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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Identification and characterization of deep nitrogen acceptors in β-Ga 2 O 3 using defect spectroscopies

The ability to achieve highly resistive beta-phase gallium oxide (β-Ga 2 O 3 ) layers and substrates is critical for β-Ga 2 O 3 high voltage and RF devices. To date, the most common approach involves doping with iron (Fe), which generates a moderately deep acceptor-like defect state located at E C -0.8 eV in the β-Ga 2 O 3 bandgap. Recently, there has been growing interest in alternative acceptors, such as magnesium (Mg) and nitrogen (N), due to their predicted deeper energy levels, which could avoid inadvertent charge modulation during device operation. In this work, a systematic study that makes direct correlations between the introduction of N using ion implantation and the observation of a newly observed deep level at E C -2.9 eV detected by deep-level optical spectroscopy (DLOS) is presented. The concentration of this state displayed a monotonic dependence with N concentration over a range of implant conditions, as confirmed by secondary ion mass spectrometry (SIMS). With a near 1:1 match in absolute N and E C -2.9 eV trap concentrations from SIMS and DLOS, respectively, which also matched the measured removal of free electrons from capacitance-voltage studies, this indicates that N contributes a very efficiently incorporated compensating defect. Density functional theory calculations confirm the assignment of this state to be an N (0/-1) acceptor with a configuration of N occupying the oxygen site III [N O(III) ]. The near ideal efficiency for this state to compensate free electrons and its location toward the midgap region of the β-Ga 2 O 3 bandgap demonstrates the potential of N doping as a promising approach for producing semi-insulating β-Ga 2 O 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2024

Evaluating the diffusion of Kr in UO 2 and ADOPT TM using time-of-flight elastic recoil detection analysis (ToF-erda)

A combination of 300 keV 84 Kr ion implantation and Time-of-Flight Elastic Recoil Detection Analysis is utilized to investigate the diffusion of Kr in UO 2 and ADOPT TM fuels. Composition depth-profiles on the nanometer scale were obtained, both for as-implanted samples and after annealing at 800°C for 1 hour. Observed drifts in the 84 Kr profiles could be associated with short-range diffusion mechanisms. The approach employed here provides the possibility to make direct comparisons with atomistic scale modelling data, and can be of service as a separate effect test in line with the Accelerated Fuel Qualification initiative.

ADOPT UO2↗
DOE OSTI2020

Comparative study of helium bubbles in a Ti-Ta alloy and a Ti/Ta nanocomposite

Here, we investigated the size, density, and distribution of helium (He) bubbles in a Ti-Ta single-phase alloy and a Ti/Ta dual-phase nanocomposite using transmission electron microscopy. The Ti/Ta nanocomposite was fabricated via phase separation during high-temperature annealing of the single-phase Ti-Ta alloy. He ion implantation in the Ti-Ta single-phase alloy leads to the formation of nano-scale He bubbles (~1.7 nm in size, ~2.6×10 5 /μm 3 in volumetric density). He bubbles were found to segregate to grain boundaries. Under identical implantation conditions, numerous He bubbles also formed in the Ti/Ta nanocomposite. Closer inspection revealed that He bubbles in the Ti-rich phase are smaller and of higher volumetric density (~1.2 nm, ~8.4×10 5 /μm 3 ) than those in the Tarich phase (~3 nm, ~1.8×10 5 /μm 3 ) and the single-phase alloy. He bubbles were also observed to decorate phase boundaries, but they were generally smaller than those on grain boundaries. These results suggest that Ti/Ta phase boundaries are less conducive to the growth of large He bubbles than grain boundaries in the Ti-Ta single phase alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Interaction between magnetic moments and itinerant carriers in $d^0$ ferromagnetic SiC

Elucidating the interaction between magnetic moments and itinerant carriers is an important step to spintronic applications. In this work, we investigate magnetic and transport properties in d0 ferromagnetic SiC single crystals prepared by postimplantation pulsed laser annealing. Magnetic moments are contributed by the p states of carbon atoms, but their magnetic circular dichroism is different from that in semi-insulating SiC samples. The anomalous Hall effect and negative magnetoresistance indicate the influence of d 0 spin order on free carriers. The ferromagnetism is relatively weak in N-implanted SiC compared with that in Al-implanted SiC after annealing. The results suggest that d 0 magnetic moments and itinerant carriers can interact with each other, which will facilitate the development of SiC spintronic devices with d 0 ferromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Using block-copolymer nanolithography as a tool to sensitively evaluate variation in chemical dry etching rates of semiconductor materials with sub-5 nm resolution

