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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Comparative Studies of Optoelectronic Properties, Structures, and Surface Morphologies for Phosphorus-Doped Poly-Si/SiOx Passivating Contacts

We investigated and compared optoelectronic properties, crystallographic structures, and nanoscale surface morphologies of ex-situ phosphorus-doped polycrystalline silicon (poly-Si)/SiO x passivating contacts, formed by different deposition methods (sputtering, plasma-enhanced chemical vapour deposition (PECVD), and low-pressure chemical vapour deposition (LPCVD)). Across all these deposition technologies, a similar trend is observed: higher diffusion temperatures yield films that are more crystalline but have rougher surface morphologies due to bigger surface crystal grains. Also, the recrystallization process of the as-deposited Si films starts from the SiO x interface, rather than from the film surface and bulk. However, there are some distinct differences among these technologies. Firstly, the LPCVD method yields the roughest surface and smallest degree of crystallinity on finished poly-Si films. In contrast, the PECVD method has the smoothest surface for both as-deposited Si and annealed poly-Si films. Secondly, as-deposited sputtered and PECVD Si films contain only an amorphous phase whereas as-deposited LPCVD films has already had some crystalline phase. Thirdly, the LPCVD phosphorus in-diffusion into the substrate depends strongly on the initial film thickness, whereas for the other two methods it is weakly dependent on thickness.

crystallographic structures↗
DOE OSTI2024

Proton rings from late-forming ballistic sheath fields

Many laser-driven ion experiments have seen ring-like patterns in the proton angular distribution across a wide array of laser and target parameters. These rings can impede measurement due to the small acceptance angle of detectors and often inhibit potential applications. A myriad of explanations for their formation have been proposed, yet most studies attribute them to some aspect of the laser–plasma interaction. Using 3D particle-in-cell simulations, we show that late-forming strong radial electric fields can arise due to charge separation while the beam is in flight, long after the laser–plasma interaction. These fields can accelerate ions to significant divergences (≈ 10°) as they propagate away from the target. We compare our results to a recent experiment where a high intensity, short pulse laser (I 0 ≈ 10 21 W/cm 2 , τ ≈ 30 fs) was incident upon thin (≈ 1 μm) liquid crystal targets. Our simulations capture all the main features of the experimental results—namely, robust ring formation and larger rings for higher energy protons. In addition, we show that rings do not form for sufficiently short preplasma scale lengths. Finally, we develop a phenomenological model to describe the spatiotemporal structure of the radial electric field and use this to explain the proton rings' energy and preplasma dependencies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

A snapshot of high-entropy alloy processing techniques and their effects on resulting mechanical properties

High-entropy alloys (HEAs) exhibit exceptional strength, corrosion resistance, and thermal stability, making them promising candidates for nuclear, aerospace, and other extreme applications. While most prior work has focused on compositional design, manufacturing techniques themselves can alter microstructure and mechanical properties as dramatically as alloy chemistry. This review compiles and compares the effects of processing routes—including arc melting, induction melting, mechanical alloying with spark plasma sintering, and additive manufacturing—on the structure and properties of HEAs. Quantitative comparisons highlight, for example, that SPS-processed alloys can achieve ∼20–45 % higher yield and tensile strength than arc-melted counterparts, while Bridgman solidification produces nearly single-crystal structures with elongation to failure exceeding 80 %. Additive manufacturing routes such as selective laser melting offer fine microstructures but also introduce anisotropy and porosity, leading to yield strengths spanning 100–600 MPa for the same composition. By synthesizing such results, this review provides actionable insight into how processing routes interact with HEA core effects (high entropy, lattice distortion, sluggish diffusion, and cocktail effect) to determine performance, thereby offering a practical guide for optimizing manufacturing strategies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

First use of an InSb crystal for x-ray imaging spectroscopy of highly ionized tungsten in the Wendelstein 7-X stellarator

