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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Low-Temperature, Solution-Processed Molybdenum Oxide Hole-Collection Layer for Organic Photovoltaics

We have utilized a commercially available metal-organic precursor to develop a new, low-temperature, solution-processed molybdenum oxide (MoO{sub x}) hole-collection layer (HCL) for organic photovoltaic (OPV) devices that is compatible with high-throughput roll-to-roll manufacturing. Thermogravimetric analysis indicates complete decomposition of the metal-organic precursor by 115 C in air. Acetonitrile solutions spin-cast in a N{sub 2} atmosphere and annealed in air yield continuous thin films of MoO{sub x}. Ultraviolet, inverse, and X-ray photoemission spectroscopies confirm the formation of MoO{sub x} and, along with Kelvin probe measurements, provide detailed information about the energetics of the MoO{sub x} thin films. Incorporation of these films into conventional architecture bulk heterojunction OPV devices with poly(3-hexylthiophene) and [6,6]-phenyl-C{sub 61} butyric acid methyl ester afford comparable power conversion efficiencies to those obtained with the industry-standard material for hole injection and collection: poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The MoO{sub x} HCL devices exhibit slightly reduced open circuit voltages and short circuit current densities with respect to the PEDOT:PSS HCL devices, likely due in part to charge recombination at Mo{sup 5+} gap states in the MoO{sub x} HCL, and demonstrate enhanced fill factors due to reduced series resistance in the MoO{sub x} HCL.

14 SOLAR ENERGY↗
DOE OSTI2013

Influence of cationic substitutions on the first charge and reversible capacities of lithium-rich layered oxide cathodes

The reversible capacity values of lithium-rich layered oxide cathodes depend on the length (capacity) of the plateau region during the first charge. With an aim to understand the factors that control the length of the plateau region and thereby enhance the reversible capacity, the effects of various cationic substitutions in Li 1.2 Mn 0.6 Ni 0.2 O 2 have been investigated systematically. Specifically, substitutions of (i) M 3+ = Al 3+ , Cr 3+ , Fe 3+ , Co 3+ , and Ga 3+ for equal amounts of Mn 4+ and Ni 2+ in Li 1.2 Mn 0.6-0.5x Ni 0.2-0.5x M x O 2 with x = 0.06, 0.13, and 0.2, (ii) Ti 4+ for Mn 4+ in Li 1.2 Mn 0.6-x Ti x Ni 0.2 O 2 with x = 0.025, 0.05, and 0.1, and (iii) Mg 2+ for Ni 2+ in Li 1.2 Mn 0.6 Ni 0.2-x Mg x O 2 with x = 0.025, 0.05, and 0.1 have been investigated. The cationic substitutions affect the first charge capacity values both in the sloping region corresponding to the oxidation of the transition-metal ions to the 4+ state and in the plateau region corresponding to the oxidation of O 2- ions to O 2 and/or transition-metal ions beyond 4+, which control the reversible capacity values in subsequent cycles. While the changes in the sloping-region capacity could be readily understood by considering the redox activities of the transition-metal ions, the plateau-region capacity is found to depend sensitively on the metal–oxygen covalence, which is dictated by the relative positions of the metal:3d band with respect to the top of the O 2- :2p band, and electron delocalization. For instance, an overlap of the Co 3+/4+ :t 2g band with the top of the O 2- :2p band along with a partially filled t 2g band across the shared octahedral edges makes the oxygen loss from the lattice and/or oxidation beyond 4+ much more facile.

solar (photovoltaic), phonons, energy storage (inc↗
DOE OSTI2013

Low temperature atomic layer deposition of highly photoactive hematite using iron(iii) chloride and water