Ion implantation is a robust and established method to customize the electronic properties of Si. However, fabricating doped, ultrafine semiconductor nanostructures can be challenging. Ion implantation has well-established effects on the dry etch rates of Si, which becomes increasingly consequential as the target dimension shrinks below a few tens of nanometers. While dry etching arrays of block copolymer-templated nanoscale holes (pitch = 37.5 nm, diameter ~25 nm) into p-type, n-type, and undoped Si, we observed that the lateral etch rate was notably larger for the n-type regions than p-type or undoped regions. By doing image analyses on high resolution electron micrographs of the nanostructured hole arrays, we were able to extract the porosity and average radii of the holes with subnanometer sensitivity and compare the relative etch rates between different doping conditions. We found that degenerately doped n-type silicon consistently etches between approximately 17% and 27% faster in the lateral direction than p-type Si, resulting in significantly larger porosity and, consequently, less mechanical stability. Here, we demonstrate that top-down dimensional analysis of a densely packed porous nanostructure is a robust method for assessing extremely small differences in the lateral, chemical etch rate of doped Si to a degree of sensitivity that was previously unachievable. The minute, dense-packed nature of block copolymer self-assembled nanostructures is shown to be ideal for this application. This proposed method could be useful for designing fabrication processes for heterogeneous nanostructures, as slight dry etch rate variations that may be within process tolerance at the micrometer-scale appear to have nontrivial consequences at the nanometer scale.

42 ENGINEERING↗
DOE OSTI2019

Various Applications of Precision Low-Energy Nuclear Electron Spectrometry in the KATRIN Tritium Neutrino Project

The energy scale of the main spectrometer in the KATRIN tritium project is required to remain stable within ±60 meV at an electron energy of 18.6 keV for two months in order to reach the intended sensitivity of 0.2 eV for the rest mass of the electron antineutrino. A natural source of reference electrons with an energy of 17824.3 ± 0.5 eV based on K -conversion electrons of the 32-keV nuclear γ-transition in {sup 83m}Kr from the decay of parent {sup 83}Rb was developed for this purpose using precision low-energy nuclear electron spectrometry. The spectroscopic parameters of {sup 83m}Kr/{sup 83}Rb sources fabricated by ion implantation into polycrystalline platinum foils were significantly better than the parameters of vacuum-deposited sources. A large-scale study of the influence of the physicochemical environment of atoms of different radioisotopes in various matrices of vacuum-deposited and implanted radioactive sources on the energy of emitted conversion and Auger electrons and on the structure of the corresponding energy spectra was conducted in the process. The possibility of application of photoelectron sources with a metallic converter as sources of reference electrons for the KATRIN project was also considered.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

X-Ray Diagnostics of Microstructure Defects of Silicon Crystals Irradiated by Hydrogen Ions

Features of formation and transformation of radiation defects in near-surface layers of silicon plates that are implanted with hydrogen ions are studied. Using the method of high-resolution double-crystal X-ray diffractometry, values of the main parameters, such as mean effective thickness L{sub eff} and mean relative deformation Δa/a of a doped layer, are determined depending on the implantation dose and substrate temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The Influence of the Surface Neutralization of Active Impurities on the Field-Electron Emission Properties of p-Type Silicon Crystals

Correlation dependences between variations of the structural-phase composition, morphology characteristics, and field-electron-emission (FEE) properties of surface-structured p-type silicon singlecrystalline (100)-oriented wafers have been studied during their stepwise high-dose carbon-ion-beam irradiation. It is established that the stepwise implantation of carbon decreases the FEE threshold and favors an increase in the maximum FEE-current density by more than two orders of magnitude. Physicochemical mechanisms involved in this modification of the properties of near-surface layers of silicon under carbon-ion implantation are considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Kinetics of Coloration in Hydrogenated Vanadium Pentoxide Films under an Internal Electrochromic Effect