Advances in time and space resolved measurements of highly charged states of tungsten (W) through x-ray imaging spectroscopy have enabled investigation of impurity transport in the Wendelstein 7-X (W7-X) stellarator. The high-resolution x-ray imaging spectrometer (HR-XIS) system on W7-X utilizes the Bragg diffraction properties of a set of multiple crystals to measure a range of impurity emission lines within sections of the 1–7 Å wavelength range, including transitions of W. A new indium–antimonide crystal has been installed on the HR-XIS system to allow viewing of the 5.5–6.2 Å region focusing on emissions of W. Consequently, many bright W emission lines from W 40+ to W 47+ were observed in this wavelength range, both in plasmas with injected W and in those with only intrinsic W impurity sources, showing the high sensitivity of the diagnostic. Three W 46+ emissions correspond in wavelength and intensity with calculated photon emissivity coefficients and can be exploited for W transport and concentration applications in plasmas with T e ≳ 2.1 keV. Here, an estimate of the core W density behavior in two separate turbulence-reduced ‘high-performance’ (HP) discharges on W7-X is done using the 5.6893 Å W 46+ line. The n W behavior in HP scenarios can be explained by previous experimental results and neoclassical predictions.

XICS↗
DOE OSTI2025

Experimental and computational studies on high-entropy carbide MoNbTaVWC 5 under high pressures

High-entropy carbide, MoNbTaVWC 5 , was synthesized from oxide precursors of the constituent metals, mixed with graphite powder in a microwave-generated hydrogen plasma at 26.66 kPa and 2100 °C. Ambient x-ray diffraction analysis confirms the full conversion of oxide precursors into a single-phase, face-centered cubic structure with a lattice parameter a = 4.3309 Å. Nanoindentation measured a hardness of 24.5 ± 1.3 GPa and an elastic modulus of 386 ± 22 GPa. The synthesized sample, mixed with a copper pressure marker, was studied by the radial x-ray diffraction technique with beryllium gasketing in a diamond anvil cell up to 70 GPa. The experimentally measured pressure–volume curve and shear strength were compared with theoretical predictions using the special quasi-random structure technique and density functional theory. MoNbTaVWC 5 achieved a 12% volume compression at 70 GPa and exhibited a high shear strength of 6.6 GPa. The present study demonstrates that the high-entropy carbide MoNbTaVWC 5 exhibits exceptional incompressibility and high strength under extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Spatiotemporally resolved measurements of electric field around a piezoelectric transformer using electric-field induced second harmonic (E-FISH) generation

When a piezoelectric transformer (PT) is actuated at its second harmonic frequency by a low input voltage, the generated electric field at the distal end can be sufficient to breakdown the surrounding gas, making them attractive power sources for non-equilibrium plasma generation. Understanding the potential and electric fields produced in the surrounding medium by the PT is important for effectively designing and using PT plasma devices. In this work, the spatiotemporally resolved characteristics of the electric field generated by a PT operating in open air have been investigated using the femtosecond electric field-induced second harmonic generation (E-FISH) method. Here, electric field components were determined by simultaneously conducting E-FISH measurements with the incident laser polarized in two orthogonal directions relative to the PT crystal. Results of this work demonstrate the spatial distribution of electric field around the PT’s output distal end and how it evolves as a function of time. Notably, the strongest electric field appears on the face of the PT’s distal surface, near the top and bottom edges and decreases by approximately 70% over 3 mm. The time delay between the PT’s input voltage and measured electric field indicates that there is an about 0.45 phase difference between the PT’s input voltage and output signal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

High-order harmonic generation in solid C 60

High-order harmonic generation (HHG) has unleashed the power of strong laser physics in solids. Here we investigate HHG from a large system, solid C 60 , with 240 valence electrons engaging harmonic generation at each crystal momentum. We employ the density functional theory and the time-dependent Liouville equation of the density matrix to compute HHG signals. We find that under a moderately strong laser pulse, HHG signals reach 15th order, consistent with the experimental results from C 60 plasma. The helicity dependence in solid C 60 is weak, due to the high symmetry. In contrast to the general belief, HHG is unsuitable for band structure mapping in C 60 . However, we find a window of opportunity using a long wavelength, where harmonics are generated through multiple-photon excitation. In particular, the fifth-order harmonic energies closely follow the transition energy dispersion between the valence and conduction bands. Finally, this finding is expected to motivate future experimental investigations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Morphology, microstructure, and doping behaviour: A comparison between different deposition methods for poly-Si/SiO x passivating contacts

