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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Atomic-Scale Behavior of Radiation-Resistant ZnO under High-Energy Electron Bombardment

Understanding the atomic structure and defect characteristics of ZnO thin films is crucial for optimizing their electronic properties and performance in advanced applications. Here, we investigate the atomic structure and defect characteristics of atomic layer deposition (ALD)-grown ZnO thin films by using aberration-corrected scanning transmission electron microscopy (STEM). Atomic-resolution imaging identifies prevalent stacking faults, dipole disorder, and various grain boundary types, which are believed to influence the electronic properties of ZnO. Additionally, real-time electron beam exposure experiments demonstrate structural transformations, including crystal growth and surface rearrangements. These findings provide insights into the growth mechanisms of ALD ZnO under high-energy electron irradiation conditions, an important finding for the use of polycrystalline ZnO wide bandgap semiconductors in space-like conditions. In conclusion, our results underscore the capability of STEM in directly visualizing and quantifying atomic-scale defects and beam-induced transformations in radiation-resistant ZnO.

Defects↗
DOE OSTI2022

Highly enhanced ferroelectricity in HfO 2 -based ferroelectric thin film by light ion bombardment

Continuous advancement in nonvolatile and morphotropic beyond-Moore electronic devices requires integration of ferroelectric and semiconductor materials. The emergence of hafnium oxide (HfO 2 )–based ferroelectrics that are compatible with atomic-layer deposition has opened interesting and promising avenues of research. However, the origins of ferroelectricity and pathways to controlling it in HfO 2 are still mysterious. We demonstrate that local helium (He) implantation can activate ferroelectricity in these materials. Additionally, the possible competing mechanisms, including He ion–induced molar volume changes, vacancy redistribution, vacancy generation, and activation of vacancy mobility, are analyzed. These findings both reveal the origins of ferroelectricity in this system and open pathways for nanoengineered binary ferroelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Near-surface damage and mixing in Si-Cl 2 -Ar atomic layer etching processes: Insights from molecular dynamics simulations

Silicon-chlorine-argon (Si-Cl 2 -Ar) atomic layer etching (ALE) is simulated using classical molecular dynamics (MD). The simulations provide a detailed view into the near-surface region during ALE processing. Bombardment of Ar + ions creates a mixed amorphous region that significantly differs from the picture of ideal ALE. There is also a significant change in the Si etch yield and the etch product distribution as a function of Ar + ion fluence. The Si etch yield is the highest at the beginning of the bombardment step but eventually decays to the physical sputtering yield. Atomic Cl and silicon chlorides are major etch products at the start of an ion bombardment step, but quickly decay. Atomic Si yields remain relatively constant as a function of Ar + ion fluence. As a result, a new schematic of Si-Cl 2 -Ar ALE is presented in order to emphasize the complex behavior observed in MD simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Production of Radioisotopes of Scandium for Imaging and Therapy (Final Report)

The theranostic approach is a powerful technique that enables scientists and physicians to diagnose and treat diseases using the same targeting moiety labeled with radionuclides for imaging and therapy. A challenge behind synthesizing and evaluating these theranostic radiopharmaceuticals lies in the production of suitable radionuclides. This study aimed to investigate the production of high radionuclidic purity 43 Sc from enriched [ 46 Ti]TiO 2 for Positron Emission Tomography (PET) and 47 Sc from enriched [ 50 Ti]TiO 2 for targeted radiotherapy, as well as establish a target recycling technique for continued production of these radionuclides. Methods: Targets were prepared with 100 mg of either enriched [ 46 Ti]TiO 2 or [ 50 Ti]TiO 2 , pressed into pellets, and placed into Ta target holders with a 0.127 mm natTi cover foil. The 46 Ti targets were bombarded with 18 MeV protons at 20 µA for 1.5 h, while 50Ti targets were bombarded with 24 MeV protons at 20 µA for 4 or 8 h. The radioscandium nuclides were purified using branched N, N, N’, N’ -tetra-2-ethylhexyldiglycolamide (DGA) resin. The titanium targets were recycled by precipitating the dissolved Ti collected from the column effluent and wash streams, pH adjustment, vacuum filtration, and then drying the solid at 250 °C prior to reforming the target for the subsequent bombardment. The apparent molar activity of the isolated radioscandiums was analyzed by titration with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). The relative imaging performance of 18 F, 43 Sc, and 68 Ga were analyzed with PET images acquired with 30-min static scans. Results: The average radioscandium recovery for 43Sc was 91.7 ± 7.4 %, with a radionuclidic purity of 98.8 %. The average recovery of 47Sc was 89.9 ± 3.9 %, with a radionuclidic purity of 90.8%. The average recovery of enriched TiO2 was 96 ± 4.0 %. The highest apparent molar activity for [43Sc]Sc-DOTA was 23.2 GBq/µmol and 3.39 GBq/µmol for [ 47 Sc]Sc-DOTA. The order of PET resolution from highest to lowest was 18 F > 43 Sc > 68 Ga. Conclusions: This work demonstrates the feasibility of using enriched recycled [ 46 Ti]TiO 2 and [ 50 Ti]TiO 2 targets for the production of the 43 Sc and 47 Sc theranostic isotope pair in high purity.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

