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At least 73 records · Page 4

All sources NASA NTRS DOE OSTI

DOE OSTI2025

Densification, microstructure, and mechanical properties of Mo–30W alloys fabricated from conditioned powders

Refractory alloys, such as molybdenum-based systems, are attracting growing interest for applications in extreme environments, such as in the nuclear and aerospace industries. Recent advances in sintering technologies, coupled with mechanical alloying, have enabled the tailored design of these alloys by leveraging powder characteristics to control final microstructures and mechanical properties. In this study, Mo-30W alloys were fabricated using electric field-assisted sintering (EFAS) from ball-milled powders with and without hydrogen treatment to investigate the influence of surface oxides on material properties and sintering behavior. The results revealed that samples processed from as-ball-milled powder contained a high density of oxides within the microstructure, whereas oxide presence was significantly reduced in samples fabricated from hydrogen-treated powders. Interestingly, the two powder types led to opposite trends in grain size distribution: samples from untreated powders exhibited grain refinement from sample periphery to the center, while samples from hydrogen-treated powders showed grain coarsening toward the center. This behavior is attributed to temperature gradients present during sintering due to electrical percolation pathway differences during Joule heating. The powder surface oxides may have influenced the temperature distribution and grain evolution. Microhardness profiles measured along both axial and thickness directions were consistent with the grain size distribution. Furthermore, oxide films on powder surfaces have delayed densification by hindering particle necking and atomic diffusion during sintering.

36 - MATERIALS SCIENCE↗

DOE OSTI2021

Finite-size correction for slab supercell calculations of materials with spontaneous polarization

Abstract The repeated slab approach has become a de facto standard to accurately describe surface properties of materials by density functional theory calculations with periodic boundary conditions. For materials exhibiting spontaneous polarization, we show that the conventional scheme of passivation with pseudo hydrogen is unable to realize a charge-neutral surface. The presence of a net surface charge induces via Gauss’s law a macroscopic electric field through the slab and results in poor size convergence with respect to the thickness of the slab. We propose a modified passivation method that accounts for the effect of spontaneous polarization, describes the correct bulk limits and boosts convergence with respect to slab thickness. The robustness, reliability, and superior convergence of energetics and electronic structure achieved by the proposed method are demonstrated using the example of polar ZnO surfaces.

Chemistry↗

NASA NTRS1975

High efficiency graded band-gap Al/x/Ga/1-x/As-GaAs p-on-n solar cell

A theoretical analysis of p-on-n (p/n) graded band-gap Al/x/Ga/1-x/As-GaAs solar cells including all practical energy loss mechanisms predicts air mass zero efficiencies of 17.3%. The energy losses include those due to spectral reflection, surface, bulk and junction recombination currents, and series resistance. The device consists of a layer of p-type Al/x/Ga/1-x/As 3.5-micron thick on top of an n-type GaAs substrate. The graded band-gap is achieved by decreasing x from 0.35 at the surface to zero at the junction. The same structure without the graded Al concentration, no longer an optimum device, has an efficiency of 10.4%. The primary function of the graded band-gap material is the reduction of surface and bulk recombination losses in the surface layer by a built-in electric field. A comparison of the p/n structure with an optimized n/p structure indicates that the latter has a slightly higher efficiency (17.7%) for assumed minority carrier diffusion lengths and surface recombination velocity.

Hutchby, J. A.↗

DOE OSTI2021

Rationalizing energy level alignment by characterizing Lewis acid/base and ionic interactions at printable semiconductor/ionic liquid interfaces

Charge transfer and energy conversion processes at semiconductor/electrolyte interfaces are controlled by local electric field distributions, which can be especially challenging to measure. Furthermore, we leverage the low vapor pressure and vacuum compatibility of ionic liquid electrolytes to undertake a layer-by-layer, ultra-high vacuum deposition of a prototypical ionic liquid EMIM + (1-ethyl-3-methylimidazolium) and TFSI – (bis(trifluoromethylsulfonyl)-imide) on the surfaces of different electronic materials. We consider a case-by-case study between a standard metal (Au) and four printed electronic materials, where interfaces are characterized by a combination of X-ray and ultraviolet photoemission spectroscopies (XPS/UPS). For template-stripped gold surfaces, we observe through XPS a preferential orientation of the TFSI anion at the gold surface, enabling large electric fields (~10 8 eV m –1 ) within the first two monolayers detected by a large surface vacuum level shift (0.7 eV) in UPS.

