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At least 955 records · Page 53

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DOE OSTI2024

Chemical and Electrochemical Characterization of Hot–Pressed Li 6 PS 5 Cl Solid State Electrolyte: Operating Pressure–Invariant High Ionic Conductivity

Sulfide solid state electrolytes (SSE) are among the most promising materials in the effort to replace liquid electrolytes, largely due to their comparable ionic conductivities. Among the sulfide SSEs, Argyrodites (Li 6 PS 5 X, X=Cl, Br, I) further stand out due to their high theoretical ionic conductivity (~1×10 –2 S cm –1 ) and interfacial stability against reactive metal anodes such as lithium. Generally, solid state electrolyte pellets are pressed from powder feedstock at room temperature, however, pellets fabricated by cold pressing consistently result in low bulk density and high porosity, facilitating interfacial degradation reactions and allowing dendrites to propagate through the pores and grain boundaries. Here, we demonstrate the mechanical and electrochemical implications of hot-pressing standalone LPSCl SSE pellets with near-theoretical ionic conductivity, superior cycling performance, and enhanced mechanical stability. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and x-ray diffraction spectroscopy (XRD) analysis reveal no chemical changes to the Argyrodite surface after hot pressing up to 250°C. Furthermore, we use electrochemical impedance spectroscopy (EIS) to understand mechanical stability of Argyrodite SSE pellets as a function of externally applied pressure, demonstrating for the first time pressed standalone Argyrodite pellets with near-theoretical conductivities at external pressures below 14 MPa.

25 ENERGY STORAGE↗

DOE OSTI2024

Hidden non-collinear spin-order induced topological surface states

Abstract Rare-earth monopnictides are a family of materials simultaneously displaying complex magnetism, strong electronic correlation, and topological band structure. The recently discovered emergent arc-like surface states in these materials have been attributed to the multi-wave-vector antiferromagnetic order, yet the direct experimental evidence has been elusive. Here we report observation of non-collinear antiferromagnetic order with multiple modulations using spin-polarized scanning tunneling microscopy. Moreover, we discover a hidden spin-rotation transition of single-to-multiple modulations 2 K below the Néel temperature. The hidden transition coincides with the onset of the surface states splitting observed by our angle-resolved photoemission spectroscopy measurements. Single modulation gives rise to a band inversion with induced topological surface states in a local momentum region while the full Brillouin zone carries trivial topological indices, and multiple modulation further splits the surface bands via non-collinear spin tilting, as revealed by our calculations. The direct evidence of the non-collinear spin order in NdSb not only clarifies the mechanism of the emergent topological surface states, but also opens up a new paradigm of control and manipulation of band topology with magnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1976

Applications of beam-foil spectroscopy to atomic collisions in solids

Some selected papers presented at the Fourth International Conference on Beam-Foil Spectroscopy, whose results are of particular pertinence to ionic collision phenomena in solids, are reviewed. The topics discussed include solid target effects and means of surmounting them in the measurement of excited projectile ion lifetimes for low-energy heavy element ions; the electron emission accompanying the passage of heavy particles through solid targets; the collision broadening of X rays emitted from 100 keV ions moving in solids; residual K-shell excitation in chlorine ions penetrating carbon; comparison between 40 MeV Si on gaseous SiH4 targets at 300 mtorr and 40 MeV Si on Al; and the emergent surface interaction in beam-foil spectroscopy. A distinct overlap of interests between the sciences of beam-foil spectroscopy and atomic collisions in solids is pointed out.

Sellin, I. A.↗

DOE OSTI2023

In Situ Attenuated Total Reflectance Infrared Spectroelectrochemistry (ATR-IR-SEC) for the Characterization of Molecular Redox Processes on Surface-Proximal Doped Silicon ATR Crystal Working Electrodes

