X-ray study of the charge-density-wave transition in single-layer TiS e 2
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Fang, Xin-Yue↗
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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↗
Thermal chemistry of the Cu-KI5 atomic layer deposition precursor on a copper surface
The thermal chemistry of a Cu(I) ketoiminate complex, Cu-KI5, resulting from the modification of the known Air Products CupraSelect{sup ®} copper CVD precursor Cu(hfac)(tmvs) designed to tether the two ligands via an isopropoxide linker, was studied under ultrahigh vacuum on a Cu(110) single-crystal surface by using a combination of temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy. Adsorption at low temperatures was determined to take place via the displacement of the vinyl ligand by the surface. Molecular desorption was seen at 210 K, and the evolution of Cu(II)-KI5{sub 2} was established to take place at 280 K, presumably from a disproportionation reaction that also leads to the deposition of Cu(0). Other sets of desorption products were seen at 150, 250, and 430 K, all containing copper atoms and small organic moieties with molecular masses below 100 amu. The latter TPD peak in particular indicates significant fragmentation of the ligands, likely at the C–N bond that holds the vinylsilane-isopropoxide moiety tethered to the ketoimine fragment, and possibly also at the union between the vinylsilane and the alkoxide linker. The 430 K temperature measured for this chemistry may set an upper limit for clean Cu film deposition, but since reactivity on the surface was also found to be inhibited at higher surface coverages, it may be delayed to higher temperatures under atomic layer deposition conditions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Influence of atomic layer deposition valve temperature on ZrN plasma enhanced atomic layer deposition growth
Atomic layer deposition (ALD) relies on a sequence of self-limiting surface reactions for thin film growth. The effect of non-ALD side reactions, from insufficient purging between pulses and from precursor self-decomposition, on film growth is well known. In this article, precursor condensation within an ALD valve is described, and the effect of the continuous precursor source from condensate evaporation on ALD growth is discussed. The influence of the ALD valve temperature on growth and electrical resistivity of ZrN plasma enhanced ALD (PEALD) films is reported. Increasing ALD valve temperature from 75 to 95 °C, with other process parameters being identical, decreased both the growth per cycle and electrical resistivity (ρ) of ZrN PEALD films from 0.10 to 0.07 nm/cycle and from 560 to 350 μΩ cm, respectively. Our results show that the non-ALD growth resulting from condensate accumulation is eliminated at valve temperatures close to the pressure corrected boiling point of precursor.
36 MATERIALS SCIENCE↗
Spatial atomic layer deposition on flexible porous substrates: ZnO on anodic aluminum oxide films and Al{sub 2}O{sub 3} on Li ion battery electrodes
Spatial atomic layer deposition (S-ALD) was examined on flexible porous substrates utilizing a rotating cylinder reactor to perform the S-ALD. S-ALD was first explored on flexible polyethylene terephthalate polymer substrates to obtain S-ALD growth rates on flat surfaces. ZnO ALD with diethylzinc and ozone as the reactants at 50 °C was the model S-ALD system. ZnO S-ALD was then performed on nanoporous flexible anodic aluminum oxide (AAO) films. ZnO S-ALD in porous substrates depends on the pore diameter, pore aspect ratio, and reactant exposure time that define the gas transport. To evaluate these parameters, the Zn coverage profiles in the pores of the AAO films were measured using energy dispersive spectroscopy (EDS). EDS measurements were conducted for different reaction conditions and AAO pore geometries. Substrate speeds and reactant pulse durations were defined by rotating cylinder rates of 10, 100, and 200 revolutions per minute (RPM). AAO pore diameters of 10, 25, 50, and 100 nm were utilized with a pore length of 25 μm. Uniform Zn coverage profiles were obtained at 10 RPM and pore diameters of 100 nm. The Zn coverage was less uniform at higher RPM values and smaller pore diameters. These results indicate that S-ALD into porous substrates is feasible under certain reaction conditions. S-ALD was then performed on porous Li ion battery electrodes to test S-ALD on a technologically important porous substrate. Li{sub 0.20}Mn{sub 0.54}Ni{sub 0.13}Co{sub 0.13}O{sub 2} electrodes on flexible metal foil were coated with Al{sub 2}O{sub 3} using 2–5 Al{sub 2}O{sub 3} ALD cycles. The Al{sub 2}O{sub 3} ALD was performed in the S-ALD reactor at a rotating cylinder rate of 10 RPM using trimethylaluminum and ozone as the reactants at 50 °C. The capacity of the electrodes was then tested versus number of charge–discharge cycles. These measurements revealed that the Al{sub 2}O{sub 3} S-ALD coating on the electrodes enhanced the capacity stability. This S-ALD process could be extended to roll-to-roll operation for the commercialization of S-ALD for coating Li ion battery electrodes.
