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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Disentangling the Physical Processes Responsible for the Kinetic Complexity in Interfacial Electron Transfer of Excited Ru(II) Polypyridyl Dyes on TiO 2

Interfacial electron transfer at titanium dioxide (TiO 2 ) is investigated herein for a series of surface bound ruthenium-polypyridyl dyes whose metal-to-ligand charge-transfer state (MLCT) energetics are tuned through chemical modification. The 12 complexes are of the form Ru II (bpy-A)(L) 2 2+ , where bpy-A is a bipyridine ligand functionalized with phosphonate groups for surface attachment to TiO 2 . Functionalization of ancillary bipyridine ligands (L) enables the potential of the excited state Ru III/ * couple, E + / *, in 0.1 M perchloric acid (HClO 4 (aq)) to be tuned from –0.69 to –1.03 V vs NHE. Each dye is excited by a 200 fs pulse of light in the visible region of the spectrum and probed with a time-delayed supercontiuum pulse (350–800 nm). Decay of the MLCT excited-state absorption at 376 nm is observed without loss of the ground-state bleach, which is a clear signature of electron injection and formation of the oxidized dye. The dye-dependent decays are biphasic with time constants in the 3–30 and 30–500 ps range. The slower injection rate constant for each dye is exponentially distributed relative to E + / *. The correlation between the exponentially diminishing density of TiO 2 sub-band acceptor levels and injection rate is well described using Marcus–Gerischer theory, with the slower decay components being assigned to injection from the thermally equilibrated state and the faster components corresponding to injection from higher energy states within the 3 MLCT manifold. These results and detailed analyses incorporating molecular photophysics and semiconductor density of states measurements indicate that the multiexponential behavior that is often observed in interfacial injection studies is not due to sample heterogeneity. Rather, this work shows that the kinetic heterogeneity results from competition between excited-state relaxation and injection as the photoexcited dye relaxes through the 3 MLCT manifold to the thermally equilibrated state, underscoring the potential for a simple kinetic model to reproduce the complex kinetic behavior often observed at the interface of mesoporous metal oxide materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Probing Depth-Dependent Transition-Metal Redox of Lithium Nickel, Manganese, and Cobalt Oxides in Li-Ion Batteries

Layered lithium nickel, manganese, and cobalt oxides (NMC) are among the most promising commercial positive electrodes in the past decades. Understanding the detailed surface and bulk redox processes of Ni-rich NMC can provide useful insights into material design options to boost reversible capacity and cycle life. Both hard X-ray absorption (XAS) of metal K-edges and soft XAS of metal L-edges collected from charged LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) showed that the charge capacity up to removing ~0.7 Li/f.u. was accompanied with Ni oxidation in bulk and near the surface (up to 100 nm). Of significance to note is that nickel oxidation is primarily responsible for the charge capacity of NMC622 and 811 up to similar lithium removal (~0.7 Li/f.u.) albeit charged to different potentials, beyond which was followed by Ni reduction near the surface (up to 100 nm) due to oxygen release and electrolyte parasitic reactions. Overall, this observation points toward several new strategies to enhance reversible redox capacities of Ni-rich and/or Co-free electrodes for high-energy Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2013

Unexpected behaviour of one Pb monolayer deposited on aluminum oxide thin film grown on Ag(111)

Using scanning tunneling microscopy (STM), Auger electron spectroscopy, and low energy electron diffraction, we have observed a surprising complete dissolution at room temperature of one lead monolayer deposited by evaporation on an aluminum oxide thin film (∼0.8 nm thick) previously grown on Ag (111). We have observed the quasi-instantaneous diffusion of the lead deposit through the oxide layer to the silver/oxide interface. After the diffusion process, lead atoms form a Moiré superstructure, which is characterized by STM through the oxide layer. This unexpected behavior puts in light the very weak interaction between the aluminum oxide and the silver substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ionic Modulation at the LaAlO 3 /KTaO 3 Interface for Extreme High-Mobility Two-Dimensional Electron Gas

