Thomas J Zega

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Journals/Publications

• Che, S., & Zega, T. J. (2023). Hydrothermal fluid activity on asteroid Itokawa. Nature Astronomy, 7, 1063-1069.
• Che, S., Domanik, K. J., & Zega, T. J. (2023). In-situ formation of halite in the Sidi El Habib 001 (H5) ordinary chondrite: Implications for hydrothermal alteration in ordinary chondrite parent bodies. \gca, 348, 85-106.
• Che, S., Domanik, K. J., Chang, Y., & Zega, T. J. (2023). The important role of fluid chemistry in the hydrothermal alteration of ordinary chondrites: Insights from halite and sphalerite in the Sidi El Habib 001 (H5) meteorite. Earth and Planetary Science Letters, 621, 118374.
• Dobric{\u{a}}, E., Ishii, H. A., Bradley, J. P., Ohtaki, K., Brearley, A. J., Noguchi, T., Matsumoto, T., Miyake, A., Igami, Y., Haruta, M., Saito, H., Hata, S., Seto, Y., Miyahara, M., Tomioka, N., Leroux, H., Le, G. C., Jacob, D., Pe{\~na}, F., , Laforet, S., et al. (2023). Nonequilibrium spherulitic magnetite in the Ryugu samples. \gca, 346, 65-75.
• Matsumoto, T., Noguchi, T., Miyake, A., Igami, Y., Haruta, M., Seto, Y., Miyahara, M., Tomioka, N., Saito, H., Hata, S., Harries, D., Takigawa, A., Nakauchi, Y., Tachibana, S., Nakamura, T., Matsumoto, M., Ishii, H. A., Bradley, J. P., Ohtaki, K., , Dobric{\v{a}}, E., et al. (2023). Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu samples. Nature Astronomy.
• Noguchi, T., Matsumoto, T., Miyake, A., Igami, Y., Haruta, M., Saito, H., Hata, S., Seto, Y., Miyahara, M., Tomioka, N., Ishii, H. A., Bradley, J. P., Ohtaki, K. K., Dobric{\v{a}}, E., Leroux, H., Le, G. C., Jacob, D., Pe{\~na}, F., Laforet, S., , Marinova, M., et al. (2023). A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu. Nature Astronomy, 7, 170-181.
• Seifert, L. B., Haenecour, P., Ramprasad, T., & Zega, T. J. (2023). An in situ study of presolar grains and the fine-grained matrices of the Meteorite Hills 00526 and Queen Alexandra Range 97008 unequilibrated ordinary chondrites. \maps, 58(8), 1079-1098.
• Seifert, L. B., Haenecour, P., Ramprasad, T., Brearley, A. J., & Zega, T. J. (2023). An in situ investigation of the preservation and alteration of presolar silicates in the Miller Range 07687 chondrite. \maps, 58(3), 360-382.
• Wilbur, Z., Barnes, J., Eckley, S., Ong, I., Brounce, M., Crow, C., Erickson, T., Kent, J., Boyce, J., Mosenfelder, J., Hahn, T., McCubbin, F., & Zega, T. (2023). Volatiles, vesicles, and vugs: Unraveling the magmatic and eruptive histories of Steno crater basalts. \maps, 58(11), 1600-1628.
• Zanetta, P., Drexler, M. S., Barton, I. F., & Zega, T. J. (2023). Vanadium Electronic Configuration Determination From L2,3 Transition in V-oxide Compounds and Roscoelite. Microscopy and Microanalysis, 29(2), 459-469.
• Zanetta, P., Manga, V. R., Chang, Y., Ramprasad, T., Weber, J., Beckett, J. R., & Zega, T. J. (2023). Atomic-scale characterization of the oxidation state of Ti in meteoritic hibonite: Implications for early solar system thermodynamics. American Mineralogist, 108(5), 881-902.
• Barnouin, O., Daly, M., Palmer, E., Gaskell, R., Weirich, J., Johnson, C., Al, A. M., Roberts, J., Perry, M., Susorney, H., Daly, R., Bierhaus, E., Seabrook, J., Espiritu, R., Nair, A., Nguyen, L., Neumann, G., Ernst, C., Boynton, W., , Nolan, M., et al. (2020). Author Correction: Shape of (101955) Bennu indicative of a rubble pile with internal stiffness. Nature Geoscience, 13(11), 764-764.
• Haenecour, P., Floss, C., Brearley, A. J., & Zega, T. J. (2020). The effects of secondary processing in the unique carbonaceous chondrite Miller Range 07687. Meteoritics and Planetary Science, 55(6), 1228-1256.
• Weber, J., Ramprasad, T., Domanik, K., Chang, Y., & Zega, T. (2020). 3D Microstructural and Microanalytical Analyses of Wark-Lovering Rims in the Allende Meteorite. Microscopy and Microanalysis, 26(S2), 2060-2061.
• Zega, T. (2020). Putting Planetary Materials into the Gap: Insights into Planetary and Stellar Processes from in Situ Measurements in the TEM. Microscopy and Microanalysis, 26(S2), 2050-2051.
• Zega, T. J., Haenecour, P., & Floss, C. (2020). An in situ investigation on the origins and processing of circumstellar oxide and silicate grains in carbonaceous chondrites. Meteoritics and Planetary Science, 55(6), 1207-1227.
• Bernal, J., Haenecour, P., Howe, J., Zega, T., Amari, S., & Ziurys, L. (2019). Formation of Interstellar C$_60$ from Silicon Carbide Circumstellar Grains. \apjl, 883(2), L43.
• Haenecour, P., Howe, J. Y., Zega, T. J., Amari, S., Lodders, K., Jos{\'e}, J., Kaji, K., Sunaoshi, T., & Muto, A. (2019). Laboratory evidence for co-condensed oxygen- and carbon-rich meteoritic stardust from nova outbursts. Nature Astronomy, 3, 626-630.
• Schrader, D. L., & Zega, T. J. (2019). Petrographic and compositional indicators of formation and alteration conditions from LL chondrite sulfides. \gca, 264, 165-179.
• Barnes, J., Thompson, M., McCubbin, F., Howe, J., Rahman, Z., Messenger, S., & Zega, T. (2018). Coordinated Microanalysis of Phosphates in High-Titanium Lunar Basalts. Microscopy and Microanalysis, 24, 2078-2079.
• Haenecour, P., Floss, C., Zega, T., Croat, T., Wang, A., Jolliff, B., & Carpenter, P. (2018). Presolar silicates in the matrix and fine-grained rims around chondrules in primitive CO3.0 chondrites: Evidence for pre-accretionary aqueous alteration of the rims in the solar nebula. \gca, 221, 379-405.
• Haenecour, P., Howe, J., Zega, T., Amari, S., Floss, C., Wallace, P., Lodders, K., Kaji, K., Sunaoshi, T., & Muto, A. (2018). Low-Voltage Energy-Dispersive X-ray Spectroscopy and Electron Energy-Loss Spectroscopy Analysis of Presolar Graphite Spherules. Microscopy and Microanalysis, 24, 2110-2111.
• Howe, J., Haenecour, P., Thompson, M., Dogel, S., Sunaoshi, T., Sagar, J., Hosseinkhannazer, H., & Zega, T. (2018). Nanoscale Investigation of Thermal Alteration of Chondritic Meteorites via Simultaneous Secondary and Transmitted Electron Imaging during In Situ Heating up to 1000 oC. Microscopy and Microanalysis, 24, 2102-2103.
• Mane, P., Wallace, S., Wallace, P., Chang, Y., Domanik, K., & Zega, T. (2018). Coordinated EBSD and TEM Analysis to Decipher Shock Deformation Effects in the Oldest Solids in the Solar System. Microscopy and Microanalysis, 24, 2092-2093.
• Nakamura-Messenger, K. .., Squyres, S., Pace, L., Messenger, S., Mitchell, D., Lauretta, D., Glavin, D., Houghton, M., Hayes, A., Nakamura, T., Dworkin, J., Nguyen, A., Clemett, S., Furukawa, Y., Kimura, Y., Takigawa, A., Blake, G., Zega, T., Mumma, M., , Milam, S., et al. (2018). The CAESAR New Frontiers Comet Sample Return Mission. Microscopy and Microanalysis, 24, 2104-2105.
• Ramprasad, T., Mane, P., & Zega, T. (2018). Aberration-corrected STEM/TEM Chemical Analysis and Imaging of Meteoritic Refractory Oxide Assemblages. Microscopy and Microanalysis, 24, 2090-2091.
• Schmidt, D., Woolf, N., Zega, T., & Ziurys, L. (2018). Extreme $^13$C,$^15$N and $^17$O isotopic enrichment in the young planetary nebula K4-47. \nat, 564, 378-381.
• Seifert, L., Haenecour, P., Zega, T., Floss, C., & Howe, J. (2018). Multi-keV Analyses of a Presolar Mg-Silicate Grain via SEM/STEM. Microscopy and Microanalysis, 24, 2098-2099.
• Slick, L., Mane, P., Howe, J., & Zega, T. (2018). Toward Quantification of Ti-Oxidation States in Planetary Materials via Application of the EELS White-Line Ratio Technique. Microscopy and Microanalysis, 24, 2086-2087.
• Zega, T., Howe, J., Sagar, J., Pinard, P., & Koch, R. (2018). Mass-Thickness Measurements in the TEM via EDS: A New Approach to Quantitative Chemical Analysis of Planetary Materials?. Microscopy and Microanalysis, 24, 2084-2085.
• Bose, M., Zega, T., Haenecour, P., & Domanik, K. (2017). Correlated Isotopic Anomalies Associated with Organic Matter in Meteorites. LPI Contributions, 2042, 4033.