α Irradiation Response on the Electronic Transport Properties of p -B 12 P 2

B 12 P 2 , a wide bandgap semiconductor, has been previously reported to self-heal from high-energy electron bombardment as determined from transmission electron microscopy. However, the effect of irradiation on the electronic transport properties of B 12 P 2 has not been studied. We report electrical transport measurements on B 12 P 2 after α irradiation. The temperature-dependent Hall effect was measured on p-type B 12 P 2 after successive α irradiation from 210 Po over a fluence range of 1 × 10 11 –1 × 10 13 α/cm 2 to test for self-healing of B 12 P 2 to α bombardment. Prior to irradiation, B 12 P 2 displayed electrical transport characteristics of both hopping and impurity/defect band conduction due to background impurities and growth-induced defects. Fluences of 5 × 10 12 α/cm 2 or greater caused a decrease in the hole mobility and an increase in defect band conduction, suggesting defect accumulation in B 12 P 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2027

Low thermal budget dopant activation in shallow junctions of implanted Si via Tunable plasma enhanced annealing

Low thermal budget (LTB) annealing has become increasingly critical for shallow junctions as semiconductor devices are scaled down. Plasma Enhanced Annealing (PEA) has emerged as a promising LTB annealing process, however its mechanisms remain unclear. In this study, arsenic and boron implanted silicon wafers were subjected to helium or argon ion bombardment generated by annealing plasmas under controlled ion energies and doses in a home-built annealing reactor. The structural and electrical changes were characterized by four-point probe measurements, secondary ion mass spectrometry, Raman spectroscopy and spectroscopic ellipsometry. A pronounced reduction in sheet resistance, accompanied by a decrease in the damage layer thickness demonstrates the surface selective annealing capability of PEA process. Comparative studies using He and Ar plasmas and related ion bombardment reveal a dependence of activation efficacy on both ion species and the dopant implantation profile. Furthermore, a multi-step annealing mechanism is proposed, consisting of an initial (low dose) structural recovery stage followed by the generation of “extended” defects and concluded at large doses by an enhanced dopant activation. The proposed annealing kinetics are thought to be controlled by ion flux, dose and energy. Finally, these results highlight PEA as an effective, surface-selective, LTB approach for shallow-dopant activation and near surface annealing, and provide mechanistic insights into PEA processes.

dopant activation↗
DOE OSTI2024

Net lithium deposition and dominant self-sputtering in lithium tokamak experiment-β with a liquid lithium wall

We observed enhanced net lithium deposition and lithium erosion, possibly dominated by physical sputtering of lithium by lithium-ion bombardment, on the outer plasma-facing surface in the Lithium Tokamak eXperiment-β (LTX-β) during liquid lithium wall operations. Silicon crystal samples with micro-trenches (30 μm × 30 μm × 2–7 μm deep) were exposed to hydrogen plasmas in LTX-β for solid and liquid lithium wall operations. Post-mortem analysis using X-ray photoelectron spectroscopy combined with argon ion sputtering measured net lithium deposition of 8.2 or 21 nm on the silicon crystal surface exposed for ~ 50 repeated shots of ~ 50-ms hydrogen plasma discharges during the liquid lithium wall operations at a vessel temperature of 475 K. Energy dispersive X-ray spectroscopy measured oxygen concentration patterns on the micro-trench floors, which were due to oxidized lithium deposition. Using the inhomogeneous oxygen concentration pattern caused by an ion-shadowing effect associated with the micro-trench’s geometric structure, we determined a polar incident ion direction of 68.4 ± 1.6° referenced to the surface normal direction. This observation was well-explained by the hypothesis that self-sputtering of Li was a dominant lithium erosion source in addition to lithium sputtering by hydrogen bombardment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS 2

Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS 2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS 2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies.

