanding how these components form is a vital step towards understanding how the galaxy has evolved into what we see today. The BUDDI-MaNGA project aims to study galaxy evolution and morphological transformations through the star-formation histories of the bulges and discs. We have applied our buddi software to galaxies from the MaNGA Survey in the SDSS DR15 in order to isolate their bulge and disc spectra, from which we derived their stellar populations. To date, this work provides the largest sample of clean bulge and disc spectra extracted from IFU datacubes using the galaxies light profile information, and will form the basis for a series of papers aiming to answer open questions on how galaxies have formed and evolved, and the role of their individual structures. Here this paper presents an introduction to the project, including an overview of these fits, a characterization of the sample, and a series of tests on the fits to ensure reliability.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A COMPARISON OF DOSE RESULTS FROM THE CLEAN AIR ACT ASSESSMENT PACKAGE-1988, PERSONAL COMPUTER (CAP88-PC), VERSION 3 TO PREVIOUS VERSIONS

EPA-approved computer software packages, including CAP88-PC, are used by Department of Energy sites to demonstrate compliance with the radionuclide air emission standard under the Clean Air Act. The most recent update, CAP88-PC version 3, was approved by EPA in February 2006 for use by Department of Energy facilities. Version 3 incorporates several major changes that have the potential to affect calculated doses relative to calculations using earlier versions. This analysis examined the types and magnitudes of changes to dose estimates for specific radionuclides calculated using the version 3 software compared with the previous versions. Total effective dose calculated with version 3 was compared to effective dose equivalent calculated with previous versions for parent radionuclides and for the total dose from radionuclide chains. Various comparisons were also performed to determine which of the updates in version 3 accounted for changes in overall dose estimates. CAP88-PC version 3 would produce substantially different results relative to previous versions of the code for a number of radionuclides, including some isotopes that may be present at Department of Energy facilities, as well as those used for industrial and medical applications. In general, doses for many radionuclides are lower using version 3 but doses for a few key radionuclides would be higher.

Rhoads, Kathleen↗
DOE OSTI2025

Linear Quantum Coupler for Clean Bosonic Control

Quantum computing with superconducting circuits relies on high-fidelity driven nonlinear processes. An ideal quantum nonlinearity would selectively activate desired coherent processes at high strength, without activating parasitic mixing products or introducing additional decoherence. The wide bandwidth of the Josephson nonlinearity makes this difficult, with undesired drive-induced transitions and decoherence limiting qubit readout, gates, couplers, and amplifiers. Significant strides have recently been made into building better “quantum mixers,” with promise being shown by Kerr-free three-wave mixers that suppress driven frequency shifts, and balanced quantum mixers that explicitly forbid a significant fraction of parasitic processes. We propose a novel mixer that combines both these strengths, with engineered selection rules that make it essentially linear (not just Kerr-free) when idle, and activate clean parametric processes even when driven at high strength. Furthermore, its ideal Hamiltonian is simple to analyze analytically, and we show that this ideal behavior is first-order insensitive to dominant experimental imperfections. We expect this mixer to allow significant advances in high-𝑄 control, readout, and amplification.

Quantum circuits↗
DOE OSTI2021

Computing partition functions in the one-clean-qubit model

We present a method to approximate partition functions of quantum systems using mixed-state quantum computation. For positive-semidefinite Hamiltonians, our method has an expected running-time that is almost linear in [M/( ε rel Z )] 2 , where M is the dimension of the quantum system, Z is the partition function, and ε rel is the relative precision. It is based on approximations of the exponential operator as linear combinations of certain operators related to block-encoding of Hamiltonians or Hamiltonian evolutions. The trace of each operator is estimated using a standard algorithm in the one-clean-qubit model. For large values of Z , our method may run faster than exact classical methods, whose complexities are polynomial in M . We also prove that a version of the partition function estimation problem within additive error is complete for the so-called DQC1 complexity class, suggesting that our method provides a superpolynomial speedup for certain parameter values. Overall, to attain a desired relative precision, we develop a classical procedure based on a sequence of approximations within predetermined additive errors that may be of independent interest.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Clean quantum point contacts in an InAs quantum well grown on a lattice-mismatched InP substrate