• Haenecour, P., Zega, T., Howe, J., Bose, M., & Wallace, P. (2017). Origins and Delivery of Volatile Elements in Terrestrial Planets: Insight from the Composition and Functional Chemistry of Organic Matter in Meteorites. LPI Contributions, 2042, 4037.
• Haenecour, P., Zega, T., Howe, J., Wallace, P., Floss, C., & Yada, T. (2017). Investigation of the Nature of Capping Layer Materials for FIB-SEM Preparation: Implications for the Study of Carbonaceous Material in Extraterrestrial Samples. Microscopy and Microanalysis, 23, 1820-1821.
• Howe, J., Ramprasad, T., Hanawa, A., Inada, H., Jimenez, J., Hoyle, D., Voelkl, E., & Zega, T. (2017). Collection Efficiency of the Twin EDS Detectors for Quantitative X-ray Analysis on A New Probe-Corrected TEM/STEM. Microscopy and Microanalysis, 23, 520-521.
• Howe, J., Thompson, M., Dogel, S., Ueda, K., Matsumoto, T., Kikuchi, H., Reynolds, M., Hosseinkhannazer, H., & Zega, T. (2017). In situ Thermal Shock of Lunar and Planetary Materials Using A Newly Developed MEMS Heating Holder in A STEM/SEM. Microscopy and Microanalysis, 23, 66-67.
• Mane, P., Wallace, S., Bose, M., Domanik, K., Zega, T., & Wadhwa, M. (2017). Coordinated X-ray, Ion, and Electron Microanalysis Approach Towards Understanding the Earliest-Formed Solids in the Solar System. Microscopy and Microanalysis, 23, 2136-2137.
• Ramprasad, T., Howe, J., Gnanaprakasa, T., Hanawa, A., Jiminez, J., Muralidharan, K., & Zega, T. (2017). The Structure and Electronic States of Self-Assembled C60 Crystals. Microscopy and Microanalysis, 23, 1818-1819.
• Thompson, M., Zega, T., & Howe, J. (2017). In situ experimental formation and growth of Fe nanoparticles and vesicles in lunar soil. Meteoritics and Planetary Science, 52, 413-427.
• Zega, T., Manga, V., Watanabe, K., Domanik, K., Mane, P., Hanawa, A., Inada, H., Howe, J., & Muralidharan, K. (2017). A Combined Atomic-Resolution STEM and First-Principles Approach Towards Understanding the Origins of the First Solar-System Solids. Microscopy and Microanalysis, 23, 396-397.
• Zega, T., Massani, B., Chang, Y., Domanik, K., Nebesny, K., Wallace, P., Armstrong, N., Corral, E., Lauretta, D., Swindle, T., Wang, W., Howe, J., Hanawa, A., & Inada, H. (2017). A New Core Facility For Electron And Ion Microscopy At The University Of Arizona. Microscopy and Microanalysis, 23, 64-65.
• {Bolser}, D., {Zega}, T., {Asaduzzaman}, A., {Bringuier}, S., {Simon}, S., {Grossman}, L., {Thompson}, M., , K. (2016). Microstructural analysis of Wark-Lovering rims in the Allende and Axtell CV3 chondrites: Implications for high-temperature nebular processes. Meteoritics and Planetary Science, 51, 743-756.
• {Gnanaprakasa}, T., {Domanik}, K., {DiRuggiero}, J., , T. (2016). Sensing Biosignatures Within Rocks of the Atacama Desert {\mdash} An Analog for Mars Environments. LPI Contributions, 1912, 2079.
• {Haenecour}, P., {Floss}, C., {Zega}, T., , R. (2016). Auger Spectroscopy Analysis of Submicron-Sized Silicate Grains in Chondrites: Insight into Their Aqueous and Thermal Alteration History. LPI Contributions, 1921, 6354.
• {Miller}, K., {Lauretta}, D., {Berger}, E., {Thompson}, M., , T. (2016). Copper Sulfides in the R Chondrites: Evidence of Hydrothermal Alteration in Low Petrologic Types. LPI Contributions, 1921, 6420.
• {Thompson}, M., {Zega}, T., , J. (2016). In Situ Heating of Lunar Soil in the Transmission Electron Microscope: Simulating Micrometeorite Impacts.. Microscopy and Microanalysis, 22, 1800-1801.
• {Thompson}, M., {Zega}, T., {Becerra}, P., {Keane}, J., , S. (2016). The oxidation state of nanophase Fe particles in lunar soil: Implications for space weathering. Meteoritics and Planetary Science, 51, 1082-1095.
• {Zega}, T., {Manga}, V., {Domanik}, K., , K. (2016). Atomic-Resolution Analysis of Perovskite from the Early Solar System. Microscopy and Microanalysis, 22, 1778-1779.
• {Schrader}, D., {Connolly}, H., {Lauretta}, D., {Zega}, T., {Davidson}, J., , K. (2015). The formation and alteration of the Renazzo-like carbonaceous chondrites III: Toward understanding the genesis of ferromagnesian chondrules. Meteoritics and Planetary Science, 50, 15-50.
• {Zega}, T., {Haenecour}, P., {Floss}, C., , R. (2015). Circumstellar Magnetite from the LAP 031117 CO3.0 Chondrite. \apj, 808, 55.
• Blinova, A. I., Zega, T. J., Herd, C. D., & Stroud, R. M. (2014). Testing variations within the tagish lake meteorite-i: Mineralogy and petrology of pristine samples. Meteoritics and Planetary Science.
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  Abstract: Four samples (TL5b, TL11h, TL11i, and TL11v) from the pristine collection of the Tagish Lake meteorite, an ungrouped C2 chondrite, were studied to characterize and understand its alteration history using EPMA, XRD, and TEM. We determined that samples TL11h and TL11i have a relatively smaller proportion of amorphous silicate material than sample TL5b, which experienced low-temperature hydrous parent-body alteration conditions to preserve this indigenous material. The data suggest that lithic fragments of TL11i experienced higher degrees of aqueous alteration than the rest of the matrix, based on its low porosity and high abundance of coarse- and fine-grained sheet silicates, suggesting that TL11i was present in an area of the parent body where alteration and brecciation were more extensive. We identified a coronal, "flower"-like, microstructure consisting of a fine-grained serpentine core and coarse-grained saponite-serpentine radial arrays, suggesting varied fluid chemistry and crystallization time scales. We also observed pentlandite with different morphologies: an exsolved morphology formed under nebular conditions; a nonexsolved pentlandite along grain boundaries; a "bulls-eye" sulfide morphology and rims around highly altered chondrules that probably formed by multiple precipitation episodes during low-temperature aqueous alteration (≥100 °C) on the parent body. On the basis of petrologic and mineralogic observations, we conclude that the Tagish Lake parent body initially contained a heterogeneous mixture of anhydrous precursor minerals of nebular and presolar origin. These materials were subjected to secondary, nonpervasive parent-body alteration, and the samples studied herein represent different stages of that hydrous alteration, i.e., TL5b (the least altered) < TL11h < TL11i (the most altered). Sample TL11v encompasses the petrologic characteristics of the other three specimens. © The Meteoritical Society, 2014.
• Blinova, A., Zega, T., Herd, C., & Stroud, R. (2014). Testing variations within the Tagish Lake meteorite—I: Mineralogy and petrology of pristine samples. Meteoritics & Planetary Science, 49(4), 473-502.
• Zega, T. J., Nittler, L. R., Gyngard, F., Alexander, C. M., Stroud, R. M., & Zinner, E. K. (2014). A transmission electron microscopy study of presolar spinel. Geochimica et Cosmochimica Acta, 124, 152-169.
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  Abstract: We report on the isotopic and microstructural properties of four presolar spinel grains identified in acid-resistant residues of the Murray CM2 and Orgueil (ORG) CI1 chondrites, and a mixture of the unequilibrated ordinary chondrites (UOC) QUE 97008 (L3.05), WSG 95300 (H3.3), and MET00452 (LL3.05) collected in Antarctica. All four grains have O-isotopic compositions indicating an origin in low-mass (~1.2-1.4M·) O-rich asymptotic giant branch (AGB) stars, although two of the grains have compositions indicating that non-standard mixing (cool-bottom processing) likely occurred in their parent stars. Three of the grains are single-crystal Mg-Al-rich spinels containing minor Fe and Cr; one is Mg deficient and one contains minor Ca. The fourth consists of an assemblage of three, Fe-Cr-rich crystalline grains with closely aligned crystallographic orientation but systematically varied cation composition. Each spinel grain within the assemblage also contains Ti-rich sub-grains (
• {Asaduzzaman}, A., {Zega}, T., {Laref}, S., {Runge}, K., {Deymier}, P., , K. (2014). A computational investigation of adsorption of organics on mineral surfaces: Implications for organics delivery in the early solar system. Earth and Planetary Science Letters, 408, 355-361.
• {Bolser}, D., , T. (2014). A Comparative Study of Electron Energy-Loss Spectroscopy (EELS) and X-ray Absorption Near Edge Structure (XANES) Spectroscopy for Probing the Oxidation State of Transition Metals in Planetary Materials. Microscopy and Microanalysis, 20, 1706-1707.
• {Bose}, M., {Zega}, T., , P. (2014). Assessment of alteration processes on circumstellar and interstellar grains in Queen Alexandra Range 97416. Earth and Planetary Science Letters, 399, 128-138.
• {Thompson}, M., , T. (2014). Electron Energy-Loss Spectroscopy of Iron Nanoparticles in Lunar Soil using an Aberration-Corrected Scanning Transmission Electron Microscope.. Microscopy and Microanalysis, 20, 1672-1673.