36 MATERIALS SCIENCE↗
Standing and sitting adlayers in atomic layer deposition of ZnO
The extent of reactivity of diethyl zinc (DEZ) with a hydroxylated surface during atomic layer deposition (ALD) of ZnO using DEZ and water is measured. Two adlayer configurations of DEZ are possible. The “standing” adlayer releases one ethyl group from DEZ. The “sitting” adlayer releases both ethyl groups, thus forming a Zn bridge between two O anions. Density functional theory calculations suggest the sitting configuration is more stable than the standing configuration by 790 meV. In situ quadrupole mass spectroscopy of by-product ethane generated in ALD half cycles indicate that ∼1.56 OH sites react with a DEZ molecule resulting in 71.6% of sitting sites. A simple simulation of a “ball-and-stick” DEZ molecule randomly collapsing on a neighboring site remarkably captures this adlayer behavior. It is concluded that DEZ fraction sitting is a competitive process of a standing DEZ molecule collapsing onto an available neighboring hydroxyl site, as sites vie for occupancy via adsorption and surface diffusion.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Atomic layer deposition of molybdenum disulfide films using MoF 6 and H 2 S
Molybdenum sulfide films were grown by atomic layer deposition on silicon and fused silica substrates using molybdenum hexafluoride (MoF6) and hydrogen sulfide at 200 degrees C. In situ quartz crystal microbalance (QCM) measurements confirmed linear growth at 0.46 angstrom/cycle and self-limiting chemistry for both precursors. Analysis of the QCM step shapes indicated that MoS2 is the reaction product, and this finding is supported by x-ray photoelectron spectroscopy measurements showing that Mo is predominantly in the Mo(IV) state. However, Raman spectroscopy and x-ray diffraction measurements failed to identify crystalline MoS2 in the as-deposited films, and this might result from unreacted MoFx residues in the films. Annealing the films at 350 degrees C in a hydrogen rich environment yielded crystalline MoS2 and reduced the F concentration in the films. Optical transmission measurements yielded a bandgap of 1.3 eV. Finally, the authors observed that the MoS2 growth per cycle was accelerated when a fraction of the MoF6 pulses were substituted with diethyl zinc. Published by the AVS
Mane, Anil U.↗
On the Impact of Barrier-Layer Doping on the Photoluminescence Efficiency of InGaAlAs/InGaAs/InP Strained-Layer Heterostructures
The photoluminescence of strained InGaAlAs/InGaAs/InP heterostructures with an active region consisting of nine In{sub 0.74}Ga{sub 0.26}As quantum wells and δ-doped In{sub 0.53}Al{sub 0.20}Ga{sub 0.27}As barrier layers grown by molecular beam epitaxy on an InP(100) substrate is investigated. Analysis of the photoluminescence spectra demonstrates that p-type doping leads to an increase in the photoluminescence efficiency at low excitation levels in comparison to a heterostructure with undoped barriers, and increasing the level of barrier doping to (1–2) × 10{sup 12} cm{sup –2} results in the suppression of nonradiative recombination.
36 MATERIALS SCIENCE↗
Catalyst-layer ionomer imaging of fuel cells
Investigation of membrane/electrode assembly (MEA) microstructure has become an essential step to optimize the MEA components and manufacturing processes or to study the MEA degradation. For these investigations, transmission electron microscopy (TEM) is a tool of choice as it provides direct imaging of the different components. TEM is then widely used for analyzing the catalyst nanoparticles and their carbon support. However, the ionomer inside the electrode is more difficult to be imaged. The difficulties come from the fact that the ionomer forms an ultrathin layer surrounding the carbon particles and in addition, these two components, having similar density, present no difference in contrast. In this paper, we show how the recent progresses in TEM techniques as spherical aberration (Cs) corrected HRTEM, electron tomography and X-EDS elemental mapping provide new possibilities for imaging this ionomer network and consequently to study its degradation.