In this work, we study how crystallographic structures, optoelectronic properties, and nanoscale surface morphologies of ex situ phosphorus-doped polycrystalline silicon (poly-Si)/SiO x passivating contacts, formed by different deposition methods (sputtering, plasma-enhanced chemical vapour deposition [PECVD], and low-pressure chemical vapour deposition [LPCVD]), are investigated and compared. Across all these deposition technologies, we noted the same trend: higher diffusion temperatures yield films that are more crystalline but that have rougher surface morphologies due to bigger surface crystal grains. Also, the recrystallization process of the as-deposited Si films starts from the SiO x interface, rather than from the film surface and bulk. However, there are some distinct differences among these technologies. First, the LPCVD method yields the lowest deposition rate, roughest surfaces, and smallest degree of crystallinity on finished poly-Si films. In contrast, the PECVD method has the highest deposition rate and smoothest surfaces for both as-deposited Si and annealed poly-Si films. Second, as-deposited sputtered and PECVD Si films contain only an amorphous phase, whereas as-deposited LPCVD films already has some crystalline phase. Third, the LPCVD phosphorus in-diffusion into the substrate depends strongly on the initial film thickness, whereas for the other two methods, it is weakly dependent on thickness. Finally, the passivation quality of every poly-Si film type has different responses to the film thickness and diffusion temperature, suggesting that the ex situ doping optimization should be performed independently.

14 SOLAR ENERGY↗
DOE OSTI2022

Commercialization of microcavity plasma devices and arrays: Systems for VUV photolithography and nanopatterning, disinfection of drinking water and air, and biofilm deactivation for medical therapeutics

Abstract A little more than two decades after the introduction of the first microcavity plasma devices, a growing body of commercial products based on the remarkable properties of these low‐temperature, atmospheric plasmas is now available. Following a brief review of early microplasma lamp development, this article describes microplasma‐based devices and systems currently being manufactured for applications in photolithography, photopatterning, and other nanofabrication processes, such as atomic layer deposition, spectroscopic identification and analysis of materials (including wide bandgap crystals), the disinfection of drinking water in off‐grid communities, deactivating COVID‐19 and other pathogens in air and on surfaces in public spaces, and vacuum ultraviolet lamps for driving atomic clocks. The microplasma‐based treatment of otitis media in the human ear will also be discussed.

42 ENGINEERING↗
DOE OSTI2026

Patterned, Low-Temperature Growth of Transition Metal Dichalcogenides for Low Resistance Raised Contacts

Transition metal dichalcogenide (TMD) monolayers are promising channel materials for next-generation electronic devices. A challenge is the high contact resistance between monolayer TMDs and metal contacts, especially for holes. Here, in this regard, raised source/drain contacts are promising. However, the direct, patterned growth of raised contacts at CMOS-compatible temperatures remains largely unresolved. We present plasma-free selenization and sulfurization of metal oxides at substrate temperatures down to 400 °C, compatible with back-end-of-line thermal budgets. To achieve growth at such temperatures, gas-phase chalcogen precursors are first thermally activated at 950 °C. Films grown on single-crystal monolayer TMDs exhibit high crystal quality, as confirmed by transmission electron microscopy. Raised contacts on WSe 2 monolayers fabricated using this approach yield a low hole contact resistance of 0.3 kΩ·μm after chemical doping. This process is shown to be applicable to growing various TMDs, including WS 2 , MoSe 2 , MoS 2 , PtSe 2 , and NbS 2 .

contact engineering↗
DOE OSTI2022

Gas-phase oxidation and nanoparticle formation in multi-element laser ablation plumes

