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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Transport in ferromagnet/superconductor spin valves

We consider charge transport properties in realistic, fabricable, ferromagnet/superconductor spin valves having a layered structure F 1 /N/F 2 /S, where F 1 and F 2 denote the ferromagnets, S the superconductor, and N the normal-metal spacer usually inserted in actual devices. Our calculation is fully self-consistent, as required to ensure that conservation laws are satisfied. We include the effects of scattering at all the interfaces. We obtain results for the device conductance G, as a function of bias voltage, for all values of the angle Φ between the magnetizations of the F 1 and F 2 layers and a range of realistic values for the material and geometrical parameters in the sample. We discuss, in the context of our results for G, the relative influence of all parameters on the spin valve properties. We also study the spin current and the corresponding spin-transfer torque in F 1 /F 2 /S structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Observation of the Same New Sheet Topology in Both the Layered Uranyl Oxide-Phosphate Cs 11 [(UO 2 ) 12 (PO 4 ) 3 O 13 ] and the Layered Uranyl Oxyfluoride-Phosphate Rb 11 [(UO 2 ) 12 (PO 4 ) 3 O 12 F 2 ] Prepared by Flux Crystal Growth

We report single crystals of four new layered uranyl phosphates, including three oxyfluoride-phosphates, were synthesized by molten flux methods using alkali chloride melts, and their structures were determined by single-crystal X-ray diffraction. Cs 11 [(UO 2 ) 12 (PO 4 ) 3 O 13 ] ( 1 ) and Rb 11 [UO 2 ) 12 (PO 4 ) 3 O 12 F 2 ] ( 2 ) contain uranyl phosphate layers exhibiting a new sheet topology that can be related to that of β-U 3 O 8 , while Cs 4.4 K 0.6 [(UO 2 ) 6 O 4 F(PO 4 ) 4 (UO 2 )] ( 3 ) and Rb 4.4 K 0.6 [(UO 2 ) 6 O 4 F(PO 4 ) 4 (UO 2 )] ( 4 ) contain layers of a known isomer of the prominent phosphuranylite topology. The location of the fluorine in structures 2 - 4 is discussed using bond valence sums. First principles calculations were used to explore why a pure oxide structure is obtained for the Cs containing phase ( 1 ) and in contrast an oxyfluoride phase for the Rb containing phase ( 2 ). Ion exchange experiments were performed on 1 and 2 and demonstrate the ability of these structures to exchange approximately half of the parent alkali cation with a target alkali cation in an aqueous concentrated salt solution. Optical measurements were performed on 1 and 2 and the UV-vis and fluorescence spectra show features characteristic of the UO 2 2 + uranyl group.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Challenges and Recent Developments of Neutron Non-Destructive Assay with UO{sub 2}F{sub 2}-Bearing Materials - 17336