Two-dimensional materials↗
DOE OSTI2025

Evidence for an Early Formation of Serenitatis Basin at 4.25 Ga Shifts Lunar Chronology

Troctolite sample 76535, collected in Serenitatis basin during Apollo 17, formed at least 50 km deep, experienced maximum shock pressures of 6 GPa, and has a 40 Ar/ 39 Ar excavation age of 4.25 Ga. Previous work attributed 76535 to the South Pole-Aitken (SPA) basin, presumably dating the SPA-impact and constraining lunar bombardment history. Here we use the iSALE-2D shock-physics code and gravity inversion modeling to determine if instead the Serenitatis impact event excavated 76535. We find nearly 140,000 km 3 of material (∼2% of near-surface ejecta) matching the depth and pressure constraints of 76535 is displaced to the surface during crater collapse of a Serenitatis-like impact event. We conclude that the Serenitatis impact event possibly excavated 76535, redefining its age to 4.25 Ga, 300 My older than the consensus age based on Apollo 17 samples. This finding would provide an important anchor point where lunar chronology where bombardment flux is especially uncertain.

Bjonnes, Evan [Lawrence Livermore National Laborat↗
DOE OSTI2020

Installation and commissioning of the ion source systems for the new spallation neutron source 2.5 MeV injector

The U.S. Spallation Neutron Source (SNS) is a state-of-the-art neutron scattering facility delivering the world’s most intense pulsed neutron beams to a wide array of instruments, which are used to conduct investigations in many fields of engineering, physics, chemistry, material science, and biology. Neutrons are produced by spallation of liquid Hg by the bombardment of short (∼1 µs), intense (∼35 A) pulses of protons delivered at 60 Hz by an accumulator ring which is fed by a high-intensity, 1 GeV, H− LINAC (linear accelerator). This facility has operated nearly continuously since 2006 but has recently undergone a 4-month maintenance period, which featured a complete replacement of the 2.5 MeV injector feeding the LINAC. The new injector was developed at ORNL in an off-line beam test facility and consists of an ion source, low energy beam transport, and a Radio Frequency Quadrupole (RFQ). This report first describes the installed configuration of the new injector detailing the ion source system. The first beam current, RFQ transmission, emittance, and energy measurements from the injector installed on the SNS are reported. These data not only show a significant performance improvement for our existing facility but will also make accessible the higher beam current requirements for future SNS upgrade projects: the proton power upgrade and second target station.

Welton, R. F.↗
DOE OSTI2026

Low-energy ion beam sputtering of polycrystalline diamond

Ion beam milling is a highly versatile and precise technique for the microfabrication of diamond films, enabling controlled material removal at both micrometer and sub-micrometer scales while accommodating complex geometries and surface features. Comprehensive sputtering yield data are essential for process optimization. In this work, we systematically measure the sputter yield of polycrystalline diamond bombarded with $\textrm{N}_2^+$, Ne + , Ar + , Kr + , and Xe + ions over an energy range of 300–900 eV and beam incidence angles of 0°−80°, providing data critical for precision machining applications. Results show that the sputter yield increases with both ion energy and the incidence angle and decreases with increasing ion mass. For $\textrm{N}_2^+$ ions, the sputter yield is largely insensitive to ion energy and exceeds values expected for pure physical sputtering. The concurrent formation of volatile C 2 N 2 molecules during $\textrm{N}_2^+$ ion bombardment suggests that the process is dominated by chemical sputtering. The absence of a peak in the dependence of the sputter yield on the beam incidence angle expected at oblique incidence angles is attributed to the effects of surface roughness.