• {Thompson}, M., {Christoffersen}, R., {Zega}, T., , L. (2014). Microchemical and structural evidence for space weathering in soils from asteroid Itokawa. Earth, Planets, and Space, 66, 89.
• T., B., Stroud, R. M., Nittler, L. R., M., C., Bassim, N. D., Cody, G. D., Kilcoyne, A. D., Sandford, S. A., Milam, S. N., Nuevo, M., & Zega, T. J. (2013). Isotopic and chemical variation of organic nanoglobules in primitive meteorites. Meteoritics and Planetary Science, 48(5), 904-928.
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  Abstract: Organic nanoglobules are microscopic spherical carbon-rich objects present in chondritic meteorites and other astromaterials. We performed a survey of the morphology, organic functional chemistry, and isotopic composition of 184 nanoglobules in insoluble organic matter (IOM) residues from seven primitive carbonaceous chondrites. Hollow and solid nanoglobules occur in each IOM residue, as well as globules with unusual shapes and structures. Most nanoglobules have an organic functional chemistry similar to, but slightly more carboxyl-rich than, the surrounding IOM, while a subset of nanoglobules have a distinct, highly aromatic functionality. The range of nanoglobule N isotopic compositions was similar to that of nonglobular 15N-rich hotspots in each IOM residue, but nanoglobules account for only about one third of the total 15N-rich hotspots in each sample. Furthermore, many nanoglobules in each residue contained no 15N enrichment above that of bulk IOM. No morphological indicators were found to robustly distinguish the highly aromatic nanoglobules from those that have a more IOM-like functional chemistry, or to distinguish 15N-rich nanoglobules from those that are isotopically normal. The relative abundance of aromatic nanoglobules was lower, and nanoglobule diameters were greater, in more altered meteorites, suggesting the creation/modification of IOM-like nanoglobules during parent-body processing. However, 15N-rich nanoglobules, including many with highly aromatic functional chemistry, likely reflect preaccretionary isotopic fractionation in cold molecular cloud or protostellar environments. These data indicate that no single formation mechanism can explain all of the observed characteristics of nanoglobules, and their properties are likely a result of multiple processes occurring in a variety of environments. © The Meteoritical Society, 2013.
• Zega, T., Nittler, L., Alexander, C., Stroud, R., & Kilcoyne, D. (2012). Measurements of the Oxidation State of Ti in Calcium Aluminate from the Early Solar System and Ancient Stars. Microscopy and Microanalysis, 18(S2), 1702-1703.
• Boercker, J. E., Clifton, E. M., Tischler, J. G., Foos, E. E., Zega, T. J., Twigg, M. E., & Stroud, R. M. (2011). Size and temperature dependence of band-edge excitons in PbSe nanowires. Journal of Physical Chemistry Letters, 2(6), 527-531.
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  Abstract: We report the attenuance and temperature-dependent photoluminescence spectra of PbSe nanowires with diameters between 5.6 and 26.4 nm (12-23% relative standard deviation) and lengths greater than 1 μm. The nanowire first exciton energy varies between 0.3 and 0.6 eV as the diameter decreases from 26.4 to 5.6 nm, respectively. Compared to spherical PbSe nanocrystals, PbSe nanowires show less quantum confinement and larger Stokes shifts. The band gap temperature coefficient (dEg/dT) decreases as the nanowire diameter decreases, consistent with previous results for PbSe spherical nanocrystals. © 2011 American Chemical Society.
• Chi, M. a., Connolly Jr., H. C., Beckett, J. R., Tschauner, O., Rossman, G. R., Kampf, A. R., Zega, T. J., A., S., & Schrader, D. L. (2011). Brearleyite, Ca₁₂Al₁₄O₃₂Cl₂, a new alteration mineral from the NWA 1934 meteorite. American Mineralogist, 96(8-9), 1199-1206.
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  Abstract: Brearleyite (IMA 2010-062, Ca12Al14O 32Cl2) is a Cl-bearing mayenite, occurring as fine-grained aggregates coexisting with hercynite, gehlenite, and perovskite in a rare krotite (CaAl2O4) dominant refractory inclusion from the Northwest Africa 1934 CV3 carbonaceous chondrite. The phase was characterized by SEM, TEM-SAED, micro-Raman, and EPMA. The mean chemical composition of the brearleyite is (wt%) Al2O3 48.48, CaO 45.73, Cl 5.12, FeO 0.80, Na2O 0.12, TiO2 0.03, -2O 1.16 2, ∑ 99.12. The corresponding empirical formula calculated on the basis of 34 O+Cl atoms is (Ca11.91 Na0.06)?11.97(Al13.89Fe 0.16Ti0.01)σ14.06O31.89Cl2.11. The Raman spectrum of brealryeite indicates very close structural similarity to synthetic Ca12Al14O32Cl2. Rietveld refinement of an integrated TEM-SAED ring pattern from a FIB section quantifies this structural relationship and indicates that brearleyite is cubic, I43d; a = 11.98(8) Å, V = 1719.1(2) Å3, and Z = 2. It has a framework structure in which AlO4 tetrahedra share corners to form eight-membered rings. Within this framework, the Cl atom is located at a special position (3/8,0,1/4) with 0.4(2) occupancy and Ca appears to be disordered on two partially occupied sites similar to synthetic Cl-mayenite. Brearleyite has a light olive color under diffuse reflected light and a calculated density of 2.797 g/cm3. Brearleyite is not only a new meteoritic Ca-,Al-phase, but also a new meteoritic Cl-rich phase. It likely formed by the reaction of krotite with Cl-bearing hot gases or fluids.
• Foos, E. E., Zega, T. J., Tischler, J. G., Stroud, R. M., & Boercker, J. E. (2011). Synthesis of PbSe nanowires: The impact of alkylphosphonic acid addition. Journal of Materials Chemistry, 21(8), 2616-2623.
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  Abstract: Reaction of Pb oleate with trioctylphosphine (TOP)/Se in 1-octadecene under appropriate conditions yields PbSe nanowires. The parameters found to be critical for the isolation of exclusively one-dimensional material are the Pb:Se ratio and the temperature profile used during synthesis. Addition of strongly coordinating tetradecylphosphonic acid (TDPA) to the system has a profound impact on the surface morphology, with increasing TDPA concentration producing narrower, smoother nanowires when all other parameters are held constant. The wire morphology and structural data are consistent with a combination of oriented attachment on 〈111〉 surfaces, yielding wires with a [100] axial orientation, and a ligand-mediated competition between growth on 〈111〉, 〈110〉 and 〈100〉 planes. The products possess 10-20 nm diameters, with lengths generally over one micron, and have been characterized through SEM, TEM, EDS, electron diffraction, and optical spectroscopy. © 2011 The Royal Society of Chemistry.
• Zega, T. J., M., C., Nittler, L. R., & Stroud, R. M. (2011). A transmission electron microscopy study of presolar hibonite. Astrophysical Journal, 730(2).
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  Abstract: We report isotopic and microstructural data on five presolar hibonite grains (KH1, KH2, KH6, KH15, and KH21) identified in an acid residue of the Krymka LL3.1 ordinary chondrite. Isotopic measurements by secondary ion mass spectrometry (SIMS) verified a presolar circumstellar origin for the grains. Transmission electron microscopy (TEM) examination of the crystal structure and chemistry of the grains was enabled by in situ sectioning and lift-out with a focused-ion-beam scanning-electron microscope (FIB-SEM). Comparisons of isotopic compositions with models indicate that four of the five grains formed in low-mass stars that evolved through the red giant/asymptotic giant branches (RGBs/AGBs), whereas one grain formed in the ejecta of a Type II supernova. Selected-area electron-diffraction patterns show that all grains are single crystals of hibonite. Some grains contain minor structural perturbations (stacking faults) and small spreads in orientation that can be attributed to a combination of growth defects and mechanical processing by grain-grain collisions. The similar structure of the supernova grain to those from RGB/AGB stars indicates a similarity in the formation conditions. Radiation damage (e.g., point defects), if present, occurs below our detection limit. Of the five grains we studied, only one has the pure hibonite composition of CaAl 12O19. All others contain minor amounts of Mg, Si, Ti, and Fe. The microstructural data are generally consistent with theoretical predictions, which constrain the circumstellar condensation temperature to a range of 1480-1743K, assuming a corresponding total gas pressure between 1 × 10-6 and 1 × 10-3atm. The TEM data were also used to develop a calibration for SIMS determination of Ti contents in oxide grains. Grains with extreme 18O depletions, indicating deep mixing has occurred in their parent AGB stars, are slightly Ti enriched compared with grains from stars without deep mixing, most likely reflecting differences in grain condensation conditions. © 2011. The American Astronomical Society. All rights reserved.
• T., B., Stroud, R. M., Nittler, L. R., Alexander, C. M., Kilcoyne, A. D., & Zega, T. J. (2010). Isotopic anomalies in organic nanoglobules from Comet 81P/Wild 2: Comparison to Murchison nanoglobules and isotopic anomalies induced in terrestrial organics by electron irradiation. Geochimica et Cosmochimica Acta, 74(15), 4454-4470.
