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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Plasma-assisted deposition and characterization of Al 2 O 3 dielectric layers on (001) β -Ga 2 O 3

In this work, we have investigated plasma-assisted deposition of Al 2 O 3 on HVPE (001) β-Ga 2 O 3 and evaluated the dielectric quality from electrical measurements on fabricated metal-oxide-semiconductor (MOS) capacitors. The interface structure and crystallinity of the films were investigated as a function of the growth temperature. The dielectric/semiconductor interfaces were found to have reverse breakdown electric fields up to 5.3 MV/cm in the β-Ga 2 O 3 , with relatively low hysteresis in capacitance–voltage and low leakage current. We determined a negative fixed interface charge density at the interface from analysis of thickness-dependent capacitance voltage data. In conclusion, this study shows the advantage of using plasma-assisted deposition to achieve high breakdown strength Al 2 O 3 /β-Ga 2 O 3 MOS structures for device application purposes.

42 ENGINEERING↗
DOE OSTI2023

β -Ga 2 O 3 trench Schottky diodes by low-damage Ga-atomic beam etching

β-Ga 2 O 3 trench Schottky barrier diodes fabricated through a Gallium atomic beam etching technique with excellent field strength and power device figure of merit are demonstrated. Trench formation was accomplished by a low-damage Ga flux etch that enables near-ideal forward operating characteristics that are independent of fin orientation. The reverse breakdown field strength of greater than 5.10 MV/cm is demonstrated at a breakdown voltage of 1.45 kV. This result demonstrates the potential for Ga atomic beam etching and high-quality dielectric layers for improved performance in β-Ga 2 O 3 vertical power devices.

42 ENGINEERING↗
DOE OSTI2023

Vertical β -Ga2O3 metal–insulator–semiconductor diodes with an ultrathin boron nitride interlayer

In this work, we demonstrate the high performance of β-Ga2O3 metal–insulator–semiconductor (MIS) diodes. An ultrathin boron nitride (BN) interlayer is directly grown on the Ga2O3 substrate by pulsed laser deposition. X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy confirm the existence of a 2.8 nm BN interlayer. Remarkably, with the insertion of the ultrathin BN layer, the breakdown voltage is improved from 732 V for Ga2O3 Schottky barrier diodes to 1035 V for Ga2O3 MIS diodes owing to the passivated surface-related defects and reduced reverse leakage currents. Our approach shows a promising way to improve the breakdown performance of Ga2O3-based devices for next-generation high-power electronics.

Physics↗
DOE OSTI2024

Single-event burnout in homojunction GaN vertical PiN diodes with hybrid edge termination design

GaN devices play a major role in modern electronics, providing high-power handling, efficient high-frequency operation, and resilience in harsh environments. However, electric field crowding at the edge of the anode often limits its full potential, leading to single-event effects (SEEs) at lower bias voltages under heavy ion radiation. Here, in this work, we report on the performance of homojunction GaN vertical PiN diodes with a hybrid edge termination design under heavy ion irradiation, specifically, oxygen ions, chlorine ions, Cf-252 fission fragments, and alpha particles from an Am-241 source. The unique hybrid edge termination (HET) design provides better electric field management, preventing breakdown from occurring at the edge of the anode at lower voltages. The results of this study reveal that these devices exhibit excellent tolerance to 12-MeV oxygen and 16-MeV chlorine ions, owing to their low linear energy transfer (LET) and range in GaN. However, single-event burnout (SEB) is observed during the Cf-252 exposure at about 50% of the diodes' electrical breakdown voltage due to the presence of higher LET and longer-range ions. Optical and scanning electron microscopy (SEM) reveal that the damage that caused by SEB lies close to the center of these devices rather than the anode edge. Devices with junction termination extension (JTE) instead of HET edge termination also show similar SEB when irradiated with Cf-252 fission fragments. Physical damage due to SEB occurs at the edge of the anode for these devices. These comparative results show the benefits of HET for enhancing the resistance of GaN-based PiN diodes to heavy ion irradiation.