Due to the coexistence of many emergent phenomena, including 2D superconductivity and a large Rashba spin-orbit coupling, 5d transition metal oxides-based two-dimensional electron systems (2DESs) have been prospected as one of the potential intrants for modern electronics. However, despite the lighter electron mass, the mobility of carriers, a key requisite for high-performance devices, in 5d-oxides devices remains far behind their 3d-oxides analogs. The carriers’ mobility in these oxides is significantly hampered by the inevitable presence of defects. Here, in this study, very high mobility (≈22 650 cm 2 V –1 s –1 ) of 5d-2DES confined at the LaAlO 3 /KTaO 3 interface is reported. The high mobility, which is beyond the values observed in SrTiO 3 2DESs in the same carrier-density range, is achieved using the ionic-liquid gating at room temperature. The authors postulate that the ionic-liquid gating affects the oxygen vacancies and efficiently reduces any disorder at the interface. Investigating density and mobility in a broad range of back-gate voltage, the authors reveal that the mobility follows the power-law µ ∝ n 1.2 , indicating the very high quality of ionic-liquid-gated LaAlO 3 /KTaO 3 devices, consistent with the postulate. Furthermore, the analysis of the quantum oscillations confirms that the high-mobility electrons occupy the electronic sub-bands emerging from the Ta:5d orbitals of KTaO 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cesium-Induced Active Sites for C–C Coupling and Ethanol Synthesis from CO 2 Hydrogenation on Cu/ZnO(000$\bar{1}$) Surfaces

The efficient conversion of carbon dioxide, a major air pollutant, into ethanol or higher alcohols is a big challenge in heterogeneous catalysis, generating great interest in both basic scientific research and commercial applications. Here, we report the facilitated methanol synthesis and the enabled ethanol synthesis from carbon dioxide hydrogenation on a catalyst generated by codepositing Cs and Cu on a ZnO(000$\bar{1}$) substrate. A combination of catalytic testing, X-ray photoelectron spectroscopy (XPS) measurements, and calculations based on density functional theory (DFT) and kinetic Monte Carlo (KMC) simulation was used. The results of XPS showed a clear change in the reaction mechanism when going from Cs/Cu(111) to a Cs/Cu/ZnO(000$\bar{1}$) catalyst. The Cs-promoting effect on C–C coupling is a result of a synergy among Cs, Cu, and ZnO components that leads to the presence of CH x and CH y O species on the surface. Furthermore, according to the DFT-based KMC simulations, the deposition of Cs introduces multifunctional sites with a unique structure at the Cu–Cs–ZnO interface, particularly being able to promote the interaction with CO 2 and thus the methanol synthesis predominantly via the formate pathway. More importantly, it tunes the CHO binding strongly enough to facilitate the HCOOH decomposition to CHO via the formate pathway, but weakly enough to allow further hydrogenation to methanol. The fine-tuning of CHO binding also enables a close alignment of a CHO pair to facilitate the C–C coupling and eventually ethanol synthesis. Our study opens new possibilities to allow the highly active and selective conversion of carbon dioxide to higher alcohols on widely used and low-cost Cu-based catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Visualizing the Nanoscale Oxygen and Cation Transport Mechanisms during the Early Stages of Oxidation of Fe–Cr–Ni Alloy Using In Situ Atom Probe Tomography

Abstract Understanding the early stages of interactions between oxygen and material surfaces—especially at very high spatial resolutions—is highly beneficial for fields ranging from materials degradation, corrosion, geological sciences, forensics, and catalysis. The ability of in situ atom probe tomography (APT) is demonstrated to track the diffusion of oxygen and metal ions at nanoscale spatial resolution during the early stages of oxidation of a model Fe–Cr–Ni alloy. Using 18 O isotope tracers in these in situ APT experiments and complementary ex situ multimodal microscopy, spectroscopy, and computational simulations allows to precisely analyze the kinetics of oxidation and determine that outward cation diffusion to oxide/air interface is the primary mechanism for intragranular oxide growth in this alloy at 300 °C. This unique in situ isotopic tracer APT approach and the insights gained can be highly beneficial for studying early stages of gas–surface reactions in a broad array of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Investigations on MGy ionizing dose effects in thin oxides of micro-electronic devices