14 SOLAR ENERGY↗

DOE OSTI2021

Propagation of atmospheric pressure plasmas through interconnected pores in dielectric materials

We report the propagation of atmospheric pressure plasmas (APPs) on and through porous dielectric materials is being investigated for plasma-catalysis and functionalizing biomedical materials for tissue scaffolding and bone regeneration. Such plasma functionalization improves wettability and cell attachment, and so uniformity of the treatment of the pore surfaces is important. The method of propagation of APPs through porous media is not well characterized. In this paper, we discuss results from a computational investigation of humid air APPs propagating through short fully interconnected pore-chains in a dielectric substrate. The properties of the dielectric and pores (diameter 150 μm) were chosen to resemble bone scaffolding. We found that photoionization is an important feature in plasma propagation through pore-chains to seed electrons in the following pore in the chain. This seeding of electrons in regions of high electric field allows for the formation of micro-streamers and surface ionization waves. This is particularly important when the openings between pores are small. The orientation of the pore-chain with respect to the applied electric field has a significant impact on plasma generation, mode of propagation, and fluences of short-lived, reactive species to the surfaces of the pores. The uniformity of fluences of charged and short-lived neutral species to the pore surfaces decreases as the angle of the pore chain deviates from being aligned with the applied electric field. Diffusion within pores

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1973

Study of photoemission and work function of large surface areas, phase 3, phase 4

The photoemission of materials which might be used in probe measurements of the exo-atmospheric electric field is considered by evaluating the wavelength dependence of their photoelectric yield for eleven elements over the range 800 to 3200 A. Yield data for zinc, copper beryllium, platinum, cadmium, graphite, carbon, gold, silver, tantalum, and tungsten show that copper-beryllium is a preferred material. Silver has one of the highest photoemissions when exposed to solar radiation.

Source record↗

DOE OSTI2023

A review of transport models in charged porous electrodes

There is increased interest in many different processes based upon interactions between a charged solid surface and a liquid electrolyte. Energy storage in capacitive porous materials, ionic membranes, capacitive deionization (CDI) for water desalination, capacitive energy generation, removal of heavy ions from wastewater streams, and geophysical applications are some examples of these processes. Process development is driven by the production of porous materials with increasing surface area. Understanding of the physical phenomena occurring at the charged solid-electrolyte interface will significantly improve the design and development of more effective applied processes. The goal of this work is to critically review the current knowledge in the field. The focus is on concepts behind different models. We start by briefly presenting the classical electrical double layer (EDL) models in flat surfaces. Then, we discuss models for porous materials containing macro-, meso-, and micro-pores. Some of the current models for systems comprising two different pore sizes are also included. Finally, we discuss the concepts behind the most common models used for ionic transport and Faradaic processes in porous media. The latter models are used for simulation of electrosorption processes in porous media.

42 ENGINEERING↗

NASA NTRS1999

Electric Field Double Probe Measurements for Ionospheric Space Plasma Experiments

Double probes represent a well-proven technique for gathering high quality DC and AC electric field measurements in a variety of space plasma regimes including the magnetosphere, ionosphere, and mesosphere. Such experiments have been successfully flown on a variety of spacecraft including sounding rockets and satellites. Typical instrument designs involve a series of trades, depending on the science objectives, type of platform (e.g., spinning or 3-axis stabilized), expected plasma regime where the measurements will be made, available telemetry, budget, etc. In general, ionospheric DC electric field instruments that achieve accuracies of 0.1 mV/m or better, place spherical sensors at large distances (10m or more) from the spacecraft body in order to extend well beyond the spacecraft wake and sheath and to achieve large signal-to-noise ratios for DC and long wavelength measurements. Additional sets of sensors inboard of the primary, outermost sensors provide useful additional information, both for diagnostics of the plasma contact potentials, which particularly enhance the DC electric field measurements on non-spinning spacecraft, and for wavelength and phase velocity measurements that use the spaced receiver or "interferometer" technique. Accurate attitude knowledge enables B times V contributions to be subtracted from the measured potentials, and permits the measured components to be rotated into meaningful geophysical reference frames. We review the measurement technique for both DC and wave electric field measurements in the ionosphere discussing recent advances involving high resolution burst memories, multiple baseline double probes, new sensor surface materials, biasing techniques, and other considerations.