In situ mid-infrared spectroscopy is a powerful technique for understanding the mechanism of CO 2 reduction (CO 2 R) catalysts because it enables the direct detection of catalytic intermediates and products. Moreover, spectroelectrochemistry (SEC), the coupling of spectroscopy with electrochemistry, allows spectroscopic changes to be correlated with applied potentials to reveal potential-dependent intermediates that are often relevant to photoelectrochemical reactions. Hybrid photoelectrodes, comprised of a narrow bandgap semiconductor, like silicon (Si), with a covalently-linked molecular catalyst, are a promising platform for sunlight-driven catalysis, but characterization of the catalytic mechanism(s) is challenging under photoelectrochemical conditions, particularly when the catalyst is present in monolayer or less concentrations. Here, we have developed a new strategy to use multiple-reflection attenuated total reflectance IR spectroscopy (ATR-IR) coupled with electrochemistry to characterize catalysts directly integrated with a semiconductor surface under applied potential. We show that by surface-proximal n-type or p-type doping of the top ~100-200 nm of the crystal surface, Si ATR crystals can be used simultaneously as the internal reflection element and semiconductor working electrode for ATR-IR-SEC measurements. The surface-proximal doping strategy yields a quasi-equipotential surface with excellent infrared transparency that would have been compromised by free carrier absorption if the crystal was uniformly doped. This approach permits the catalytically-active functionalized surface to be directly probed without modification and overcomes signal-to-noise limitations of other strategies that use separately deposited working electrodes on Si ATR crystals. Proof-of-concept ATR-IR-SEC spectra were collected during the reduction and oxidation of monolayers of Re- and Ru-based transition metal carbonyl complexes, respectively, verifying the viability of the technique to probe redox processes associated with CO 2 R catalysts on Si electrode surfaces with high sensitivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1984

Remote sensing of vegetation at regional scales

Relations between spectroscopy and the concept of inferring surface cover type and condition from measurements of reflected or emitted radiation are examined, taking into account the observation of 'spectral signatures'. It has now become evident that the paradigm which had provided the basis for the spectroscopic identification of materials, is incomplete when applied to the inference of type and condition of materials in a natural environment. It was found that one could not collect a remote sensing signature from an unknown ground cover class at a particular time and place and match that signature with an a priori catalog value to infer the properties of the unknown cover class. The spectroscopy paradigm was, therefore, largely abandoned in favor of decision theoretic approaches. Attention is given to the temporal greenness profile feature space, the crop stage of development estimation using a temporal greenness profile, the temporal greenness profile for crop yield, and applications to regional scales.

Hall, F. G.↗

NASA NTRS1991

An e.s.c.a. study of atomic oxygen interactions with phosphazene-coated polyimide films

Metallic as well as most nonmetallic materials experience oxidation and mass loss via surface erosion in low earth orbit as shown in previous Space Shuttle flights. This study is an evaluation of select polyphosphazene polymers and their resistance to atomic oxygen attack. Electron spectroscopy for chemical analysis examinations of the surfaces of polyphosphazene coatings were monitored for microstructural changes induced during exposures to atomic oxygen. Sample exposures in oxygen plasmas and O(3P) beam were compared as to their effect on surface compositional changes in the polyphosphazene coating. High resolution line scans revealed rearrangements in the polymer backbone and scissioning reactions involving fluorocarbon units of long chain fluoroalkoxy pendant groups. Atom percents and peak areas of all species provided a detailed profile of the microstructural changes induced in phosphazene polymers as a result of exposures to atomic oxygen.

Fewell, Larry L.↗

DOE OSTI2019

Influence of Surface Ligands on Energetics at FASnI 3 /C 60 Interfaces and Their Impact on Photovoltaic Performance

Interfacial chemistry and energetics significantly impact the performance of photovoltaic devices. In the case of Pb-containing organic metal halide perovskites, photoelectron spectroscopy has been used to determine the energetic alignment of frontier electronic energy levels at various interfaces present in the photovoltaic device. For the Sn-containing analogues, which are less toxic, no such measurements have been made. Through a combination of ultraviolet, inverse, and X-ray photoelectron spectroscopy (UPS, IPES, and XPS, respectively) measurements taken at varying thickness increments during stepwise deposition of C 60 on FASnI 3 , we present the first direct measurements of the frontier electronic energy levels across the FASnI 3 /C 60 interface. The results show band bending in both materials and transport gap widening in FASnI 3 at the interface with C 60 . The XPS results show that iodide diffuses into C 60 and results in n-doping of C 60 . This iodide diffusion out of FASnI 3 impacts the valence and conduction band energies of FASnI 3 more than the core levels, with the core level shifts displaying a different trend than the valence and conduction bands. Surface treatment of FASnI 3 with carboxylic acids and bulky ammonium substituted surface ligands results in slight alterations in the interfacial energetics, and all surface ligands result in similar or improved PV performance relative to the untreated devices. Finally, the greatest PV stability results from treatment with a fluorinated carboxylic acid derivative; however, iodide diffusion is still observed to occur with this surface ligand.

