A5068482803- Planetary Science and Exploration
- Astro and Planetary Science
- Ion-surface interactions and analysis
- Geological and Geochemical Analysis
- Atomic and Molecular Physics
- Electron and X-Ray Spectroscopy Techniques
- Isotope Analysis in Ecology
- Space Science and Extraterrestrial Life
- High-pressure geophysics and materials
- Nuclear Physics and Applications
- Laser-induced spectroscopy and plasma
- Space Exploration and Technology
- Mass Spectrometry Techniques and Applications
- Astrophysics and Star Formation Studies
- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Radioactive element chemistry and processing
- Geomagnetism and Paleomagnetism Studies
- Fusion materials and technologies
- Particle accelerators and beam dynamics
- Scientific Research and Discoveries
- Calibration and Measurement Techniques
- Semiconductor Quantum Structures and Devices
- Advanced Semiconductor Detectors and Materials
- Radioactivity and Radon Measurements
University of Virginia
2015-2025
McCormick (United States)
2010-2025
Ansys (United States)
2019
Synopsys (United States)
2019
University of Calabria
2015-2016
Johnson Space Center
2015
We have studied the effects of 4 keV He + ion irradiation on olivine while measuring, in situ, changes near‐infrared (NIR) reflectance and chemical composition surface. The observed are reddening attenuation Fe‐3d absorption bands NIR. Spectral irradiated powder (<45 μ m) correlates with amount metallic iron formed by impact, consistent idea that space‐weathering olivine‐bearing S type asteroids due to formation iron. metallization rate is about half a sectioned rock olivine, which we...
As a first step in preparing for the return of samples from Moon by Artemis Program, NASA initiated Apollo Next Generation Sample Analysis Program (ANGSA). ANGSA was designed to function as low-cost sample mission and involved curation analysis previously returned 17 that remained unopened or stored under unique conditions 50 years. These include lower portion double drive tube sealed on lunar surface, upper had unopened, variety at −27 °C approximately constitutes preliminary examination...
We report energy distributions of electrons emitted from Al and Mg surfaces bombarded by 30--4500 eV ${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$ ions, which contain structure consistent with the decay surface bulk plasmons. propose that plasmon excitation is due to sudden change dipole (incident ion plus image charge) resulting disappearance charge appearance a hole in metal.
Laboratory simulations of solar wind irradiation olivine, a constituent ordinary chondritic meteorites and S‐type asteroids, show dramatic chemical reduction surface iron and, to lesser extent, silicon. Earth's atmosphere oxidizes any reduced instantaneously, whereas irradiated material on the an asteroid would remain reduced. Changes in optical reflectance, due metallization surface, provide possible explanation for differences near‐infrared spectra chondrite their likely parent bodies,...
While a significant fraction of silicate dust in stellar winds has crystalline structure, the interstellar medium nearly all it is amorphous. One possible explanation for this observation amorphization silicates by relatively ‘‘low’’ energy, heavy-ion cosmic rays. Here we present results multiple laboratory experiments showing that single-crystal synthetic forsterite (Mg2SiO4) amorphizes when irradiated 10 MeV Xe ions at large...
We performed H+ and He+ irradiation experiments on slabs of the Murchison CM2 meteorite to simulate solar wind carbonaceous asteroids. Two separate 6 mm × regions were irradiated with 1 keV 4 He+, respectively, fluences 8.1 1017 ions/cm2 for 1018 He+. Unirradiated surfaces analyzed using X-ray photoelectron spectroscopy (XPS), visible near-infrared (VNIR; 0.35–2.5 μm), microprobe two-step laser-desorption mass spectrometry (μL2MS). also analytical field-emission scanning transmission...
High-purity niningerite (MgS) was synthesized by BenchChem under vacuum conditions for use in laboratory simulations of solar-ion space weathering sulfide minerals that are expected to be present on the surface Mercury. MgS initially characterized via x-ray photoelectron spectroscopy prior investigations into preferential loss near-surface sulfur with 2 keV H2+ irradiation. Survey and high-resolution (Mg 1s, Mg 2p, S 2p) spectra as-received magnesium powder (99.9%) presented, including...
Abstract Pulsed‐laser irradiation causes the visible‐near‐infrared spectral slope of olivine (Fo 90 and Fo 99+ ) SiO 2 to increase (redden), while samples darken brighten slightly. XPS analysis shows that produces metallic Fe. Analytical SEM TEM measurements confirm reddening in correlates with production “nanophase” Fe (npFe 0 grains, 20–50 nm size. The observed sample is consistent formation or other x species absorb visible. weak brightening induced by laser a change surface topography...
Abstract Solar wind interactions with the surfaces of asteroids and small moons eject atoms molecules from uppermost several nanometers regolith grains through a process called sputtering. A fraction sputtered species, secondary ions, leave surface in an ionized state, these are diagnostic composition. Detection ions using ion mass spectrometry (IMS) provides powerful method analysis due to low backgrounds high instrument sensitivities. However, yield atomic composition not 1‐to‐1...
Space weathering is a key process in the interpretation of airless planetary surfaces. As we engage new missions to objects with potentially novel surfaces such as 16 Psyche, there renewed interest expanding our knowledge space effects wider variety analog materials, including physical/chemical solar-wind ions on regoliths. We have experimentally simulated solar two polished thick sections meteoritic troilite (FeS) via irradiation 1 keV hydrogen (H
Abstract Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate surface compositions, structural profiles, and valence distributions of oxides, carbides, impurities niobium (Nb) niobium–tin (Nb 3 Sn) situ under different processing conditions. We establish underlying mechanisms vacuum baking nitrogen Nb demonstrate that carbide formation induced during high-temperature baking, regardless gas...
Magnetite is a relevant mineral component of asteroids as it has been identified in carbonaceous chondrites, on the surface asteroid Bennu through remote sensing observations, and samples returned from Ryugu. However, effects space weathering processes magnetite have not yet explored. To investigate how this phase responds to weathering, here we simulate micrometeoroid bombardment solar wind irradiation using pulsed laser ion experiments. We performed X-ray photoelectron spectroscopy (XPS),...
The unprecedented wide bandgap tunability (∼1 eV) of AlxIn1-xAsySb1-y lattice-matched to GaSb enables the fabrication photodetectors over a range from near-infrared mid-infrared. In this paper, valence band-offsets in with different Al compositions are analyzed by tight binding calculations and X-ray photoelectron spectroscopy measurements. observed weak variation band offsets is consistent lack any minigaps band, compared conduction band.
We have studied electron emission from solid Ar, Kr, and Xe films induced by impact of 10--100 keV protons at normal incidence. Electron yields were measured as a function applied anode voltage film thickness 200 to 7000 \AA{}. The observed are huge---hundreds electrons per incident ion: higher, amount electronic energy deposited, than for any other material so far. extend an model, developed metals, the case insulators, obtain escape depths hundreds nm when fitted dependence yield on target...
Creation of plasmons in water by energetic particles biological tissue is important because this form energy can migrate from the place excitation and be transferred to nearby molecules like DNA. We have searched for evidence solid water, using electron-energy-loss secondary electron spectroscopies excited 70--1000-eV electrons. find that main excitation, often attributed plasmons, depends on exciting electron, unlike expected plasmon behavior. The spectrum electrons shows presence...