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  Abstract: Nanoglobules are a form of organic matter found in interplanetary dust particles and primitive meteorites and are commonly associated with 15N and D isotopic anomalies that are suggestive of interstellar processes. We report the discovery of two isotopically-anomalous organic globules from the Stardust collection of particles from Comet 81P/Wild 2 and compare them with nanoglobules from the Murchison CM2 meteorite. One globule from Stardust Cometary Track 80 contains highly aromatic organic matter and a large 15N anomaly (δ15N=1120‰). Associated, non-globular, organic matter from this track is less enriched in 15N and contains a mixture of aromatic and oxidized carbon similar to bulk insoluble organic material (IOM) from primitive meteorites. The second globule, from Cometary Track 2, contains non-aromatic organic matter with abundant nitrile (CN) and carboxyl (COOH) functional groups. It is significantly enriched in D (δD=1000‰) but has a terrestrial 15N/14N ratio. Experiments indicate that similar D enrichments, unaccompanied by 15N fractionation, can be reproduced in the laboratory by electron irradiation of epoxy or cyanoacrylate. Thus, a terrestrial origin for this globule cannot be ruled out, and, conversely, exposure to high-energy electron irradiation in space may be an important factor in producing D anomalies in organic materials. For comparison, we report two Murchison globules: one with a large 15N enrichment and highly aromatic chemistry analogous to the Track 80 globule and the other only moderately enriched in 15N with IOM-like chemistry. The observation of organic globules in Comet 81P/Wild 2 indicates that comets likely sampled the same reservoirs of organic matter as did the chondrite parent bodies. The observed isotopic anomalies in the globules are most likely preserved signatures of low temperature (
• Tischler, J. G., Kennedy, T. A., Glaser, E. R., Efros, A. L., Foos, E. E., Boercker, J. E., Zega, T. J., Stroud, R. M., & Erwin, S. C. (2010). Band-edge excitons in PbSe nanocrystals and nanorods. Physical Review B - Condensed Matter and Materials Physics, 82(24).
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  Abstract: We investigate the fine structure of band-edge excitons in PbSe nanocrystals and nanorods using circularly polarized magnetophotoluminescence and optically detected magnetic resonance and, based on the results, propose a singlet-triplet model of exciton photoluminescence from nondegenerate conduction and valence bands. From the data and model we extract g -factors for electrons and holes of +1.2 and +0.8, respectively. The splitting of the triplet ground state, which is responsible for the low-temperature photoluminescence, is 88μeV for nanorods, and less than 20μeV for nanocrystals. The intervalley splitting of the electron and hole levels in the nanocrystals is much larger than the electron-hole exchange interaction. © 2010 The American Physical Society.
• Zega, T. J., M., C., Busemann, H., Nittler, L. R., Hoppe, P., Stroud, R. M., & Young, A. F. (2010). Mineral associations and character of isotopically anomalous organic material in the Tagish Lake carbonaceous chondrite. Geochimica et Cosmochimica Acta, 74(20), 5966-5983.
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  Abstract: We report a coordinated analytical study of matrix material in the Tagish Lake carbonaceous chondrite in which the same small (≤20 μm) fragments were measured by secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), electron energy-loss spectroscopy (EELS), and X-ray absorption near-edge spectroscopy (XANES). SIMS analysis reveals H and N isotopic anomalies (hotspots), ranging from hundreds to thousands of nanometers in size, which are present throughout the fragments. Although the differences in spatial resolution of the SIMS techniques we have used introduce some uncertainty into the exact location of the hotspots, in general, the H and N isotopic anomalies are spatially correlated with C enrichments, suggesting an organic carrier. TEM analysis, enabled by site-specific extraction using a focused-ion-beam scanning-electron microscope, shows that the hotspots contain an amorphous component, Fe-Ni sulfides, serpentine, and mixed-cation carbonates. TEM imaging reveals that the amorphous component occurs in solid and porous forms, EDS indicates that it contains abundant C, and EELS and XANES at the C K edge reveal that it is largely aromatic. This amorphous component is probably macromolecular C, likely the carrier of the isotopic anomalies, and similar to the material extracted from bulk samples as insoluble organic matter. However, given the large sizes of some of the hotspots, the disparity in spatial resolution among the various techniques employed in our study, and the phases with which they are associated, we cannot entirely rule out that some of the isotopic anomalies are carried by inorganic material, e.g., sheet silicates. The isotopic composition of the organic matter points to an initially primitive origin, quite possibly within cold interstellar clouds or the outer reaches of the solar protoplanetary disk. The association of organic material with secondary phases, e.g., serpentine and carbonates, suggests that the organic matter was susceptible to parent-body processing, and thus, isotopic dilution. © 2010.
• Busemann, H., Nguyen, A. N., Cody, G. D., Hoppe, P., Kilcoyne, A. D., Stroud, R. M., Zega, T. J., & Nittler, L. R. (2009). Ultra-primitive interplanetary dust particles from the comet 26P/Grigg-Skjellerup dust stream collection. Earth and Planetary Science Letters, 288(1-2), 44-57.
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  Abstract: Cometary material and pristine interplanetary dust particles (IDPs) best resemble the unaltered components from which our solar system was built because they have remained largely unaltered in a cold undisturbed environment since accretion in the outer protoplanetary disk. IDPs might supply more primitive assemblages for laboratory analysis than Stardust samples from comet 81P/Wild 2 but their individual provenances are typically unknown. We speculate that some IDPs collected by NASA in April 2003 may be associated with comet 26P/Grigg-Skjellerup because their particularly pristine character coincides with the collection period that was predicted to show an enhanced flux of particles from this Jupiter-family comet. Some IDPs from this collection contain the most primitive assembly of interstellar matter found to date including an unusually high abundance of presolar grains and very isotopically anomalous and disordered organic matter as well as fine-grained carbonates and an amphibole associated with a GEMS-like object (glass with embedded metals and sulfides) that potentially imply formation in a nebular rather than planetary environment. The two most primitive IDPs may contain assemblages of molecular cloud material at the percent level which is supported by the presence of four rare 17O-depleted presolar silicate grains possibly of supernova(e) origin within one ~ 70 μm2-sized IDP and the close association of a Group 1 Mg-rich olivine from a low-mass red giant star with a carbonaceous nano-globule of potentially interstellar origin. Our study together with observations of comet 9P/Tempel 1 during the Deep Impact experiment and 81P/Wild 2 dust analyses reveal some compositional variations and many similarities among three Jupiter-family comets. Specifically carbonates and primitive organic matter or amorphous carbon were widespread in the comet-forming regions of the outer protoplanetary disk and not all comets contain as much inner solar system material as has been inferred for comet 81P/Wild 2. The bulk and hotspot hydrogen and nitrogen isotopic anomalies as well as the carbon Raman characteristics of the organic matter in IDPs and the most primitive meteorites are remarkably similar. This implies that the same mixture of molecular cloud material had been transported inward into the meteorite-forming regions of the solar system. © 2009 Elsevier B.V.
• Baturina, O. A., Garsany, Y., Zega, T. J., Stroud, R. M., Schull, T., & Swider-Lyons, K. E. (2008). Oxygen reduction reaction on platinum/tantalum oxide electrocatalysts for PEM fuel cells. Journal of the Electrochemical Society, 155(12), B1314-B1321.
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  Abstract: We investigate platinum supported on tantalum oxide as a possible catalyst for oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells. Three synthetic routes are evaluated to compare activities of tantalum-oxide-supported platinum fuel cell electrocatalysts: (i) deposition of platinum colloids on tantalum oxide followed by mechanical grinding with Vulcan carbon (VC); (ii) deposition of tantalum oxide on VC, followed by the deposition of platinum colloids; and (iii) deposition of Pt colloids on VC, followed by deposition of tantalum oxide. These are compared to a PtVC standard made with the same Pt colloids. The area-specific activities for the ORR at 0.9 V are a factor of 1.5 higher for catalysts synthesized via preparation route (ii) compared to a PtVC standard. The area-specific activities of the catalysts synthesized via routes (i) and (iii) are close to that of PtVC. The higher area-specific activity of the catalyst synthesized by route (ii) may be due to the preferential adsorption of OH groups to the oxide vs platinum surface. © 2008 The Electrochemical Society.
• Busemann, H., M., C., Nittler, L. R., Stroud, R. M., Zega, T. J., Cody, G. D., Yabuta, H., & Kilcoyne, A. D. (2008). Structural, chemical and isotopic examinations of interstellar organic matter extracted from meteorites and interstellar dust particles. Proceedings of the International Astronomical Union, 4(S251), 333-334.
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  Abstract: Meteorites and Interplanetary Dust Particles (IDPs) are supposed to originate from asteroids and comets, sampling the most primitive bodies in the Solar System. They contain abundant carbonaceous material. Some of this, mostly insoluble organic matter (IOM), likely originated in the protosolar molecular cloud, based on spectral properties and H and N isotope characteristics. Together with cometary material returned with the Stardust mission, these samples provide a benchmark for models aiming to understand organic chemistry in the interstellar medium, as well as for mechanisms that secured the survival of these fragile molecules during Solar System formation. The carrier molecules of the isotope anomalies are largely unknown, although amorphous carbonaceous spheres, so-called nanoglobules, have been identified as carriers. We are using Secondary Ion Mass Spectrometry to identify isotopically anomalous material in meteoritic IOM and IDPs at a ~100-200 nm scale. Organics of most likely interstellar origin are then extracted with the Focused-Ion-Beam technique and prepared for synchrotron X-ray and Transmission Electron Microscopy. These experiments yield information on the character of the H- and N-bearing interstellar molecules: While the association of H and N isotope anomalies with nanoglobules could be confirmed, we have also identified amorphous, micron-sized monolithic grains. D-enrichments in meteoritic IOM appear not to be systematically associated with any specific functional groups, whereas 15N-rich material can be related to imine and nitrile functionality. The large 15N- enrichments observed here (δ15N > 1000 %) cannot be reconciled with models using interstellar ammonia ice reactions, and hence, provide new constraints for understanding the chemistry in cold interstellar clouds. © 2008 International Astronomical Union.