In the enrichment process of an operating Gaseous Diffusion Plant (GDP), such as the Portsmouth and Paducah facilities, UF6 gas will immediately hydrolyze forming the chemical compound UO{sub 2}F{sub 2} (Uranyl Fluoride). This mostly happens in Alumina (Al{sub 2}O{sub 3}) traps where the UF6 adsorbs to moistened Alumina pellets forming a UO{sub 2}F{sub 2} layer around the pellet. Similarly, NaF.UF{sub 6} absorption traps produce the complex Na{sub 2}UF{sub 8} which also hydrolyzes when exposed to moist air. UO{sub 2}F{sub 2} can also be formed in many other processes where UF6 gas comes into contact with moisture within structures and objects such as pipes, converters compressors and coolers. When the structures are refurbished, or designated for D and D, UO{sub 2}F{sub 2}-bearing objects are generated both in situ and ex situ requiring fissile (U-235) characterization. In addition, ex situ waste streams are generated when UO{sub 2}F{sub 2}-bearing materials are placed in drummed or boxed waste containers. Gamma spectroscopy Non-Destructive Assay (NDA) is commonly utilized to characterize UO{sub 2}F{sub 2}-bearing waste but generally has high associated Total Measurement Uncertainties (TMU's) and, in some cases, Data Quality Objectives (DQO's) cannot be met. In addition, high UO{sub 2}F{sub 2} mass loadings, such as hold-up materials, require gamma modeling when infinitely thick to the Uranium energy lines. A common neutron NDA technique, or method, is to exploit the neutrons generated from the F-19(a, n)Na-22 reaction which has an appreciable reaction cross-section. The isotopes of Uranium are a-emitters, and, in particular, U-234 has a significantly higher a-decay reaction cross-section leading to a significant relative neutron Specific Activity (nSA). Neutron NDA is appealing since, in some cases, it has potentially lower TMU's than gamma NDA and neutron detector slabs facilitate surrounding large, complex-shaped, objects. Characterizing UO{sub 2}F{sub 2}-bearing waste for fissile content using neutrons generated from U-234, requires the U-235/U-234 ratio as well as the enrichment as well as the corresponding nSA's. It is also noted that U-238 has a considerable, relative, spontaneous fission nSA and this is a higher concern for low-enrichments where the mass of U-238 dominates. Additional neutron interfering elements include cosmic-ray induced spallation within the objects and background from other, in situ, UO{sub 2}F{sub 2}-bearing objects. In this paper we present the challenges and recently developed hardware and algorithmic strategies for quantifying fissile mass both in situ and ex situ using neutron NDA that works in conjunction to gamma spectroscopy NDA, or process knowledge, for objects and drummed/boxed waste containing UO{sub 2}F{sub 2}-bearing materials leading to minimal TMU's and achievable DQO's. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Physical properties of the layered $\mathcal{f}$-electron van der Waals magnet Ce 2 Te 5

Here. we report a detailed study of the magnetic, transport, and thermodynamic properties of Ce 2 Te 5 single crystals, a layered $\mathcal{f}$-electron van der Waals magnet. Four consecutive transitions at ~5.2, 2.1, 0.9, and 0.4 K were observed in the ac-plane electrical resistivity $\rho(T)$, which were further confirmed in specific heat $C_\text{p}(T)$ measurements. Analysis of the magnetic susceptibility $\chi(T)$, the magnetic-field variation of $\rho(T)$, and the increase of the first transition temperature ($T_c$ ~ 5.2 K) with applied magnetic field indicates ferromagnetic order, while the decrease of the other transitions with field suggests different states with dominant antiferromagnetic interactions below $T_2$ ~ 2.1 K, $T_3$ ~ 0.9 K, and $T_4$ = 0.4 K. Critical behavior analysis around Tc that gives critical exponents $\beta$ = 0.31(2), $\gamma$ = 0.99(2), $\delta$ = 4.46(1), and $T_c$ = 5.32(1) K indicates that Ce 2 Te 5 shows a three-dimensional magnetic critical behavior. Moreover, the Hall resistivity ρxy indicates that Ce2Te5 is a multiband system with a relatively high electron mobility ~2900 cm 2 V –1 s –1 near $T_c$, providing further opportunities for future device applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Atomic layer deposition of boron-containing films using B{sub 2}F{sub 4}