Materials science↗
DOE OSTI2025

Grid-Assisted Direct-Current Magnetron Sputtering of Titanium: Plasma Discharge Diagnostics

Grid-assisted magnetron sputtering is attractive for the deposition of ultrathick Be coatings in inertial confinement fusion (ICF) applications because it offers improved control over the plasma. Here, we investigate the plasma discharge characteristics of grid-assisted direct current magnetron sputtering with Ti as a surrogate sputter target material instead of Be. We map the magnetic field of our magnetron source assembly, study the current-voltage characteristics of both the source and the substrate, and measure the energy distributions of ions bombarding the film surface during growth. The results reveal a slightly asymmetric magnetic field of the magnetron source array and strong dependencies of the plasma discharge characteristics on both the grid and the substrate voltages. Positive grid voltage increases both target and substrate currents, increases the plasma potential, and broadens the energy distributions of ions bombarding the substrate. Grid biasing effects on the plasma discharge characteristics and substrate current can be attributed to corresponding changes to the plasma potential, while substrate biasing effects are more complex and nonlinear. Furthermore, these results demonstrate that grid-assisted deposition offers additional flexibility in controlling the deposition process for tuning properties of ultrathick films for ICF applications.

ICF targets↗
DOE OSTI2020

Superconducting films of MgB 2 via ion beam mixing of Mg/B multilayers

The growth of smooth superconducting MgB 2 films in a non-epitaxial regime is challenging. Here, we study the formation of superconducting MgB 2 films by solid-phase reactive inter-diffusion of sputter-deposited Mg/B multilayers, employing ion beam mixing to disperse the multilayers prior to thermal annealing. The multilayers are intermixed by room-temperature bombardment with 500 keV Xe ions to doses up to 4 × 10 16 cm –2 , followed by thermal annealing to form MgB 2 . Results show that such an intermixing step leads to a dramatic reduction in surface roughness of superconducting films. However, lattice defects produced by ion bombardment reduce the critical superconducting transition temperature, an effect which scales monotonically with ion dose. The critical temperature can be recovered by an additional defect annealing step at $700\ ^{\circ}{\rm C}$.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Atomic scale etching of diamond: insights from molecular dynamics simulations

Diamond is a promising material for multiple applications in quantum information processing and sensing as well as applications in microelectronics. However, diamond devices can be limited by surface defects that compromise charge stability and spin coherence, among others. Improved strategies in plasma etching of diamond could play an important role in minimizing or eliminating these defects. In this work, we explore plasma-assisted atomic scale etching of diamond using argon ions (Ar + ), hydrogen ions (H + ) and hydrogen atoms (H). We employ classical molecular dynamics (MD) simulations and test several interatomic potentials based on the Reactive Empirical Bond Order (REBO) form with comparisons to a variety of published experimental results. We performed MD simulations of low-energy hydrogen ($\leqslant$50 eV) and argon ( $\leqslant$200 eV) ion bombardment of diamond surfaces. Ar + bombardment can be used to locally smooth initially rough diamond surfaces via the formation of an amorphous C layer, the thickness of which increases with argon ion energy. Subsequent exposure with hydrogen ions (or fast neutrals) will selectively etch this amorphous C layer, leaving the underlying diamond layer mostly intact if the H energy is maintained below about 10 eV. The simulations suggest that combining Ar + smoothing with selective, near threshold energy H removal of amorphous C can be an effective strategy for diamond surface engineering, leading to more reliable and sensitive diamond color center devices.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Sub Coulomb barrier d+ 208 Pb scattering in the time-dependent basis function approach

We employ the non-perturbative time-dependent basis function (tBF) approach to study the scattering of the deuteron on 208 Pb below the Coulomb barrier. We obtain the bound and discretized scattering states of the projectile, which form the basis representation of the tBF approach, by diagonalizing a realistic Hamiltonian in a large harmonic oscillator basis. We find that the higher-order inelastic scattering effects are noticeable for sub barrier scatterings with the tBF method. We have successfully reproduced experimental sub Coulomb barrier elastic cross section ratios with the tBF approach by considering only the electric dipole (E1) component of the Coulomb interaction between the projectile and the target during scatterings. Here, we find that the correction of the polarization potential to the Rutherford trajectory is dominant in reproducing the data at very low bombarding energies, whereas the role of internal transitions of the deuteron projectile induced by the E1 interaction during the scattering becomes increasingly significant at higher bombarding energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