Pfaff, R.↗

NASA NTRSDate not supplied

Electrostatic charging of the lunar regolith

Lunar regolith dust particles accumulate charge and interact electrostatically with rover wheels, astronaut boots, and equipment. We have developed instrumentation for in situ measurements of the electrostatic charge developed by the interactions of lunar regolith dust with the space-rated materials on these devices. This instrument is also capable of measuring the distribution of electric fields on or near the lunar surface and the ion currents present near the lunar surface. We also report on our efforts to characterize the charging behavior of lunar dust in low gravity environments. This behavior is nonintuitive due to complex interactions between individual dust grains. We are developing an experiment to study this interaction in a microgravity vacuum environment. Better understanding of this interaction will allow for improved dust mitigation on the lunar surface.

electrostatics↗

DOE OSTI2024

Massive, long-lived electrostatic potentials in a rotating mirror plasma

Abstract Hot plasma is highly conductive in the direction parallel to a magnetic field. This often means that the electrical potential will be nearly constant along any given field line. When this is the case, the cross-field voltage drops in open-field-line magnetic confinement devices are limited by the tolerances of the solid materials wherever the field lines impinge on the plasma-facing components. To circumvent this voltage limitation, it is proposed to arrange large voltage drops in the interior of a device, but coexist with much smaller drops on the boundaries. To avoid prohibitively large dissipation requires both preventing substantial drift-flow shear within flux surfaces and preventing large parallel electric fields from driving large parallel currents. It is demonstrated here that both requirements can be met simultaneously, which opens up the possibility for magnetized plasma tolerating steady-state voltage drops far larger than what might be tolerated in material media.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Production of warm ions in electron beam generated E × B plasma

Several recent experiments have demonstrated low-damage processing of 2D materials, such as graphene and single crystal diamond, using electron beam (e-beam) generated plasmas with applied crossed electric and magnetic (E × B) fields. Here, the low damage of these sensitive materials is commonly attributed to the low energy of ions incident to the substrate surface and the ion confinement in E x B fields. In this work, measurements of atom and ion velocity distribution functions in an e-beam E × B plasma at sub-mTorr argon pressures using a laser-induced fluorescence diagnostic revealed the presence of a warm population of ions with temperatures of ~ 1 eV that are sufficient to destroy the ion confinement in E × B fields and drive the ion flux by cross field diffusion in the direction opposite to the applied electric field, toward the plasma-bounded walls or substrate. Thus, it is this nearly ambipolar diffusion process that is responsible for the flux of charged particles impinging on the wall/substrate surface.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1975

Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon, George Williams College, Lake Geneva, Wis., September 30-October 4, 1974, Proceedings

The papers deal with solar-wind and magnetospheric interactions with the moon, ancient and present-day lunar surface magnetic and electric fields, the dynamics and evolution of the lunar atmosphere, the lunar record of solar radiation, and nonmeteoric transport of lunar surface materials. Topics discussed include bow-shock protons in the lunar environment, energetic ion events during the lunar night, mapping of the lunar surface magnetic field from orbital observations of mirrored electrons, geomagnetic disturbances induced by the moon, the relationship between lunar topography and limb compressions, measurements of lunar sky brightness, atmospheric supply and loss mechanisms on the moon, the nature and composition of the lunar atmosphere, molecular gas species in that atmosphere, and vacuum-UV spectroscopic measurements of the surface properties of lunar materials. Individual items are announced in this issue.

Source record↗

NASA NTRS1986

Static current-sheet models of quiescent prominences

A particular class of theoretical models idealize the prominence to be a discrete flat electric-current sheet suspended vertically in a potential magnetic field. The weight of the prominence is supported by the Lorentz force in the current sheet. These models can be extended to have curved electric-current sheets and to vary three-dimensionally. The equation for force balance is 1 over 4 pi (del times B) times Bdel p- p9 z=zero. Using Cartesian coordinates we take, for simplicity, a uniform gravity with constant acceleration g in the direction -z. If we are interested not in the detailed internal structure of the prominence, but in the global magnetic configuration around the prominence, we may take prominence plasma to be cold. Consideration is given to how such equilibrium states can be constructed. To simplify the mathematical problem, suppose there is no electric current in the atmosphere except for the discrete currents in the cold prominence sheet. Let us take the plane z =0 to be the base of the atmosphere and restrict our attention to the domain z greater than 0. The task we have is to solve for a magnetic field which is everywhere potential except on some free surface S, subject to suit able to boundary conditions. The surface S is determined by requiring that it possesses a discrete electric current density such that the Lorentz force on it is everywhere vertically upward to balance the weight of the material m(S). Since the magnetic field is potential in the external atmosphere, the latter is decoupled from the magnetic field and its plane parallel hydrostatic pressure and density can be prescribed.