42 ENGINEERING↗
DOE OSTI2026

Dielectric properties of neutron and proton irradiated polymeric nanocomposite insulation for superconducting magnets of fusion power plants

Studies on radiation-resistant electrical insulation for superconducting magnets of nuclear fusion power plants are discussed. Metal oxide nanoparticle-incorporated organic polymer composite (MONAP) insulation films were manufactured and studied for their dielectric breakdown strength after exposure to neutrons and proton radiation at varying levels. Samples with up to 5 wt% of nanoparticles (NPs) of SiO 2 , MgO, and ZrO 2 were studied. The samples were exposed to radiation of up to 2 × 10 16 neutrons/cm 2 and 200 Mrad of protons. The addition of the nanoparticles improved the radiation resistance of the MONAP, and the performance depended on the type of NPs and the radiation exposure. Dielectric breakdown measurements at 77 K showed little degradation. Enhancement of dielectric strength was observed in some instances.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interactions between atmospheric pressure plasmas and metallic catalyst particles in packed bed reactors

Atmospheric-pressure plasmas sustained in packed bed reactors (PBRs) are being investigated for chemical conversion of gases and pollution control. Metallic catalysts added to the surfaces of the dielectric beads of PBRs can increase the energy efficiency and selectivity of chemical processes by reducing operating temperature and providing additional reaction pathways. In this paper, results from a computational investigation of plasma surface interactions between micron-scale metallic catalysts and humid-air plasmas in PBRs are discussed. Here we found that high plasma density regions form in the proximity of the metallic catalysts. These higher-density plasma regions were confirmed experimentally using ICCD imaging. The intense plasmas result from geometrical electric field enhancement and redistribution of charges within the conductive particles, leading to further enhancement. The high electric field at the triple points of the catalysts can produce electric field emission of electrons, which provides a pre-ionization source or additional source of electrons. These regions of high electric field and sources of electrons guide discharges towards the catalysts and increases fluxes of excited species, ions, electrons and photons to their surfaces. These fluxes are focused primarily at the triple points between the metal, dielectric and gas. As a result, the catalyst is locally heated, which could lead to further increased rates of thermocatalytic reactions on the surface. Surface roughness of the metal inclusions can lead to additional electric field enhancement, which changes the character of the discharges in the vicinity of the catalysts while reducing breakdown voltage.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Triboplasma assisted chemical conversion in granular systems: a semi-analytic model

We present a semi-analytic model for a novel plasma-assisted chemical conversion pathway using triboplasmas generated in granular flows. Triboelectric charge relaxation is a well known phenomena where the potential generated from contact charging of particles exceeds the breakdown voltage of the background gas. In this work, we extend the triboelectric charge relaxation theory to include non equilibrium plasma energy and particle balance equations to predict the formation of dissociated and excited species that act as precursors to chemical conversion, for example in plasma-assisted ammonia synthesis. Our example case study with nitrogen background gas and teflon/aluminum tribomaterial system yielded high excited nitrogen species densities per collision that are comparable to current plasma-assisted conversion pathways. We also present a regime diagram for various gases where Paschen breakdown parameters are used to determine whether triboplasmas can be formed for a given effective work-function difference between two materials. Our sensitivity studies indicate particle velocity, particle radius, solids fraction and space charge effects play a critical role in overall plasma densities and excited species production.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Plasma decay of nanosecond pulsed laser-produced Ar and Ar–H 2 O sparks at atmospheric pressure

Time-resolved diagnostics were applied to investigate free-electron properties in nanosecond laser-produced discharges generated in atmospheric pressure Ar and in Ar–3%H 2 O. The discharges were generated using 23 ns, 1064 nm laser pulses. Broadband plasma imaging and laser Thomson scattering were combined with optical emission spectroscopy, with particular emphasis on the Stark broadening of the H α and H β lines. The plasma exhibited a bright emission that persists for up to 30–40 µs after breakdown. Plasma emission was then followed by a very weak glow emission that persisted for up to 19 ms after breakdown. Peak electron number density of ∼2 × 10 17 cm −3 and electron temperature of ∼7 eV were measured. An excellent agreement between both techniques was obtained regarding absolute electron number densities. The inferred free-electron temporal decay dynamics are consistent with processes dominated by hydrodynamic expansion and two- and three-body electron–ion recombination. These results provide benchmark data for modeling nanosecond laser discharges and demonstrate the reliability of combining Thomson scattering with Stark broadening in atmospheric laser sparks.

Thomson scattering↗
DOE OSTI2024

Development and Verification of an Improved Wake-Added Turbulence Model in FAST.Farm

We introduce a generalized wake-added turbulence (WAT) model in the multiphysics, multiturbine simulation tool FAST.Farm. The WAT model introduces additional small-scale turbulence that represents the breakdown of vortical structures and shear layers in the wake. The article describes the development, implementation, calibration, and verification of the model. The novelties of the model include support for wake asymmetry, buildup of WAT across the wind farm, and secondary effects of wake-induced turbulence (e.g., wake meandering) driven by smaller-scale turbulence structures that arise from wake breakdown. Large-eddy simulations were run to support the calibration of the WAT parameters and verification of the model. Previous studies hypothesized that the lack of WAT modeling was the source of underprediction of fatigue loads, in particular for cases at low turbulence intensities and/or stable atmospheric boundary layers. This study confirms that the newly implemented WAT model enhances the loads predictions in these cases.

