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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Strain-Driven Evolution of Structural and Carrier Recombination Dynamics in Germanium

Strain engineering in group-IV semiconductors, in particular germanium (Ge), offers a promising route for advancing next-generation optoelectronic device performance. High minority carrier lifetime serves as a direct indicator of superior material quality and device efficiency. Several factors govern the minority carrier lifetime in both strained Ge and strained GeSn, such as strain level, epilayer thickness, defects, surface roughness, and Sn alloying. In this study, the impact of biaxial strain on effective minority carrier lifetimes of tensile-strained Ge (0% ..epsilon..-Ge/Al?As, 0.78% ..epsilon..-Ge/In0.115?Ga0.885?As, and 0.93% ..epsilon..-Ge/In0.16?Ga0.84?As) and compressively strained GeSn (-0.53% c-Ge0.97?Sn0.03/Al?As) epilayers, grown by molecular beam epitaxy, was experimentally investigated via the microwave-reflection photoconductive decay (..mu..-PCD) technique as a simultaneous function of thickness and strain. The structural and strain-relaxation properties were analyzed by high-resolution x-ray diffraction and Raman spectroscopy, while surface morphology analysis using atomic force microscopy provided insights into the surface roughness of strained Ge-based epilayers. Defect characterization by cross-section transmission electron microscopy revealed superior crystalline quality of ..epsilon..-Ge in one epilayer, while twin boundary formation was observed in the other. We investigated the carrier recombination dynamics in epitaxially strained Ge by extracting the bulk recombination lifetime and surface recombination velocity using the thickness-dependent minority carrier lifetime. High effective minority carrier lifetimes of approximately 60-340 ns were achieved at high strain levels with minimal dependence on the thickness of the strained Ge-based epilayers by means of the ..mu..-PCD technique. Minority carrier lifetimes in Ge-based epilayers exhibit a quadratic dependence on the biaxial strain, ranging from -0.88% (compressive) to +1.6% (tensile). The analysis of the carrier recombination dynamics in strained Ge-based heterostructures offers a pathway to designing group-IV based optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Picosecond lifetime measurements of resonances using a thick-target invariant-mass technique

Here, a new technique is presented for measuring the half-lives of resonances in the picosecond range using presently available invariant-mass apparatus and a thick target. For short-lived resonances, the energy losses of the decay fragments in the target material change their relative velocities giving rise to a poor invariant-mass resolution. However, for longer-lived resonances that travel through the remaining target material before decaying outside of the target, this dominant contribution to the resolution is eliminated. The measured invariant-mass peak will then display a narrow peak from these events which sits on a wider structure associated with the remaining events that decay in the target. The fraction of the events in the narrow peak is related to the probability that the resonance leaves the target before decaying and hence is related to the lifetime. This technique is exercised for the 2.685-MeV resonance in 33 Cl which decays by emitting an f -wave proton. A half-life of T 1/2 =5.7$^{+4.1}_{-2.5}$ ps was measured which is consistent with values inferred from other known properties of this resonance.

lifetimes & widths↗
DOE OSTI2024

Midgap state requirements for optically active quantum defects

Abstract Optically active quantum defects play an important role in quantum sensing, computing and communication. The electronic structure and the single-particle energy levels of these quantum defects in the semiconducting host have been used to understand their optoelectronic properties. Optical excitations that are central for their initialization and readout are linked to transitions between occupied and unoccupied single-particle states. It is commonly assumed that only quantum defects introducing levels well within the band gap and far from the band edges are of interest for quantum technologies as they mimic an isolated atom embedded in the host. In this perspective, we contradict this common assumption and show that optically active defects with energy levels close to the band edges can display similar properties. We highlight quantum defects that are excited through transitions to or from a band-like level (bound exciton) such as the T center and Se S i + in silicon. We also present how defects such as the silicon split-vacancy in diamond can involve transitions between localized levels that are above the conduction band or below the valence band. Loosening the commonly assumed requirement on the electronic structure of quantum defects offers opportunities in quantum defects design and discovery especially in smaller band gap hosts such as silicon. We discuss the challenges in terms of operating temperature for photoluminescence or radiative lifetime in this regime. We also highlight how these alternative type of defects bring their own needs in terms of theoretical developments and fundamental understanding. This perspective clarifies the electronic structure requirement for quantum defects and will facilitate the identification and design of new color centers for quantum applications especially driven by first principles computations.

