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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Getters for Reliable Hermetic Packages

A variety of sealed-off devices such as cathode ray tubes (CRT's) electron tubes, plasma displays, particle accelarators and colliders vacuum thermal insulation, ultra-high vacuum (UHV), extreme high vacuum (XHV) systems for semiconductor processing, X-ray tubes, lamps, field-emission displays (FEDs) flat panel displays (FPDs), some microelectromechanical systems (MEMS) and science instruments for space applications, nuclear systems require a vacuum for their successful operation.

getters hermetic packaging electronic↗
DOE OSTI2016

Dynamics of charge at water-to-semiconductor interface: Case study of wet [0 0 1] anatase TiO 2 nanowire

Here, the behavior of water molecules on the surfaces of the TiO 2 nanowire grown in [0 0 1] direction has been investigated by combining theoretical calculations and experiments. Calculated UV–visible absorption spectra reproduce the main features of the experimental spectra. Computations predict that a photoexcitation followed by a sequence of relaxation events results in photoluminescence across the gap. TiO 2 nanowires in vacuum and aqueous environment exhibit different dynamics of photo-excited charge carriers. In water, computed relaxation of electrons (holes) is approximately 2 (4) times faster compared with vacuum environment. Faster relaxation of holes vs. electrons and specific spatial localization of holes result to formation of long lived charge transfer excitation with positive charge at the surface of the nanowire. Comparison of relaxation process in TiO 2 /water interfaces focusing on different surfaces and nanostructures has potential in identifying structural characteristics of TiO 2 materials important for efficient photo-electrochemical water splitting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Calculation of synchrotron radiation from high intensity electron beam at eRHIC

The Electron-Relativistic Heavy Ion Collider (eRHIC) at Brookhaven National Lab is an upgrade project for the existing RHIC. A 30 GeV energy recovery linac (ERL) will provide a high charge and high quality electron beam to collide with proton and ion beams. This will improve the luminosity by at least 2 orders of magnitude. The synchrotron radiation (SR) from the bending magnets and strong quadrupoles for such an intense beam could be penetrating the vacuum chamber and producing hazards to electronic devices and undesired background for detectors. In this paper, we calculate the SR spectral intensity, power density distributions and heat load on the chamber wall. We suggest the wall thickness required to stop the SR and estimate spectral characteristics of the residual and scattered background radiation outside the chamber.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Quantum electron liquid and its possible phase transition

Purely quantum electron systems exhibit intriguing correlated electronic phases by virtue of quantum fluctuations in addition to electron–electron interactions. To realize such quantum electron systems, a key ingredient is dense electrons decoupled from other degrees of freedom. Here, we report the discovery of a pure quantum electron liquid that spreads up to ~3 Å in a vacuum on the surface of an electride crystal. Its extremely high electron density and weak hybridization with buried atomic orbitals show the quantum and pure nature of the electrons, which exhibit a polarized liquid phase, as demonstrated by our spin-dependent measurement. Furthermore, upon enhancing the electron correlation strength, the dynamics of the quantum electrons change to that of a non-Fermi liquid along with an anomalous band deformation, suggestive of a transition to a hexatic liquid crystal phase. Here, our findings develop the frontier of quantum electron systems and serve as a platform for exploring correlated electronic phases in a pure fashion.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Measurement of vacuum space potential by an emissive probe

The use of an electron-emitting probe (Langmuir and Compton, 1931) to measure the space potential in the vacuum between parallel metal plates is demonstrated, extending the inflection-point interpretation technique of Smith et al. (1979) to the vacuum case. Measurements are made at the off half cycle of during half-wave-rectified sine-wave heating of 3-mm-long 30-micron-diameter W probes positioned with 1-mm precision between 18 x 23-cm Al or Cu plates 7.6 cm apart. The results are presented graphically: potentials of up to + or 30 V are measured with accuracy + or - 0.4 V.