17 WIND ENERGY↗
DOE OSTI2023

Analysis of humidity sensitivity of silicon strip sensors for ATLAS upgrade tracker, pre- and post-irradiation

During the prototyping phase of the new ATLAS Inner-Tracker (ITk) strip sensors, a degradation of the device breakdown voltage at high humidity was observed. Although the degradation was temporary, showing a fast recovery in dry conditions, the study of the influence of humidity on the sensor performance was critical to establish counter-measures and handling protocols during production testing in order to ensure the proper performance of the upgraded detector. The work presented here has the objective to study for the first time the breakdown voltage deterioration in presence of ambient humidity of ATLAS ITk production-layout strip sensors with different surface properties, before and after proton, neutron and gamma irradiations. A study of the humidity sensitivity of miniature ATLAS ITk strip sensors, before and after proton irradiations, is also presented to compare the sensitivity of devices with different sizes. The sensors were also exposed for several days to high humidity with the aim to recreate and evaluate the influence of the detector integration environment expected during the Large Hadron Collider (LHC) Long Shutdown 3 (LS3) in 2026, where the sensors will be exposed to ambient humidity for prolonged times.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Design, characterization and installation of the NEXT-100 cathode and electroluminescence regions

NEXT-100 is currently being constructed at the Laboratorio Subterráneo de Canfranc in the Spanish Pyrenees and will search for neutrinoless double beta decay using a high-pressure gaseous time projection chamber (TPC) with 100 kg of xenon. Charge amplification is carried out via electroluminescence (EL) which is the process of accelerating electrons in a high electric field region causing secondary scintillation of the medium proportional to the initial charge. The NEXT-100 EL and cathode regions are made from tensioned hexagonal meshes of 1 m diameter. This paper describes the design, characterization, and installation of these parts for NEXT-100. Simulations of the electric field are performed to model the drift and amplification of ionization electrons produced in the detector under various EL region alignments and rotations. Measurements of the electrostatic breakdown voltage in air characterize performance under high voltage conditions and identify breakdown points. Furthermore, the electrostatic deflection of the mesh is quantified and fit to a first-principles mechanical model. Measurements were performed with both a standalone test EL region and with the NEXT-100 EL region before its installation in the detector. Finally, we describe the parts as installed in NEXT-100, following their deployment in Summer 2023.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Response of interferometers to the vacuum of quantum gravity

It has recently been suggested that exotic quantum gravity effects could lead to large vacuum fluctuations, potentially observable with realistic detectors. Experiments are currently being built to search for these signals. Here we analyze the minimal model of quantum gravity at low energies—the usual effective quantum field theory of gravitons—and show that it unambiguously predicts an unobservably small variation in the measured interferometer length Δ⁢𝐿 ∼ ℓ pl ∼ 10 −35 m. In particular, there are no divergences signaling a breakdown of this calculation in the low energy regime. Thus, detection of a large, gravitationally induced length variation would signal a severe breakdown of effective quantum field theory in low energy quantum gravity.

Carney, Daniel [Lawrence Berkeley National Laborat↗
DOE OSTI2025

Mechanical form factors and densities of nonrelativistic fermions

The hadron physics community has been actively debating the interpretation of so-called mechanical properties of hadrons. Nonrelativistic quantum-mechanical systems like the hydrogen atom have been appealed to in these debates as analogies. Since such appeals are likely to continue, it is important to have Galilei-covariant expressions for matrix elements of the energy-momentum tensor. In this work, I obtain Galilei-covariant breakdowns of such matrix elements into mechanical form factors, with a special focus on spin-half states. I additionally study the spatial densities associated with these form factors, using the pilot wave interpretation to guide their breakdown into contributions from internal structure and from quantum-mechanical effects such as wave packet dispersion. For completeness, I also obtain nonrelativistic Breit frame densities.

form factors↗
DOE OSTI2025

Remote detection of radioactive material using a short-pulse CO 2 laser

Detection of radioactive material at distances greater than the radiated particle range is an important goal with applications in areas such as national defense and disaster response. Here, we demonstrate avalanche-breakdown-based remote detection of a 3.6 mCi α-particle source at a standoff distance of 10 m, using 70 ps, long-wave infrared (λ = 9.2 µm) CO 2 laser pulses. This is ∼10 times longer than our previous results using a mid-IR laser. The primary detection method is direct backscatter from microplasmas generated in the laser focal volume. The backscatter signal is amplified as it propagates back through the CO 2 laser chain, enhancing sensitivity by >100 times. Here we also characterize breakdown plasmas with fluorescence imaging, and present a simple model to estimate backscattered signals as a function of the seed density profile in the laser focal volume. All of this is achieved with a relatively long-drive laser focal geometry (f/200) that is readily scalable to >100 m.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