Xiong, Yihuang (ORCID:0000000178096047)↗
DOE OSTI2021

Anthraquinone Flow Battery Reactants with Nonhydrolyzable Water-Solubilizing Chains Introduced via a Generic Cross-Coupling Method

Water-soluble anthraquinones (AQs) hold great promise serving as redox-active species in aqueous organic flow batteries. Systematic investigations into how the properties of redox molecules depend on the water-solubilizing groups (WSGs) and the way in which they are bound to the redox core are, however, still lacking. We introduce WSGs linked to anthraquinone by C=C bonds via a cross-coupling reaction and convert C=C to C–C bonds through hydrogenation. The anthraquinone and the WSGs are connected via (un)branched chains with (un)saturated bonds. We investigate the influence of chains and ionic ending groups on the redox potentials of the molecules and identify three important trends: (1) The electron-withdrawing ending groups can affect the redox potentials of AQs with two unsaturated hydrocarbons on the chains through π-conjugation. (2) For chains with two (un)saturated straight hydrocarbons, WSGs increase the redox potentials of the AQs in the order PO 3 2– < CO 2 – < SO 3 – . (3) AQs with (un)saturated chains at high pH possess desirably low redox potentials, high solubilities, and high stability. Disproportionation leads to the formation of anthrone, which can be regenerated to anthraquinone. Tautomerization results in the saturation of alkene chains, stabilizing the structure. Here, we utilize these observations to identify a potentially low-cost and long-lifetime negative electrolyte that demonstrates a temporal fade rate as low as 0.0128%/day when paired with a potassium ferrocyanide positive electrolyte.

25 ENERGY STORAGE↗
DOE OSTI2021

Excitonic structure and charge separation in the heliobacterial reaction center probed by multispectral multidimensional spectroscopy

Photochemical reaction centers are the engines that drive photosynthesis. The reaction center from heliobacteria (HbRC) has been proposed to most closely resemble the common ancestor of photosynthetic reaction centers, motivating a detailed understanding of its structure-function relationship. The recent elucidation of the HbRC crystal structure motivates advanced spectroscopic studies of its excitonic structure and charge separation mechanism. We perform multispectral two-dimensional electronic spectroscopy of the HbRC and corresponding numerical simulations, resolving the electronic structure and testing and refining recent excitonic models. Through extensive examination of the kinetic data by lifetime density analysis and global target analysis, we reveal that charge separation proceeds via a single pathway in which the distinct A 0 chlorophyll a pigment is the primary electron acceptor. In addition, we find strong delocalization of the charge separation intermediate. Our findings have general implications for the understanding of photosynthetic charge separation mechanisms, and how they might be tuned to achieve different functional goals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ground-state and decay properties of neutron-rich 106 Nb

The ground-state properties of neutron-rich 106 Nb and its β decay into 106 Mo have been studied using the CARIBU radioactive-ion-beam facility at Argonne National Laboratory. Niobium-106 ions were extracted from a 252 Cf fission source and mass separated before being delivered as low-energy beams to the Canadian Penning Trap, as well as the X-Array and SATURN β-decay-spectroscopy station. The measured 106 Nb ground-state mass excess of –66202.0(13) keV is consistent with a recent measurement but has three times better precision; this work also rules out the existence of a second long-lived, β-decaying state in 106 Nb above 5 keV in excitation energy. The decay half-life of 106 Nb was measured to be 1.097(21) s, which is 8% longer than the adopted value. Here, the level scheme of the decay progeny, 106 Mo, has been expanded up to ≈ 4 MeV. The distribution of decay strength and considerable population of excited states in 106 Mo of J ≥ 3 emphasizes the need to revise the adopted J π = 1 – ground-state spin-parity assignment of 106 Nb; it is more likely to be J ≥ 3.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurement of the 136 Xe two-neutrino double-β-decay half-life via direct background subtraction in NEXT

Here, we report a measurement of the half-life of the 136 Xe two-neutrino double-β decay performed with a novel direct-background-subtraction technique. The analysis relies on the data collected with the NEXT-White detector operated with 136 Xe-enriched and 136 Xe-depleted xenon, as well as on the topology of double-electron tracks. With a fiducial mass of only 3.5 kg of Xe, a half-life of 2.34$_{-0.46}^{+0.80}$(stat)$_{-0.17}^{+0.30}$(sys)×10 21 yr is derived from the background-subtracted energy spectrum. The presented technique demonstrates the feasibility of unique background-model-independent neutrinoless double-β-decay searches.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

The Case for an EIC Theory Alliance

This documents outlines the case for the creation of an EIC Theory Alliance. The EIC will be a unique and versatile facility that will enable the understanding of some of the most compelling questions in the physics of the strong nuclear force. To fully exploit the potential of the EIC, a focused theory effort will be required. The goal of the EIC Theory Alliance is to provide support and stewardship of the theory effort in EIC physics, broadly defined, over the lifetime of the facility. It will promote EIC theory and contribute to workforce development through: support of graduate students; EIC Theory Fellowships for postdocs; bridge positions at universities; and short and long term visitor programs to enhance collaboration between groups. In addition, the alliance will organize topical schools and workshops. The EIC Theory Alliance will be a decentralized organization, open to participation by anyone in the community who is interested in EIC physics, i.e., it will be a membership organization, where members elect an executive board which will effectively run the alliance. The executive board will determine the major scientific thrusts of the theory alliance, make decisions regarding at which universities bridge faculty positions will be created, and serve as a search committee for EIC-related positions. Furthermore, the executive board will coordinate the organization of workshops and schools related to the research activities of the alliance. In addition, the EIC theory alliance will seek out and nurture international cooperation to maximally leverage the available funding. The EIC theory alliance has a wider range of physics goals and longer lifetime, commensurate with that of the EIC research program, than individual nuclear theory topical collaborations. The structure of the EIC Theory Alliance will build on previous examples of successful alliances in nuclear theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

A digital twin solution for floating offshore wind turbines validated using a full-scale prototype

Abstract. In this work, we implement, verify, and validate a physics-based digital twin solution applied to a floating offshore wind turbine. The digital twin is validated using measurement data from the full-scale TetraSpar prototype. We focus on the estimation of the aerodynamic loads, wind speed, and section loads along the tower, with the aim of estimating the fatigue lifetime of the tower. Our digital twin solution integrates (1) a Kalman filter to estimate the structural states based on a linear model of the structure and measurements from the turbine, (2) an aerodynamic estimator, and (3) a physics-based virtual sensing procedure to obtain the loads along the tower. The digital twin relies on a set of measurements that are expected to be available on any existing wind turbine (power, pitch, rotor speed, and tower acceleration) and motion sensors that are likely to be standard measurements for a floating platform (inclinometers and GPS sensors). We explore two different pathways to obtain physics-based models: a suite of dedicated Python tools implemented as part of this work and the OpenFAST linearization feature. In our final version of the digital twin, we use components from both approaches. We perform different numerical experiments to verify the individual models of the digital twin. In this simulation realm, we obtain estimated damage equivalent loads of the tower fore–aft bending moment with an accuracy of approximately 5 % to 10 %. When comparing the digital twin estimations with the measurements from the TetraSpar prototype, the errors increased to 10 %–15 % on average. Overall, the accuracy of the results is promising and demonstrates the possibility of using digital twin solutions to estimate fatigue loads on floating offshore wind turbines. A natural continuation of this work would be to implement the monitoring and diagnostics aspect of the digital twin to inform operation and maintenance decisions. The digital twin solution is provided with examples as part of an open-source repository.

17 WIND ENERGY↗
DOE OSTI2023

NOTCH EFFECT ON CREEP-FATIGUE BEHAVIOR OF ALLOY 617 AT ELEVATED TEMPERATURE

High-temperature reactor structural components are often under the complex multiaxial creep-fatigue (CF) loading conditions throughout the lifetime because of geometric and/or metallurgical discontinuities and complex loading paths. To assess the multiaxial CF deformation behavior and to evaluate the CF design rules in the ASME BPVC Section III, Division 5, Subsection HB, Subpart B, experimental and numerical studies are performed on Alloy 617 at 950°C using notch specimen geometries under CF loading in this study.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

MARVEL Utilization Plan

This report provides a high-level overview of the operational plan for the MARVEL microreactor. The main focus is on discussing testing and application demonstration opportunities that leverage the reactor. With the reactor rapidly progressing towards demonstration, along with the short operational window (2 years), it was deemed critical to start establishing a basis for how stakeholders can engage with the program and leverage the reactor as a testbed. The report discusses potential opportunities for using MARVEL leveraging from data/design access, novel controls testing, novel nuclear-electric applications, to novel nuclear-heat applications. It also provides guidance for interested stakeholders on potential funding opportunities that can be pursued to support tests during the operational lifetime of the reactor. The report also discusses the recommended strategy for outreach and the organization structure to review and down select project. It is important to emphasize that this is intended to be a living document with revisions issued as the MARVEL demonstration timeline evolves. Similarly, the framework for engagement is subject to change as the project nears construction. As such, this first revision to the original test plan highlights the new Microreactor Program-sponsored pathway for engaging with stakeholders via an Expression of Interest and Notice of Opportunity.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

CdSexTe1-x /CdTe Devices With Reduced Interface Recombination Through Novel Back Contacts and Doping Strategies

In order to study rear interface recombination in CdSexTe1-x/CdTe solar cells, several back contact structures were fabricated using combinations of tellurium, alumina, amorphous silicon, and indium tin oxide. Film side Time-Resolved Photoluminescence measurements were taken to measure carrier lifetimes and interface recombination at the back interface. We show increasingly improved interface passivation through the subsequent use of alumina, amorphous silicon, and ITO. Additionally, we provide evidence that an arsenic-doped absorber forms a better interface with numerous back contact structures. Reductions in the back interface recombination velocity are shown to correlate with improvements in device external radiative efficiency.

13 HYDRO ENERGY↗
DOE OSTI2023

Photo-excited charge carrier lifetime enhanced by slow cation molecular dynamics in lead iodide perovskite FAPbI3

Using muon spin relaxation measurements on formamidinium lead iodide [FAPbI3, where FA denotes HC(NH2)2], we show that, among the five structurally distinct phases of FAPbI3 exhibited through two different temperature hysteresis, the reorientation motion of FA molecules is quasi-static below ≈50 K over the time scale of 10−6 s in the low-temperature (LT) hexagonal (Hex-LT, <160 K) phase, which has a relatively longer photo-excited charge carrier lifetime (τc∼10−6 s). In contrast, a sharp increase in the FA molecular motion was found above ≈50 K in the Hex-LT phase, LT-tetragonal phase (Tet-LT, <140 K), the high-temperature (HT) hexagonal phase (Hex-HT, 160–380 K), and the HT-tetragonal phase (Tet-HT, 140–280 K), where τc decreases with increasing temperature. More interestingly, the reorientation motion is further promoted in the cubic phase at higher temperatures (>380/280 K), while τc is recovered to comparable or larger than that of the LT phases. These results indicate that there are two factors that determine τc, one related to the local reorientation of cationic molecules that is not unencumbered by phonons and the other to the high symmetry of the bulk crystal structure.