Ultrathin and conformal boron-containing atomic layer deposition (ALD) films could be used as a shallow dopant source for advanced transistor structures in microelectronics manufacturing. With this application in mind, diboron tetrafluoride (B{sub 2}F{sub 4}) was explored as an ALD precursor for the deposition of boron containing films. Density functional theory simulations for nucleation on silicon (100) surfaces indicated better reactivity of B{sub 2}F{sub 4} in comparison to BF{sub 3}. Quartz crystal microbalance experiments exhibited growth using either B{sub 2}F{sub 4}-H{sub 2}O for B{sub 2}O{sub 3} ALD, or B{sub 2}F{sub 4}-disilane (Si{sub 2}H{sub 6}) for B ALD, but in both cases, the initial growth per cycle was quite low (≤0.2 Å/cycle) and decreased to near zero growth after 8–30 ALD cycles. However, alternating between B{sub 2}F{sub 4}-H{sub 2}O and trimethyl aluminum (TMA)-H{sub 2}O ALD cycles resulted in sustained growth at ∼0.65 Å/cycle, suggesting that the dense –OH surface termination produced by the TMA-H{sub 2}O combination enhances the uptake of B{sub 2}F{sub 4} precursor. The resultant boron containing films were analyzed for composition by x-ray photoelectron spectroscopy, and capacitance measurements indicated an insulating characteristic. Finally, diffused boron profiles less than 100 Å were obtained after rapid thermal anneal of the boron containing ALD film.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

2D Homologous Series SrFM n BiS n +2 (M = Pb, Ag 0.5 Bi 0.5 ; n = 0, 1) and Commensurately Modulated Sr 2 F 2 Bi 2/3 S 2

In this work, we report three new mixed-anion two-dimensional (2D) compounds: SrFPbBiS 3 , SrFAg 0.5 Bi 1.5 S 3 , and Sr 2 F 2 Bi 2/3 S 2 . Their structures as well as the parent compound SrFBiS 2 were refined using single-crystal X-ray diffraction data, with the sequence of SrFBiS 2 , SrFPbBiS 3 , and SrFAg 0.5 Bi 1.5 S 3 defining the new homologous series SrFM n BiS n+2 (M = Pb, Ag 0.5 Bi 0.5 ; n= 0, 1). Sr 2 F 2 Bi 2/3 S 2 has a different structure, which is modulated with a q vector of 1/3b* and was refined in superspace group X2/m(0 β 0)00 as well as in the 1x3x1 superstructure with space group C2/m (with similar results). Sr 2 F 2 Bi 2/3 S 2 features hexagonal layers of alternating [Sr 2 F 2 ] 2+ and [Bi 2/3 S 2 ] 2- , and the modulated structure arises from the unique ordering pattern of Sr 2+ cations. SrFPbBiS 3 , SrFAg 0.5 Bi 1.5 S 3 , and Sr 2 F 2 Bi 2/3 S 2 are semiconductors with band gaps of 1.31, 1.21, and 1.85 eV, respectively. The latter compound exhibits room temperature red photoluminescence at ~ 700 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

An evidence for prompt electric field disturbance driven by changes in the solar wind density under northward IMF B z condition

Before the onset of a geomagnetic storm on 22 January 2012 (Ap = 24), an enhancement in solar wind number density from 10/cm 3 to 22/cm 3 during 0440–0510 UT under northward interplanetary magnetic field (IMF Bz) condition is shown to have enhanced the high-latitude ionospheric convection and also caused variations in the geomagnetic field globally. Some conspicuous changes in ΔX are observed not only at longitudinally separated low-latitude stations over Indian (prenoon), South American (midnight), Japanese (afternoon), Pacific (afternoon) and African (morning) sectors but also at latitudinally separated stations located over high and middle latitudes. The latitudinal variation of the amplitude of the ΔX during 0440–0510 UT is shown to be consistent with the characteristics of prompt penetration electric field disturbances. Most importantly, the density pulse event caused enhancements in the equatorial electrojet strength and the peak height of the F layer (h m F 2 ) over the Indian dip equatorial sector. Furthermore, the concomitant enhancements in electrojet current and F layer movement over the dip equator observed during this space weather event suggest a common driver of prompt electric field disturbance at this time. Such simultaneous variations are found to be absent during magnetically quiet days. In the absence of significant change in solar wind velocity and magnetospheric substorm activity, these observations point toward perceptible prompt electric field disturbance over the dip equator driven by the overcompression of the magnetosphere by solar wind density enhancement.