Total ionizing dose (TID) effects have been studied for a long time in micro-electronic components designed to operate in natural and artificial environments. In most cases, TID induces both charge trapping in the bulk of irradiated oxides and the buildup of interface traps located at semiconductor/dielectric interfaces. Such effects result from basic mechanisms driven by both the shape of the electric field which stands into the oxide and by fabrication process parameters inducing pre-existing traps in the oxide's bulk. From the pioneering studies based on 'thick' oxide technologies to the most recent ones dedicated to innovative technologies, most studies concluded that the impact of total ionizing dose effects reduces with the oxide thinning. This is specifically the case for the gate-oxide of Metal-Oxide-Semiconductor Field Effect Transistors (MOSFET) for which it is generally considered that TID is not a major issue anymore at kGy dose ranges. TID effects are now mainly due to charge trapping in the field oxides such as Shallow Trench Isolation. This creates either parasitic conduction paths or Radiation-Induced Narrow Channel Effects (RINCE). Static current-voltage (I-V) electrical characteristics are then modified through a significant increase of the off-current of NMOS transistors or by shifting the whole I-V curves (of both NMOS and PMOS transistors). Based on these assumptions, no significant shift of I-V curves should be observed in modern bulk CMOS technologies. However, such phenomenon may not be directly extrapolated to higher TID ranges, typically of several MGy for which only few data are available in the literature. This paper presents evidences of large threshold voltage shifts measured at MGy dose levels despite the fact that transistors are designed in a submicron bulk technology which features a 7-nm thin gate-oxide on GO2 transistors dedicated to mixed analog/digital integrated circuits. Such electrical shifts are encountered on PMOS transistors of different widths, W{sub NARROW} = 0.24 μm and W{sub WIDE} = 10 μm. The devices are irradiated using 10 keV X-rays at several total dose steps up to 3 MGy. On the one hand, negative threshold voltage shifts of more than 3.3 V are extracted after 3 MGy on narrow transistors. Even very high, this voltage shift is consistent with RINCE in narrow open layout transistors. On the other hand, voltage shifts greater than 2.5 V are extracted on wide transistors. Obviously, this result should not be associated neither to positive charge trapping in the thin gate oxide nor to any RINCE in this very wide transistor geometry. NMOS and PMOS transistors exhibit a clear asymmetrical behaviour. But contrary to what is commonly observed at 'low' TID range, the PMOS transistor is here more impacted than the NMOS one. The final paper will thus provide an extensive study of these phenomena using other device designs and geometries tested with dedicated TID experiments to discuss whether or not this effect revealed at very high TID, i.e. several MGy, may be attributed to an enhanced high-TID induced charge trapping mechanism in thin gate oxides. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Impact of annealing on the chemical structure and morphology of the thin-film CdTe/ZnO interface

To enable an understanding and optimization of the optoelectronic behavior of CdTe-ZnO nanocomposites, the morphological and chemical properties of annealed CdTe/ZnO interface structures were studied. For that purpose, CdTe layers of varying thickness (4–24 nm) were sputter-deposited on 100 nm-thick ZnO films on surface-oxidized Si(100) substrates. The morphological and chemical effects of annealing at 525 °C were investigated using X-ray Photoelectron Spectroscopy (XPS), X-ray-excited Auger electron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy. We find a decrease of the Cd and Te surface concentration after annealing, parallel to an increase in Zn and O signals. While the as-deposited film surfaces show small grains (100 nm diameter) of CdTe on the ZnO surface, annealing induces a significant growth of these grains and separation into islands (with diameters as large as 1 μm). The compositional change at the surface is more pronounced for Cd than for Te, as evidenced using component peak fitting of the Cd and Te 3d XPS peaks. The modified Auger parameters of Cd and Te are also calculated to further elucidate the local chemical environment before and after annealing. Together, these results suggest the formation of tellurium and cadmium oxide species at the CdTe/ZnO interface upon annealing, which can create a barrier for charge carrier transport, and might allow for a deliberate modification of interface properties with suitably chosen thermal treatment parameters.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Native oxide transport and removal during the atomic layer deposition of Ta{sub 2}O{sub 5} on InAs(100) surfaces