Nanostructured hematite (α-Fe2O3) has been widely studied for use in a variety of thin film applications including solar energy conversion, water oxidation, catalysis, lithium-ion batteries, and gas sensing. Among established deposition methods, atomic layer deposition (ALD) is a leading technique for controlled synthesis of a wide range of nanostructured materials. In this work, ALD of Fe2O3 is demonstrated using FeCl3 and H2O precursors at growth temperatures between 200 and 350 °C. Self-limiting growth of Fe2O3 is demonstrated with a growth rate of ~0.6 Å per cycle. As-deposited, films are nanocrystalline with low chlorine impurities and a mixture of α- and γ-Fe2O3. Post-deposition annealing in O2 leads to phase-pure α-Fe2O3 with increased out-of-plane grain size. Photoelectrochemical measurements under simulated solar illumination reveal high photoactivity toward water oxidation in both as-deposited and post-annealed films. Planar films deposited at low temperature (235 °C) exhibit remarkably high photocurrent densities ~0.71 mA cm-2 at 1.53 V vs. the reversible hydrogen electrode (RHE) without further processing. Films annealed in air at 500 °C show current densities of up to 0.84 mA cm-2 (1.53 V vs. RHE).

36 MATERIALS SCIENCE↗
DOE OSTI2013

Numerical analysis of three complex three-dimensional shock wave / turbulent boundary layer interaction flows

A set of Reynolds-averaged Navier-Stokes (RANS) computations with turbulence closure provided by the Spalart-Allmaras (SA) model have been carried out for prediction of shock-induced three-dimensional (3D) turbulent separated flows. The experimental data for different aerodynamic test configurations have been used for assessing credibility of the numerical method employed. Particularly, shock wave / turbulent boundary layer interactions (SWTBLI) in the vicinity of an asymmetric sharp double-fin (DF) with different (7° and 11°) deflection angles mounted on a flat plate and two conically sharp cylindrical bodies at varying interbody distances and nose cone angles 60° and 40° mounted over a flat plate at freestream Mach number 4, as well as a transonic fan stage operating in the near-stall regime are considered. The gas dynamic structure and topology of 3D separated flows, surface flow patterns, and pressure distributions as well as body aerodynamic force prediction are analyzed. A transonic fan stage operating in the near-stall regime and a possibility of applying flow control is investigated. High Performance Computing was employed to make high resolution computations of these flows possible, and advanced 3D visualization techniques were employed in order to improve understanding of the separating flow phenomena.

42 ENGINEERING↗
DOE OSTI2013

Mechanical properties of irradiated single-layer graphene

The mechanical properties of irradiated single-layer graphene sheets are determined as a function of inserted vacancy concentration. We find that the vacancy-induced crystalline-to-amorphous transition is accompanied by a brittle-to-ductile transition in the failure response of irradiated graphene sheets for inserted vacancy concentrations of 8%-12%. While point defects and larger voids appreciably degrade the strength of pristine graphene, we find that even heavily damaged samples ({approx}20% vacancies) exhibit tensile strengths of {approx}30 GPa, in significant excess of those typical of engineering materials. Our results suggest that defect engineering of graphene is feasible without incurring a complete loss of its desirable mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Thermal conductivity of Er{sup +3}:Y{sub 2}O{sub 3} films grown by atomic layer deposition

Cross-plane thermal conductivity of 800, 458, and 110 nm erbium-doped crystalline yttria (Er{sup +3}:Y{sub 2}O{sub 3}) films deposited via atomic layer deposition was measured using the 3ω method at room temperature. Thermal conductivity results show 16-fold increase in thermal conductivity from 0.49 W m{sup −1}K{sup −1} to 8 W m{sup −1}K{sup −1} upon post deposition annealing, partially due to the suppression of the number of the -OH/H{sub 2}O bonds in the films after annealing. Thermal conductivity of the annealed film was ∼70% lower than undoped bulk single crystal yttria. The cumulative interface thermal resistivity of substrate-Er{sup +3}:Y{sub 2}O{sub 3}-metal heater was determined to be ∼2.5 × 10{sup −8} m{sup 2} K/W.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Biexciton formation and exciton coherent coupling in layered GaSe

