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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Enhanced Tunability of Gold Nanoparticle Size, Spacing, and Shape for Large-Scale Plasmonic Arrays

Gold nanoparticles are important constituents in plasmonic arrays, lending themselves to electronic, optical, biomedical, sensing, and catalytic applications, among numerous others. Process variables that must be controlled when engineering plasmonic nanoparticle ensembles include nanoparticle size, shape, and spatial distribution on surfaces. The challenge in generating arrays of nanoparticles with control over these three parameters increases dramatically as spatial requirements for uniformity extend to larger processing areas. In this paper, we present a procedure that exploits thermally driven solid-state diffusional dewetting to yield considerable flexibility in generating ensembles of gold nanoparticles. Such submelting dewetting introduces fine control over particle spatial features that are currently difficult to achieve through conventional methods of generating nanoparticle arrays. Because of the simplicity of the process and its area-scalability, solid-state diffusional dewetting is shown here to be a method that could be easily scaled up to apply to large-area plasmonic fabrication processes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Janus Monolayers for Ultrafast and Directional Charge Transfer in Transition Metal Dichalcogenide Heterostructures

Charge transfer properties of van der Waals heterostructures formed by Janus and regular transition metal dichalcogenide monolayers are studied by time-resolved pump–probe measurements and photoluminescence spectroscopy. Measurements of electron and hole transfer in three heterostructures with atomic layer sequences of S–W–Se/S–W–S, Se–W–S/S–W–S, and S–W–Se/Se–W–Se reveal that charge transfer from regular to Janus monolayers is ultrafast regardless of the direction of the built-in electric field of the Janus monolayer (Janus field). However, the charge transfer from Janus to regular layers is directional and controlled by the Janus field. When the current direction is along the field, the charge transfer is ultrafast and efficient, while the field blocks the charge transfer with an opposite charge current direction. The transferred carriers form interlayer excitons with extended lifetimes compared to the intralayer excitons. The demonstrated ultrafast and directional charge transfer between Janus and regular TMD layers shows that the Janus structures can be used to make 2D heterostructures with efficient and directional charge transfer properties.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Nonlinear optical diode effect in a magnetic Weyl semimetal

Diode effects are of great interest for both fundamental physics and modern technologies. Electrical diode effects (nonreciprocal transport) have been observed in Weyl systems. Optical diode effects arising from the Weyl fermions have been theoretically considered but not probed experimentally. Here, we report the observation of a nonlinear optical diode effect (NODE) in the magnetic Weyl semimetal CeAlSi, where the magnetization introduces a pronounced directionality in the nonlinear optical second-harmonic generation (SHG). We demonstrate a six-fold change of the measured SHG intensity between opposite propagation directions over a bandwidth exceeding 250 meV. Supported by density-functional theory, we establish the linearly dispersive bands emerging from Weyl nodes as the origin of this broadband effect. We further demonstrate current-induced magnetization switching and thus electrical control of the NODE. Our results advance ongoing research to identify novel nonlinear optical/transport phenomena in magnetic topological materials and further opens new pathways for the unidirectional manipulation of light.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Denary oxide nanoparticles as highly stable catalysts for methane combustion

Oxide nanoparticles with elemental and structural diversity are widely studied for catalysis and energy applications. While compositional control holds great promise for materials discovery, current oxide nanoparticles are typically limited to a few cations due to the intrinsic complexity in nanoscale multi-element mixing. Here we report the rational design and synthesis of single-phase multi-element oxide nanoparticles with tunable composition, size and structure. We have identified temperature-, oxidation- and entropy-driven synthesis strategies to mix a range of elements with largely dissimilar oxidation potentials (including palladium), thus greatly expanding the compositional space. Through rapid synthesis and screening, we obtained a denary multi-element oxide catalyst showing high performance and superior stability for catalytic methane combustion over 100 hours due to the high-entropy design and stabilization. Finally, our work therefore provides a viable synthesis route with clear guidelines for multi-element oxide nanoparticles and enables materials design in the multi-element space towards highly stable catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Interfacial band configuration and electrical properties of LaAlO{sub 3}/Al{sub 2}O{sub 3}/hydrogenated-diamond metal-oxide-semiconductor field effect transistors

