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Results for “transient electronics”

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

Mammalian complex III heme dynamics studied with pump-probe spectroscopy and red light illuminations

The electronic or molecular mechanisms which initiate photobiomodulation (PBM) in cells are not yet fully understood. Porcine complex III (C-III) of the electron transport chain was characterized with transient absorption spectroscopy (TAS). Then we applied our recently developed continuous wave laser coupled TAS procedure (CW-TAS) to investigate the effect of red light irradiances on the heme dynamics of C-III in its c 1 reduced state. The time constants associated with the axial ligand photodissociation were found to be 3.3 ± 0.3 ps for the oxidized state and 4.9 ± 0.4 ps for the c 1 reduced state. The analysis of the CW-TAS procedure yielded no significant changes in the C-III heme dynamics. We rule out the possibility of 635 nm CW light at 4.7 mW/cm 2 inducing a PBM effect on the heme dynamic of C-III, specifically with the photodissociation of its axial ligand.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Thermal and electromechanical response of ultra-thin carbon-strip polarimeter targets in relativistic bunched beams

Thin carbon-strip targets provide fast relative hadron beam polarimetry, but their response in intense relativistic bunched beams is not governed by local stopping-power heating alone. We develop a coupled response model that combines beam-target overlap, secondary-electron escape, retained heat, target motion, transient heat transport, RF-induced strip-end heating, beam-induced forces, resistance changes, and slack-strip deformation. RHIC target observations constrain the relevant motion, force, and nonlocal-heating scales and show that target survival depends on both beam-center heating and electromagnetic boundary conditions near the strip ends. Applying the model to Booster, AGS, RHIC, and EIC proton and 3 He cases shows that the RHIC proton lifetime scale is reproduced at the order-of-magnitude level, while the RHIC target-holder fin results require the additional RF/end-heating mechanism. For EIC proton flattop operation, carbon-strip polarimetry may remain viable only with reduced dwell time, sufficient detector acceptance, and suppression of RF-induced end heating. For cooled-emittance 3 He, the calculated sublimation-loss scale is far beyond a straightforward RHIC-like carbon-strip extrapolation. Conventional carbon strips are therefore unlikely to remain viable for the most demanding EIC light-ion cases without major changes in target motion, target technology, or diagnostic concept.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Networked HIL Simulation System for Modeling Large-scale Power Systems

This paper presents a network hardware-in-the-loop (HIL) simulation system for modeling large-scale power systems. Researchers have developed many HIL test systems for power systems in recent years. Those test systems can model both microsecond-level dynamic responses of power electronic systems and millisecond-level transients of transmission and distribution grids. By integrating individual HIL test systems into a network of HIL test systems, we can create large-scale power grid digital twins with flexible structures at required modeling resolution that fits for a wide range of system operating conditions. This will not only significantly reduce the need for field tests when developing new technologies but also greatly shorten the model development cycle. In this paper, we present a networked OPAL-RT based HIL test system for developing transmission-distribution coordinative Volt-VAR regulation technologies as an example to illustrate system setups, communication requirements among different HIL test systems, and connection mechanisms. Impacts of communication delays, information exchange cycles, and computing delays are illustrated. Simulation results show that the performance of a networked HIL test system is satisfactory.

digital twin, distribution system, co-simulation, ↗
DOE OSTI2025

Pre-steady-state kinetics of nanocrystal:molybdenum nitrogenase biohybrids reveals hole-scavenging efficiency is critical to N 2 reduction

Molybdenum (Mo) nitrogenase is a two-component enzyme complex that catalyzes the reduction of dinitrogen to ammonia and protons to hydrogen gas. We have shown that electrons for dinitrogen reduction can be delivered photochemically to the catalytic MoFe protein component by cadmium sulfide (CdS) nanocrystals. In this study, we used electron paramagnetic resonance spectroscopy to measure the transient populations of catalytic intermediates. We fit the populations with a pre-steady-state kinetic model, which allowed us to distinguish between productive and non-productive reaction pathways and extract the rate constants for the reaction. Our results demonstrated that the rate of catalytic electron delivery into MoFe protein increased with the concentration of the sacrificial electron donor. This enabled electron delivery to exceed the rate of hydride protonation, a relaxation pathway that competes with N 2 binding. Thus, managing the balance between electron transfer and hole transfer reactions is required to achieve a kinetic regime that favors N 2 reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Kinetic Model of Photochemical Nitrogen Reduction [SWR-25-97]

The code in this repository was used to model the kinetics of photochemical nitrogen reduction. Each directory represents a manuscript. The directory titled Dahl_CRPS_2025 contains the code used to fit the kinetic models presented in the manuscript titled, "Pre-steady-state kinetics of nanocrystal:molybdenum nitrogenase biohybrids reveals hole-scavenging efficiency is critical to achieving N2 reduction" by Peter J. Dahl, Lauren M. Pellows, Zhi-Yong Yang, Lance C. Seefeldt, John W. Peters, Gordana Dukovic, David W. Mulder, and Paul W. King. Molybdenum (Mo) nitrogenase is a two-component enzyme complex that catalyzes the reduction of dinitrogen to ammonia and protons to hydrogen gas. We have shown that electrons for dinitrogen reduction can be delivered photochemically to the catalytic MoFe protein component by CdS nanocrystals. In this study, we used electron paramagnetic resonance spectroscopy to measure the transient populations of catalytic intermediates. We fit the populations with a pre-steady-state kinetic model which allowed us to distinguish between productive and non-productive reaction pathways and extract the rate constants for the reaction. Our results demonstrated that the rate of catalytic electron delivery into MoFe protein increased with the concentration of sacrificial electron donor. This enabled electron delivery to exceed the rate of hydride protonation, a relaxation pathway which competes with N2 binding. Thus, managing the balance between electron transfer and hole transfer reactions is required to achieve a kinetic regime that favors N2 reduction.

Dahl, Peter [National Renewable Energy Laboratory ↗
DOE OSTI2022

Managing photoinduced electron transfer in AgInS2–CdS heterostructures

Ternary semiconductors such as AgInS2, with their interesting photocatalytic properties, can serve as building blocks to design light harvesting assemblies. The intraband transitions created by the metal ions extend the absorption well beyond the bandgap transition. The interfacial electron transfer of AgInS2 with surface bound ethyl viologen under bandgap and sub-bandgap irradiation as probed by steady state photolysis and transient absorption spectroscopy offers new insights into the participation of conduction band and trapped electrons. Capping AgInS2 with CdS shifts emission maximum to the blue and increases the emission yield as the surface defects are remediated. CdS capping also promotes charge separation as evident from the efficiency of electron transfer to ethyl viologen, which increased from 14% to 29%. The transient absorption measurements that elucidate the kinetic aspects of electron transfer processes in AgInS2 and CdS capped AgInS2 are presented. The improved performance of CdS capped AgInS2 offers new opportunities to employ them as photocatalysts.

Kipkorir, Anthony↗
DOE OSTI2024

Validation of Phasor-Domain Transmission and Distribution Co-simulation Against Electromagnetic Transient Simulation

The rapid deployment of renewable energy resources has led to the widespread use of power electronics in modern power systems. As these systems transition from being dominated by large synchronous machines to increasingly incorporating inverter-based resources (IBRs), traditional methods are becoming inadequate. Addressing this challenge, this paper introduces a scalable phasor-domain T\&D co-simulation framework based on open-source software. It focuses on the framework's validation against the PSCAD Electromagnetic Transient (EMT) analysis tool. The validation results demonstrate the framework's high-fidelity and a computational time speed-up of 60 to 100 times, marking a pioneering validation effort in T\&D co-simulation research.

Inverter-based resources, co-simulation, Electroma↗
DOE OSTI2024

Time-Resolved X-ray Emission Spectroscopy and Synthetic High-Spin Model Complexes Resolve Ambiguities in Excited-State Assignments of Transition-Metal Chromophores: A Case Study of Fe-Amido Complexes

To fully harness the potential of abundant metal coordination complex photosensitizers, a detailed understanding of the molecular properties that dictate and control the electronic excited-state population dynamics initiated by light absorption is critical. In the absence of detectable luminescence, optical transient absorption (TA) spectroscopy is the most widely employed method for interpreting electron redistribution in such excited states, particularly for those with a charge-transfer character. The assignment of excited-state TA spectral features often relies on spectroelectrochemical measurements, where the transient absorption spectrum generated by a metal-to-ligand charge-transfer (MLCT) electronic excited state, for instance, can be approximated using steady-state spectra generated by electrochemical ligand reduction and metal oxidation and accounting for the loss of absorptions by the electronic ground state. However, the reliability of this approach can be clouded when multiple electronic configurations have similar optical signatures. Using a case study of Fe(II) complexes supported by benzannulated diarylamido ligands, we highlight an example of such an ambiguity and show how time-resolved X-ray emission spectroscopy (XES) measurements can reliably assign excited states from the perspective of the metal, particularly in conjunction with accurate synthetic models of ligand-field electronic excited states, leading to a reinterpretation of the long-lived excited state as a ligand-field metal-centered quintet state. Furthermore, a detailed analysis of the XES data on the long-lived excited state is presented, along with a discussion of the ultrafast dynamics following the photoexcitation of low-spin Fe(II)-N amido complexes using a high-spin ground-state analogue as a spectral model for the 5 T 2 excited state.

14 SOLAR ENERGY↗
DOE OSTI2022

Coupling Pulse Radiolysis with Nanosecond Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy: Broadband Mid-Infrared Detection of Radiolytically Generated Transients

We describe the first implementation of broadband, nanosecond time-resolved step-scan Fourier transform infrared (S 2 -FT-IR) spectroscopy at a pulse radiolysis facility. This new technique allows the rapid acquisition of nano- to microsecond time-resolved infrared (TRIR) spectra of transient species generated by pulse radiolysis of liquid samples at a pulsed electron accelerator. Wide regions of the mid-infrared can be probed in a single experiment, which often takes < 20–30 min to complete. It is therefore a powerful method for rapidly locating the IR absorptions of short-lived, radiation-induced species in solution, and for directly monitoring their subsequent reactions. Time-resolved step-scan FT-IR detection for pulse radiolysis thus complements our existing narrowband quantum cascade laser-based pulse radiolysis-TRIR detection system, which is more suitable for acquiring single-shot kinetics and narrowband TRIR spectra on small-volume samples and in strongly absorbing solvents, such as water. We have demonstrated the application of time-resolved step-scan FT-IR spectroscopy to pulse radiolysis by probing the metal carbonyl and organic carbonyl vibrations of the one-electron-reduced forms of two Re-based CO 2 reduction catalysts in acetonitrile solution. Transient IR absorption bands with amplitudes on the order of 1 × 10 −3 are easily detected on the sub-microsecond timescale using electron pulses as short as 250 ns.

(S2-FT-IR)↗
DOE OSTI2024

Spatiotemporal dynamics of fast electron heating in solid-density matter via XFEL

Abstract High-intensity, short-pulse lasers are crucial for generating energetic electrons that produce high-energy-density (HED) states in matter, offering potential applications in igniting dense fusion fuels for fast ignition laser fusion. High-density targets heated by these electrons exhibit spatially non-uniform and highly transient conditions, which have been challenging to characterize due to limitations in diagnostics that provide simultaneous high spatial and temporal resolution. Here, we employ an X-ray Free Electron Laser (XFEL) to achieve spatiotemporally resolved measurements at sub-micron and femtosecond scales on a solid-density copper foil heated by laser-driven fast electrons. Our X-ray transmission imaging reveals the formation of a solid-density hot plasma localized to the laser spot size, surrounded by Fermi degenerate, warm dense matter within a picosecond, and the energy relaxation occurring within the hot plasma over tens of picoseconds. These results validate 2D particle-in-cell simulations incorporating atomic processes and provide insights into the energy transfer mechanisms beyond current simulation capabilities. This work significantly advances our understanding of rapid fast electron heating and energy relaxation in solid-density matter, serving as a key stepping stone towards efficient high-density plasma heating and furthering the fields of HED science and inertial fusion energy research using intense, short-pulse lasers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Spectroscopic Investigation of Shallow Hole Traps in Ga- and B-doped Czochralski Silicon: Insight into Light-Induced Degradation

We report the minority carrier lifetime in B-doped Czochralski (Cz) Si declines upon carrier injection due to light-induced degradation (LID), which is attributed to the formation of a recombination-active boron-oxygen complex. Ga-doped Cz Si does not undergo LID. Previously, we showed that B-doped Cz Si undergoes a transition from paramagnetic to diamagnetic due to LID. Herein, we show that Ga-doped Cz Si remains paramagnetic upon carrier injection. This suggests that either the shallow hole traps that are formed in B-doped Cz Si are absent in Ga-doped Cz Si, or the negative-U centers in Ga-doped Cz Si do not transform into a recombination-active configuration, because the shallow acceptor trap state is shallower than the Ga acceptor level in the forbidden gap. In contrast to B-doped Cz Si, the defect signatures in Ga-doped Cz Si do not change upon light exposure, as detected by both electron paramagnetic resonance and deep-level transient spectroscopy.

14 SOLAR ENERGY↗
DOE OSTI2021

Optical transient grating pumped X-ray diffraction microscopy for studying mesoscale structural dynamics

Abstract A fundamental understanding of materials’ structural dynamics, with fine spatial and temporal control, underpins future developments in electronic and quantum materials. Here, we introduce an optical transient grating pump and focused X-ray diffraction probe technique (TGXD) to examine the structural evolution of materials excited by modulated light with a precisely controlled spatial profile. This method adds spatial resolution and direct structural sensitivity to the established utility of a sinusoidal transient-grating excitation. We demonstrate TGXD using two thin-film samples: epitaxial BiFeO 3 , which exhibits a photoinduced strain (structural grating) with an amplitude proportional to the optical fluence, and FeRh, which undergoes a magnetostructural phase transformation. In BiFeO 3 , structural relaxation is location independent, and the strain persists on the order of microseconds, consistent with the optical excitation of long-lived charge carriers. The strain profile of the structural grating in FeRh, in comparison, deviates from the sinusoidal excitation and exhibits both higher-order spatial frequencies and a location-dependent relaxation. The focused X-ray probe provides spatial resolution within the engineered optical excitation profile, resolving the spatiotemporal flow of heat through FeRh locally heated above the phase transition temperature. TGXD successfully characterizes mesoscopic energy transport in functional materials without relying on a specific transport model.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Conversion between triplet pair states is controlled by molecular coupling in pentadithiophene thin films

In singlet fission (SF) the initially formed correlated triplet pair state, 1 (TT), may evolve toward independent triplet excitons or higher spin states of the (TT) species. The latter result is often considered undesirable from a light harvesting perspective but may be attractive for quantum information sciences (QIS) applications, as the final exciton pair can be spin-entangled and magnetically active with relatively long room temperature decoherence times. In this study we use ultrafast transient absorption (TA) and time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy to monitor SF and triplet pair evolution in a series of alkyl silyl-functionalized pentadithiophene (PDT) thin films designed with systematically varying pairwise and long-range molecular interactions between PDT chromophores. The lifetime of the (TT) species varies from 40 ns to 1.5 μs, the latter of which is associated with extremely weak intermolecular coupling, sharp optical spectroscopic features, and complex TR-EPR spectra that are composed of a mixture of triplet and quintet-like features. On the other hand, more tightly coupled films produce broader transient optical spectra but simpler TR-EPR spectra consistent with significant population in 5 (TT) 0 . These distinctions are rationalized through the role of exciton diffusion and predictions of TT state mixing with low exchange coupling J versus pure spin substate population with larger J. The connection between population evolution using electronic and spin spectroscopies enables assignments that provide a more detailed picture of triplet pair evolution than previously presented and provides critical guidance for designing molecular QIS systems based on light-induced spin coherence.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Photodoping of graphene with long-lived electrons by interfacing with Janus WSSe

The performance of semiconductor optoelectronic devices depends on efficient photodoping of active materials, where optical excitation generates photocarriers. Despite more than two decades of research, efficient photodoping in graphene remains elusive due to the formation of neutral excitons with ultrashort lifetimes. Here, by interfacing graphene with a Janus WSSe monolayer, we achieve unipolar photodoping of graphene with long-lived carriers. The Janus monolayer was synthesized via selenium implantation of WS 2 monolayers grown by chemical vapor deposition. We fabricated the heterostructure by transferring a mechanically exfoliated graphene monolayer onto the Se-terminated side of WSSe. Through photoluminescence and transient absorption spectroscopy, we demonstrate that photoexcited electrons in WSSe transfer efficiently to graphene, while a portion of the photoexcited holes remains confined in WSSe due to its built-in electric field. This charge separation leads to a net electron population in graphene. These electrons exhibit extended lifetimes due to spatial separation from their recombination partners, offering a promising route to enhancing the performance of graphene-based optoelectronic devices.

Zheng, Ting [Southeast Univ., Nanjing (China); Uni↗
DOE OSTI2022

Ultrafast Electron Transfer in Au-Cyanobacteria Hybrid for Solar to Chemical Production

The rise of inorganic-biohybrid organisms for solar-to-chemical production has spurred mechanistic investigations into the dynamics of the biotic-abiotic interface to drive the development of next-generation hybrid systems. The model system, cyanobacteria-gold nanoparticle hybrids, combines a light harvester with a photosynthetic bacterium to drive the reduction of CO2 to glycerol with improved efficiency and increased glycerol production by 14.6%, in comparison to cyanobacteria only. In this work, we report insights into this unique photochemical behavior and propose a charge-transfer pathway from Au nanoparticle to cyanobacteria. Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates are on the order of a few ps to the potential electron acceptor in photosystem II. This work represents a promising platform to utilize a conventional spectroscopic methodology to extract insights from more complex biotic-abiotic hybrid systems.

charge transfer↗
DOE OSTI2024

Direct observation of strong momentum-dependent electron-phonon coupling in a metal

Phonon scattering in metals is one of the most fundamental processes in materials science. However, understanding such processes has remained challenging and requires detailed information on interactions between phonons and electrons. We use an ultrafast electron diffuse scattering technique to resolve the nonequilibrium phonon dynamics in femtosecond–laser-excited tungsten in both time and momentum. We determine transient populations of phonon modes which show strong momentum dependence initiated by electron-phonon coupling. For phonons near Brillouin zone border, we observe a transient rise in their population on a timescale of approximately 1 picosecond driven by the strong electron-phonon coupling, followed by a slow decay on a timescale of approximately 8 picosecond governed by the weaker phonon-phonon relaxation process. We find that the exceptional harmonicity of tungsten is needed for isolating the two processes, resulting in long-lived nonequilibrium phonons in a pure metal. Our finding highlights that electron-phonon scattering can be the determinant factor in the phonon thermal transport of metals.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Attosecond spectroscopy reveals alignment dependent core-hole dynamics in the ICl molecule

The removal of electrons located in the core shells of molecules creates transient states that live between a few femtoseconds to attoseconds. Owing to these short lifetimes, time-resolved studies of these states are challenging and complex molecular dynamics driven solely by electronic correlation are difficult to observe. Here, few-femtosecond core-excited state lifetimes of iodine monochloride are obtained by attosecond transient absorption on iodine 4d-16p transitions around 55 eV. Core-level ligand field splitting allows direct access of excited states aligned along and perpendicular to the ICl molecular axis. Lifetimes of 3.5 fs and 4.3 fs are obtained for core-hole states parallel to the bond and 6.5 fs and 6.9 fs for perpendicular states, while nuclear motion is essentially frozen on this timescale. Theory shows that the dramatic decrease of lifetime for core-vacancies parallel to the covalent bond is a manifestation of non-local interactions with the neighboring Cl atom of ICl.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