Strong spin-orbit coupling, the resulting large g factor, and small effective mass make InAs an attractive material platform for inducing topological superconductivity. The surface Fermi level pinning in the conduction band enables highly transparent ohmic contact without excessive doping. In this study, we investigate electrostatically defined quantum point contacts (QPCs) in a deep-well InAs two-dimensional electron gas. Despite the 3.3% lattice mismatch between the InAs quantum well and the InP substrate, we report clean QPCs with up to eight pronounced quantized conductance plateaus at zero magnetic field. Source-drain dc bias spectroscopy reveals a harmonic confinement potential with a nearly 5 meV subband spacing. We find a many-body exchange interaction enhancement for the out-of-plane g factor |$g^{*}_{⊥}$|=27±1 , whereas the in-plane g factor is isotropic |$g^{*}_{x}$|=|$g^{*}_{y}$|=12±2 , close to the bulk value for InAs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Almost strong ( 0 , π ) edge modes in clean interacting one-dimensional Floquet systems

We present that certain periodically driven quantum many-particle systems in one dimension are known to exhibit edge modes that are related to topological properties and lead to approximate degeneracies of the Floquet spectrum. A similar situation occurs in spin chains, where stable edge modes were shown to exist at all energies in certain integrable spin chains. Moreover, these edge modes were found to be remarkably stable to perturbations. Here we investigate the stability of edge modes in interacting, periodically driven, clean systems. Finally, we introduce a model that features edge modes that persist over times scales well in excess of the time needed for the bulk of the system to heat to infinite temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

The Simons Observatory: Combining cross-spectral foreground cleaning with multitracer B -mode delensing for improved constraints on inflation

The Simons Observatory (SO), due to start full science operations in early 2025, aims to set tight constraints on inflationary physics by inferring the tensor-to-scalar ratio r from measurements of cosmic microwave background (CMB) polarization B-modes. Its nominal design including three small-aperture telescopes (SATs) targets a precision σ⁡(r = 0) ≤ 0.003 without delensing. Achieving this goal and further reducing uncertainties requires a thorough understanding and mitigation of other large-scale B-mode sources such as Galactic foregrounds and weak gravitational lensing. We present an analysis pipeline aiming to estimate r by including delensing within a cross-spectral likelihood, and demonstrate it for the first time on SO-like simulations accounting for various levels of foreground complexity, inhomogeneous noise and partial sky coverage. As introduced in an earlier SO delensing paper, lensing B-modes are synthesized using internal CMB lensing reconstructions as well as Planck-like cosmic infrared background maps and LSST-like galaxy density maps. We then extend SO’s power-spectrum-based foreground-cleaning algorithm to include all auto- and cross-spectra between the lensing template and the SAT B-modes in the likelihood function. This allows us to constrain r and the parameters of our foreground model simultaneously. Within this framework, we demonstrate the equivalence of map-based and cross-spectral delensing and use it to motivate an optimized pixel-weighting scheme for power spectrum estimation. We start by validating our pipeline in the simplistic case of uniform foreground spectral energy distributions. In the absence of primordial B-modes, we find that the 1⁢σ statistical uncertainty on r, σ⁡(r), decreases by 37% as a result of delensing. Tensor modes at the level of r = 0.01 are successfully detected by our pipeline. Even when using more realistic foreground models including spatial variations in the dust and synchrotron spectral properties, we obtain unbiased estimates of r both with and without delensing by employing the moment-expansion method. In this case, uncertainties are increased due to the higher number of model parameters, and delensing-related improvements range between 27% and 31%. These results constitute the first realistic assessment of the delensing performance at SO’s nominal sensitivity level.

79 ASTRONOMY AND ASTROPHYSICS↗