Kenta K. Ohtaki
A5069651991- Astro and Planetary Science
- Planetary Science and Exploration
- Geological and Geochemical Analysis
- Nuclear materials and radiation effects
- Advanced ceramic materials synthesis
- Geology and Paleoclimatology Research
- High-pressure geophysics and materials
- Isotope Analysis in Ecology
- Paleontology and Stratigraphy of Fossils
- Chalcogenide Semiconductor Thin Films
- Electron and X-Ray Spectroscopy Techniques
- Advanced battery technologies research
- Electronic and Structural Properties of Oxides
- Electrocatalysts for Energy Conversion
- Cultural Heritage Materials Analysis
- Mineralogy and Gemology Studies
- Ion-surface interactions and analysis
- Astrophysics and Star Formation Studies
- Quantum Dots Synthesis And Properties
- Radioactive element chemistry and processing
- Nuclear Materials and Properties
- Fuel Cells and Related Materials
- X-ray Spectroscopy and Fluorescence Analysis
- Building materials and conservation
- Space Exploration and Technology
University of Hawaiʻi at Mānoa
2019-2024
University of Hawaii System
2019-2022
Honolulu University
2021
University of California, Irvine
2016-2020
Irvine University
2016-2020
Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through collective process called space weathering. The return samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study space-weathering signatures on most abundant type inner solar system body: C-type asteroid, composed materials largely unchanged since formation...
Abstract Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range morphologies, elemental compositions, and carbon functional chemistries consistent with those carbonaceous chondrites have experienced low‐temperature aqueous alteration. Both nanoglobules diffuse are abundant. Non‐globular particles also present, including some contain nanodiamond clusters. Diffuse is finely distributed in around phyllosilicates, forms coatings on other...
Abstract Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport these nitrogen-bearing solids into near-Earth region is not well understood. Here, we report discovery iron nitride on magnetite grains from surface C-type carbonaceous asteroid Ryugu, suggesting inorganic fixation. Micrometeoroid impacts solar wind irradiation have caused selective loss volatile species major iron-bearing minerals to form metallic iron. Iron a...
Amorphous silicates in meteoritic samples are significant as potential surviving interstellar dust from the formation of Solar System. silicate-rich grains called GEMS, glass with embedded metal and sulfides, abundant anhydrous interplanetary particles some ultracarbonaceous Antarctic micrometeorites that have high presolar grain abundances. Some GEMS within these objects been confirmed to be presolar. GEMS-like material, consisting amorphous silicate opaque inclusions, has identified...
Abstract Samples returned from the carbonaceous asteroid (162173) Ryugu by Hayabusa2 mission revealed that is composed of materials consistent with CI chondrites and some types space weathering. We report detailed mineralogy fine‐grained samples allocated to our “Sand” team additional weathering features found on grains. The dominant a mixture Mg‐rich saponite serpentine, magnetite, pyrrhotite, pentlandite, dolomite, Fe‐bearing magnesite. These grains have comparable chondrites, showing...
Radiation damage tolerance for a variety of ceramics at high temperatures depends on the material's resistance to nucleation and growth extended defects. Such processes are prevalent in employed space, nuclear fission/fusion waste environments. This report shows that random heterointerfaces materials with sub-micron grains can act as highly efficient sinks point defects compared grain boundaries single-phase materials. The concentration dislocation loops radiation damage-prone phase (Al2O3)...
Abstract Samples were recently collected from the carbonaceous asteroid (162173) Ryugu, by Japan Aerospace Exploration Agency (JAXA) Hayabusa2 mission. They resemble CI chondrites material, thus showing clear evidence of extensive aqueous alteration attested widespread presence a mixture serpentine and saponite. We present here scanning transmission electron microscopy study Ryugu dominant lithology phyllosilicate matrix at nanometer scale, which we compare with that Orgueil chondrite. In...
Abstract The Hayabusa2 mission from the Japan Aerospace Exploration Agency (JAXA) returned to Earth samples of carbonaceous asteroid (162173) Ryugu. This offers a unique opportunity investigate in laboratory C‐type asteroid, without physical or chemical alteration by terrestrial atmosphere. Here, we report on an investigation mineralogy and organo‐chemistry using combination micro‐ nano‐infrared spectroscopy. Particles investigated with conventional FTIR spectroscopy have spectra dominated...
Abstract The surface morphology of regolith grains from the C‐type asteroid Ryugu was studied in search evidence impact events on asteroid. Scanning electron microscopy revealed that ~8% C0105‐042 have a smooth one side grains. One these has striated linear grooves (striations) its surface. Transmission grain showed porous fine‐grained Mg‐Fe phyllosilicate assemblage, which is main component grains, compacted near with striations closely resembles slickenside, characteristic texture found...
<italic>In situ</italic> incorporation of nanosized amorphous Al<sub>2</sub>O<sub>3</sub> for defect passivation in solution-processed CuIn(S,Se)<sub>2</sub> solar cells was demonstrated with significant efficiency enhancement.
Abstract A new transmission electron microscopy (TEM) specimen preparation method that utilizes a combination of focused ion beam (FIB) methods and ultramicrotomy is demonstrated. This combined retains the benefit site-specific sampling by FIB but eliminates beam-induced damage except at edges allows recovery many consecutive sections. It best applied to porous and/or fine-grained materials are amenable located in bulk samples not. The ideal for unique from which every precious, we...
Photocurrent density in excess of 10 mA cm −2 reported on 2.0 eV CuInGaS 2 solar cells integrated SnO :F substrates, yet new wide bandgap n-type buffers required to achieve higher photoconversion efficiency.
Abstract Ryugu asteroid grains brought back to the Earth by Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate mineralogy of their phyllosilicate‐rich matrix with four‐dimensional scanning transmission electron microscopy (4D‐STEM). We have identified mapped mineral phases at nanometer scale (serpentine, smectite, pyrrhotite), observed presence Ni‐bearing pyrrhotite, serpentine polymorph as lizardite, in agreement reported...
Abstract Regolith samples returned from asteroid 162173 Ryugu by the Hayabusa2 mission provide direct means to study how space weathering operates on surfaces of hydrous asteroids. The mechanisms weathering, its effects mineral surfaces, and characteristic time scales which alteration occurs are central understanding spectroscopic properties taxonomy asteroids in solar system. Here, we investigate behavior iron monosulfides pyrrhotite (Fe 1− x S) at earliest stages weathering. Using electron...
Abstract The “Search for life”, which may be extinct or extant on other planetary bodies is one of the major goals NASA exploration missions. Finding such evidence biological residue in a vast landscape an enormous challenge. We have developed highly sensitive instrument, “Compact Color Biofinder”, can locate minute amounts material large area at video speed from standoff distance. Here we demonstrate efficacy Biofinder to detect fossils that still possess strong bio-fluorescence signals...
Journal Article Radiation Damage Behavior in Multiphase Ceramics Get access Kenta K Ohtaki, Ohtaki University of California, Irvine, Chemical Engineering and Materials Science, CA USA Search for other works by this author on: Oxford Academic Google Scholar Maulik Patel, Patel Tennessee, Knoxville, Science Engineering, TN Martha L Mecartney Microscopy Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 1464–1465, https://doi.org/10.1017/S1431927616008163 Published: 25 2016
Journal Article Analytical STEM/EDS Characterization of Elemental Segregation and Solid Solution Formation in Multiphase Ceramics Get access Komal Syed, Syed Department Materials Science & Engineering, University California, Irvine, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Mingjie Xu, Xu USAIrvine Research Institute (IMRI), David Kok, Kok Kenta K Ohtaki, Ohtaki Martha L Mecartney Microscopy Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages...