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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Spectroscopic Characterisation of a Bio-Inspired Ni-Based Proton Reduction Catalyst Bearing a Pentadentate N 2 S 3 Ligand with Improved Photocatalytic Activity

Inspired by the sulfur-rich environment found in active hydrogenase enzymes, a Ni-based proton reduction catalyst with pentadentate N 2 S 3 ligand was synthesised. When coupled with [Ru(bpy) 3 ] 2+ (bpy=2,2 '-bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N 2 S 2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time-resolved X-ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. Furthermore, the Ni-II catalyst undergoes a photoinduced metal-centred reduction to form a Ni-I intermediate with distorted square-bipyramidal geometry. Further kinetic analyses revealed differences in charge-separation dynamics between the pentadentate and tetradentate forms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Controlled Pyroshock Transients Can Be Used To Better Match Operational Shock Transients and Improve Shock Analysis and Testing

SRS analysis and testing to SRS is known to be conservative since SRS is generated from maxi-max shock transient data, maximum peaks are assumed to occur for each mode simultaneously, and the structural dynamics are not accounted for between the shock source and the test article. Knowing the structural dynamics of a shock test setup it is possible to subscribe a force shock transient applied at a particular strike location and direction to achieve a desired shock transient at a test reference accelerometer. The SRS at this test accelerometer reference location can be used to compare to the reference SRS, but the key reference is the shock transient not the SRS, which should lead to more realistic shock testing that better matches operational shock transient data and reduces artificial test failures that don’t occur in operational usage. The desired test shock transient should match operational shock transients. As such, the test shock transient should look similar to the operational shock transient and have similar positive and negative peaks, the same shape, and the same duration. Many shock transients can be created that satisfy an SRS, but better control of these shock transient parameters is needed to better match operational shock transients so that more realistic and less conservative shock testing can be performed. Three different shock transients are presented that satisfy a given SRS and the results are compared for an electronic board (test article) attached to a circular shock resonance test plate.

SRS, shock transient, frequency domain, FRF↗
DOE OSTI2021

Excitonic Dynamics in Janus MoSSe and WSSe Monolayers

We report here details of steady-state and time-resolved spectroscopy of excitonic dynamics for Janus transition metal dichalcogenide monolayers, including MoSSe and WSSe, which were synthesized by low-energy implantation of Se into transition metal disulfides. Absorbance and photoluminescence spectroscopic measurements determined the room-temperature exciton resonances for MoSSe and WSSe monolayers. Transient absorption measurements revealed that the excitons in Janus structures form faster than those in pristine transition metal dichalcogenides by about 30% due to their enhanced electron–phonon interaction by the built-in dipole moment. Here, by combining steady-state photoluminescence quantum yield and time-resolved transient absorption measurements, we find that the exciton radiative recombination lifetime in Janus structures is significantly longer than in their pristine samples, supporting the predicted spatial separation of the electron and hole wave functions due to the built-in dipole moment. These results provide fundamental insight in the optical properties of Janus transition metal dichalcogenides.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ab-initio simulations of coherent phonon-induced pumping of carriers in zirconium pentatelluride

Abstract Laser-driven coherent phonons can act as modulated strain fields and modify the adiabatic ground state topology of quantum materials. Here we use time-dependent first-principles and effective model calculations to simulate the effect of the coherent phonon induced by strong terahertz electric field on electronic carriers in the topological insulator ZrTe 5 . We show that a coherent A 1g Raman mode modulation can effectively pump carriers across the band gap, even though the phonon energy is about an order of magnitude smaller than the equilibrium band gap. We reveal the microscopic mechanism of this effect which occurs via Landau–Zener-Stückelberg tunneling of Bloch electrons in a narrow region in the Brillouin zone center where the transient energy gap closes when the system switches from strong to weak topological insulator. The quantum dynamics simulation results are in excellent agreement with recent pump-probe experiments in ZrTe 5 at low temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Low voltage AC electroluminescence in silicon MOS capacitors

