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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Safeguards Technology Development Program. FY2021 Mid-Year Report, Encryption of Signal Pulses

Summary statement of work: Develop a signal pulse digital signing and encryption in-line device to verify signal integrity and point of origin for TTL pulse data used in IAEA systems, and to avoid the need for expensive tamper-indicating conduit or techniques. This device will be called Transparent Remote Encryption of Correlated Signals (TRECS). TRECS consists of two parts, a head end which is located in or near the detector assembly and a tail end that is located with the data acquisition electronics, i.e. MiniGrand, UMSR, UDL1 or JSR.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Femtosecond laser fabrication of nanograting-based distributed fiber sensors for extreme environmental applications

Abstract The femtosecond laser has emerged as a powerful tool for micro- and nanoscale device fabrication. Through nonlinear ionization processes, nanometer-sized material modifications can be inscribed in transparent materials for device fabrication. This paper describes femtosecond precision inscription of nanograting in silica fiber cores to form both distributed and point fiber sensors for sensing applications in extreme environmental conditions. Through the use of scanning electron microscope imaging and laser processing optimization, high-temperature stable, Type II femtosecond laser modifications were continuously inscribed, point by point, with only an insertion loss at 1 dB m −1 or 0.001 dB per point sensor device. High-temperature performance of fiber sensors was tested at 1000 °C, which showed a temperature fluctuation of ±5.5 °C over 5 days. The low laser-induced insertion loss in optical fibers enabled the fabrication of a 1.4 m, radiation-resilient distributed fiber sensor. The in-pile testing of the distributed fiber sensor further showed that fiber sensors can execute stable and distributed temperature measurements in extreme radiation environments. Overall, this paper demonstrates that femtosecond-laser-fabricated fiber sensors are suitable measurement devices for applications in extreme environments.

Wang, Mohan (ORCID:0000000166784993)↗
DOE OSTI2021

Graded Buffer Bragg Reflectors with High Reflectivity and Transparency for Metamorphic Optoelectronics

A graded buffer Bragg reflector (GBBR) is a bifunctional device component that provides the reflection of a distributed Bragg reflector and the adjustable lattice constant of a compositionally graded buffer. Prior work showed that these properties can be combined with low threading dislocation density and high reflectivity. Here, we design and demonstrate complex GBBRs for specific metamorphic solar cell applications. We design buffers that provide (1) high reflectivity over a narrow bandwidth, for quantum well solar cells, (2) reflectivity over a wide bandwidth, for optically thin solar cells, and (3) low sidelobe reflection, for multijunction devices that demand low out-of-band reflection. Apodized and triple GBBRs are demonstrated, and transparency is always considered, requiring designs with carefully engineered material combinations. A GBBR with a reflection of 99% is demonstrated, as well as a triple GBBR that has over 80% reflection for 100?nm of the spectrum around 800?nm. We also analyze potential deviations in a baseline GBBR from that of a perfect DBR using transmission electron microscopy to analyze imperfections in the material and modeling to analyze the impact of imperfect refractive index data for lattice-mismatched AlGaInAs. Minimal crosshatch roughness and unintentional thickness variation occur throughout the buffer, which likely influences reflection slightly. Small deviations between the calculated AlGaInAs and utilized AlGaAs refractive index exist, giving methods for future GBBR improvement. While the GBBR designs are intended for metamorphic solar cells, the broad and high reflection may also be useful for other optoelectronic devices such as light-emitting diodes or lasers.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2025

Long-range optical coupling with epsilon-near-zero materials

Long-range resonant quantum tunneling of electrons happens across potential barriers when the wavefunction interferes constructively outside the barrier. Here we demonstrate an analogy in optical systems based on epsilon-near-zero materials, achieving phase-modulated, long-range optical interactions between transparent semiconducting oxide layers beyond the evanescent photonic coupling. Distinct from weak thin-film interference, intense electromagnetic fields confined within the epsilon-near-zero thin films show anti-correlated intensity oscillations as a function of interlayer separation up to hundreds of microns. The oscillatory, anti-correlated electromagnetic field intensities were probed by second harmonic generation from wedged indium tin oxide multilayers. Such a system that hosts subwavelength mode footprint and simultaneously long-range radiative coupling offers prospects for long-distance optical communication, large-scale photonic circuits, and hybrid quantum photonic systems.