30 DIRECT ENERGY CONVERSION↗
Examining Ohmic Losses in Fuel-Cell Catalyst Layers with Different Pt/C Ratios
A model of a fuel-cell cathode with distinct proton conductivities at the agglomerate and electrode scales was used to simulate polarization curves under conditions with facile oxygen transport. Here, the model was applied to electrodes containing agglomerates with different ratios of platinum to carbon in order to examine the hypothesis that intra-agglomerate proton conductivity is substantially lower than ionomer conductivity. The model predicts decreasing performance and increasing sensitivity to Pt/C ratio as intra-agglomerate conductivity declines relative to a constant through-electrode conductivity. Experiments on catalyst layers with Vulcan supports do not show the predicted trend indicating that mesoscale intra-agglomerate conductivity is not orders of magnitude lower than bulk ionomer conductivity.
08 HYDROGEN↗
X-Ray-Induced Changes to Passivation Layers of Lithium-Ion Battery Electrodes
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99 GENERAL AND MISCELLANEOUS↗
A layered nonstoichiometric lepidocrocite-type sodium titanate anode material for sodium-ion batteries
A lepidocrocite-structured sodium titanate prepared by ion-exchange of a Cs-containing precursor shows promise as an anode material for sodium ion batteries, with a discharge capacity of up to 229 mAh g -1 at an average potential of about 0.6 V vs. Na + /Na. Titanium vacancies in the metal oxide layers provide additional sites for sodium intercalation in addition to interlayer sites, which accounts for the higher capacity compared to other previously reported lepidocrocite-structured titanates. By screening a series of electrolyte formulations and binders, we were able to improve the first-cycle coulombic efficiency to 81.8% and 94.7% respectively using CMC/SBR-based and binder-free electrodes in ether electrolytes. Finally, the electrochemical consequences of short-term air-exposure on the electrodes are also discussed.
25 ENERGY STORAGE↗
A Comparison of the Solubility Products of Layered Me(II)–Al(III) Hydroxides Based on Sorption Studies with Ni(II), Zn(II), Co(II), Fe(II), and Mn(II)
The precipitation of mixed metal–aluminum-layered double hydroxides (Me(II)–Al(III)-LDH)) may be an important control of the solubility of Mn(II), Fe(II), Ni(II), Zn(II), and Co(II) in soils, but assessment of this process is hindered by a lack of thermodynamic data. Here, we determined the solubility products (Ksp) of the Me(II)–Al(III)-LDHs formed by these metals based on long-term Me(II)–γAl2O3 sorption studies complemented with X-ray absorption spectroscopy (XAS) measurements. The LDH phases had the chemical formula Me(II)2/3Al1/3(OH)2Cl1/3. Solubility products were derived as Ksp = (Me2+)aq2/3(Al3+)aq1/3(OH−)aq2(Cl−)aq1/3, where brackets represent aqueous activity values determined from the equilibrium solution chemistry of the sorption samples. The Ksps are metal-dependent, with values increasing by two orders of magnitude in the order Ni(II) < Zn(II) < Co(II) < Fe(II) < Mn(II). Comparison to the solubility of β-Me(OH)2 suggests considerable thermodynamic preference of Me(II)–Al(III)-LDH over β-Me(OH)2 in soil environments and reveals a linear relation between the log-transformed Ksp values of Me(II)–Al(III)-LDH and β-Me(OH)2. Solubility plots suggest that Ni(II)–, Zn(II)–, and Co(II)–Al(III)-LDH may form in metal-polluted soils. Fe(II)–Al(III)-LDH may occur in riparian soils undergoing reduction, but precipitation of Mn(II)–Al(III)-LDH appears unlikely as it requires [Mn2+]aq much higher than commonly encountered in reducing soils. Additional thermodynamic and field studies are needed to further assess the importance of Me(II)–Al(III)-LDHs in soils and related geochemical systems.
Bhattacharya, Lasita↗
An analysis of the coupled chemically reacting boundary layer and charring ablator. Part 3 - Nonsimilar solution of the multicomponent laminar boundary layer by an integral matrix method
Laminar boundary layer problems solved by integral matrix methods
Bartlett, E. P.↗
An analysis of the coupled chemically reacting boundary layer and charring ablator. Part 4 - A unified approximation for mixture transport properties for multicomponent boundary-layer applications
Bifurcation approximation for binary and thermal diffusion coefficients, mixture viscosity, and thermal conductivity of laminar boundary layer
Bartlett, E. P.↗