Atomic layer deposition (ALD) was used to deposit Ta{sub 2}O{sub 5} on etched and native oxide-covered InAs(100) using pentakis dimethyl amino tantalum and H{sub 2}O at 200–300 °C. The transport and removal of the native oxides during the ALD process was investigated using x-ray photoelectron spectroscopy (XPS). Depositions above 200 °C on etched surfaces protected the interface from reoxidation. On native oxide-covered surfaces, depositions resulted in enhanced native oxide removal at higher temperatures. The arsenic oxides were completely removed above 250 °C after 3 nm of film growth, but some of the As{sub 2}O{sub 3} remained in the film at lower temperatures. Angle-resolved and sputter depth profiling XPS confirmed indium and arsenic oxide migration into the Ta{sub 2}O{sub 5} film at deposition temperatures as low as 200 °C. Continuous removal of both arsenic and indium oxides was confirmed even after the deposition of several monolayers of a coalesced Ta{sub 2}O{sub 5} film, and it was demonstrated that native oxide transport is a prevalent component of the interface “clean-up” mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Al{sub 2}O{sub 3}/GeO{sub x} gate stack on germanium substrate fabricated by in situ cycling ozone oxidation method

Al{sub 2}O{sub 3}/GeO{sub x}/Ge gate stack fabricated by an in situ cycling ozone oxidation (COO) method in the atomic layer deposition (ALD) system at low temperature is systematically investigated. Excellent electrical characteristics such as minimum interface trap density as low as 1.9 × 10{sup 11 }cm{sup −2 }eV{sup −1} have been obtained by COO treatment. The impact of COO treatment against the band alignment of Al{sub 2}O{sub 3} with respect to Ge is studied by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Based on both XPS and SE studies, the origin of gate leakage in the ALD-Al{sub 2}O{sub 3} is attributed to the sub-gap states, which may be correlated to the OH-related groups in Al{sub 2}O{sub 3} network. It is demonstrated that the COO method is effective in repairing the OH-related defects in high-k dielectrics as well as forming superior high-k/Ge interface for high performance Ge MOS devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Influence of controlled surface oxidation on the magnetic anisotropy of Co ultrathin films

We studied the influence of controlled surface-limited oxidation of electrodeposited epitaxial Co(0001)/Au(111) films on their magnetic anisotropy energy using real time in situ magneto optical Kerr effect and density functional theory (DFT) calculations. We investigated the Co first electrochemical oxidation step which we demonstrate to be completely reversible and determined the structure of this oxide layer. We show that the interface magnetic anisotropy of the Co film increases by 0.36 erg/cm{sup 2} upon Co surface oxidation. We performed DFT calculations to determine the different surface structures in a wide potential range as well as the charge transfer at the Co surface. Our results suggest that the magnetic anisotropy change is correlated with a positive charge increase of 0.54 e{sup −} for the Co surface atom upon oxidation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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 OSTI2025

Design of Sodium Chalcohalide Solid Electrolytes with Mixed Anions for All‐Solid‐State Sodium‐Ion Batteries

Solid-state sodium-ion batteries (SSNIBs) have emerged as a promising alternative to lithium-ion systems for grid-scale energy storage, owing to sodium's abundance and the improved safety of solid-state designs. Among various solid-state electrolytes (SSEs), halide-based Na + SSEs offer high electrochemical stability but are limited by low ionic conductivity and poor thermal stability. Herein, a novel class of sodium hafnium chalcohalide SSEs is reported with a dual-anion (S 2− /Cl − ) framework, with a high ionic conductivity of 4.5 × 10 −4 S cm −1 . The incorporation of sulfur enhances Na⁺ mobility by reducing the migration barrier through increased anion polarizability and expanded diffusion pathways. Additionally, S 2− contributes to stronger interatomic bonding, leading to higher cohesive energy density, improved thermal stability, and mechanical robustness. These SSEs exhibit minimal sulfur oxidation and excellent chemical/electrochemical interface stability with different cathode materials, such as O3-layered NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , P2/O3 layered Na 0.85 Mn 0.5 Ni 0.4 Fe 0.1 O 2 , and Na 3 V 2 (PO 4 ) 3 cathodes. As a result, SSNIBs with P2/O3 layered Na 0.85 Mn 0.5 Ni 0.4 Fe 0.1 O 2 employing the sodium hafnium chalcohalide SSEs demonstrate outstanding cycling performance, achieving a capacity retention of 88.5% after 200 cycles at 0.1 C. This study establishes a new design strategy for high-performance SSEs, demonstrating that mixed-anion frameworks offer a viable route to overcome the intrinsic limitations of single-anion electrolytes in next-generation SSNIBs.