Wang, Danqing [Fudan University, Shanghai (China);↗
DOE OSTI2022

Metal-Tipped and Electrochemically Wired Semiconductor Nanocrystals: Modular Constructs for Directed Charge Transfer

In our 2017 proposal to the Solar Photochemistry division of DOE/BES/Office of Science we targeted the creation, characterization and integratation of new II-IV semiconductor heterostructured nanomaterials into ultra-thin film (tethered) nanocrystalline arrays on transparent metal oxide (TCO) supports. Materials were to include CdSe quantum dots (QDs), asymmetric CdSe@CdS tetrapods (TPs) and CdSe@CdS nanorods (NRs), into unique photoelectrochemical platforms. The ultimate goal was to tether these new nanomaterials to either electron- or hole-selective oxide interlayers that would afford vectoral photo-induced charge transfer and ultimately formation of molecular products such as H 2 . This was an ambitious set of goals but integrated well with our previous work in this general area.

14 SOLAR ENERGY↗
DOE OSTI2024

Screen-Printed Complex Ag Inks for Si HJT Metallization

Metallization using reactive metal inks has recently attracted significant research interest due to its advantages in cost of materials and manufacturing, while still achieving performance comparable to traditional fire-through particle pastes. Here, we present for the first time the use of reactive silver (Ag) inks via industrial screen-printing and inkjet printing methods for the metallization of different Si surfaces used in tunneling oxide passivating contacts (TOPCon) and Silicon heterojunction (SHJ) solar cells. Printed Ag lines exhibit a conductivity of ~5 Mu O·cm, which is approximately 3 times that of bulk Ag (1.59 µO·cm). The printed metal has a thickness of ~0.5-1.5 Mu m, an order of magnitude smaller than the current fire-through metal finger thickness (~15 Mu m). Contact resistivity measurements of the screen-printed and inkjet-printed samples on a transparent conducting oxide (TCO) surface show a very low value of ~0.2-12 mO·cm 2. Photoluminescence images of the metallized samples demonstrate minimal surface passivation degradation compared to the non-metallized areas (?iVoc <3.5 mV). Scanning electron microscopy images (SEM) reveal the structure of the printed metals on the Si surfaces as porous but much denser than fire-through Ag by nanoparticle paste. In the final presentation, we will showcase our results of printing these reactive Ag inks on high-efficiency heterojunction and TOPCon solar cells with full-area M6 wafers. Additionally, the adhesion of these reactive Ag inks on different Si surfaces according to ASTM D3359-17, as well as the performance of solar cells after standard IEC 61215 freeze/thaw and damp heat tests, will be presented. These new metal inks show promising potential as an alternative to the currently dominant particle-based pastes, offering lower Ag consumption and lower processing temperatures without compromising performance.

heterojunction solar cells↗
DOE OSTI2022

MISPR : an open-source package for high-throughput multiscale molecular simulations