The kinetics of coloration in thin hydrogenated vanadium pentoxide films under the internal electrochromic effect is studied alongside with the influence of their hydrogenation by means of plasma-immersion ion implantation on this process. The variant of uniform implantation and the nonuniform case when a film is partially subjected to ion treatment are considered. Based on the experiments on measuring the electrochromically colored surface area growth rate and the passing current, it has been revealed that the electrochromic effect becomes much stronger in the nonuniform variant, when the cathode is placed on the nonhydrogenated part of a film, and the anode is located on its hydrogenated part.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of helium on dispersoid evolution under self-ion irradiation in a dual-phase 12Cr oxide-dispersion-strengthened alloy

As one candidate alloy for future Generation IV and fusion reactors, a dual-phase 12Cr oxide-dispersion-strengthened (ODS) alloy was developed for high temperature strength and creep resistance and has shown good void swelling resistance under high damage self-ion irradiation at high temperature. However, the effect of helium and its combination with radiation damage on oxide dispersoid stability needs to be investigated. In this study, 120 keV energy helium was preloaded into specimens at doses of 1 × 10 15 and 1 × 10 16 ions/cm 2 at room temperature, and 3.5 MeV Fe self-ions were sequentially implanted to reach 100 peak displacement-per-atom at 475 °C. He implantation alone in the control sample did not affect the dispersoid morphology. After Fe ion irradiation, a dramatic increase in density of coherent oxide dispersoids was observed at low He dose, but no such increase was observed at high He dose. The study suggests that helium bubbles act as sinks for nucleation of coherent oxide dispersoids, but dispersoid growth may become difficult if too many sinks are introduced, suggesting that a critical mass of trapping is required for stable dispersoid growth.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Activity in the ferret: oestradiol effects and circadian rhythms

The present study was conducted to determine whether oestradiol increases activity in the European ferret (Mustela furo), whether this effect is sexually dimorphic, and whether a 24-h rhythm is present in the ferret's daily activity. The activity of male and female adult, postpubertally gonadectomized ferrets was monitored while they were maintained singly on a 13:11 light-dark cycle, before and after implantation with oestradiol-17 beta. Gonadectomized male and female ferrets exhibited equal levels of activity, and neither sex exhibited a significant change in activity following oestradiol implantation. None of the ferrets exhibited a strong circadian rhythm, although weak 24-h rhythms and shorter harmonic rhythms were present. Golden hamsters (Mesocricetus auratus), monitored in an identical manner, exhibited strong circadian rhythms. It was concluded that oestradiol administration may not cause an increase in activity in the ferret, and that this species lacks a strong circadian activity rhythm.

Non-NASA Center↗
NASA NTRS1998

T wave alternans as a predictor of recurrent ventricular tachyarrhythmias in ICD recipients: prospective comparison with conventional risk markers

INTRODUCTION: The current standard for arrhythmic risk stratification is electrophysiologic (EP) testing, which, due to its invasive nature, is limited to patients already known to be at high risk. A number of noninvasive tests, such as determination of left ventricular ejection fraction (LVEF) or heart rate variability, have been evaluated as additional risk stratifiers. Microvolt T wave alternans (TWA) is a promising new risk marker. Prospective evaluation of noninvasive risk markers in low- or moderate-risk populations requires studies involving very large numbers of patients, and in such studies, documentation of the occurrence of ventricular tachyarrhythmias is difficult. In the present study, we identified a high-risk population, recipients of an implantable cardioverter defibrillator (ICD), and prospectively compared microvolt TWA with invasive EP testing and other risk markers with respect to their ability to predict recurrence of ventricular tachyarrhythmias as documented by ICD electrograms. METHODS AND RESULTS: Ninety-five patients with a history of ventricular tachyarrhythmias undergoing implantation of an ICD underwent EP testing, assessment of TWA, as well as determination of LVEF, baroreflex sensitivity, signal-averaged ECG, analysis of 24-hour Holter monitoring, and QT dispersion from the 12-lead surface ECG. The endpoint of the study was first appropriate ICD therapy for electrogram-documented ventricular fibrillation or tachycardia during follow-up. Kaplan-Meier survival analysis revealed that TWA (P < 0.006) and LVEF (P < 0.04) were the only significant univariate risk stratifiers. EP testing was not statistically significant (P < 0.2). Multivariate Cox regression analysis revealed that TWA was the only statistically significant independent risk factor. CONCLUSIONS: Measurement of microvolt TWA compared favorably with both invasive EP testing and other currently used noninvasive risk assessment methods in predicting recurrence of ventricular tachyarrhythmias in ICD recipients. This study suggests that TWA might also be a powerful tool for risk stratification in low- or moderate-risk patients, and needs to be prospectively evaluated in such populations.