In order to search a gate dielectric with high permittivity on hydrogenated-diamond (H-diamond), LaAlO{sub 3} films with thin Al{sub 2}O{sub 3} buffer layers are fabricated on the H-diamond epilayers by sputtering-deposition (SD) and atomic layer deposition (ALD) techniques, respectively. Interfacial band configuration and electrical properties of the SD-LaAlO{sub 3}/ALD-Al{sub 2}O{sub 3}/H-diamond metal-oxide-semiconductor field effect transistors (MOSFETs) with gate lengths of 10, 20, and 30 μm have been investigated. The valence and conduction band offsets of the SD-LaAlO{sub 3}/ALD-Al{sub 2}O{sub 3} structure are measured by X-ray photoelectron spectroscopy to be 1.1 ± 0.2 and 1.6 ± 0.2 eV, respectively. The valence band discontinuity between H-diamond and LaAlO{sub 3} is evaluated to be 4.0 ± 0.2 eV, showing that the MOS structure acts as the gate which controls a hole carrier density. The leakage current density of the SD-LaAlO{sub 3}/ALD-Al{sub 2}O{sub 3}/H-diamond MOS diode is smaller than 10{sup −8} A cm{sup −2} at gate bias from −4 to 2 V. The capacitance-voltage curve in the depletion mode shows sharp dependence, small flat band voltage, and small hysteresis shift, which implies low positive and trapped charge densities. The MOSFETs show p-type channel and complete normally off characteristics with threshold voltages changing from −3.6 ± 0.1 to −5.0 ± 0.1 V dependent on the gate length. The drain current maximum and the extrinsic transconductance of the MOSFET with gate length of 10 μm are −7.5 mA mm{sup −1} and 2.3 ± 0.1 mS mm{sup −1}, respectively. The enhancement mode SD-LaAlO{sub 3}/ALD-Al{sub 2}O{sub 3}/H-diamond MOSFET is concluded to be suitable for the applications of high power and high frequency electrical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Spectra of surface plasmon polariton enhanced electroluminescence from electroformed Al-Al{sub 2}O{sub 3}-Ag diodes

Narrow band-pass filters have been used to measure the spectral distribution of electroluminescent photons with energies between 1.8 eV and 3.0 eV from electroformed Al-Al{sub 2}O{sub 3}-Ag diodes with anodic Al{sub 2}O{sub 3} thicknesses between 12 nm and 18 nm. Electroforming of metal-insulator-metal (MIM) diodes is a non-destructive dielectric breakdown that results in a conducting channel in the insulator and changes the initial high resistance of the MIM diode to a low resistance state. It is a critical step in the development of resistive-switching memories that utilize MIM diodes as the active element. Electroforming of Al-Al{sub 2}O{sub 3}-Ag diodes in vacuum results in voltage-controlled negative resistance (VCNR) in the current-voltage (I-V) characteristics. Electroluminescence (EL) and electron emission into vacuum (EM) develop simultaneously with the current increase that results in VCNR in the I-V characteristics. EL is due to recombination of electrons injected at the Al-Al{sub 2}O{sub 3} interface with radiative defect centers in Al{sub 2}O{sub 3}. Measurements of EL photons between 1.8 eV and 3.0 eV using a wide band-pass filter showed that EL intensity is exponentially dependent on Al{sub 2}O{sub 3} thickness for Al-Al{sub 2}O{sub 3}-Ag diodes between 12 nm and 20 nm thick. Enhanced El intensity in the thinnest diodes is attributed to an increase in the spontaneous emission rate of recombination centers due to high electromagnetic fields generated in Al{sub 2}O{sub 3} when EL photons interact with electrons in Ag or Al to form surface plasmon polaritons at the Al{sub 2}O{sub 3}-Ag or Al{sub 2}O{sub 3}-Al interface. El intensity is a maximum at 2.0–2.2 eV for Al-Al{sub 2}O{sub 3}-Ag diodes with Al{sub 2}O{sub 3} thicknesses between 12 nm and 18 nm. EL in diodes with 12 nm or 14 nm of Al{sub 2}O{sub 3} is enhanced by factors of 8–10 over EL from a diode with 18 nm of Al{sub 2}O{sub 3}. The extent of EL enhancement in the thinnest diodes can vary significantly between samples. A narrow band of recombination centers was found in one Al-Al{sub 2}O{sub 3}-Ag diode with 12 nm of Al{sub 2}O{sub 3}; it had EL intensity 100 times greater at 2.15 eV than the diode with 18 nm of Al{sub 2}O{sub 3}. EL intensity for photons with energies greater than 2.6 eV is nearly the same for all diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Synthesis of FeCoNi nanoparticles by galvanostatic technique