• Leroux, H., Rietmeijer, F. J., Velbel, M. A., Brearley, A. J., Jacob, D., Langenhorst, F., Bridges, J. C., Zega, T. J., Stroud, R. M., Cordier, P., Harvey, R. P., Lee, M., Gounelle, M., & Zolensky, M. E. (2008). A TEM study of thermally modified comet 81P/Wild 2 dust particles by interactions with the aerogel matrix during the Stardust capture process. Meteoritics and Planetary Science, 43(1-2), 97-120.
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  Abstract: We report the results of high-resolution, analytical and scanning transmission electron microscopy (STEM), including intensive element mapping, of severely thermally modified dust from comet 81P/Wild 2 caught in the silica aerogel capture cells of the Stardust mission. Thermal interactions during capture caused widespread melting of cometary silicates, Fe-Ni-S phases, and the aerogel. The characteristic assemblage of thermally modified material consists of a vesicular, silica-rich glass matrix with abundant Fe-Ni-S droplets, the latter of which exhibit a distinct core-mantle structure with a metallic Fe,Ni core and a iron-sulfide rim. Within the glassy matrix, the elemental distribution is highly heterogeneous. Localized amorphous "dust-rich" patches contain Mg, Al, and Ca in higher abundances and suggest incomplete mixing of silicate progenitors with molten aerogel. In some cases, the element distribution within these patches seems to depict the outlines of ghost mineral assemblages, allowing the reconstruction of the original mineralogy. A few crystalline silicates survived with alteration limited to the grain rims. The Fe- and Cl-normalized bulk composition derived from several sections show Cl-chondrite relative abundances for Mg, Al, S, Ca, Cr, Mn, Fe, and Ni. The data indicate a 5 to 15% admixture of fine-grained chondritic comet dust with the silica glass matrix. These strongly thermally modified samples could have originated from a fine-grained primitive material, loosely bound Wild 2 dust aggregates, which were heated and melted more efficiently than the relatively coarse-grained material of the crystalline particles found elsewhere in many of the same Stardust aerogel tracks (Zolensky et al. 2006). © The Meteoritical Society, 2008. Printed in USA.
• Zega, T. J., Kilcoyne, A. L., & Stroud, R. M. (2008). Nanobeam analysis of the oxidation states of transition metals in primitive planetary materials. Microscopy and Microanalysis, 14(SUPPL. 2), 524-525.
• Zolensky, M., Nakamura-Messenger, K., Rietmeijer, F., Leroux, H., Mikouchi, T., Ohsumi, K., Simon, S., Grossman, L., Stephan, T., Weisberg, M., Velbel, M., Zega, T., Stroud, R., Tomeoka, K., Ohnishi, I., Tomioka, N., Nakamura, T., Matrajt, G., Joswiak, D., , Brownlee, D., et al. (2008). Comparing Wild 2 particles to chondrites and IDPs. Meteoritics and Planetary Science, 43(1-2), 261-272.
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  Abstract: We compare the observed composition ranges of olivine, pyroxene, and Fe-Ni sulfides in Wild 2 grains with those from chondritic interplanetary dust particles (IDPs) and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fa0-96, with a pronounced frequency peak at Fa1. The composition range displayed by the low-calcium pyroxene is also very extensive, from Fs48 to Fs0, with a significant frequency peak centered at Fs5. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe-Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom% Ni; to date, only two pentlandite grains have been found among the Wild grains, suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e., did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water-bearing minerals, the presence of Ni-bearing sulfides, and magnesium-dominated olivine and low-Ca pyroxene does not rule out their presence at low abundance. We do conclude that new investigations of major- and minor- element compositions of chondrite matrix and IDPs are required. © The Meteoritical Society, 2008. Printed in USA.
• Bassim, N. D., Twigg, M. E., Mastro, M. A., Eddy Jr., C. R., Zega, T. J., Henry, R. L., Culbertson, J. C., Holm, R. T., Neudeck, P., Powell, J. A., & Trunek, A. J. (2007). Dislocations in III-nitride films grown on 4H-SiC mesas with and without surface steps. Journal of Crystal Growth, 304(1), 103-107.
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  Abstract: Using transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films deposited by metalorganic vapor phase epitaxy on the (0 0 0 1) surface of epitaxially grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations. We compare the excess stress associated with strain relief for each mechanism and find that the driving force for plastic flow is much greater for threading dislocation tilt than for half-loop propagation. © 2007 Elsevier B.V. All rights reserved.
• Baturina, O. A., Garsany, Y., Zega, T. J., Stroud, R. M., & Swider-Lyons, K. E. (2007). Oxygen reduction reaction on platinum/tantalum oxide electrocatalysts for PEM fuel cells. ECS Transactions, 11(1 PART 1), 197-204.
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  Abstract: Three synthetic routes are evaluated to obtain highly dispersed platinum on tantalum oxide supported catalysts: a) deposition of platinum colloids on tantalum oxide followed by mechanical grinding with Vulcan carbon; b) deposition of tantalum oxide on Vulcan carbon, followed by the deposition of platinum colloids; and c) deposition of Pt colloids on Vulcan carbon, followed by deposition of tantalum oxide. Specific activities for oxygen reduction reaction at 0.9V are a factor of two higher for catalysts synthesized via preparation routes a and b compared to Pt/VC. In comparison, the activity of catalysts synthesized via route c is close to that of Pt/VC. Mass activities for the catalysts possessing high specific activities are lower than for Pt/VC due to their low electrochemically available platinum surface area. © The Electrochemical Society.
• Zega, T. J., Nittler, L. R., Busemann, H., Hoppe, P., & Stroud, R. M. (2007). Coordinated isotopic and mineralogic analyses of planetary materials enabled by in situ lift-out with a focused ion beam scanning electron microscope. Meteoritics and Planetary Science, 42(7-8), 1373-1386.
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  Abstract: We describe a focused ion beam scanning electron microscope (FIB-SEM) technique that enables coordinated isotopic and mineralogic analysis of planetary materials. We show that site-specific electron-transparent sections can be created and extracted in situ using a microtweezer and demonstrate that they are amenable to analysis by secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These methods greatly advance the ability to address several fundamental questions in meteoritics, such as accretion and alteration histories of chondrules and the origin and history of preserved nebular and presolar materials. © The Meteoritical Society, 2007.
• Brownlee, D., Tsou, P., Aléon, J., M., C., Araki, T., Bajt, S., Baratta, G. A., Bastien, R., Bland, P., Bleuet, P., Borg, J., Bradley, J. P., Brearley, A., Brenker, F., Brennan, S., Bridges, J. C., Browning, N. D., Brucato, J. R., Bullock, E., , Burchell, M. J., et al. (2006). Comet 81P/wild 2 under a microscope. Science, 314(5806), 1711-1716.
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  PMID: 17170289;Abstract: The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.
• Stroud, R. M., Zega, T. J., & Taheri, M. L. (2006). In situ lift-out for coordinated structure-electron transport and structure-isotope studies. Microscopy and Microanalysis, 12(SUPPL. 2), 1266-1267.
• Zega, T. J., Garvie, L. A., Dódony, I., Friedrich, H., Stroud, R. M., & Buseck, P. R. (2006). Polyhedral serpentine grains in CM chondrites. Meteoritics and Planetary Science, 41(5), 681-688.
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  Abstract: We used high-resolution transmission electron microscopy (HRTEM), electron tomograpy, electron energy-loss spectroscopy (EELS), and energy-dispersive spectroscopy (EDS) to investigate the structure and composition of polyhedral serpentine grains that occur in the matrices and fine-grained rims of the Murchison, Mighei, and Cold Bokkeveld CM chondrites. The structure of these grains is similar to terrestrial polygonal serpentine, but the data show that some have spherical or subspherical, rather than cylindrical morphologies. We therefore propose that the term polyhedral rather than polygonal be used to describe this material. EDS shows that the polyhedral grains are rich in Mg with up to 8 atom% Fe. EELS indicates that 70% of the Fe occurs as Fe3+. Alteration of cronstedtite on the meteorite parent body under relatively oxidizing conditions is one probable pathway by which the polyhedral material formed. The polyhedral grains are the end-member serpentine in a mineralogic alteration sequence for the CM chondrites. © The Meteoritical Society, 2006.
• Zega, T. J., Hanbicki, A. T., Erwin, S. C., Žutić, I., Kioseoglou, G., Li, C. H., Jonker, B. T., & Stroud, R. M. (2006). Determination of interface atomic structure and its impact on spin transport using Z-contrast microscopy and density-functional theory. Physical Review Letters, 96(19).
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  Abstract: We combine Z-contrast scanning transmission electron microscopy with density-functional-theory calculations to determine the atomic structure of the Fe/AlGaAs interface in spin-polarized light-emitting diodes. A 44% increase in spin-injection efficiency occurs after a low-temperature anneal, which produces an ordered, coherent interface consisting of a single atomic plane of alternating Fe and As atoms. First-principles transport calculations indicate that the increase in spin-injection efficiency is due to the abruptness and coherency of the annealed interface. © 2006 The American Physical Society.
• Zega, T. J., Hanbicki, A. T., Erwin, S. C., Žutić, I., Kioseoglou, G., Li, C. H., Jonker, B. T., & Stroud, R. M. (2006). Z-contrast-microscopy and density-functional-theory determination of the atomic structure of the Fe/AlGaAs interface and its impact on spin transport. Microscopy and Microanalysis, 12(SUPPL. 2), 972-973.