Low power silicon based light source and detector are attractive for on-chip photonic circuits given their ease of process integration. However, conventional silicon light emitting diodes emit photons with energies near the band edge where the corresponding silicon photodetectors lack responsivity. On the other hand, previously reported hot carrier electroluminescent silicon devices utilizing a reverse biased diode require high operating voltages. Here, we investigate hot carrier electroluminescence in silicon metal–oxide–semiconductor capacitors operating under transient voltage conditions. Further, during each voltage transient, large energy band bending is created at the edge of the source contact, much larger than what is achievable at a steady state. As a result, electrons and holes are injected efficiently from a single source contact into the silicon channel at the corresponding voltage transient, where they subsequently undergo impact ionization and phonon-assisted interband recombination. Notably, we show low voltage operation down to 2.8 V by using a 20 nm thick high-κ gate dielectric. We show further voltage scaling is possible by reducing the gate dielectric thickness, thus presenting a low voltage platform for silicon optoelectronic integrated circuits.

42 ENGINEERING↗
DOE OSTI2024

Nanoscale polarization transient gratings

Light manipulation at the nanoscale is essential both for fundamental science and modern technology. The quest to shorter lengthscales, however, requires the use of light wavelengths beyond the visible. In particular, in the extreme ultraviolet regime these manipulation capabilities are hampered by the lack of efficient optics, especially for polarization control. Here, we present a method to create periodic, polarization modulations at the nanoscale using a tailored configuration of the FERMI free electron laser and demonstrate its capabilities by comparing the dynamics induced by this polarization transient grating with those driven by a conventional intensity grating on a thin ferrimagnetic alloy. While the intensity grating signal is dominated by the thermoelastic response, the polarization grating excitation minimizes it, uncovering helicity-dependent responses previously undetected. We anticipate nanoscale polarization transient gratings to become useful for the study of physical, chemical and biological systems possessing chiral symmetry.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Excited State Covalency, Dynamics, and Photochemistry of Square Planar Ni-Thiolate Complexes Revealed by Ultrafast X-ray Absorption

Highly covalent Ni bis(dithiolene) and related complexes provide an ideal platform for investigating the effects of metal–ligand orbital hybridization on excited state character and dynamics. In particular, we focus on the ligand field excited states that dominate the photophysics of first-row transition metal complexes. Here, we investigate if they can be significantly delocalized off the metal center, possibly yielding photochemical reactivity more similar to charge transfer excited states than metal-centered ligand field excited states. Here [Ni(mpo) 2 ] (mpo = 2-mercaptopyridine- N-oxide) provides a representative example for the larger chemical class and is an active electro- and photo-catalyst for proton reduction. A detailed characterization of the excited state electronic structure, dynamics, and photochemistry of [Ni(mpo) 2 ] is presented based on ultrafast transient X- ray absorption spectroscopy at the Ni and S 1s core absorption K-edges. By comparing the ultrafast Ni K-edge absorption to ab initio calculations, we identify an excited state relaxation mechanism where an initial ligand-to-metal charge transfer excitation results in both excited state electron transfer (generating a catalytically relevant reduced photoproduct [Ni(mpo) 2 ] − ) and relaxation to a pseudo-tetrahedral triplet ligand field excited state. From the ultrafast S K-edge absorption, the ligand field excited state is found to be highly delocalized onto the thiolate ligands and a tetrahedral structural distortion is shown to substantially influence the degree of delocalization. The results identify a significant structural coordinate to target when aiming to control the excited state covalency in square planar complexes.

Lim, Hyeongtaek [SLAC National Accelerator Laborat↗
DOE OSTI2025

P–P Coupling with and without Terminal Metal–Phosphorus Intermediates

Terminal metal–phosphorus (M–P) complexes are of significant contemporary interest as potential platforms for P-atom transfer (PAT) chemistry. Decarbonylation of metal–phosphaethynolate (M–PCO) complexes has emerged as a general synthetic approach to terminal M–P complexes. M–P complexes that are stabilized by strong M–P multiple bonds are kinetically persistent and isolable. In the absence of strong M–P stabilization, the formation of diphosphorus-bridged complexes (i.e., M–P–P–M species) is often interpreted as evidence for the intermediacy of reactive, unobserved M–P species. Here, we demonstrate that while diphosphorus complexes can arise from reactive M–P species, P–P coupling can also proceed directly from M–PCO species without the intermediacy of M–P complexes. Photochemical decarbonylations of a pincer-supported Ni (II)–PCO complex at 77 K afford a spectroscopically observed terminal Ni–P complex, which is best described as a triplet, Ni(II)-metallophosphinidene with two unpaired electrons localized on the atomic phosphorus ligand. Thermal annealing of this transient Ni–P complex results in rapid dimerization to afford the corresponding P 2 2– -bridged dinickel complex. Unexpectedly, the same P 2 2– -bridged dinickel complex can also be accessed via a thermally promoted process in the absence of light. The analysis of reaction kinetics, isotope-labeling studies, and computational results indicate that the thermal P–P coupling process proceeds via a noncanonical mechanism that avoids terminal M–P intermediates. Together, these results represent the first observation of P–P coupling from characterized terminal M–P species and demonstrate that terminal M–P intermediates are not required to obtain P–P coupling products. These observations provide critical mechanistic understanding of the activation modes relevant to P-atom transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Nanoscale ultrafast lattice modulation with a free-electron laser

Ultrafast optical laser-based techniques have enabled the probing of atomistic processes at their intrinsic temporal scales with femto- and attosecond resolution. However, the long wavelengths of optical lasers have prevented their interrogation and manipulation with nanoscale spatial specificity. Advances in hard X-ray free-electron lasers have enabled progress in developing X-ray transient-grating spectroscopy, a technique that aims to coherently control elementary excitations with nanoscale X-ray standing waves. Thus far, the realization of this technique at the nanoscale has been a challenge. Here we demonstrate X-ray transient-grating spectroscopy with spatial periods of the order of 10 nm via the subfemtosecond synchronization of two hard X-ray pump pulses at a precisely controlled crossing angle. This creates a thermal grating and preferentially excites coherent longitudinal acoustic phonon modes with the transient-grating wavevector. On probing with a third, variably delayed, X-ray pulse with the same photon energy, time-and-wavevector-resolved measurements of the modulation of the induced scattering intensity provide evidence of ballistic thermal transport at nanometre scales. Finally, these results highlight the potential of X-ray transient gratings as a powerful platform for studying nanoscale transport in condensed matter and the coherent control of nanoscale dynamics.

nonlinear optics↗
DOE OSTI2022

Harmonic Modeling, Data Generation and Analysis of Power Electronics-Interfaced Residential Loads

The share of electronics-based residential load is expected to rise as devices such as variable frequency drives (VFDs), electric vehicle chargers, and inverter-based distributed energy resources (DERs), e.g., photovoltaic (PV) systems become more common. These loads may introduce significant harmonics into power networks that need to be closely studied in order to perform accurate load modeling and forecasting. However, it can be difficult to obtain harmonic-rich voltage and current data - necessary for identifying accurate load models - for residential electrical loads. Recognizing this need, we identify and model a set of electronics-based end-use loads and DERs in an electromagnetic transients program (EMTP) tool for a residence with a single- phase split-phase supply. Further, a procedure is developed to model harmonic interactions between end-use loads connected to the same non-ideal supply voltage in a residential setting. Finally, a harmonic-rich dataset produced via the proposed procedure is utilized to identify frequency coupling matrix (FCM) based load model. Numerical results demonstrate the accuracy of the model, and explore model identifiability with limited data points.

harmonics, power quality, load modeling↗
DOE OSTI2021

pnnl/pecblocks

ConverterBlocks uses the output of detailed electromagnetic transient (EMT) simulations to produce generalized block diagram models of power electronic systems. The process uses deep learning with customized block architectures. The outputs are reduced-order models that meet specified accuracy requirements, while providing important advantages over the original EMT models: ConverterBlock models have fewer nodes and can take longer time steps, resulting in shorter simulation times ConverterBlock models are continuously differentiable, making them compatible with control design methodsGeneralized block diagram modeling of power electronic converters for grid solar and storage applications.

McDermott, Tom↗
DOE OSTI2025

Organic Direct-Bonded-Copper-Based Rapid Prototyping for Silicon Carbide Power Module Packaging

Silicon carbide (SiC) power devices are playing ever- growing roles in high-power-density power electronics converters by offering benefits such as high voltage rating, fast transients, and high thermal performance. Organic direct-bonded copper (ODBC)-based packaging, due to its ductility and ease of han- dling, allows the possibility of a more flexible layout design that may better tap the potential of SiC benefits. In this work, an ODBC-based prototyping routine is developed that accelerates the iterations of packaging layout design with low cost. The properties of ODBC and its handling are briefly introduced, and tools and fabrication steps are explained. Following this routine, a 1.2-kV SiC half-bridge power module is designed and fabricated with the focus on sub-nanohenry ultra-low loop inductance. Simulation and experimental validation are also conducted.

25 ENERGY STORAGE↗
DOE OSTI2022

Transient behavior of drift and ionization in atmospheric pressure nitrogen discharge

The fluid models are frequently used to describe a non-thermal plasma such as a streamer discharge. The required electron transport data and rate coefficients for the fluid model are parametrized using the local field approximation (LFA) in first order models and the local-mean-energy approximation (LMEA) in second order models. We performed Monte Carlo simulations in Nitrogen gas with step changes in the E/N (reduced electric field) to study the behavior of the transport properties in the transient phase. During the transient phase of the simulation, we extract the instantaneous electron mean energy, which is different from the steady state mean electron energy, and the corresponding transport parameters and rate coefficients. Our results indicate that the mean electron energy is not a suitable parameter for mobility/drift of electrons due to big difference in momentum relaxation and energy relaxation. Furthermore, the high energy threshold rates such as ionization show a strong correlation to mean electron energy. In second order models where the energy-balance equation is solved, we suggest that it would rather be appropriate to use the local electric field to find electron drift velocity in gases such as Nitrogen and the local mean electron energy to determine the ionization and excitation rates.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Unveiling the underlying interactions in Ta 2 NiSe 5 from photoinduced lifetime change

We present a generic procedure for quantifying the interplay of electronic and lattice degrees of freedom in photodoped insulators through a comparative analysis of theoretical many-body simulations and time- and angle-resolved photoemission spectroscopy (TR-ARPES) of the transient response of the candidate excitonic insulator Ta 2 NiSe 5 . Our analysis demonstrates that the electron-electron interactions dominate the electron-phonon ones. In particular, a detailed analysis of the TR-ARPES spectrum enables a clear separation of the dominant broadening (electronic lifetime) effects from the much smaller band-gap renormalization. Theoretical calculations show that the observed strong spectral broadening arises from the electronic scattering of the photoexcited particle-hole pairs and cannot be accounted for in a model in which electron-phonon interactions are dominant. The competing interactions were quantified using the scaling analysis in the weak fluence regime. We demonstrate that the magnitude of the weaker subdominant band-gap renormalization sensitively depends on the distance from the semiconductor/semimetal transition in the high-temperature state, which could explain the apparent contradictions between various TR-ARPES experiments. The analysis presented here indicates that electron-electron interactions play a vital role (albeit not the sole one) in stabilizing the insulating state, and establishes the comparison between lifetime and gap evolution as an important probe of correlated insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Minimization of thermal deformation in crystal optics for high repetition-rate FEL

Minimizing thermal deformation in X-ray crystal optics is crucial for preserving coherence and wavefront in high-repetition-rate free-electron lasers (FELs). This study presents two approaches to reduce pulse-by-pulse transient thermal deformation in diamond crystals used in cavity-based X-ray FELs (CBXFELs): (1) cryogenic cooling with liquid nitrogen (LN₂), and (2) second-order correction via focusing optics. We revisit the temperature-dependent thermal-mechanical properties of diamond and silicon, implement a finite-element analysis (FEA) method to accelerate convergence to a quasisteady-state regime. Results show that LN₂-cooled diamond crystals meet the stringent deformation requirement of less than 15 pm RMS for the pulse at mJ scale at 1 MHz repetition frequency, and up to 1.5 mJ for 100 kHz. Second-order correction by using focusing elements within the cavity can reduce the impact of thermal deformation for both liquid nitrogen and water cooling.