Cho, M. H.↗
DOE OSTI2025

Characterization of Cs 3 Sb photocathodes at cryogenic temperatures

Here, we report measurements of quantum efficiency (QE) and mean transverse energy (MTE) from Cs 3 Sb photocathodes in a wide range of photon energies at both room and cryogenic temperatures. Our measurements show a strong temperature dependence of MTE even at photon energies well above threshold, indicating the presence of strong inelastic scattering of excited electrons during transport before emission into vacuum. We also demonstrate a cathode cooling method that largely preserves the QE while reducing MTE, allowing us to achieve MTEs as low as 58 meV with 3% QE in green light from Cs 3 Sb photocathodes. Our results are crucial for producing brighter electron beams for various photoinjector applications like ultrafast electron diffraction and microscopy, x-ray free-electron lasers, and particle colliders.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis of bismuth tungstate (Bi{sub 2}WO{sub 6}) nanoflakes and their field emission investigation

The nanoflakes of Bismuth Tungstate (Bi{sub 2}WO{sub 6}) were successfully synthesized by a one-step facile hydrothermal route without using any templates or surfactants and field emission investigations of the Bi{sub 2}WO{sub 6} nanoflakes emitter are reported. Structural and morphological analysis of as-synthesized Bi{sub 2}WO{sub 6} nanoflakes has been carried out using X-ray diffraction (XRD) and scanning electron microscope (SEM). Moreover, the field emission characteristics of the Bi{sub 2}WO{sub 6} nanoflakes are found to be superior to the other semiconductor emitters. The synthesized Bi{sub 2}WO{sub 6} nanoflakes emitter delivers current density of ~222.35 μA/cm{sup 2} at an applied electric field of ~7.2 V/μm. The emission current stability investigated at pre-set value of ~2 μA is observed to be fairly good. These observed results demonstrate potential candidate of the Bi{sub 2}WO{sub 6} cathode as an electron source for practical applications in vacuum microelectronic device.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Polarized quasiperiodic structures in pulsar radio emission reflect temporal modulations of non-stationary plasma flow

Bright single pulses of many radio pulsars show rapid intensity fluctuations (called microstructure) when observed with time resolutions of tens of microseconds. Here, we report an analysis of Arecibo 59.5 μs resolution polarimetric observations of 11 P-band and 32 L-band pulsars with periods ranging from 150 ms to 3.7 s. These higher-frequency observations form the most reliable basis for detailed microstructure studies. Close inspection of individual pulses reveals that most pulses exhibit quasi-periodicities with a well-defined periodicity timescale (P{sub μ}). While we find some pulses with deeply modulating microstructure, most pulses show low-amplitude modulations on top of broad smooth subpulse features, thereby making it difficult to infer periodicities. We have developed a method for such low-amplitude fluctuations wherein a smooth subpulse envelope is subtracted from each de-noised subpulse; the fluctuating portion of each subpulse is then used to estimate P{sub μ} via autocorrelation analysis. We find that the microstructure timescale P{sub μ} is common across all Stokes parameters of polarized pulsar signals. Moreover, no clear signature of curvature radiation in vacuum in highly resolved microstructures was found. Our analysis further shows strong correlation between P{sub μ} and the pulsar period P. We discuss implications of this result in terms of a coherent radiation model wherein radio emission arises due to formation and acceleration of electron–positron pairs in an inner vacuum gap over magnetic polar cap, and a subpulse corresponds to a series of non-stationary sparking discharges. We argue that in this model, P{sub μ} reflects the temporal modulation of non-stationary plasma flow.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Photon mirror acceleration in the quantum regime

Reflection of an electron beam by an intense laser pulse is considered. This is the so-called photon mirror configuration for laser acceleration in vacuum, where the energy of the incident electron beam is nearly double-Doppler shifted due to reflection on the laser pulse front. A wave-electron optical description for electron reflection and resonant backscattering, due to both linear electric field force and quadratic ponderomotive force, is provided beyond the paraxial approximation. This is done by assuming that the single electron of the beam is spin-less and therefore its motion can be described by a quantum scalar field whose spatiotemporal evolution is governed by the Klein-Gordon equation (Klein-Gordon field). Our present model, not only confirms the classical results but also shows the occurrence of purely quantum effects, such as partial reflection of the incident electron beam and enhanced backscattering due to Bragg resonance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Generation and characterization of ultrathin free-flowing liquid sheets