Wu, F.↗

DOE OSTI2026

Toward the origins of binding energy shifts and “satellites” formation during plasma-XPS measurements

In-plasma x-ray photoelectron spectroscopy (plasma-XPS) emerges as a powerful platform for real-time, in situ chemical analysis under conditions relevant to semiconductor processing and other plasma-enabled technologies. This study investigates the origins of binding energy (BE) shifts and the formation of “satellite” peaks observed during plasma-XPS measurements across conductive, dielectric, and gas-phase systems. Using a standard laboratory-based ambient pressure XPS apparatus coupled with an alternating current (AC)-driven capacitively coupled plasma source, we demonstrate that metastable surface species, such as transient Au oxides, can be detected during plasma exposure, revealing chemical states that are hardly accessible using conventional ultrahigh vacuum (UHV) XPS. In dielectric samples (e.g., undoped diamond, sapphire), we observe pressure- and plasma-type-dependent BE shifts of more than 50 eV, attributed to x-ray-induced and plasma-mediated surface charging. These shifts are mitigated at higher pressures/plasmas or in electronegative plasmas (e.g., O 2 ), the latter due to enhanced charge compensation mechanisms involving slow negative ions. For gas-phase species, AC-plasma excitation leads to spectral broadening and the emergence of “satellite” peaks with energy separations of a few electron volts, linked to oscillating local plasma potentials in the probing volume. Furthermore, these findings highlight the complex and important interplay between plasma parameters, surface charging, and local electric fields in shaping XPS spectra. Overall, plasma-XPS emerges as a critical metrological tool for probing transient surface chemistry, with implications for semiconductor processing, material synthesis, and plasma diagnostics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1975

A method for unique identification of relativistic /greater than 0.5/ magnetic monopoles with a fast film Cerenkov detector

A magnetic monopole traversing a dielectric medium at a velocity greater than the phase velocity of light in that medium, will give rise to Cerenkov radiation with the electric field tangent to the cone generated by the photon wave propagation vector, and the magnetic field normal to that surface. This is the opposite polarization to that encountered with an electric charge. It is proposed that either by inserting a linearly polarizing layer between the radiator and the photographic emulsion, or by selecting a linearly polarizing material as the radiator, one could directly observe the field polarization by examining the photographic image and thus uniquely identify a magnetic monopole. The ability of the detector is further enhanced by the index of refraction dependence of the Cerenkov output from a magnetic monopole.

Pinsky, L. S.↗

DOE OSTI2026

Plasmon and Photon Excitations in Two-Dimensional and Layered Materials

Light-matter interactions in layered and two-dimensional materials allows one to achieve extreme optical confinement approaching the atomic scale, enabling exploration of new materials phenomena. Layered narrow bandgap and zero bandgap materials, such as black phosphorus and graphene, support unusual and intriguing quantum-confined electronic states in thin layers and surface electronic states. The incomplete screening of applied electrostatic fields in ultrathin materials permits the exploration of light-matter interactions at high electric fields and over a wide range of carrier densities in a single sample, facilitating exploration of the optical and plasmonic properties of ultrathin and layered materials under electrochemical potential control. We have made advances in understanding the nature of optical interband and intraband plasmon excitations in layered materials such as graphene, black phosphorus, molybdenum diselenide, and molybdenum ditelluride.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2026

Measuring Loss Tangents of Substrates for Superconducting Qubits with Part-per-Billion Precision

We report precision measurements of dielectric loss tangents in substrates for superconducting qubits using an ultra-high quality factor niobium SRF cavity operating at millikelvin temperatures and low electric fields. Multiple substrate types and surface treatments are compared to assess how processing impacts microwave dissipation. The RF results are correlated with materials analysis, including ToF-SIMS and XPS, to identify dominant loss mechanisms. This combined study links microscopic surface chemistry to macroscopic performance and provides a framework for materials-driven improvements in qubit coherence and device design.

Bafia, Daniel [Fermilab]↗

DOE OSTI2026

Measuring Loss Tangents of Substrates for Superconducting Qubits with Part-per-Billion Precision

Bafia, Daniel [Fermilab]↗