Computational tools provide a unique opportunity to study and design optimal materials by enhancing our ability to comprehend the connections between their atomistic structure and functional properties. However, designing materials with tailored functionalities is complicated due to the necessity to integrate various computational-chemistry software (not necessarily compatible with one another), the heterogeneous nature of the generated data, and the need to explore vast chemical and parameter spaces. The latter is especially important to avoid bias in scattered data points-based models and derive statistical trends only accessible by systematic datasets. Here, we introduce a robust high-throughput multi-scale computational infrastructure coined MISPR (Materials Informatics for Structure–Property Relationships) that seamlessly integrates classical molecular dynamics (MD) simulations with density functional theory (DFT). By enabling high-performance data analytics and coupling between different methods and scales, MISPR addresses critical challenges arising from the needs of automated workflow management and data provenance recording. The major features of MISPR include automated DFT and MD simulations, error handling, derivation of molecular and ensemble properties, and creation of output databases that organize results from individual calculations to enable reproducibility and transparency. In this work, we describe fully automated DFT workflows implemented in MISPR to compute various properties such as nuclear magnetic resonance chemical shift, binding energy, bond dissociation energy, and redox potential with support for multiple methods such as electron transfer and proton-coupled electron transfer reactions. The infrastructure also enables the characterization of large-scale ensemble properties by providing MD workflows that calculate a wide range of structural and dynamical properties in liquid solutions. MISPR employs the methodologies of materials informatics to facilitate understanding and prediction of phenomenological structure–property relationships, which are crucial to designing novel optimal materials for numerous scientific applications and engineering technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Computationally-driven discovery of second harmonic generation in EuBa 3 (B 3 O 6 ) 3 through inversion symmetry breaking

Nonlinear optical (NLO) crystals with superior properties are significant for advancing laser technologies and applications. Introducing rare earth metals to borates is a promising and effective way to modify the electronic structure of a crystal to improve its optical properties in the visible and ultraviolet range. In this work, we computationally discover inversion symmetry breaking in EuBa 3 (B 3 O 6 ) 3 , which was previously identified as centric, and demonstrate noncentrosymmetry via synthesizing single crystals for the first time by the floating zone method. We determine the correct space group to be P 6¯. The material has a large direct bandgap of 5.56 eV and is transparent down to 250 nm. The complete anisotropic linear and nonlinear optical properties were also investigated with a d 11 of ∼0.52 pm/V for optical second harmonic generation. Further, it is Type I and Type II phase matchable. This work suggests that rare earth metal borates are an excellent crystal family for exploring future deep ultraviolet (DUV) NLO crystals. It also highlights how first principles computations combined with experiments can be used to identify noncentrosymmetric materials that have been wrongly assigned to be centrosymmetric.

He, Jingyang (ORCID:0000000238863659)↗
DOE OSTI2026

Temperature-dependent dielectric function of tantalum nitride formed by atomic layer deposition for tunnel barriers in Josephson junctions

Here, we report the dielectric functions of insulating tantalum nitride (TaN) films deposited by atomic layer deposition (ALD) on 300 mm Si/SiO 2 substrates to evaluate their suitability as tunnel barriers in tantalum-based Josephson junctions (JJs) for superconducting quantum circuits. Temperature-dependent ellipsometric angles were measured for ALD TaN films with nominal thicknesses of 13 and 25 nm at an incidence angle of 70°, over photon energy ranges of 0.03–0.7 eV (80–300 K) and 0.5–6.5 eV (80–600 K). These data were used to develop a dispersion model for insulating ALD TaN that incorporates a Tauc–Lorentz oscillator with an optical bandgap of 1.5–1.8 eV to describe interband transitions. The extracted dielectric function shows insulating behavior (mid-infrared transparency) at all temperatures and for both film thicknesses tested. In particular, ALD TaN does not exhibit infrared absorption due to free carriers, even at elevated temperatures, consistent with the insulating behavior required for a JJ tunnel barrier. Results from transmission electron microscopy (including selected area electron diffraction) and x-ray diffraction are also discussed. Sputter depth-profile x-ray photoelectron spectroscopy shows an N/Ta ratio of ∼1.2 throughout the film. The lower bandgap, low roughness, and thermal stability of ALD TaN compared to AlO x suggest the possibility of fabricating JJs with thicker barriers while achieving critical current densities required for qubits, enabling improved thickness and composition control, reduced topography, and resistance to aging.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Synthesis of motif and symmetry for accelerated learning, discovery, and design of electronic structures for energy conversion applications (Final Technical Report)