58 GEOSCIENCES↗
DOE OSTI2016

Effect of the chamber wall on fluorocarbon-assisted atomic layer etching of SiO{sub 2} using cyclic Ar/C{sub 4}F{sub 8} plasma

The authors studied the effect of the temperature and chemical state of the chamber wall on process performance for atomic layer etching of SiO{sub 2} using a steady-state Ar plasma, periodic injection of a defined number of C{sub 4}F{sub 8} molecules, and synchronized plasma-based Ar{sup +} ion bombardment. To evaluate these effects, the authors measured the quartz coupling window temperature. The plasma gas phase chemistry was characterized using optical emission spectroscopy. It was found that although the thickness of the polymer film deposited in each cycle is constant, the etching behavior changed, which is likely related to a change in the plasma gas phase chemistry. The authors found that the main gas phase changes occur after C{sub 4}F{sub 8} injection. The C{sub 4}F{sub 8} and the quartz window react and generate SiF and CO. The emission intensity changes with wall surface state and temperature. Therefore, changes in the plasma gas species generation can lead to a shift in etching performance during processing. During initial cycles, minimal etching is observed, while etching gradually increases with cycle number.

42 ENGINEERING↗
DOE OSTI2016

The mechanism of the area negative thermal expansion in KBe{sub 2}BO{sub 3}F{sub 2} family crystals: A first-principles study

A very recent study demonstrated that the KBe{sub 2}BO{sub 3}F{sub 2} (KBBF) family of crystals, including KBBF, RbBe{sub 2}BO{sub 3}F{sub 2}, and CsBe{sub 2}BO{sub 3}F{sub 2}, are the only known borates exhibiting a rarely occurring isotropic area negative thermal expansion (NTE) behavior, over a very large temperature range. In the present work, the NTE mechanism in these crystals is comprehensively investigated using the first-principles calculations. It is revealed that the area NTE behavior mainly originates from the concerted distortion of [BeO{sub 3}F] tetrahedra in the two-dimensional [Be{sub 2}BO{sub 3}F{sub 2}]{sub ∞} framework with respect to temperature, while the [BO{sub 3}] triangles remain almost rigid. Moreover, the different magnitude of NTE effect in the three crystals is attributed to the interaction difference between the alkali metal atoms (K, Rb, or Cs) and the [Be{sub 2}BO{sub 3}F{sub 2}]{sub ∞} layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Fluorocarbon assisted atomic layer etching of SiO{sub 2} and Si using cyclic Ar/C{sub 4}F{sub 8} and Ar/CHF{sub 3} plasma

The need for atomic layer etching (ALE) is steadily increasing as smaller critical dimensions and pitches are required in device patterning. A flux-control based cyclic Ar/C{sub 4}F{sub 8} ALE based on steady-state Ar plasma in conjunction with periodic, precise C{sub 4}F{sub 8} injection and synchronized plasma-based low energy Ar{sup +} ion bombardment has been established for SiO{sub 2} [Metzler et al., J. Vac. Sci. Technol. A 32, 020603 (2014)]. In this work, the cyclic process is further characterized and extended to ALE of silicon under similar process conditions. The use of CHF{sub 3} as a precursor is examined and compared to C{sub 4}F{sub 8}. CHF{sub 3} is shown to enable selective SiO{sub 2}/Si etching using a fluorocarbon (FC) film build up. Other critical process parameters investigated are the FC film thickness deposited per cycle, the ion energy, and the etch step length. Etching behavior and mechanisms are studied using in situ real time ellipsometry and x-ray photoelectron spectroscopy. Silicon ALE shows less self-limitation than silicon oxide due to higher physical sputtering rates for the maximum ion energies used in this work, ranged from 20 to 30 eV. The surface chemistry is found to contain fluorinated silicon oxide during the etching of silicon. Plasma parameters during ALE are studied using a Langmuir probe and establish the impact of precursor addition on plasma properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tuning the Hydrophobicity of Layer-Structure Silicates To Promote Adsorption of Nonaqueous Fluids: Effects of F – for OH – Substitution on CO 2 Partitioning into Smectite Interlayers