1.2-kV Vertical GaN PIN Rectifier With Ion-Implanted Floating Guard Rings

Here, this work reports on the fabrication and properties of a homojunction gallium nitride (GaN) p-i-n (PIN) rectifier fabricated on a free-standing GaN substrate. Uniform device performance is achieved with breakdown voltage (BV) >1.2 kV and low ON-resistance × area ( R ON A ). The statistics of the BV measurements show 58.5% of devices achieve BV >1.3 kV, and 71.1% of devices achieve BV >1.2 kV, as attributed to high quality and control in both epitaxial growth and device process. At room temperature, R ON A is 0.23 mΩ∙ cm 2 at a current density ( J ) of 6.9 kA/cm2. The corresponding Baliga’s figure of merit is >5.97 GW/cm 2 . Temperature-dependent reverse I – V measurements were performed and show a positive temperature coefficient of 0.42 V/K, indicating the avalanche capability of reverse breakdown. Further analysis with the Poole-Frenkel model on the temperature-dependent measurement suggested that a trap-assisted tunneling process contributed to the reverse leakage current. Floating guard rings (FGRs) formed by nitrogen implantation serve as an effective edge termination technique in these GaN PIN rectifiers, resulting in uniform performance in both forward and reverse bias.

42 ENGINEERING↗
DOE OSTI2024

Trap Passivation for Reducing On-Resistance and Saturation Voltage in Wafer-Bonded InGaAs-Channel/GaN-Drain Vertical FETs

High frequency and high power are the driving forces behind semiconductor transistor technology. However, conventional devices have the tradeoff of either being high speed or high breakdown—but not both. Wafer-bonded current aperture vertical electron transistors (BAVETs) help eliminate the tradeoff by combining a high-speed III-As channel to a high-breakdown III-N drift region. The device presented herein comprises of an InAlAs gate-barrier/InGaAs channel, wafer-bonded to an InGaN/GaN drift region, with the InGaAs/InGaN interface referred to as the wafer-bonded interface (WBI). The electronic behavior of WBIs is yet less known but necessary in realizing the potential of a BAVET. Herein, strong trap activity at the WBI is shown to be the cause of abnormally high saturation voltage ( V DS_SAT ) in BAVETs. The traps cause unintentional space charge (SC) region in the drain region of the device. This causes a drain resistance, a higher ON-resistance ( R ON ), and a higher V DS_SAT . Here, the challenge is overcome by hydrogen passivation of traps at WBI by using a p-doping for the InAlAs layer, which reduces the trap-charge concentration at the WBI. Consequently, the width of the SC region is reduced and a reduction in V DS_SAT is demonstrated, wherein it reduces from >12 to 5 V.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Plastoquinone redox status influences carboxysome integrity via a RpaA ‐ and reactive oxygen species‐dependent regulatory network

SUMMARY Carboxysomes are bacterial microcompartments that encapsulate Rubisco and are a core component of the cyanobacterial carbon concentration mechanism (CCM). While carboxysome number, size, and spatial organization vary in different environmental conditions (CO 2 , light availability, redox state, temperature, and light quality), the molecular mechanisms underlying this potentially adaptive process remain elusive. Herein, we observe that mutants of the circadian rhythm/metabolism factor, Regulator of Phycobilisome Association A (RpaA), exhibit a striking breakdown of carboxysomes under certain environmental conditions. We find that conditions leading to overreduction of the plastoquinone (PQ) pool (mixotrophic growth, high irradiance, or chemical inhibition of electron transfer from PQ to the cytochromeb 6 fcomplex) are accompanied by an elevated generation of reactive oxygen species (ROS) and correlate with the loss of carboxysome integrity. Carboxysome breakdown is reversed by environmental conditions or chemical inhibitors that prevent PQ overreduction and accompanying ROS generation. Taken together, our data support a novel link between the redox status of the PQ pool and carboxysome integrity. Our results have implications for the fundamental understanding of cyanobacterial energy‐balancing pathways and may indicate new research directions for understanding how the carboxysome is remodeled in response to changing environments.

Plant Sciences↗
DOE OSTI2021

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot products as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot-flame efficacy increases with pilot-flame equivalence ratio until it matches the main-flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot-flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation (LES) to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. Furthermore, the simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

42 ENGINEERING↗