The overall goal of the projects is to develop a framework to incorporate structure motifs and crystal/orbital symmetries into the data-driven materials discovery infrastructure. The PI proposed to develop structure-motif- and symmetry-based graph convolutional networks for effective learning and efficient predictions of electronic structures and related properties. Fundamental understanding of the roles of structure motif and symmetry will establish new hypothesis and design rules, which will be combined with high-throughput computations based on density functional theory to discover novel light absorbers, transparent conductors, as well as 2D light emitting materials and heterojunctions for optoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Molecular theory capability: LANL-PEM-Atomic implements universal descriptions of molecular photoionization

Photoionization of atomic ions, the process through which atoms in bound states absorb radiation by losing electrons, is a vital part of describing radiative transfer in mission-relevant dynamics. The photoionization of molecules dominates radiative transfer of ultraviolet (UV) and extreme UV (EUV) radiation in colder atmospheres (temperature < 30,000 degrees Kelvin). Consequently, air, which is quite transparent to our eyes (i.e., in the visible frequency regime) is remarkably opaque to radiation in much of the UV and EUV frequency regimes. This opacity makes air and other gas systems quite efficient at absorbing UV and EUV radiation, which heats the gas until ionization makes it transparent. This effect is important in describing a host of relevant phenomena, ranging from charge separation in high-altitude nuclear events and the dynamics of a nuclear fireball to the electrostatic discharges (sparks) that complicate weapons disassembly at Pantex.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Distinct Optical Excitation Mechanisms of a Coherent Magnon in a van der Waals Antiferromagnet

The control of antiferromagnets with ultrashort optical pulses has emerged as a prominent field of research. Tailored laser excitation can launch coherent spin waves at terahertz frequencies, yet a comprehensive description of their generation mechanisms is still lacking despite extensive efforts. Using terahertz emission spectroscopy, we investigate the generation of a coherent magnon mode in the van der Waals antiferromagnet NiPS 3 under a range of photoexcitation conditions. By tuning the pump photon energy from transparency to resonant with a 𝑑−𝑑 transition, we reveal a striking change in the coherent magnon’s dependence on the pump polarization, indicating two distinct excitation mechanisms. Furthermore, our findings provide a strategy for the manipulation of magnetic modes via photoexcitation around subgap electronic states.

Light-induced magnetic effects↗
DOE OSTI2026

Collaborative R&D with REEL Solar Inc (REEL) to Understand and Overcome Performance Limitations in CdTe Solar Cells: Cooperative Research and Development (Final Report)

This CRADA will focus on processing, advanced characterization, and testing of photovoltaic materials and devices to understand and improve REEL CdTe solar technology. This will include examining process variations and different buffer, absorber, and contact layers from REEL and NLR to maximize performance. The unique and diverse advanced characterization tools at NLR, such as time-resolved photoluminescence, capacitance-voltage measurements, electron beam scattered diffraction, cathodoluminescence, electron microscopy, TOF-SIMS, and other measurements will be applied to characterize REEL processing to improve understanding and guide experimental directions. Accelerated stability and potential induced degradation tests will be used to analyze metastability, short-and-long term degradation, and improve bankability. A second and major thrust this period will be joint development of Si/CdTe tandem solar cells to overcome industry wide terrestrial solar efficiency limits with the two lowest cost and manufacturable solar materials today. This will include developing novel transparent back contacts that can be incorporated into tandem structures and other novel solar applications, detailed analysis of designs and configurations for CdTe/Si tandem modules, and prototyping REEL CdTe Technology with Si bottom cells in tandem structures.