The intercalation of nonaqueous fluids in the nanopores of organic and inorganic materials is of significant interest, particularly in the energy science community. Recently, X-ray powder diffraction and computational modeling results have shown that structural F – for OH – substitution in layered silicates makes them more hydrophobic. Here, we use grand canonical molecular dynamics calculations to investigate how increasing the F – /(F – + OH – ) ratio of a prototypical layered silicate (the smectite Na-hectorite) impacts the intercalation behavior of CO 2 and H 2 O at elevated temperature and pressure. At the conditions of this study ( T = 323 K, P = 90 bar, water-saturated CO 2 ), increasing F – for OH – substitution causes decreasing total CO 2 + H 2 O intercalation, increasing CO 2 /(CO 2 + H 2 O) ratios in the interlayer galleries, and an increasing energy barrier to CO 2 and H 2 O intercalation. CO 2 intercalation is the greatest at monolayer basal spacings, and the results support the idea that with Na + as the exchangeable cation, the interlayers must be propped open by some H 2 O molecules to allow CO 2 to enter the interlayer galleries. The computed immersion energies suggest that the bilayer or a more expanded structure is the stable state under these conditions, in agreement with experimental results, and that the basal spacings of the minimum energy 2L structures increase with increasing F – for OH – substitution. Finally, these results are consistent with a wide range of experimental data for smectites at ambient conditions and elevated pressures and temperatures and suggest that F – for OH – substitution in conjunction with reduced structural charge and exchange with large, low charge cations may increase the ability of smectite minerals to incorporate hydrophobic species such as CH 4 , CO 2 , H 2 , and other organic compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Hybrid Heterostructures to Generate Long-Lived and Mobile Photocarriers in Graphene

We report the generation of long-lived and highly mobile photocarriers in hybrid van der Waals heterostructures that are formed by monolayer graphene, few-layer transition metal dichalcogenides, and the organic semiconductor F 8 ZnPc. Samples are fabricated by dry transfer of mechanically exfoliated MoS 2 or WS 2 few-layer flakes on a graphene film, followed by deposition of F 8 ZnPc. Transient absorption microscopy measurements are performed to study the photocarrier dynamics. In heterostructures of F 8 ZnPc/few-layer-MoS 2 /graphene, electrons excited in F 8 ZnPc can transfer to graphene and thus be separated from the holes that reside in F 8 ZnPc. By increasing the thickness of MoS 2 , these electrons acquire long recombination lifetimes of over 100 ps and a high mobility of 2800 cm 2 V–1 s –1 . Graphene doping with mobile holes is also demonstrated with WS 2 as the middle layers. Furthermore, these artificial heterostructures can improve the performance of graphene-based optoelectronic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Calcium intercalation into layered fluorinated sodium iron phosphate

Here, the energy density and cost of battery systems could be improved by moving to alternative battery chemistries such as Ca-ion. However, in order to switch chemistries many problems need to be solved including the identification of cathode materials with high energy density, and electrolytes that can plate and strip calcium metal. Herein, the feasibility and cycling performance of Ca 2+ intercalation into a desodiated layered Na 2 FePO 4 F host is described. This is the first demonstration of Ca 2+ intercalation into a polyanionic framework, which implies that other polyanionic framework materials may be active for Ca 2+ intercalation. Although substantial effort is still needed to identify a high energy density cathode material, this study and others demonstrate the feasibility of Ca 2+ intercalation into multiple materials making it more probable that such a cathode material can be found.