DFT calculation↗
DOE OSTI2016

Interfacial Characteristics of Efficient Bulk Heterojunction Solar Cells Fabricated on MoOx Anode Interlayers

The role of the interface between an MoOx anode interlayer and a polymer:fullerene bulk heterojunction is investigated. Processing differences in the MoOx induce large variations in the vertical stratification of the bulk heterojunction films. These variations are found to be inconsistent in predicting device performance, with a much better gauge being the quantity of polymer chemisorbed to the anode interlayer.

14 SOLAR ENERGY↗
DOE OSTI2025

Pushing the Limits: Maximizing Energy Density in Silicon Sulfide Solid‐State Batteries

Here, for the first time, we demonstrate a silicon solid-state battery (SSB) architecture that achieves >400 Wh kg −1 , approaching the theoretical limit for silicon-based SSBs. This configuration features a 99.9 wt% micro-Si, a thin sulfide solid electrolyte (SSE), and a high-loading NMC811. Key to these results is strategically selecting and evaluating the processing techniques, whether wet or dry, for the negative electrode, positive electrode and thin sheet-type SSE. Excessive lithium incorporation into the silicon host, beyond the Li 3.75 +Si phase to form a LiSi composite, is essential to match the high capacity of the positive electrode. This SSB achieves over 1000 cycles for a 2 mAh cm −2 with ≈80% capacity retention and 94% capacity retention for 3 mAh cm −2 over 500 cycles at 25 °C. Post analysis identifies the primary capacity decay mechanisms as oxidation at the NMC/SSE interface and structural disruptions within NMC. Meanwhile, the Si electrode maintains a robust solid-electrolyte interphase layer, minimizing capacity decay. This study highlights the necessity for improved NMC coatings, lattice oxygen stabilization, and a durable positive electrode-electrolyte interface to improve the long-term stability of SSBs. Strategies leading to a single-layer pouch cell SSB exceeding 400 Wh kg −1 are developed.

25 ENERGY STORAGE↗
DOE OSTI2018

Effect of TiN Addition on 3Y-TZP Ceramics with Emphasis on Making EDM-Able Bodies

In this study, to produce electrically conductive ceramics, rapid hot press (RHP) sintering of 3 mol.% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 3Y-TZP/TiN composites with TiN amounts of 25, 35, and 45 vol.% was performed at 1300, 1350, and 1400 °C. Interestingly, the toughness and hardness were improved in the presence of TiN up to 35 vol.% and maximum fracture toughness and hardness of 5.40 ± 0.05 MPa m{sup 1/2} and 14.50 ± 0.06 GPa, respectively, were obtained. However, the bending strength was decreased which could be attributed to the rather weak interfaces of nitride and oxide phases. Regarding the zirconia matrix, the effect of grain size on fracture toughness of the samples has been studied using x-ray diffraction and field emission scanning electron microscope (FESEM) analysis. It was also found that electrical resistivity decreased to the value of 6.88 × 10{sup −6} Ω m at 45 vol.% of TiN. It seems the TiN grains form a network to impose conductivity on the ZrO{sub 2} body; however, below 35 vol.% TiN, due to lack of percolation effect, this conductivity could not be maintained according to FESEM studies. Finally, electrically conductive samples were successfully machined by electrical discharge machining (EDM).

36 MATERIALS SCIENCE↗