14 SOLAR ENERGY↗
DOE OSTI2023

The Future Electron-Ion Collider

Generalized Parton Distributions include rich information and became a powerful tool for studying hadron structure. Deeply Virtual Compton Scattering is the golden channel to access GPDs. The development of high luminosity and high-acceptance detectors (Electron-Ion Collider) allows physicists to overcome the difficulty of DVCS measurements. The outstanding performance of the accelerator performs the eA collisions at the center of mass energy from 20 to 140 GeV, while the luminosity at the scale of 1034 cm?2s?1. The new type of high-density crystal, PWO-II, produced by CRYTUR in 2×2×20 cm3 will be utilized in the calorimeter. The transparency of PWO-II crystals is > 70% at 620 nm, > 60% at 420 nm, and >35% at 360 nm. The crystals also show good radiation hardness under 30 Gy radiation exposure. Ten PWO-II crystals have a uniform light yield at 30 p.e./MeV, providing sufficient light yield to reduce the fluctuation of the energy measurements. Near 3000 crystals were constructed inside the 12-sided polygon supporting structure in the simulation. The island clustering algorithm was used for reconstructed the energy. The energy resolution study by the particle gun shows the stochastic term and constant term are 1.8% and 1.2%, respectively. The spatial resolution of NEEMC varies from 5% to 15% of the crystal?s width depending on the particle?s incident angle. The pion rejection of NEEMC can reach 103 with electron efficiency > 85% when the particle?s energy is larger than 1GeV. The Pi0- identified efficiency study can be interpreted as finding the local maxima in the single cluster caused by two high energy close photons. The study results show that efficiency is nearly 100% for pi0 energy is smaller than 10 GeV, and efficiency drops to 30% with 20 GeV pi0. The new type of 3x3 pixelated AC-LGAD were wire bonded to ALTIROC for performance test. The cross-talk between the adjacent channels is about 20% for VPA and 10% for TZ. A series of the TDC characteristic measurements show that the jitter for both preamplifiers is about 20 ps, and the time-walk effect is mild for inject charge > 12 pF. Furthermore, the beta source radiation results quantify the sharing scale of the 3x3 pixels AC-LGAD (? 20%). The electronics simulation study results show no significant changes in the spatial resolution, whether ADC resolution is 8, 10, or 12 bits. The 8-bit ADC is decided to use in the EICROC as it has a smaller size and power consumption than the 10-bit and 12-bit ADC. The ECCE is one of the full detector proposals for EIC. The new type of DVCS generator, called TOPEG, is used to generate the high acceptance beam configurations of 18×110 GeV2 electron and 4He. The acceptance study shows a -1.8 < ? < -1.4 gap between the BEMC and EEMC. The 10?x,y geometry cut is applied on the Roman Pots, so the acceptance of Roman Pots quickly drops to 0% when the polar angle of the recoiled 4He < 2 mrad. This primary ECCE simulation study suggests extending the acceptance of BEMC longitudinally as the structure limits the radial size of EEMC. The acceptance of the Roman Pots is still challenging. In 2023, The overall design of ePIC was finalized by merging two full detector proposals (ECCE and ATHENA) after a series of intensive simulation studies.

Wang, Pu-Kai↗
DOE OSTI2023

BiVO 4 –Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

BiVO 4 is an important photoanode material for water oxidation, but its photoelectrochemistry regarding the triiodide/iodide redox couple is not well understood. Here, we use a combination of open circuit potential measurements, photoelectrochemical scans, and liquid surface photovoltage spectroscopy (SPS) to confirm that BiVO 4 /triiodide/iodide electrolyte contacts produce up to 0.55 V photovoltage under 23 mW/cm –2 illumination from a 470 nm LED. Inspired by these results, we construct FTO/BiVO 4 /KI(I 2 ) aq /Pt sandwich photoelectrochemical cells from electrochemically grown 0.5 × 0.5 cm 2 BiVO 4 and Mo-doped BiVO 4 films. Under AM 1.5 illumination, the devices have up to 0.22% energy conversion efficiency, 0.32 V photovoltage, and 1.8 mA cm –2 photocurrent. Based on SPS, hole transfer to iodide is sufficiently fast to prevent the competing water oxidation reaction. Mo doping increases the incident photon-to-current efficiency to up to 55% (at 425 nm under front illumination) by improving the BiVO 4 conductivity, but this comes at the expense of a lower photovoltage resulting from recombination at the Mo defects and a detrimental Schottky junction at the interface with FTO. Additional photovoltage losses are caused by the offset between the BiVO 4 valence band edge and the triiodide/iodide electrochemical potential and by electron back transfer to iodide at the FTO back contact (shunting). Overall, this work provides the first example of a BiVO 4 –liquid photovoltaic cell and an analysis of its limitations. Finally, even though the larger band gaps of metal oxides constrain their solar energy conversion efficiency, their transparency to visible light and deep valence bands makes them suitable for tandem photovoltaic devices.