25 ENERGY STORAGE↗
DOE OSTI2023

Scalar Flux Profiles in the Unstable Atmospheric Surface Layer Under the Influence of Large Eddies: Implications for Eddy Covariance Flux Measurements and the Non‐Closure Problem

How convective boundary-layer (CBL) processes modify fluxes of sensible (SH) and latent (LH) heat and CO 2 (F c ) in the atmospheric surface layer (ASL) remains a recalcitrant problem. Here, large eddy simulations for the CBL show that while SH in the ASL decreases linearly with height regardless of soil moisture conditions, LH and F c decrease linearly with height over wet soils but increase with height over dry soils. This varying flux divergence/convergence is regulated by changes in asymmetric flux transport between top-down and bottom-up processes. Such flux divergence and convergence indicate that turbulent fluxes measured in the ASL underestimate and overestimate the “true” surface interfacial fluxes, respectively. While the non-closure of the surface energy balance persists across all soil moisture states, it improves over drier soils due to overestimated LH. The non-closure does not imply that F c is always underestimated; F c can be overestimated over dry soils despite the non-closure issue.

Geology↗
DOE OSTI2016

Novel phosphate halides BaMn{sup III}[PO{sub 4}]FCl and BaMn{sup III}[PO{sub 4}]F{sub 2}: Effects of mixed halides on crystal structures and magnetic properties

Two new phosphate halides BaMn{sup III}[PO{sub 4}]FCl (1) and BaMn{sup III}[PO{sub 4}]F{sub 2} (2), have been synthesized under hydrothermal conditions. Structural characterizations show that both new compounds adopt layered structures but with different polyhedral linkages. Introduction of Cl into Compound (1) results in isolated hemimorphic [MnO{sub 4}FCl] octahedra, different from the chain of [MnO{sub 4}F{sub 2}]/[MnO{sub 2}F{sub 4}] octahedra in Compound (2). These compounds have significantly different molecular vibration modes and thermal stabilities. Magnetic measurements reveal that Compound (2) has larger antiferromagnetic interactions than Compound (1), because the former has strong interactions between Mn{sup 3+}-Mn{sup 3+} ions within corner-shared Mn{sup 3+}-octahedral chains whereas the latter only possesses isolated Mn{sup 3+}-octahedra. Both compounds transform to a new orthorhombic compound BaMn{sup II}(PO{sub 4})F (3) after thermal decomposition. - Graphical abstract: The large radius of Cl{sup -} ions makesBaMn{sup III}[PO{sub 4}]FCl to adopt isolated [MnO{sub 4}FCl] rather than corner-sharing octahedra as observed in BaMn{sup III}[PO{sub 4}]F{sub 2}. - Highlights: • Two novel phosphate halides BaMn[PO{sub 4}]FCl and BaMn[PO{sub 4}]F{sub 2} have been prepared. • These new compounds adopt different types of layered structures. • They have different molecular vibration modes and thermal stabilities. • BaMn[PO{sub 4}]FCl has weaker antiferromagnetic interactions than BaMn[PO{sub 4}]F{sub 2}. • The former adopts isolated octahedra whereas the latter adopts octahedral chains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Pomeranchuk Instability of Composite Fermi Liquids

Nematicity in quantum Hall systems has been experimentally well established at excited Landau levels. The mechanism of the symmetry breaking, however, is still unknown. Pomeranchuk instability of Fermi liquid parameter F ℓ ≤ –1 in the angular momentum ℓ = 2 channel has been argued to be the relevant mechanism, yet there are no definitive theoretical proofs. Here we calculate, using the variational Monte Carlo technique, Fermi liquid parameters F ℓ of the composite fermion Fermi liquid with a finite layer width. We consider F ℓ in different Landau levels n = 0, 1, 2 as a function of layer width parameter η. We find that unlike the lowest Landau level, which shows no sign of Pomeranchuk instability, higher Landau levels show nematic instability below critical values of η. Furthermore, the critical value η c is higher for the n = 2 Landau level, which is consistent with observation of nematic order in ambient conditions only in the n = 2 Landau levels. As a result, the picture emerging from our work is that approaching the true 2D limit brings half-filled higher Landau-level systems to the brink of nematic Pomeranchuk instability.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