Soft magnetic nanoparticles of FeCoNi have been becoming interesting objects for many researchers due to its potential application in electronic devices. One of the most promising methods for material preparation is the electrodeposition which capable of growing nanoparticles alloy directly onto the substrate. In this paper, we report our electrodeposition studies on nanoparticles synthesis using galvanostatic electrodeposition technique. Chemical composition of the synthesized FeCoNi was successfully controlled through the adjustment of the applied currents. It is revealed that the content of each element, obtained from quantitative analysis using atomic absorption spectrometer (AAS), could be modified by the adjustment of current in which Fe and Co content decreased at larger applied currents, while Ni content increased. The nanoparticles of Co-rich FeCoNi and Ni-rich FeCoNi were obtained from sulphate electrolyte at the range of applied current investigated in this work. Broad diffracted peaks in the X-ray diffractograms indicated typical nanostructures of the solid solution of FeCoNi.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Transport barriers in bootstrap-driven tokamaks

Experiments have demonstrated improved energy confinement due to the spontaneous formation of an internal transport barrier in high bootstrap fraction discharges. Gyro kinetic analysis, and quasilinear predictive modeling, demonstrates that the observed transport barrier is caused by the suppression of turbulence primarily from the large Shafranov shift. It is shown, that the Shafranov shift can produce a bifurcation to improved confinement in regions of positive magnetic shear or a continuous reduction in transport for weak or negative magnetic shear. Operation at high safety factor lowers the pressure gradient threshold for the Shafranov shift driven barrier formation. Two self-organized states of the internal and edge transport barrier are observed. It is further shown that these two states are controlled by the interaction of the bootstrap current with magnetic shear, and the kinetic ballooning mode instability boundary. Election scale energy transport is shown to be dominant in inner 60% of the profile. Energetic particle driven instabilities could also be playing a role in the thermal energy transport in this region.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Predict-first experimental analysis using automated and integrated magnetohydrodynamic modeling

An integrated-modeling workflow has been developed in this paper for the purpose of performing predict-first analysis of transient-stability experiments. Starting from an existing equilibrium reconstruction from a past experiment, the workflow couples together the EFIT Grad-Shafranov solver [L. Lao et al., Fusion Sci. Technol. 48, 968 (2005)], the EPED model for the pedestal structure [P. B. Snyder et al., Phys. Plasmas 16, 056118 (2009)], and the NEO drift-kinetic-equation solver [E. A. Belli and J. Candy, Plasma Phys. Controlled Fusion 54, 015015 (2012)] (for bootstrap current calculations) in order to generate equilibria with self-consistent pedestal structures as the plasma shape and various scalar parameters (e.g., normalized β, pedestal density, and edge safety factor [q 95 ]) are changed. These equilibria are then analyzed using automated M3D-C1 extended-magnetohydrodynamic modeling [S. C. Jardin et al., Comput. Sci. Discovery 5, 014002 (2012)] to compute the plasma response to three-dimensional magnetic perturbations. This workflow was created in conjunction with a DIII-D experiment examining the effect of triangularity on the 3D plasma response. Several versions of the workflow were developed, and the initial ones were used to help guide experimental planning (e.g., determining the plasma current necessary to maintain the constant edge safety factor in various shapes). Subsequent validation with the experimental results was then used to revise the workflow, ultimately resulting in the complete model presented here. We show that quantitative agreement was achieved between the M3D-C1 plasma response calculated for equilibria generated by the final workflow and equilibria reconstructed from experimental data. A comparison of results from earlier workflows is used to show the importance of properly matching certain experimental parameters in the generated equilibria, including the normalized β, pedestal density, and q 95 . On the other hand, the details of the pedestal current did not significantly impact the plasma response in these equilibria. A comparison to the experimentally measured plasma response shows mixed agreement, indicating that while the equilibria are predicted well, additional analysis tools may be needed. In conclusion, we note the implications that these results have for the success of future predict-first studies, particularly the need for scans of uncertain parameters and for close collaboration between experimentalists and theorists.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Thermal transistor and thermometer based on Coulomb-coupled conductors

We study a three-terminal setup consisting of a single-level quantum dot capacitively coupled to a quantum point contact. The point contact connects to a source and drain reservoir while the quantum dot is coupled to a single base reservoir. This setup has been used to implement a noninvasive, nanoscale thermometer for the bath reservoir by detecting the current in the quantum point contact. Here, we demonstrate that the device can also be operated as a thermal transistor where the average (charge and heat) current through the quantum point contact is controlled via the temperature of the base reservoir. We characterize the performances of this device both as a transistor and a thermometer and derive the operating condition maximizing their respective sensitivities. Furthermore, the present analysis is useful for the control of charge and heat flow and high precision thermometry at the nanoscale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

In-plane hexagonal antiferromagnet in the Cu-Mn-As system Cu 0.82 Mn 1.18 As

We report the single-crystal growth and characterization of a hexagonal phase Cu 0.82 Mn 1.18 As, in the Cu-Mn-As system. This compound contains the same square-pyramidal MnAs 5 units as the tetragonal and orthorhombic polymorphs of CuMnAs. Calorimetry, magnetometry, and neutron diffraction measurements reveal antiferromagnetic ordering at 270 K. The magnetic structure consists of a triangular arrangement of spins in the ab plane. Hexagonal Cu 0.82 Mn 1.18 As shows resistivity that varies only weakly from 5 to 300 K, and is many times higher than tetragonal CuMnAs, indicative of a strongly scattering metal. First-principles calculations confirm the metallic band structure with a small density of states at the Fermi energy. The neutron-refined magnetic ground state is close to the computationally determined minimum energy configuration. This compound should serve as a clear control when disentangling the effects of current-driven Néel switching of metallic antiferromagnets since it exhibits in-plane spins but the magnetic ordering does not break degeneracy along the a and b directions, unlike tetragonal CuMnAs.

36 MATERIALS SCIENCE↗
DOE OSTI2015

IEEE 1547 Standards Advancing Grid Modernization

Technology advances including development of advanced distributed energy resources (DER) and grid-integrated operations and controls functionalities have surpassed the requirements in current standards and codes for DER interconnection with the distribution grid. The full revision of IEEE Standards 1547 (requirements for DER-grid interconnection and interoperability) and 1547.1 (test procedures for conformance to 1547) are establishing requirements and best practices for state-of-the-art DER including variable renewable energy sources. The revised standards will also address challenges associated with interoperability and transmission-level effects, in addition to strictly addressing the distribution grid needs. This paper provides the status and future direction of the ongoing development focus for the 1547 standards.

1547↗
DOE OSTI2017

Multidimensional Cyclic Voltammetry Simulations of Pseudocapacitive Electrodes with a Conducting Nanorod Scaffold

This paper aims to understand the effect of nanoarchitecture on the performance of pseudocapacitive electrodes consisting of conducting scaffold coated with pseudocapacitive material. To do so, two-dimensional numerical simulations of ordered conducting nanorods coated with a thin film of pseudocapacitive material were performed. The simulations reproduced three-electrode cyclic voltammetry measurements based on a continuum model derived from first principles. Two empirical approaches commonly used experimentally to characterize the contributions of surface-controlled and diffusion-controlled charge storage mechanisms to the total current density with respect to scan rate were theoretically validated for the first time. Moreover, the areal capacitive capacitance, attributed to EDL formation, remained constant and independent of electrode dimensions, at low scan rates. However, at high scan rates, it decreased with decreasing conducting nanorod radius and increasing pseudocapacitive layer thickness due to resistive losses. By contrast, the gravimetric faradaic capacitance, due to reversible faradaic reactions, decreased continuously with increasing scan rate and pseudocapacitive layer thickness but was independent of conducting nanorod radius. Note that the total gravimetric capacitance predicted numerically featured values comparable to experimental measurements. Finally, an optimum pseudocapacitive layer thickness that maximizes total areal capacitance was identified as a function of scan rate and confirmed by scaling analysis.

42 ENGINEERING↗
DOE OSTI2017

Prospects for commercial production of diatoms

In this paper, a simple procedure that portends the open-pond growth of commercially viable diatoms is discussed. We examined a number of topics relevant to the production and harvesting of diatoms as well as topics concerning the production of bioproducts from diatoms. Among the former topics, we show that it is currently possible to continuously grow diatoms and control the presence of invasive species without chemical toxins at an average annual yield of 132 MT dry diatoms ha -1 over a period of almost 5 years, while maintaining the dominancy of the optimal diatom species on a seasonal basis. The dominant species varies during the year. The production of microalgae is essentially agriculture, but without the ability to control invasive species in the absence of herbicides and insecticides, pollution and production costs would be prohibitive. Among the latter topics are the discussions of whether it is better to produce lipids and then convert them to biofuels or maximize the production of diatom biomass and then convert it to biocrude products using, for example, hydrothermal processes. It is becoming increasingly evident that without massive public support, the commercial production of microalgal biofuels alone will remain elusive. While economically competitive production of biofuels from diatoms will be difficult, when priority is given to multiple high-value products, including wastewater treatment, and when biofuels are considered co-products in a systems approach to commercial production of diatoms, an economically competitive process will become more likely.

09 BIOMASS FUELS↗
DOE OSTI2026

WholeTraveler Anonymized Data Phase 1

Phase 1 of the WholeTraveler Study data collection consisted of an online-only survey. This survey captured data on three categories of observable variation in the population relevant to transportation decisions. First, the survey collected traditional demographic data such as age, gender, income, and education level. Second, it collected data across personality, psychological, and preference categories. This included: 1. The "Big Five" inventory personality traits: openness to new experience, conscientiousness, extroversion, agreeableness, and neuroticism; 2. Risk and time preferences; and 3. Environmental preferences. Third, the survey collected data on historical behavior patterns including: 1. Adoption of (as well as interest in) new technologies or innovations (e.g., smartphones, PEVs, solar panels, adaptive cruise control [ACC]); 2. Car ownership history and current car ownership status; 3. Recent mode use across different time scales (e.g., previous week, previous month, previous year); and 4. Timing of major life events such as starting a family as well as overall lifecycle trajectory patterns. Data from Phase 1 and Phase 2 are linked by a unique respondent identifier. Anonymized versions of the Phase 1 and Phase 2 data are both available on Livewire.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

What is needed for BISCO to work in a dipole insert for 20 tesla hybrid accelerator magnets

Developing HTS dipole inserts producing fields larger than 5 T within 15 T Nb3Sn outserts is necessary to generate 20 T or higher fields for future high energy colliders. Dipole inserts based on the cos-theta coil geometry with various stress management concepts and Bi2212 super-conducting strand and cable are being developed at Fermilab both within and beyond the U.S. national effort. On paper, the potential reach for the maximum magnetic field in existing or planned Nb3Sn outserts is close to 20 T, thanks to the progress realized in Bi2212 wires’ critical current density. To achieve the Bi2212 potential in accelerator magnets, however, a number of technological challenges still have to be faced. These for instance include the need to design billets that are adequate for Rutherford cabling; developing insulation processes and materials that prevent leaks, which reduce transport current and increase the risk of shorts; control and limit Bi2212 coils’ stresses and strains; reconsider the Split Melt Process (SMP) to lower costs and simplify the processing. This paper reviews Bi2212 conductor properties and coil technolo-gies, and proposes new ideas to face the challenges that Bi2212 still presents as an accelerator magnet conductor.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Measurement of trigger and cascade section runtimes in 6MV switches using fiber coupled photo detectors

Since October 2007 Sandia National Laboratories operates the refurbished Z machine at an improved load current of 26 MA yielding 400 TW of x-ray power. The current pulse shape to the load is controlled by 36 independently timed laser-triggered gas switches (LTGS). As part of the refurbishment effort, a fiber coupled laser spark detector (LSD) system has been installed which is able to detect the laser generated plasma in situ inside the trigger section of the HV switch. In this paper we describe how this detection system can be used to characterize the discharge dynamics of these 5.9 MV, 820 kA switches.

Schwarz, Jens↗
DOE OSTI2012

Tunable Diode Laser Absorption Spectroscopy Using a Multi-Pass White Cell for O 2 Detection

Two forms of Tunable Diode Laser Absorption Spectroscopy (TDLAS), direct absorbance spectroscopy and wavelength modulation spectroscopy (WMS), for O 2 detection were carried out using a tunable 763-nm vertical cavity surface emitting laser (VCSEL) in a multi-pass White cell with an optical path length of 2.6 m. The cell was fitted with a gas flow mechanism for concentration studies. The output wavelength of the tunable VCSEL was increased by ramping the drive current from 0-5 mA while temperature controlling the device to 20 °C. The output wavelength of the VCSEL was mapped using a spectrum analyzer.

42 ENGINEERING↗