The physics and chemistry of liquid solutions play a central role in science, and our understanding of life on Earth. Unfortunately, key tools for interrogating aqueous systems, such as infrared and soft X-ray spectroscopy, cannot readily be applied because of strong absorption in water. Here we use gas-dynamic forces to generate free-flowing, sub-micron, liquid sheets which are two orders of magnitude thinner than anything previously reported. Optical, infrared, and X-ray spectroscopies are used to characterize the sheets, which are found to be tunable in thickness from over 1 μm down to less than 20 nm, which corresponds to fewer than 100 water molecules thick. At this thickness, aqueous sheets can readily transmit photons across the spectrum, leading to potentially transformative applications in infrared, X-ray, electron spectroscopies and beyond. Lastly, the ultrathin sheets are stable for days in vacuum, and we demonstrate their use at free-electron laser and synchrotron light sources.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Direct synthesis of Cu{sub 2}O-RGO nanocomposite on Cu foil by thermal evaporation method and its field emission study

In this work, a facile one step thermal evaporation method for deposition of Cu{sub 2}O nanoparticles on RGO sheets to form Cu{sub 2}O-RGO nanocomposite is discussed. To the best of our knowledge, this is the first report on Cu{sub 2}O-RGO nanocomposite, directly grown on Cu foil by a simple thermal evaporation route. The as –prepared nanocomposite exhibits well dispersed Cu{sub 2}O nanoparticles distributed all over the graphene sheet. Field emission properties of the nanocomposite were investigated at a base pressure of 1*10{sup −8} torr. The turn on field, required to draw emission current density of 0.1µA/cm2, was found to be 3.8V/µm with a maximum emission current density of 80 µA/cm2 at an applied field of 6.8 V/µm. Moreover, the nanocomposite shows fairly good emission stability without significant degradation of emission current. The FE results seem to be encouraging, indicative of potential candidature of the Cu{sub 2}O-RGO nanocomposite emitter as an electron source for practical applications in vacuum nanoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10{sup −5 }Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when no electrons were emitted to the vacuum chamber wall. In addition, the anode fall growth limited the maximum propellant unitization to below ≈75% in the discharge loss curves for this ion stage. Detailed measurements on the plasma properties were carried out for the no-electron emission and 3 A emission conditions. The experimental data are compared with 1-D models, and the effectiveness of the model is discussed. The four key issues that played important roles in the process of building the near-zero different resistance I-V regime are: a significant amount of ionization by the emission electrons, a decrease in the number of reflected electrons in the plume, the electron-temperature increment, and low initial ion energy at the source outlet.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Exploring New Science Domains with Atom Probe Tomography Enabled by an Environmental Transfer Hub

The liquid/solid and gas/solid interface represents a rich scientific and technological frontier for discovery and innovation in many areas of science. However, the direct nano- to atomic-scale characterization of these interfaces is technically challenging within broad range of analytical tools that require high to ultrahigh vacuum conditions. This challenge has been largely addressed within the electron microscopy (EM) community through the development of unique specimen holders and differentially-pumped vacuum systems that allow researchers to probe, in situ, liquid/solid and gas/solid interfaces using electron probes [1]. However, the direct application of APT to liquid/solid and gas/solid interfaces is not possible and requires the development of unique specimen preparation and handling of cryogenically-frozen specimens and/or work with specimens under environmentally-protected conditions. At PNNL, we have developed unique suite of hardware and experimental protocols for the preparation and handling of environmentally-sensitive materials centered around the combination of a unique environmental transfer hub, specimen suitcase device, and modified cryo FIB/SEM capabilities (Fig. 1a) [2-3]. The ability to prepare, manipulate, and transfer specimens under either cryogenic or vacuum conditions thus provides a means to uniquely apply APT analysis to a wide variety of material systems that would not be possible otherwise. Here we describe some specific examples, shown in Figure 1b, of APT analysis applied to temperature sensitive material systems requiring cryo specimen preparation and transfer, as well as air sensitive materials systems requiring vacuum or inert vacuum transfer.