free electron laser↗
DOE OSTI2021

Measurements of nonequilibrium interatomic forces using time-domain x-ray scattering

Here, we demonstrate an experimental approach to determining the excited-state interatomic forces using femtosecond x-ray pulses from an x-ray free-electron laser. We determine experimentally the excited-state interatomic forces that connect photoexcited carriers to the nonequilibrium lattice dynamics in the prototypical Peierls-distorted material, bismuth. The forces are obtained by a constrained least-squares fit of a pairwise interatomic force model to the excited-state phonon dispersion relation as measured by the time- and momentum-resolved x-ray diffuse scattering. We find that photoexcited carriers weaken predominantly the nearest-neighbor forces, which drives the measured softening of the transverse acoustic modes throughout the Brillouin zone as well as the zone-center A 1g optical mode. This demonstrates a bond-selective approach to measuring electron-phonon coupling relevant to a broad range of photoinduced phase transitions and transient light-driven states in quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Role of deep levels and barrier height lowering in current-flow mechanism in 150 μ m thick epitaxial n-type 4H–SiC Schottky barrier radiation detectors

Schottky barrier detectors (SBDs) require larger surface areas than conventional electronics to increase the detection efficiency although such SBDs manifest large diode ideality factors due to inhomogeneous areal distribution of surface barrier height (SBH). Inhomogeneous SBH distributions lead to various current flow mechanisms in SBDs, which need to be identified to optimize detector performance. In this Letter, we identify the current flow mechanism in large area Schottky barrier diodes for radiation detection fabricated on 150 μm thick n-4H–SiC epitaxial layers. The analysis of temperature-dependent forward current–voltage (I–V–T) characteristics of SBDs revealed two linear regions in current–voltage curves up to 450 K, one corresponding to the current flow through a low barrier patch, while the other corresponds to that of average barrier distribution. Applying a SBH distribution model to the reverse I–V–T characteristics, an activation energy of 0.76 eV for the current flow over the Schottky barrier was calculated. Additionally, the activation energy did not directly correspond to any of the defect levels observed from the deep level transient spectroscopy (DLTS). Above 450 K, a Schottky type barrier lowering suggested a current flow through a low barrier patch of ≈ 0.8 eV. The absence of any SBH lowering below 450 K indicated that the current corresponded to a neutrally charged trap level at ≈ 0.6 eV below the conduction band edge, which was consistent with DLTS measurements revealing the presence of an electron trap level Z1/2 at 0.59 eV below the conduction band edge.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Structure of a photosystem I-ferredoxin complex from a marine cyanobacterium provides insights into far-red light photoacclimation

Far-red light photoacclimation (FaRLiP) exhibited by some cyanobacteria allows these organisms to use light of the far-red region of the solar spectrum (700 to 800 nm) for photosynthesis. Part of this process includes the replacement of six photosystem I (PSI) subunits with isoforms that confer the binding of chlorophyll (Chl) f molecules that are synthesized by chlorophyll f synthase and that absorb far-red light. However, the exact sites at which Chl f molecules are bound are still challenging to determine. To aid in the identification of Chl fbinding sites, we solved the cryo-EM structure of PSI from far-red light-acclimated cells (FRLPSI) of the cyanobacterium Synechococcus sp. PCC 7335. We identified six sites that bind Chl f with high specificity, and three additional sites that are likely to bind Chl f at lower specificity. All of these binding sites are in the core antenna regions of PSI, and Chl f was not observed among the electron transport cofactors. This structural analysis also reveals both conserved and non-conserved Chl f-binding sites, the latter of which exemplify the diversity in FRL-PSI among species. We found that the FRL-PSI structure also contains a bound soluble ferredoxin, PetF1, at low occupancy, which suggests that ferredoxin binds less transiently than expected according to the canonical view of ferredoxin-binding to facilitate electron transfer. We suggest that this may result from structural changes in FRL-PSI that occur specifically during FaRLiP.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