Non-NASA Center↗
NASA NTRS1997

The effects of programmed administration of human parathyroid hormone fragment (1-34) on bone histomorphometry and serum chemistry in rats

PTH treatment can result in dramatic increases in cancellous bone volume in normal and osteopenic rats. However, this potentially beneficial response is only observed after pulsatile treatment; continuous infusion of PTH leads to hypercalcemia and bone abnormalities. The purpose of these studies was to determine the optimal duration of the PTH pulses. A preliminary study revealed that human PTH-(1-34) (hPTH) is cleared from circulation within 6 h after sc administration of an anabolic dose of the hormone (80 microg/kg). To establish the effects of gradually extending the duration of exposure to hPTH without increasing the daily dose, we programmed implanted Alzet osmotic pumps to deliver the 80 microg/kg x day dose of the hormone during pulses of 1, 2, and 6 h/day, or 40 microg/kg x day continuously. Discontinuous infusion was accomplished by alternate spacing of external tubing with hPTH solution and sesame oil. After 6 days of treatment, we evaluated serum chemistry and bone histomorphometry. As negative and positive controls, groups of rats received pumps that delivered vehicle only and 80 microg/kg x day hPTH by daily sc injection, respectively. Dynamic and static bone histomorphometry revealed that the daily sc injection and 1 h/day infusion dramatically increased osteoblast number and bone formation in the proximal tibial metaphysis, whereas longer infusion resulted in systemic side-effects, including up to a 10% loss in body weight, hypercalcemia, and histological changes in the proximal tibia resembling abnormalities observed in patients with chronic primary hyperparathyroidism, including peritrabecular marrow fibrosis and focal bone resorption. Infusion for as little as 2 h/day resulted in minor weight loss and changes in bone histology that were intermediate between sc and continuous administration. The results demonstrate that the therapeutic interval for hPTH exposure is brief, but that programmed administration of implanted hormone is a feasible alternative to daily injection as a route for administration of the hormone.

Non-NASA Center↗
DOE OSTI2018

Flexible Electronics: Stretchable Electrodes and Their Future

Flexible electronics, as an emerging and exciting research field, have brought great interest to the issue of how to make flexible electronic materials that offer both durability and high performance at strained states. With the advent of on-body wearable and implantable electronics, as well as increasing demands for human-friendly intelligent soft robots, enormous effort is being expended on highly flexible functional materials, especially stretchable electrodes, by both the academic and industrial communities. Among different deformation modes, stretchability is the most demanding and challenging. This review focuses on the latest advances in stretchable transparent electrodes based on a new design strategy known as kirigami (the art of paper cutting) and investigates the recent progress on novel applications, including skin-like electronics, implantable biodegradable devices, and bioinspired soft robotics. By comparing the optoelectrical and mechanical properties of different electrode materials, some of the most important outcomes with comments on their merits and demerits are raised. Key design considerations in terms of geometries, substrates, and adhesion are also discussed, offering insights into the universal strategies for engineering stretchable electrodes regardless of the material. Finally, it is suggested that highly stretchable and biocompatible electrodes will greatly boost the development of next-generation intelligent life-like electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A Printed Microscopic Universal Gradient Interface for Super Stretchable Strain‐Insensitive Bioelectronics

Abstract Stretchable electronics capable of conforming to nonplanar and dynamic human body surfaces are central for creating implantable and on‐skin devices for high‐fidelity monitoring of diverse physiological signals. While various strategies have been developed to produce stretchable devices, the signals collected from such devices are often highly sensitive to local strain, resulting in inevitable convolution with surface strain‐induced motion artifacts that are difficult to distinguish from intrinsic physiological signals. Here all‐printed super stretchable strain‐insensitive bioelectronics using a unique universal gradient interface (UGI) are reported to bridge the gap between soft biomaterials and stiff electronic materials. Leveraging a versatile aerosol‐based multi‐materials printing technique that allows precise spatial control over the local stiffnesses with submicron resolution, the UGI enables strain‐insensitive electronic devices with negligible resistivity changes under a 180% uniaxial stretch ratio. Various stretchable devices are directly printed on the UGI for on‐skin health monitoring with high signal quality and near‐perfect immunity to motion artifacts, including semiconductor‐based photodetectors for sensing blood oxygen saturation levels and metal‐based temperature sensors. The concept in this work will significantly simplify the fabrication and accelerate the development of a broad range of wearable and implantable bioelectronics for real‐time health monitoring and personalized therapeutics.