Physics↗
DOE OSTI2025

Build-to-Replace Strategy to Reduce Operations and Maintenance Costs for Advanced Reactors

This paper targets the reduction of fixed operations and maintenance (O&M) costs for advanced reactor (AR) designs. This goal will be severely constrained if the underlying assumptions of O&M approaches and practices are not questioned and reexamined, especially today when changes can be implemented effectively and efficiently. Achieving a reduction in AR O&M costs requires a completely new way of thinking -a paradigm shift- not through incremental, technology-focused approaches alone. Here, we address this challenge by evaluating the impact of moving to a shorter design life for major structures, systems, and components and shorter, more predictable refurbishment cycles as modeled by the commercial airline industry: the build-to-replace approach. This paper provides a brief overview of this different mindset to O&M applied to ARs and it provided a set of analytical tools based on multi-objective optimization to identify the benefits of such an approach. In conclusion, we provide a direct example analysis of a build-to-replace scenario by identifying and evaluating scenarios for reduced system and component lifetimes and associated replacement and refurbishment schedules to evaluate impacts on O&M costs and other lifecycle elements, such as structure, system, and component reliability.

97 - MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Abrupt structural transition in exotic molybdenum isotopes unveils an isospin-symmetric island of inversion

Like electrons in atoms, protons and neutrons in nuclei occupy orbitals in a shell structure with energy gaps at magic numbers. Radioactive-beam experiments revealed the disappearance of magic numbers in some neutron-rich isotopes. In these nuclei, configurations involving particles excited across the shell gap gain correlation energy, becoming the ground state. Neutron-rich regions of the nuclear chart that exhibit this property are known as “Islands of Inversion”. Here we present the lifetime measurement of the first 2 + states in 84 Mo (N = Z) and 86 Mo (N = Z + 2) revealing an unexpected sharp structural change between them defining the edge of the region of deformation around 80 Zr. Similarly to the neutron-rich N = 40 Island of Inversion near 64 Cr where cross-shell excitations dominate, we identify this region as an Island of Inversion with symmetrical proton and neutron excitations that we term “Isospin-Symmetric Island of Inversion”. Three-nucleon forces are suggested to drive Mo isotope structural changes.

experimental nuclear physics↗
DOE OSTI2022

Structural and optical properties of cubic GaN on U-grooved Si (100)

Cubic GaN epitaxy on large-area U-grooved silicon (100) dies is demonstrated by metalorganic chemical vapor deposition, and its structural and optical properties are reported. Scanning electron, atomic force, and transmission electron microscopy studies reveal that cubic GaN shows no discernible threading dislocations and a low stacking fault density of 3.27 ± 0.18 × 10 4 cm –1 . Temperature-dependent photoluminescence studies reveal as-grown cubic GaN band edge emission internal quantum efficiency as 25.6% ± 0.9%. Selective etching of the low-temperature AlN buffer layer, SiO 2 sidewalls, and hexagonal-phase GaN is demonstrated, which increases the cubic GaN band edge emission internal quantum efficiency to 31.6% ± 0.8%. This increase is attributed to the decrease in the radiative recombination lifetime via the removal of defective hexagonal-phase GaN. Altogether, cubic GaN on U-grooved silicon with high structural and optical quality is reported, promising its suitability for next-generation devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Photocarrier Dynamics in TlGaS 2 Nanoflakes and van der Waals Heterostructures with Hexagonal Boron Nitride and WS 2 Nanoflakes: Implications for Optoelectronic Applications

We present an experimental investigation on photocarrier dynamics in a TlGaS 2 bulk crystal and its heterostructures with hexagonal BN and WS 2 . The samples were obtained by mechanical exfoliation and dry transfer techniques. The photocarrier dynamics was monitored by a transient absorption technique. We observed a direct optical transition of about 555 nm in the TlGaS 2 crystal. By utilizing transient absorption of that transition, we obtained a hot-carrier energy relaxation time of less than 1 ps and a carrier lifetime of about 300 ps in TlGaS 2 at room temperature. In the hexagonal-BN-TlGaS 2 heterostructure, the photocarrier dynamics was similar to that in TlGaS 2 , indicating the type-I band alignment of this structure with both band extremes located in TlGaS 2 . In the monolayer WS 2 -TlGaS 2 heterostructure, we observed charge transfer from TlGaS 2 to WS 2 and an extended lifetime of the transferred carriers in WS 2 . Here, these results introduce TlGaS 2 as a promising layered material for developing two-dimensional van der Waals materials that can be combined with other two-dimensional materials for various optoelectronic devices.

36 MATERIALS SCIENCE↗