interfacial energetics↗

NASA NTRS1976

Adsorption of oxygen on W/100/ - Adsorption kinetics and structure

The adsorption of oxygen on W(100) single-crystal surfaces is studied by Auger electron spectroscopy (AES), flash desorption, low-energy electron diffraction (LEED), and retarding-field work-function measurements. The AES results reveal stepwise changes in the sticking coefficients in the coverage range 0 to 1 and activated adsorption at higher coverages. Upon room-temperature adsorption, a series of complex LEED patterns is observed. In layers adsorbed at 1050 K and cooled to room temperature, the p(2 x 1) structure is the first ordered structure observed. This structure shows a reversible order-disorder transition between 700 and 1000 K and is characterized by a work function which is lower than that of the clean surface. Heating room-temperature adsorbates changes their structure irreversibly. At temperatures below 750 K, some new structures are observed.

Bauer, E.↗

DOE OSTI2021

Distinguishing bulk and surface recombination in CdTe thin films and solar cells using time-resolved terahertz and photoluminescence spectroscopies

Understanding the nature of recombination and its dependence on defects and interfaces is essential for engineering materials and contacts for higher open circuit voltage (V oc ) and power conversion efficiency in photovoltaic (PV) devices. Time-resolved photoluminescence (TRPL) has conventionally been used to evaluate recombination, but carrier redistribution often dominates the response at short times. In this work, we report on the quantification of carrier dynamics and recombination mechanisms by complementary use of both time-resolved terahertz spectroscopy (TRTS) and TRPL combined with numerical modeling of the continuity equations and Poisson’s equation. We have demonstrated this approach using CdTe thin films. A thin film stack with CdTe fabricated by vapor transport deposition and treated with CdCl 2 exhibited a bulk lifetime of 1.7 ± 0.1 ns, negligible CdTe/CdS interface recombination velocity, and back surface recombination velocity of 6.3 ± 1.3 x10 4 cm/s. In contrast, a film stack without CdCl 2 treatment had a bulk lifetime of only 68 ± 12 ps and a higher interface recombination velocity of 4 ± 2 x10 8 cm/s. By determining the locus and mechanisms of performance-limiting recombination, we can accelerate the development of thin-film PVs with higher V oc and efficiency. While the method has been demonstrated here using CdTe, it is also applicable to perovskites, Cu(InGa)Se 2 , Cu2ZnSn(S,Se) 4, and emerging technologies.

14 SOLAR ENERGY↗

NASA NTRSDate not supplied

Hydrogen Plasma Reduction of Silicates for Lunar Oxygen Liberation

As crewed missions to the moon become closer, the focus on in-situ resource utilization efforts has increased. Since lunar soil has abundant oxygen on the surface of the moon, work has been done to process this resource in an efficient manner. Hydrogen reduction of lunar regolith has emerged as a method of liberating oxygen that can be used for fuel and water production. Traditional reduction techniques require high temperatures and increased complexity when dealing with high amounts of silicates. Plasma can reduce silicates efficiently and thus has become of high interest for use in the lunar highlands where silicates exist in high quantities. NASA’s Kennedy Space Center is exploring the use of low temperature plasmas for the reduction of silicates. This work shows that exposing silicates to a hydrogen plasma produces water. Residual gas analysis and optical emission spectroscopy were used to measure the relative quantities of water vapor production and OH (A-X) emission for hydrogen plasma interactions with lunar highland simulant and silica. X-ray photo-electron spectroscopy and scanning electron microscopy/energy-dispersive X-ray spectroscopy were also used to observe surface modifications to the silicates that reflect the key chemical reactions that occurred. From this data, plasma has emerged as a promising solution to produce oxygen on the lunar surface. *Work supported by NASA's Science Technology Mission Directorate Center Innovation Fund.