14 SOLAR ENERGY↗
DOE OSTI2022

Phase tuning of multiple Andreev reflections of Dirac fermions and the Josephson supercurrent in Al–MoTe 2 –Al junctions

When an electron is incident on a superconductor from a metal, it is reflected as a hole in a process called Andreev reflection. If the metal N is sandwiched between two superconductors S in an SNS junction, multiple Andreev reflections (MARs) occur. We have found that, in SNS junctions with high transparency (τ → 1) based on the Dirac semimetal MoTe 2 , the MAR features are observed with exceptional resolution. By tuning the phase difference φ between the bracketing Al superconductors, we establish that the MARs coexist with a Josephson supercurrent I s =I A sin φ. As we vary the junction voltage V, the supercurrent amplitude I A varies in step with the MAR order n, revealing a direct relation between them. Two successive Andreev reflections serve to shuttle a Cooper pair across the junction. If the pair is shuttled coherently, it contributes to I s . The experiment measures the fraction of pairs shuttled coherently vs. V. Surprisingly, superconductivity in MoTe 2 does not affect the MAR features.

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

Uncovering phase transformation, morphological evolution, and nanoscale color heterogeneity in tungsten oxide electrochromic materials

Controlling the electrochemical interfacial processes that govern the durability of electrochromic devices represents a key challenge in developing sustainable and cost-effective smart windows. Here, we revisit the classical tungsten trioxide (WO 3 ) materials as a platform to uncover the previously unknown interrelationship between phase transformation, morphological evolution, and nanoscale color heterogeneity in these materials. Through synchrotron/electron spectroscopic and imaging analyses, we report that the WO 3 –electrolyte interface is influenced by the tungsten dissolution and redeposition during the electrochemical cycling. The tungsten redeposition provokes the in situ crystal growth, which ultimately leads to the phase transformation from the semicrystalline WO 3 to a nanoflake-shaped, proton-trapped tungsten trioxide dihydrate (H x WO 3 · 2 H 2 O). The multidimensional quantification of the electronic structure reveals that the tungsten reduction caused by the proton trapping is heterogeneous at the nanometric scale and is responsible for the nanoscale color heterogeneity. The interplay between phase transformation, morphological evolution, and nanoscale color heterogeneity results in degraded optical modulation, switching kinetics, coulombic efficiency, and bleached-state transparency. Our results highlight that the high interfacial reactivity near the electrode surface may be the underlying mechanism for undesired bulk structural changes of electrochromic materials, and calls for fundamental studies in probing and controlling the electrode–electrolyte interfacial processes in electrochromic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Resonant propagation of x rays from the linear to the nonlinear regime

We present a theoretical study of temporal, spectral, and spatial reshaping of intense, ultrafast x-ray pulses propagating through a resonant medium. Our calculations are based on the solution of a three-dimensional time-dependent Schrodinger-Maxwell equation, with the incident x-ray photon energy on resonance with the core-level is-3p transition in neon. We study the evolution of the combined incident and medium-generated field, including the effects of stimulated emission, absorption, ionization, and Auger decay, as a function of the input pulse energy and duration. We find that stimulated Raman scattering between core-excited states 1s -1 3p and 2p -1 3p occurs at high x-ray intensity, and that the emission around this frequency is strongly enhanced when also including the similar 1s -1 -2p -1 response of the ion. We also explore the dependence of x-ray self-induced transparency (SIT) and self-focusing on the pulse intensity and duration, and we find that the stimulated Raman scattering plays an important role in both effects. Finally, we discuss how these nonlinear effects may potentially be exploited as control parameters for pulse properties of x-ray free-electron laser sources.

74 ATOMIC AND MOLECULAR PHYSICS↗