• Zolensky, M. E., Zega, T. J., Yano, H., Wirick, S., Westphal, A. J., Weisberg, M. K., Weber, I., Warren, J. L., Velbel, M. A., Tsuchiyama, A., Tsou, P., Toppani, A., Tomioka, N., Tomeoka, K., Teslich, N., Taheri, M., Susini, J., Stroud, R., Stephan, T., , Stadermann, F. J., et al. (2006). Mineralogy and petrology of comet 81P/wild 2 nucleus samples. Science, 314(5806), 1735-1739.
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  PMID: 17170295;Abstract: The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.
• Garvie, L. A., Zega, T. J., Rez, P., & Buseck, P. R. (2004). Nanometer-scale measurements of Fe³⁺/ΣFe by electron energy-loss spectroscopy: A cautionary note. American Mineralogist, 89(11-12), 1610-1616.
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  Abstract: The effects of electron-beam damage on the Fe3+/ΣFe (total iron) ratio were measured by electron energy-loss spectroscopy (EELS) with a transmission electron microscope (TEM). Spectra were acquired from crushed and ion-beam-thinned cronstedtite. For fluences below 1 × 104 e/Å2, the Fe 3+/ΣFe values from crushed grains range between 0.43 and 0.49, consistent with undamaged material. These measurements were acquired from flakes 180 to 1000 Å thick. With increase in fluence, samples 0.5. The critical fluence for radiation damage by 100 kV electrons as defined by Fe3+ /ΣFe 0.7. With increase in sample thickness, the Fe3+/ΣFe values decrease to a minimum, consistent with data from the undamaged material. The increase of Fe3+/ΣFe with respect to electron-beam irradiation is likely caused by loss of H. At low fluences, the loss of H is negligible, thus allowing consistent Fe3+/ΣFe values to be measured. The cronstedtite study illustrates the care required when using EELS to measure Fe3+/ΣFe values. Similar damage effects occur for a range of high-valence and mixed-oxidation state metals in minerals. EELS is the only spectroscopic method that can be used routinely to determine mixed-valence ratios at the nanometer scale, but care is required when measuring these data. Consideration needs to be given to the incident beam current, fluence, fluence rate, and sample thickness.
• Zega, T. J., Garvie, L. A., Dédony, I., & Buseck, P. R. (2004). Erratum: "Serpentine nanotubes in the Mighei CM chondrite" (Earth and Planetary Science Letters (2004) vol. 223 (141-146) 10.1016/j.epsl.2004.04.005). Earth and Planetary Science Letters, 226(1-2), 123-.
• Zega, T. J., Garvie, L. A., Dódony, I., & Buseck, P. R. (2004). Serpentine nanotubes in the Mighei CM chondrite. Earth and Planetary Science Letters, 223(1-2), 141-146.
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  Abstract: We report the discovery of serpentine nanotubes in the Mighei CM chondrite. High-resolution transmission electron microscope (HRTEM) images show that the nanotubes are multiwalled, containing from 3 to 11 layers with periodicities of 0.68±0.08 nm. Some nanotubes appear capped. Their lengths and inner diameters range from 20 to 230 nm and 2 to 9 nm, respectively, with internal volumes of 200-11,300 nm3. Chemical analyses made using electron energy-loss spectroscopy (EELS) give Mg1.7Fe 0.52+Fe0.73+[Si1.5 Fe0.53+O5]H1.8([ ]1.0O2.4S0.6)∑=4, with H determined by difference. The S-bearing and Fe-rich composition of these nanotubes is distinct from previously reported meteoritic and terrestrial materials, and we believe them to be a new variety of serpentine. These intriguing structures likely formed during aqueous-alteration events early in the history of the solar system and potentially served as containers of primordial fluids. © 2004 Elsevier B.V. All rights reserved.
• Zega, T. J., Stroud, R. M., Hanbicki, A. T., Kioseoglou, G., Erve, O. V., Li, C. H., Jonker, B. T., Itskos, G., Mallory, R., Yasar, M., & Petrou, A. (2004). Effects of the heteroepitaxial interface on spin injection in Fe/AlGaAs. Microscopy and Microanalysis, 10(SUPPL. 2), 334-335.
• Zega, T. J., & Buseck, P. R. (2003). Fine-grained-rim mineralogy of the Cold Bokkeveld CM chondrite. Geochimica et Cosmochimica Acta, 67(9), 1711-1721.
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  Abstract: A chrysotile-like phase, cronstedtite, polygonal serpentine, pentlandite, and finely intergrown tochilinite comprise the fine-grained rim (FGR) mineralogy of the Cold Bokkeveld CM chondrite. Transmission electron microscope images combined with compositional data indicate reaction among cronstedtite, the chrysotile-like phase, and polygonal serpentine. The Mg/(Mg+Fe) ratios of the cronstedtite are higher than those reported for the less altered Murchison CM chondrite. Cronstedtite grains exhibit layer separations, particularly at their boundaries. The FGRs surround different chondrule types but have similar bulk compositions and mineralogy. Ca is depleted in the FGRs relative to the bulk CM chondrite. The FGRs display non-uniform thicknesses, especially where they coat embayed chondrule areas, and they exhibit grain-size coarsening outward from the chondrules they enclose. FGR formation in Cold Bokkeveld is most plausibly explained by multiple accretionary episodes during which progressively coarser dust was deposited onto chondrules, presumably in the solar nebula. The compositional and mineralogic data are consistent with aqueous alteration on the parent body. © 2003 Elsevier Science Ltd.
• Zega, T. J., Garvie, L. A., & Buseck, P. R. (2003). Nanometer-scale measurements of iron oxidation states of cronstedtite from primitive meteorites. American Mineralogist, 88(7), 1169-1172.
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  Abstract: We report the first nanometer-scale measurements of the iron (III) to total iron (Fe3+/ΣFe) ratios from primitive meteorites. These ratios from the matrices and fine-grained rims (FGRs) of the Murchison, Murray, and Cold Bokkeveld CM chondrites fall within a tight range, from 0.45 to 0.54 (±0.02). The measurements were made using electron energy-loss spectroscopy (EELS) on cronstedtite, which is a product of aqueous alteration early in the history of the solar system. The results indicate that the alteration of these meteorites, which display a broad range of alteration intensity, occurred under similar redox conditions and, further, that alteration likely occurred in situ on asteroidal bodies rather than in the solar nebula.

Proceedings Publications

• Che, S., Domanik, K., & Zega, T. (2023, mar). Halite and Sphalerite in the Sidi El Habib 001 (H5) Ordinary Chondrite: Insights into Microchemistry-Controlled Hydrothermal Alternation on its Parent Body. In LPI Contributions, 2806.
• Barnes, J., Wilbur, Z., Ong, L., Eckley, S., Brounce, M., Pomeroy, S., Crow, C., Boyce, J., Mosenfelder, J., Erickson, T., Hahn, T., Fires, M., & Zega, T. (2022, oct). A Multifaceted Approach to Investigating the Magmatic and Post-Magmatic History of Volatiles in Basalts from the Rim of Steno Crater. In LPI Contributions, 2704.
• Benner, M., Zega, T., & Ziurys, L. (2022, aug). Alteration of P-Bearing Phases in Allan Hills 77307 and Murchison Meteorites. In LPI Contributions, 2695.
• Bernal, J., Zega, T., & Ziurys, L. (2022, aug). Experimental Insights into the Formation of Fullerenes and Carbon Nanotubes in Interstellar Space. In LPI Contributions, 2695.
• Brounce}, M., Barnes, J., Crow, C., Economos, R., Erickson, T., Boyce, J., Wilbur, Z., McCubbin, F., Mosenfelder, J., Zega, T., & Team, {. S. (2022, mar). Measuring the Oxidation State of Sulfur in Apatites in Thin Sections of Meteorites versus Apollo Rocks. In 53rd Lunar and Planetary Science Conference, 2678.
• Che, S., & Zega, T. (2022, aug). In-situ Formation of Halite in the Sidi El Habib 001 Ordinary Chondrite. In LPI Contributions, 2695.
• Che, S., & Zega, T. (2022, mar). NaCl in an Itokawa Particle: Terrestrial or Asteroidal?. In 53rd Lunar and Planetary Science Conference, 2678.
• Manga, V., & Zega, T. (2022, mar). First-Principles Thermodynamic of Ultra-Refractory Inclusions: Condensation Temperature of Allendeite. In 53rd Lunar and Planetary Science Conference, 2678.
• Manga, V., Ramprasad, T., & Zega, T. (2022, aug). Condensation Phase Diagram of Ultra-Refractory Materials Pertaining to the High Temperature Region of Early Solar Protoplanetary Disk. In LPI Contributions, 2695.
• Noguchi, T., Matsumoto, T., Miyake, A., Igami, Y., Haruta, M., Saito, H., Hata, S., Seto, Y., Miyahara, M., Tomioka, N., Ishii, H., Bradley, J., Ohtaki, K., Dobric{\u{a}}, E., Leroux, H., LeGuillou, C., Jacob, D., Pe{\~na}, F., Laforet, S., , Marinova, M., et al. (2022, aug). Dehydration Decomposition of Phyllosilicates in the C-Type Asteroid Ryugu Material by Space Weathering. In LPI Contributions, 2695.
• Noguchi, T., Matsumoto, T., Miyake, A., Igami, Y., Haruta, M., Saito, H., Hata, S., Seto, Y., Miyahara, M., Tomioka, N., Ishii, H., Bradley, J., Otaki, K., Dobric{\u{a}}, E., Leroux, H., Le Guillou, C., Jacob, D., Marinova, M., Pe{\~na}, F., , Langenhorst, F., et al. (2022, mar). Mineralogy and Space Weathering of Fine Fraction Recovered from Asteroid (162173) Ryugu. In 53rd Lunar and Planetary Science Conference, 2678.