Song, Kaidong [Department of Aerospace and Mechani↗
DOE OSTI2022

Integration of polyurethane meniscus scaffold during ACL revision is not reliable at 5 years despite favourable clinical outcome

Abstract Purpose The aim of this study was to evaluate the clinical outcome at 5‐year follow‐up of a one‐step procedure combining anterior cruciate ligament (ACL) reconstruction and partial meniscus replacement using a polyurethane scaffold for the treatment of symptomatic patients with previously failed ACL reconstruction and partial medial meniscectomy. Moreover, the implanted scaffolds have been evaluated by MRI protocol in terms of morphology, volume, and signal intensity. Methods Twenty patients with symptomatic knee laxity after failed ACL reconstruction and partial medial meniscectomy underwent ACL revision combined with polyurethane‐based meniscal scaffold implant. Clinical assessment at 2‐ and 5‐year follow‐ups included VAS, Tegner Activity Score, International Knee Documentation Committee (IKDC), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Lysholm Score. MRI evaluation of the scaffold was performed according to the Genovese scale with quantification of the scaffold’s volume at 1‐ and 5‐year follow‐ups. Results All scores revealed clinical improvement as compared with the preoperative values at the 2‐ and 5‐year follow‐ups. However, a slight, but significant reduction of scores was observed between 2 and 5 years. Concerning the MRI assessment, a significant reduction of the scaffold’s volume was observed between 1 and 5 years. Genovese Morphology classification at 5 years included two complete resorptions (Type 3) and all the remaining patients had irregular morphology (Type 2). With regard to the Genovese Signal at the 5‐year follow‐up, three were classified as markedly hyperintense (Type 1), 15 as slightly hyperintense (Type 2), and two as isointense (Type 1). Conclusion Simultaneous ACL reconstruction and partial meniscus replacement using a polyurethane scaffold provides favourable clinical outcomes in the treatment of symptomatic patients with previously failed ACL reconstruction and partial medial meniscectomy at 5 years. However, MRI evaluation suggests that integration of the scaffold is not consistent. Level of evidence Level IV.

Pereira, Hélder↗
DOE OSTI2019

Shear wave elastography prior to transjugular intrahepatic portosystemic shunt may predict the decrease in hepatic vein pressure gradient

Background: Transjugular intrahepatic portosystemic shunt (TIPS) is a procedure used to treat portal hypertension complications. Our aim was to evaluate liver and spleen stiffness measurement (LSM and SSM, respectively) changes using acoustic radiation force impulse imaging (ARFI) in comparison to Child–Pugh scores for predicting hepatic venous pressure gradient (HVPG) decreases after TIPS implantation. Methods: This prospective study included 31 consecutive clinically significant portal hypertension patients with TIPS indication. All patients received LSM and SSM before TIPS, at baseline, 2 days (follow-up 1) and 6 weeks (follow-up 2) post-implantation. HVPG was performed during the TIPS procedure. Results: The mean decrease in HVPG after TIPS was 63%. LSM and SSM decreased significantly between baseline and follow-up 2 (p < 0.001 and p < 0.001, respectively). At baseline, follow-up 1 and follow-up 2, significant correlations were detected between mean SSM and mean HVPG (p = 0.026; p = 0.018; p = 0.002, respectively). HVPG decreased to ≤ 10 mmHg in 61% of patients for which LSM, SSM, and Child–Pugh score were predictors (p = 0.033, p = 0.002 and p = 0.030, respectively). The area under the curve (AUC) for LSM, SSM, and Child–Pugh was 0.88, 0.90, and 0.84, respectively, with close sensitivity and specificity. SSM had the highest diagnostic accuracy for predicting an HVPG decrease to ≤ 10 mmHg in comparison to LSM and Child–Pugh score. Conclusion: Spleen stiffness is superior to liver stiffness and Child–Pugh score as a non-invasive surveillance tool for evaluating patients with clinically significant portal hypertension (HVPG ≥ 10 mmHg) prior to TIPS.

62 RADIOLOGY AND NUCLEAR MEDICINE↗