The evolution from gas-phase oxidation to nanoparticle and agglomerate formation was studied in nanosecond laser-produced plasmas of a multi-principal element alloy target in air. Here gas-phase oxidation of plasma species was monitored in situ via optical emission spectroscopy, while a custom-built single particle mass spectrometer was used to measure size and compositions of agglomerated nanoparticles formed in laser ablation plumes. Ex situ analysis employing transmission electron microscopy was used to study nanoparticle morphology, crystal structure, and element distribution at the nanoscale. Emission spectra indicate that gas-phase oxidation of elements in the alloy target are formed at varying times during plume evolution, and mass spectrometry results indicate fractal agglomerates contain all principal alloying elements and their oxides. Finally, electron microscopy characterization illustrates that these agglomerates consist of multiple material types: sub-10 nm diameter amorphous, multi-element nanoparticles, ≈10–30 nm diameter Ti-rich crystalline oxide nanoparticles, and ejected base material. Results highlight that the multi-component target composition impacts molecular formation in the gas phase and the morphology, composition, and structure of nanoparticles and agglomerates formed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ion Binding Properties of a Naturally Occurring Metalloantibody

LT1009 is a humanized version of murine LT1002 IgG1 that employs two bridging Ca2+ ions to bind its antigen, the biologically active lipid sphingosine-1-phosphate (S1P). We crystallized and determined the X-ray crystal structure of the LT1009 Fab fragment in 10 mM CaCl2 and found that it binds two Ca2+ in a manner similar to its antigen-bound state. Flame atomic absorption spectroscopy (FAAS) confirmed that murine LT1002 also binds Ca2+ in solution and inductively-coupled plasma-mass spectrometry (ICP-MS) revealed that, although Ca2+ is preferred, LT1002 can bind Mg2+ and, to much lesser extent, Ba2+. Isothermal titration calorimetry (ITC) indicated that LT1002 binds two Ca2+ ions endothermically with a measured dissociation constant (KD) of 171 μM. Protein and genome sequence analyses suggested that LT1002 is representative of a small class of confirmed and potential metalloantibodies and that Ca2+ binding is likely encoded for in germline variable chain genes. To test this hypothesis, we engineered, expressed, and purified a Fab fragment consisting of naïve murine germline-encoded light and heavy chain genes from which LT1002 is derived and observed that it binds Ca2+ in solution. We propose that LT1002 is representative of a class of naturally occurring metalloantibodies that are evolutionarily conserved across diverse mammalian genomes.

Farokhi, Elinaz↗
DOE OSTI2021

Deuterium retention in MeV ion-irradiated beryllium

Beryllium, as the material of choice for the ITER first wall, will be subject to high energy neutrons during the operation of the fusion device. Such irradiation will create displacement damage in the crystal lattice, which is known to influence hydrogen isotope retention, e.g. in iron and tungsten. Here in our study, we irradiated beryllium samples with high-energy oxygen ions up to various dpa levels (0.01 dpa, 0.1 dpa, and 1 dpa) and subsequently exposed the samples to deuterium plasma at 370 K and 573 K. The amount of retained deuterium was measured by thermal desorption spectroscopy and nuclear reaction analysis and was found to decrease by about 18% in the samples damaged up to 0.1 dpa compared to the undamaged ones. Further damaging up to 1 dpa did not show any additional effects on deuterium retention. Transmission electron microscopy was used to check for the existence of bubbles after plasma exposure.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Design of a Multi-Monochromatic X-ray Imager (MMI) for Kr K-shell line emission

We report the Multi-Monochromatic X-ray Imager (MMI) is a time-gated spectrometer used in implosion experiments at the OMEGA laser facility. From the data, electron temperature and density spatial distributions can be obtained at different implosion times. Previous MMI designs used Ar K-shell emission (3–6 keV) as a spectroscopic tracer and provided a spectral resolution of around 20 eV. However, Ar K-shell line emission becomes less useful at electron temperatures above 2 keV due to over-ionization. Kr K-shell (12–16 keV) has been shown to be an attractive alternative to diagnose hot implosion cores in recent publications. The purpose of this paper is to show a new point design that allows the MMI to detect this higher photon energy range with suitable spectral resolution. The algorithm used to find the optimal design couples a ray-tracing code and an exhaustive parameter space search. This algorithm may be useful as a tool to find optimal MMI designs for other purposes, i.e., other spectral regions for other spectroscopic tracers. So, the main change between the two designs is the replacement of the multi-layer mirror with a flat Bragg Ge (220) crystal. The final Kr K-shell MMI design has a photon energy range from 12 to 16.1 keV.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

The influence of temperature history and flow mixing on the vapor-phase speciation of uranium oxide nanoparticles

The transport of radioactive material following a nuclear event depends heavily on fallout characteristics (e.g., composition, shape, and size), which in turn are controlled by the conditions under which the fallout forms. To this end, we use a novel plasma flow reactor (PFR) to explore how conditions including temperature history and gas mixing influence the chemical speciation and physical characteristics of uranium oxide nanoparticles. The PFR consists of a glass tube attached to an inductively coupled plasma (ICP) torch via an adaptor piece (ring flow injector) located downstream of the plasma-generating RF coil. We increase the gas flow rates from normal ICP operating conditions to higher values both upstream at the RF coil and downstream at the ring flow injector to create four distinct temperature profiles and two distinct gas flow mixing conditions (normal and higher Ar atomic ratios). Ex situ transmission electron microscopy (TEM) analysis is used to determine the crystal structure, morphology, and size distribution of the synthesized particles as a function of temperature and mixing. The particles display a striking dependence on these conditions in terms of the resulting speciation of uranium oxide: lower temperature (higher upstream) and slower cooling (normal downstream with normal Ar atomic ratio mixing) favor the formation of α-UO 3 particles, while faster cooling (higher downstream with higher Ar atomic ratio mixing) and higher temperature (normal upstream) favor the formation of UO 2 particles. The extent of gas mixing dictates particle aggregation: better mixing encourages the particles to aggregate more extensively. Here these results demonstrate the sensitivity of uranium to initial local conditions and can be used to improve our understanding of the kinetics that drive uranium speciation and ultimately inform fallout transport models.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Orientation Control in Epitaxial PdO Thin Films Grown on MgO (001) – Role of Oxygen Chemical Potential

Control of crystal orientations in thin films of functional materials allowsedictive tuning of their strain states, electronic properties, and surface chemical reactivity. Here, conditions for orientation control in epitaxial PdO films are investigated. Due to its tetragonal structure, PdO can form two orientational relationships with the MgO (001). It is shown that, under an oxygen-rich environment provided by oxygen-plasma-assisted molecular beam epitaxy, both (00l)- and (100)-oriented PdO domains form on MgO (001). Subsequent thermal annealing in a vacuum promotes film restructuring to a predominantly (100)-oriented PdO with improved crystallinity. Ab initio calculations reveal that the (001) orientation has lower strain energy but weaker interfacial interactions and serves as an oxygen vacancy sink, whereas the (100) orientation benefits from significantly stronger MgO─PdO bonding. Consequently (100)-oriented domains become favored under oxygen-poor conditions. A mechanism is proposed whereby vacuum annealing drives orientation transformation by generating oxygen vacancies that destabilize the (001) domains and promote (100) ordering. These findings deepen the understanding of how oxygen content impacts interfacial stability and reorganization, thereby offering a route to tune domain orientations in oxide thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Proton damage in (Y,Lu,Gd) 3 (Al,Ga) 5 O 12 :Ce mixed garnet scintillators

Scintillators are vital components for nuclear instrumentation and its applications, including plasma diagnostics and imaging. As yields in controlled fusion experiments increase, the radiation tolerance of scintillator candidates for use in instrumentation is of particular importance. High radiation exposure can damage scintillating materials and alter the optical properties. The effects of radiation damage in Ce-doped mixed garnet ceramics over the compositional range (Y,Gd,Lu) 3 (Al,Ga) 5 O 12 are investigated using optical techniques. The samples were exposed to 200 keV protons to an accumulated fluence of 10 16 protons per square centimeter, then characterized using diffuse reflectance spectroscopy (DRS). DRS with visible light can assess the radiation tolerance of opaque poly-crystalline samples, which can be easily sintered from powders and thus offer distinct advantages in characterization compared to single crystals. Qualitative trends in induced absorption are presented as a function of composition, and the ideal cerium dopant concentration for Y 2 LuAl 5 O 12 is determined to be 0.60–0.75 mol.%.

47 OTHER INSTRUMENTATION↗