• Pomeroy, S., Crow, C., Wilbur, Z., Barnes, J., Boyce, J., Mosenfelder, J., Brounce, M., Erikson, T., & Zega, T. (2022, mar). Chronology of Steno Crater Basalts. In 53rd Lunar and Planetary Science Conference, 2678.
• Ramprasad, T., Seifert, L., Mane, P., & Zega, T. (2022, mar). A Transmission Electron Microscopy Study of a Refractory Metal Grain from a Calcium-Aluminum-Rich Inclusion in the Leoville CV3 Chondrite. In 53rd Lunar and Planetary Science Conference, 2678.
• Schrader, D., Davidson, J., Foustoukos, D., Alexander, C. O., Torrano, Z., Cloutis, E., Applin, D., Zega, T., Nakamura, T., & Matsuoka, M. (2022, mar). Tarda and Tagish Lake: Samples from the Same Outer Solar System Asteroid?. In 53rd Lunar and Planetary Science Conference, 2678.
• Schrader, D., Zega, T., Davidson, J., McCoy, T., & Domanik, K. (2022, aug). Pentlandite in Chondrites: A Compositional Indicator of Oxygen Fugacity. In LPI Contributions, 2695.
• Seifert, L., Haenecour, P., Ramprasad, T., & Zega, T. (2022, mar). Transmission Electron Microscopy Study of a Presolar Silicate from the Miller Range 07687 Chondrite. In 53rd Lunar and Planetary Science Conference, 2678.
• Thompson, M., Schrader, D., Davidson, J., & Zega, T. (2022, aug). Formation of Fe Whiskers Through Simulated Micrometeoroid Bombardment. In LPI Contributions, 2695.
• Thompson, M., Zanetta, P. -., Zega, T., Noguchi, T., Yurimoto, H., Nakamura, T., Yabuta, H., Naraoka, N., Okazaki, R., Sakamoto, K., Tachibana, S., Watanabe, S., & Tsuda, Y. (2022, mar). Evidence for Micrometeoroid Bombardment on the Surface of Asteroid Ryugu. In 53rd Lunar and Planetary Science Conference, 2678.
• Wilbur}, Z., Barnes, J., Eckley, S., Brounce, M., Pomeroy, S., Crow, C., Boyce, J., Mosenfelder, J., Zega, T., & Team, {. S. (2022, mar). From Source to Surface: An Investigation of Magmatic Lunar Volatiles. In 53rd Lunar and Planetary Science Conference, 2678.
• Zanetta, P. -., Rao Manga, V., Thakur, A., Zega, T., & Muralidharan, K. (2022, aug). Development of Hibonite as a Barometer for Nebular Oxygen Fugacity. In LPI Contributions, 2695.
• Zanetta}, P. -., Thompson, M., Zega, T., Noguchi, T., Yurimoto, H., Nakamura, T., Yabuta, H., Naraoka, N., Okazaki, R., Sakamoto, K., Tachibana, S., Watanabe, S., Tsuda, Y., & Sub-Team, {. (2022, mar). Effect of Space Weathering on the Iron Oxidation State of Ryugu Samples, a STEM-EELS Study. In 53rd Lunar and Planetary Science Conference, 2678.
• Brounce}, M., Barnes, J., Boyce, J., Wilbur, Z., McCubbin, F., Crow, C., Mosenfelder, J., Zega, T., & Team, {. S. (2021, mar). The Oxidation State of Sulfur in Apollo Samples 71035 and 71055. In 52nd Lunar and Planetary Science Conference.
• Manga, V., Zanetta, P., Thakur, A., Muralidharan, K., & Zega, T. (2021, aug). Thermodynamic Modeling of Equilibrium Solubilities of Ti in Minerals of Calcium-and-Aluminum-Rich Inclusions Under Nebular Conditions. In 84th Annual Meeting of the Meteoritical Society, 84.
• Ramprasad, T., Seifert, L., & Zega, T. (2021, aug). A Microstructural Examination of a Refractory-Siderophile Nugget from the Northwest Africa 8323 CV3 Chondrite. In 84th Annual Meeting of the Meteoritical Society, 84.
• Schmidt, D., Ziurys, L., Woolf, N., & Zega, T. (2021, jun). Unusual C, N, O Isotopic Ratios in Planetary Nebulae. In American Astronomical Society Meeting Abstracts, 53.
• Schrader, D., Davidson, J., McCoy, T., Zega, T., Russell, S., Domanik, K., & King, A. (2021, mar). The Fe/S Ratio of Pyrrhotite Group Sulfides in Chondrites is Related to the Degree of Oxidation. In 52nd Lunar and Planetary Science Conference.
• Seifert, L., Haenecour, P., Ramprasad, T., & Zega, T. (2021, aug). Transmission Electron Microscopy Study of a Presolar Silicate Grain from the Uniquely Altered Miller Range 07687 Chondrite. In 84th Annual Meeting of the Meteoritical Society, 84.
• Stadermann, A., Barnes, J., Erickson, T., & Zega, T. (2021, aug). Apollo Sample 64455: Petrologic and Geochemical Characterization of a Glass-Coated Impact Melt Rock. In 84th Annual Meeting of the Meteoritical Society, 84.
• Zanetta, P. -., Manga, V., Chang, Y. -., Ramprasad, T., & Zega, T. (2021, aug). Multistage Non-Equilibrium Processes Recorded by a Hibonite Grain in the Northwest Africa 5028 CR2 Chondrite. In 84th Annual Meeting of the Meteoritical Society, 84.
• Zega, T., & Schrader, D. (2021, aug). Microstructural Analysis of a Sulfide Grain in the Matrix of the Sutter's Mill CM-Like Carbonaceous Chondrite. In 84th Annual Meeting of the Meteoritical Society, 84.
• Mane, P., Zega, T., Nguyen, A., & Simon, J. (2020, mar). Isotopic and Microstructural Analyses of Opaque Mineral Assemblages and Their Alteration Products Hosted in a Refractory Inclusion. In Lunar and Planetary Science Conference.
• Manga, V., & Zega, T. (2020, mar). The Thermodynamics of Sc- and Ti-Bearing Refractory Mineral Phases in Calcium-Aluminum-Rich Inclusions: Revisiting the Condensation Sequence of Early Solar Nebula. In Lunar and Planetary Science Conference.
• Ramprasad, T., Seifert, L., & Zega, T. (2020, mar). Microstructural Analysis of a Refractory-Siderophile Grain, Found in a Calcium-Aluminum-Rich Inclusion. In Lunar and Planetary Science Conference.
• Schrader, D., Davidson, J., Zega, T., Russell, S., & McCoy, T. (2020, mar). The Fe/S Ratio of Pyrrhotite in Carbonaceous Chondrites Relevant to Bennu and Ryugu: An Indicator of Parent Asteroid Aqueous and Thermal Alteration. In Lunar and Planetary Science Conference.
• Seifert, L., Haenecour, P., Ramprasad, T., & Zega, T. (2020, mar). Structure and Chemistry of a Supernova Orthopyroxene Grain in the CO Chondrite Dominion Range 08006. In Lunar and Planetary Science Conference.
• Wilbur, Z., Barnes, J., Eckley, S., Boyce, J., Brounce, M., Crowe, C., Mosenfelder, J., & Zega, T. (2020, mar). Investigating the Magmatic History of Volatiles in Apollo 17 Basalts, Apollo Next Generation Sample Analysis. In Lunar and Planetary Science Conference.
• Zega, T., & Schrader, D. (2020, mar). The Microstructures of Sulfide Grains from the Vic\^encia LL3.2, Hamlet LL4, and Appley Bridge LL6 Chondrites. In Lunar and Planetary Science Conference.
• Bernal, J., Ziurys, L. M., Haenecour, P., Howe, J., Zega, T. J., & Amari, S. (2019, Jun). Formation of Interstellar C$_60$ from Silicon Carbide Circumstellar Grains. In 74th International Symposium on Molecular Spectroscopy.
• Bernal, J., Ziurys, L. M., Haenecour, P., Howe, J., Zega, T., & Amari, S. (2019, Jun). Formation of Interstellar C$_60$ from Silicon Carbide Circumstellar Grains. In American Astronomical Society Meeting Abstracts \#234, 234.
• Glavin}, D., Squyres, S., Nakamura-Messenger, K. .., Hayes, A., Mitchell, D., Moran, V., Houghton, M., Douglas-Bradshaw, D. .., Lauretta, D., Messenger, S., Yamada, K., Okazaki, S., Satoh, Y., Maru, Y., Nakao, T., Kukita, A., Shimoda, T., Yamawaki, T., Nakamura, T., , Parker, J., et al. (2019, Jul). Overview of the Comet Astrobiology Exploration Sample Return (CAESAR) New Frontiers Mission. In 82nd Annual Meeting of The Meteoritical Society, 82.
• Haenecour, P., Floss, C., Brearley, A., Howe, J., & Zega, T. (2019, Mar). A Large Donut-Shaped Presolar Silicate from the MIL 07687 Carbonaceous Chondrite. In Lunar and Planetary Science Conference.
• Haenecour, P., Howe, J., Zega, T., Sunaoshi, T., Thompson, M., Dogel, S., & Sagar, J. (2019, Mar). Thermal Alteration of Organics and Volatiles in Carbonaceous Chondrites: Insights from In-Situ Heating Experiments. In Lunar and Planetary Science Conference.
• Jadhav, M., Haenecour, P., Amari, S., Davidson, J., & Zega, T. (2019, Mar). A Preliminary Search for Presolar Grains in a New Acid Residue of the Tagish Lake Meteorite. In Lunar and Planetary Science Conference.