Cryo atom probe tomography, Atom Probe, cryogenic ↗
DOE OSTI2016

New design of the pulsed electro-acoustic upper electrode for space charge measurements during electronic irradiation

The behaviour of space charges injected in irradiated dielectrics has been studied for many years for space industry applications. In our case, the pulsed electro-acoustic method is chosen in order to determine the spatial distribution of injected electrons. The feasibility of a ring-shaped electrode which will allow the measurements during irradiation is presented. In this paper, a computer simulation is made in order to determine the parameters to design the electrode and find its position above the sample. The obtained experimental results on polyethylene naphthalate samples realized during electronic irradiation and through relaxation under vacuum will be presented and discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Reducing Thermal Degradation of Perovskite Solar Cells during Vacuum Lamination by Internal Diffusion Barriers

Current photovoltaic (PV) panels typically contain interconnected solar cells that are vacuum laminated with a polymer encapsulant between two pieces of glass or glass with a polymer backsheet. This packaging approach is ubiquitous in conventional photovoltaic technologies such as silicon and thinfilm solar modules, contributing to thermal management, mechanical reinforcement, and environmental protection to enable the long lifetimes necessary to become financially acceptable. Commercial vacuum lamination processes typically occur at 150 °C to ensure cross-linking and/or glass bonding of the encapsulant to the glass and PV cells. Perovskite solar cells (PSCs) have emerged as a promising next-generation PV technology that is known to degrade under thermal stresses, especially at temperatures above 100 °C. In this study, we determine degradation modes during lamination and engineer internal diffusion barriers within the PSC to withstand the harsh thermal conditions of vacuum lamination. PSCs with self-assembled monolayers at the ITO interface and SnO X layers deposited by atomic layer deposition at the electron extraction side of the device endured vacuum lamination at conditions typical of commercial PV processes (150 °C) without degradation. This work demonstrates that perovskite PV can be integrated into the existing module lamination process, enabling future single- and multijunction modules utilizing perovskite absorbers.

14 SOLAR ENERGY↗
NASA NTRS1983

In-situ TEM investigations of graphic-epitaxy and small particles

Palladium was deposited inside a controlled-vacuum specimen chamber of a transmission electron microscope (TEM) onto MgO and alpha-alumina substrate surfaces. Annealing and various effects of gas exposure of the particulate Pd deposits were studied in-situ by high resolution TEM and electron diffraction. Whereas substrate temperatures of 500 C or annealing of room temperature (RT) deposits to 500 C were needed to obtain epitaxy on sapphire, RT deposits on MgO were perfectly epitaxial. For Pd/MgO a lattice expansion of 2 to 4% was noted; the highest values of expansion were found for the smallest particles. The lattice expansion of small Pd particles on alumina substrates was less than 1%. Long-time RT exposure of Pd/MgO in a vacuum yielded some moblity and coalescence events, but notably fewer than for Pd on sapphire. Exposure to air or oxygen greatly enhanced the particle mobility and coalescence and also resulted in the flattening of Pd particles on MgO substrates. Electron-beam irradiation further enhanced this effect. Exposure to air for several tens of hours of Pd/MgO led to strong coalescence.

Heinemann, K.↗
NASA NTRSDate not supplied

Thermal Analysis of the Advanced Modular Power Systems (AMPS) Power Electronic Modules

In an effort to transform future space power system architectures and operations, the Advanced Modular Power Systems (AMPS) project is currently developing an interface standard for power electronic modules to enable modular architectures for space power systems. Each architecture would consist of one or more modular electronic units (MEU) that would comprise of a tailored combination of modules. The standard currently comprises modules enabling switchgear, power conversion, and data interfacing. The objective of the AMPS project is to enable the modularity and interchangeability of different architectures using these standardized modules in hopes of reducing complexity and cost, increasing inherent redundancy and reliability, and minimizing power system redesign for future programs. A key enabler to these future modular architectures will be the thermal management system, which has to contend with acquiring heat from the electronics modules at the card level and then transporting that heat to the radiator of the larger system. The focus of this paper, therefore, will be the thermal design and analysis of multiple AMPS power electronics modules and the development of their thermal-vacuum test.

Modular Power Electronics↗
DOE OSTI2015

Suppression of shunting current in a magnetically insulated coaxial vacuum diode

Real-time investigations of the dynamics of explosive electron emission from a high-voltage cathode holder made of nonmagnetic stainless steel in a magnetically insulated coaxial vacuum diode have been performed. It has been shown that aging the cathode with several tens of voltage pulses at a field of 1–2 MV/cm provides a stray emission delay ranging from hundreds of picoseconds to a nanosecond or more. In addition, the magnetic field must be configured so that the magnetic lines would not cross the vacuum gap between the diode case and the cathode holder in the region behind the emitting edge of the cathode. These efforts provide conditions for stable emission of the working beam from a graphite cathode with a sharp emitting edge.

36 MATERIALS SCIENCE↗