Nonlinear two-dimensional Fourier transform (2DFT) and linear absorption spectroscopy are used to study the electronic structure and optical properties of excitons in the layered semiconductor GaSe. At the 1s exciton resonance, two peaks are identified in the absorption spectra, which are assigned to splitting of the exciton ground state into the triplet and singlet states. 2DFT spectra acquired for co-linear polarization of the excitation pulses feature an additional peak originating from coherent energy transfer between the singlet and triplet. At cross-linear polarization of the excitation pulses, the 2DFT spectra expose a new peak likely originating from bound biexcitons. The polarization dependent 2DFT spectra are well reproduced by simulations using the optical Bloch equations for a four level system, where many-body effects are included phenomenologically. Although biexciton effects are thought to be strong in this material, only moderate contributions from bound biexciton creation can be observed. The biexciton binding energy of ∼2 meV was estimated from the separation of the peaks in the 2DFT spectra. Temperature dependent absorption and 2DFT measurements, combined with “ab initio” theoretical calculations of the phonon spectra, indicate strong interaction with the A{sub 1}{sup ′} phonon mode. Excitation density dependent 2DFT measurements reveal excitation induced dephasing and provide a lower limit for the homogeneous linewidth of the excitons in the present GaSe crystal.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Probing the atmospheric boundary layer with integrated remote-sensing platforms during the American WAKE ExperimeNt (AWAKEN) campaign

The American WAKE ExperimeNt (AWAKEN) collaboration is an observational-based field campaign in northern Oklahoma intended to analyze the potential influence of onshore wind farms and their collective wakes on wind power production, turbine structural loads, and on the atmospheric boundary layer (ABL). Focusing on the ABL effects, the University of Oklahoma and the Lawrence Livermore National Laboratory collected continuous high-resolution kinematic and thermodynamic profile measurements during 2022 and Summer 2023. The deployment strategy for these campaigns is detailed first, followed by an initial comparison of data from two sites in the AWAKEN domain: a near-farm site to examine collective wake impacts on the ABL, and a far-field site remaining outside the wind farm-waked region. Here, we summarize the datasets available and demonstrate the benefits of these observations and multiple value-added products (VAPs) for investigation of ABL features observed during AWAKEN. We also highlight examples of preliminary analyses, including ABL height detection and nocturnal low-level jet examination, which are produced using novel VAPs based on optimal estimation to retrieve deeper Doppler lidar wind profiles than previously resolved, along with their uncertainty. By including the near-farm and far-field site in these analyses, we identified a pattern of stronger lower-atmospheric mixing at the near-farm site than the far-field site, motivating deeper investigation into the relationship between wind farms and general ABL characteristics. Future analysis will delve deeper into this relationship by examining other ABL characteristics, such as atmospheric stability and convection.

17 WIND ENERGY↗
DOE OSTI2015

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a “highfoot” laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10 16 neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Plasma etch characteristics of aluminum nitride mask layers grown by low-temperature plasma enhanced atomic layer deposition in SF{sub 6} based plasmas

The plasma etch characteristics of aluminum nitride (AlN) deposited by low-temperature, 200 deg. C, plasma enhanced atomic layer deposition (PEALD) was investigated for reactive ion etch (RIE) and inductively coupled plasma-reactive ion etch (ICP-RIE) systems using various mixtures of SF{sub 6} and O{sub 2} under different etch conditions. During RIE, the film exhibits good mask properties with etch rates below 10r nm/min. For ICP-RIE processes, the film exhibits exceptionally low etch rates in the subnanometer region with lower platen power. The AlN film's removal occurred through physical mechanisms; consequently, rf power and chamber pressure were the most significant parameters in PEALD AlN film removal because the film was inert to the SF{sub x}{sup +} and O{sup +} chemistries. The etch experiments showed the film to be a resilient masking material. This makes it an attractive candidate for use as an etch mask in demanding SF{sub 6} based plasma etch applications, such as through-wafer etching, or when oxide films are not suitable.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Fluorine contamination in yttrium-doped barium zirconate film deposited by atomic layer deposition

The authors have investigated the change of chemical composition, crystallinity, and ionic conductivity in fluorine contaminated yttrium-doped barium zirconate (BYZ) fabricated by atomic layer deposition (ALD). It has been identified that fluorine contamination can significantly affect the conductivity of the ALD BYZ. The authors have also successfully established the relationship between process temperature and contamination and the source of fluorine contamination, which was the perfluoroelastomer O-ring used for vacuum sealing. The total removal of fluorine contamination was achieved by using all-metal sealed chamber instead of O-ring seals.

36 MATERIALS SCIENCE↗