R. P. Gott↗

NASA NTRSDate not supplied

Plasma Reduction of Regolith for Oxygen Liberation

Ryan Gott↗

DOE OSTI2020

Si-based materials for lithium-ion batteries II. Surface-modified Si/C/polyethylene glycol powder

X-ray photoelectron spectroscopy was used to analyze Si/C/polyethylene glycol powder obtained from Paraclete Energy, Inc. The spectra were obtained using incident monochromatic Al K α radiation at 1486.6 eV (0.834 01 nm). An initial survey spectrum together with O 1s, C 1s, and Si 2p are presented. A final survey spectrum was collected to ascertain the amount of beam-induced damage, which appears to be minimal. Finally, the spectra indicate the principal core level photoelectron and Auger electron signals, with only minor calcium and nitrogen signal, and show the expected silicon-carbon species related to the surface modification process in addition to oxidized carbon and silicon due to atmospheric exposure.

25 ENERGY STORAGE↗

NASA NTRS2001

The X-Ray Spectrometer for Mercury MESSENGER

Mercury is the closest planet to the Sun and because it is so close, it is difficult to study from Earth-based observatories. Its proximity to the Sun has also limited the number of spacecraft to visit this tiny planet to just one, Mariner 10, which flew by Mercury twice in 1974 and once in 1975. Mariner 10 provided a wealth of new information about Mercury, yet much still remains unknown about Mercury's geologic history and the processes that led to its formation. The origin of Mercury's metal-rich composition is just one area of investigation awaiting more and improved data to sort between competing hypotheses. Mercury plays an important role in comparative planetology, and many of the processes that were important during its formation are relevant to the Earth's early history. MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) is a Discovery mission that has been designed to fly by and orbit Mercury. It will launch in March 2004, flyby Mercury in 2007 and 2008 and enter an elliptical orbit in April 2009. During the one-year orbital phase, a suite of instruments on board the MESSENGER spacecraft will study the exosphere, magnetosphere, surface, and interior of Mercury. One of these instruments will be an X-Ray Spectrometer (XRS) that will measure surface elemental abundances. Remote X-ray spectroscopy has been accomplished before on the Apollo 15 and 16 missions, and more recently on NEAR Shoemaker. The MESSENGER XRS will measure characteristic X-ray emissions induced in the surface of Mercury by the incident solar flux. The Ka lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected with spatial resolution on the order of 40 km when counting statistics are not a limiting factor. These measurements can be used to obtain quantitative information on elemental composition.

Starr, R. D.↗

DOE OSTI2023

Near-field spectroscopy of Dirac plasmons in Bi 2 Se 3 ribbon arrays

Plasmons supported in the massless electron surface states of topological insulators (TIs), known as Dirac plasmons, have great potential in next generation optoelectronics. However, their inherent confinement to the surface makes the investigation of Dirac plasmons challenging. Near-field techniques provide the ideal platform to directly probe Dirac plasmons due to the sensitivity to evanescent fields at the surface. Here, we demonstrate the use of aperture near-field spectroscopy for the investigation of localized terahertz (THz) Dirac plasmon resonances in Bi 2 Se 3 ribbon arrays with widths ranging from 10 to 40 µm. Unlike scattering THz near-field techniques, the aperture method is most sensitive to plasmons with the relevant lower-momenta corresponding to plasmon wavelengths on the scale of ~20 µm. The combination of THz time-domain spectroscopy and aperture near-field microscopy enables sampling of localized Dirac plasmons in the near-field zone in the 0.5–2.5 THz range. We map the plasmon dispersion, which reveals a coupled plasmon–phonon polariton interaction. The near-field spectra show a higher contrast of the upper polariton branch in comparison with far-field observations. The information revealed by aperture near-field spectroscopy could deepen our understanding of the behavior of Dirac plasmons, leading to the potential development of real-world TI devices.

42 ENGINEERING↗

DOE OSTI2022

Particle–hole asymmetry and quantum confinement effects on the magneto-optical response of topological insulator thin-films

Intrinsically broken symmetries in the bulk of topological insulators (TIs) are manifested in their surface states. Despite particle–hole asymmetry in TIs, it has often been assumed that their surface states are characterized by a particle–hole symmetric Dirac energy dispersion. In this work, we demonstrate that the effect of particle–hole asymmetry is essential to correctly describe the energy spectrum and the magneto-optical response in TIs thin-films. In thin-films of TIs with a substantial degree of particle–hole symmetry breaking, such as Sb 2 Te 3 , the longitudinal optical conductivity displays absorption peaks arising from optical transitions between bulk and surface Landau levels for low photon energies. The transition energies between the bulk and surface Landau levels exhibit clearly discernable signatures from those between surface Landau levels due to their distinct magnetic field dependence. Furthermore, bulk contributions to the magneto-optical conductivity in a TI thin-film are enhanced via one type of doping while being suppressed by the other. This asymmetric dependence on the type of doping aids in revealing the particle–hole asymmetry in TI thin-films.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Advances in solid-state NMR for the studies of mesoporous solids: fast magic spinning and dynamic nuclear polarization

Here, this review provides an up-to-date account of the development of two solid-state (SS)NMR methods for enhancing resolution and sensitivity, fast magic angle spinning (MAS) and dynamic nuclear polarization (DNP), and the resulting progress in surface science. We demonstrate the high resolution and efficiency that can be achieved by using two-dimensional homo- and heteronuclear correlation experiments with small rotors capable of MAS at rates exceeding 100 kHz. DNP has offered significant enhancements in signal sensitivity and allowed access to nuclei and experiments that are beyond the limits of conventional SSNMR. The continuing progress in fast MAS and DNP methodologies in recent years generated an unprecedented shift in SSNMR’s capabilities in the studies of surface and interface regions of solids, especially mesoporous supports and catalysts. We give numerous examples of recent applications and discuss the prospects for further improvements of both methods.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Si-based materials for lithium-ion batteries III: Surface-modified Si/C/polyvinylidine difluoride powder

X-ray photoelectron spectroscopy was used to analyze Si/C/polyvinylidine difluoride powder obtained from Paraclete Energy Inc. The spectra were obtained using incident monochromatic Al K α radiation at 1486.6 eV (0.834 01 nm). An initial survey spectrum together with F 1s, O 1s, C 1s, and Si 2p are presented. A final survey spectrum was collected to ascertain the amount of beam-induced damage, which appears to be minimal. Finally, the spectra indicate the principal core level photoelectron and Auger electron signals with only minor nitrogen signal and show the expected silicon-carbon and silicon-fluorine species related to the surface modification process in addition to oxidized carbon and silicon due to atmospheric exposure.

25 ENERGY STORAGE↗

DOE OSTI2020

Nature of Terminating Hydroxyl Groups and Intercalating Water in Ti 3 C 2 T x MXenes: A Study by 1 H Solid-State NMR and DFT Calculations

Since the discovery of two-dimensional transition metal carbides, referred to as MXenes, research efforts targeted their applications in energy storage, as lithium-ion batteries and supercapacitors. This interest is attributable to MXenes’ large volumetric capacitance, high rate handling capability and stable cycling performance, which largely rely on surface chemistry provided by the terminating groups, such as -OH, -O, and -F. However, the atomic-scale characterization of these surface terminations challenges the diffraction methods. Solid-state (SS)NMR spectroscopy, especially 1 H SSNMR, is a promising approach for scrutinizing the surface terminations and the intercalated water in an atomistic-scale, yet only a few SSNMR studies in MXenes have been reported to date offering conflicting results and limited understanding of -OH terminations. Here, we used 1 H SSNMR experiments in concert with the DFT calculations of NMR parameters to identify multiple types of -OH groups, residing on the external and internal surfaces, in a commonly studied MXene, Ti 3 C 2 T x . The study also identifies bulk-like water trapped between the MXene flakes and interfacial water stranded on the surface. Lastly, two-dimensional 1 H -1 H correlation spectra elucidated the water-surface interactions and the mechanism of de-intercalation of water upon annealing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