• Lauretta, D., Squyres, S., Berm{\'udez}, L., Blake, G., Canham, J., Chu, P., Clemett, S., Dworkin, J., Furukawa, Y., Gerakines, P., Glavin, D., Herd, C., Houghton, M., Kimura, Y., Lorenston, C., Makowski, J., Messenger, S., Milam, S., Mumma, M., , Nakamura-Messenger, K. .., et al. (2019, Mar). The CAESAR New Frontiers Mission: 1. Expected Nature of the Returned Comet Sample. In Lunar and Planetary Science Conference.
• Manga, V., Zega, T., & Muralidharan, K. (2019, Jul). Thermodynamic Modeling of Pyroxene Solid Solutions: Revisiting the Condensation Sequence of Refractory Minerals in Calcium- and Aluminium-Rich Inclusions. In 82nd Annual Meeting of The Meteoritical Society, 82.
• Manga, V., Zega, T., & Muralidharan, K. (2019, Mar). Thermodynamics of Twin Complexions in Spinel: Deducing the Loci of Temperature and Pressure of Deformation Processes Within the Solar Protoplanetary Disk. In Lunar and Planetary Science Conference.
• O'Brien, P., Byrne, S., & Zega, T. (2019, Mar). Lunar Landscape Evolution and Space Weathering. In Lunar and Planetary Science Conference.
• Ramprasad, T., Haenecour, P., & Zega, T. (2019, Mar). Microstructural Analysis of a Compact Type-A Calcium-Aluminum Rich Inclusion in the Northwest Africa (NWA) 5028 CR2 Chondrite. In Lunar and Planetary Science Conference.
• Schrader, D., & Zega, T. (2019, Jul). Determining the Geothermometry of a Hayabusa-Returned Sulfide Particle. In 82nd Annual Meeting of The Meteoritical Society, 82.
• Schrader, D., & Zega, T. (2019, Mar). Comparison of the Sulfide-Bearing Hayabusa Particles RB-CV-0234 and RB-QD04-0039 to LL Chondrite Sulfides. In Lunar and Planetary Science Conference.
• Seifert, L., Haenecour, P., & Zega, T. (2019, Mar). Elemental Composition and Microstructure of a Supernova Polycrystalline Olivine Aggregate in the CO Chondrite Dominion Range 08006. In Lunar and Planetary Science Conference.
• Thompson, M., Haenecour, P., Howe, J., Laczniak, D., Zega, T., Hu, J., Chen, W., Keller, L., & Christoffersen, R. (2019, Mar). Simulating Space Weathering in the Transmission Electron Microscope via Dynamic In Situ Heating and Helium Irradiation of Olivine. In Lunar and Planetary Science Conference.
• Zega, T., Bernal, J., Howe, J., Haenecour, P., Amari, S., & Ziurys, L. (2019, Mar). In Situ Irradiation and Heating of Synthetic SiC and Implications for the Origins of C-Rich Circumstellar Materials. In Lunar and Planetary Science Conference.
• Barnes, J., Thompson, M., McCubbin, F., Howe, J., Rahman, Z., Messenger, S., & Zega, T. (2018, mar). Coordinated Microanalysis of Phosphates in Apollo 11 High-Titanium Basalts. In Lunar and Planetary Science Conference, 49.
• Haenecour, P., Howe, J., Zega, T., Wallace, P., Amari, S., Floss, C., Lodders, K., Kaji, K., Sunaoshi, T., & Atsushi, M. (2018, mar). Microstructure and Inclusions of In-Situ and Acid-Residue Presolar Graphite Grains. In Lunar and Planetary Science Conference, 49.
• Haenecour, P., Howe, J., Zega, T., Wallace, P., Atsushi, M., Takeshi, S., Kaji, K., Floss, C., & Yada, T. (2018, mar). Mineralogy and 15N-Rich Organic Matter in the Fine-Grained Antarctic Micrometeorite T98G8: Evidence for a Cometary Origin?. In Lunar and Planetary Science Conference, 49.
• Keller, L., Howe, J., Rahman, Z., Thompson, M., & Zega, T. (2018, mar). In Situ Heating Experiments on Patina Coated Lunar Rock 76015. In Lunar and Planetary Science Conference, 49.
• Lauretta, D., Squyres, S., Messenger, S., Nakamura-Messenger, K. .., Nakamura, T., Glavin, D., Dworkin, J., Nguyen, A., Clemett, S., Furukawa, Y., Kimura, Y., Takigawa, A., Blake, G., Zega, T., Mumma, M., Milam, S., Herd, C., & Team, C. P. (2018, mar). The CAESAR New Frontiers Mission: 2. Sample Science. In Lunar and Planetary Science Conference, 49.
• Mane, P., Chang, Y., Wallace, P., & Zega, T. (2018, mar). Transmission Electron Microscope Analysis of High Temperature Rims Around Type-B CAIs. In Lunar and Planetary Science Conference, 49.
• Mane, P., Wallace, S., Wallace, P., Domanik, K., & Zega, T. (2018, mar). Electron Backscatter Diffraction Analysis of the Earliest-Formed Solids in the Solar System. In Lunar and Planetary Science Conference, 49.
• Nakamura-Messenger}, K., Berm{\'udez}, L., Canham, J., Chu, P., Clemett, S., Dworkin, J., Gerakines, P., Herd, C., Houghton, M., Lauretta, D., Lorentson, C., Makowski, J., Messenger, S., Milam, S., Nakamura, T., Oberg, D., Pace, L., Spring, J., Violet, M., , Zacny, K., et al. (2018, mar). The CAESAR New Frontiers Mission: 5. Contamination, Recovery, and Curation. In Lunar and Planetary Science Conference, 49.
• Ramprasad, T., Mane, P., & Zega, T. (2018, mar). Transmission Electron Microscope Analysis of a Spinel-Perovskite Assemblage Within a Refractory Inclusion from the Northwest Africa (NWA) 5028 CR2 Chondrite. In Lunar and Planetary Science Conference, 49.
• Schrader, D., & Zega, T. (2018, mar). Pyrrhotite and Pentlandite in LL3 to LL6 Chondrites: Determining Compositional and Microstructural Indicators of Formation Conditions. In Lunar and Planetary Science Conference, 49.
• Seifert, L., Haenecour, P., Zega, T., & Floss, C. (2018, mar). TEM Analysis of Presolar Silicate Grain in the Dominion Range 08006, CO Chondrite. In Lunar and Planetary Science Conference, 49.
• Zega, T., & Mane, P. (2018, mar). Nanoscale Analysis of a Metal-Perovskite Assemblage in the Northwest Africa 5028 CR2 Chondrite. In Lunar and Planetary Science Conference, 49.
• Haenecour, P., Floss, C., Zega, T., Croat, T., Wang, A., Jolliff, B., & Carpenter, P. (2017, mar). Pre-Accretionary Aqueous Alteration of Dust in Fine-Grained Chondrule Rims: Evidence from Presolar Grain Abundances and Mineralogy in Primitive CO3.0 Chondrites. In Lunar and Planetary Science Conference, 48.
• Mane, P., Wallace, S., Zega, T., Wadhwa, M., & Wallace, P. (2017, mar). Electron Back-Scattered Diffraction Analysis of a Refractory Inclusion and Its Wark-Lovering Rims. In Lunar and Planetary Science Conference, 48.
• Thompson, M., Zega, T., & Howe, J. (2017, mar). TEM Analysis of Space Weathering Features in an Itokawa Soil Grain with a Polyphasic Mineralogy. In Lunar and Planetary Science Conference, 48.
• Zega, T., Manga, V., Domanik, K., Howe, J., & Muralidharan, K. (2017, mar). Nanoscale Analysis of Perovskite Grains from Allende and Axtell Meteorites. In Lunar and Planetary Science Conference, 48.
• Zega, T., Thompson, M., & Howe, J. (2017, mar). Microstructure Analysis of a Soil Grain Returned from Asteroid Itokawa. In Lunar and Planetary Science Conference, 48.
• {Bose}, M., {Zega}, T., , K. (2016, mar). Nitrogen and Carbonaceous Isotopic Variations in Several Carbonaceous Chondrites {\mdash} A Hunt for the Carrier Phases. In Lunar and Planetary Science Conference, 47.
• {Thompson}, M., {Zega}, T., , J. (2016, mar). Simulation of Micrometeorite Impacts Through In Situ Dynamic Heating of Lunar Soil. In Lunar and Planetary Science Conference, 47.
• {Zega}, T., {Manga}, V., {Domanik}, K., , K. (2016, mar). Nanostructural Analysis of Several Perovskite Grains from an Allende CAI: Evidence for Equilibrium or Non-Equilibrium Condensation?. In Lunar and Planetary Science Conference, 47.
• {Haenecour}, P., {Zega}, T., {Floss}, C., {Croat}, T., , B. (2015, mar). Abundances and Elemental Compositions of Presolar Silicates in CO3.0 Chondrites: Possible Indicators of Secondary Processing?. In Lunar and Planetary Science Conference, 46.
• {Thompson}, M., , T. (2015, jul). Simulation of Micrometeorite Impacts Through In Situ Dynamic Heating of Lunar Soils. In 78th Annual Meeting of the Meteoritical Society, 1856.
• {Thompson}, M., , T. (2015, nov). Simulation of Micrometeorite Impacts Through In Situ Dynamic Heating of Lunar Soil. In Space Weathering of Airless Bodies: An Integration of Remote Sensing Data, Laboratory Experiments and Sample Analysis Workshop, 1878.
• {Thompson}, M., {Zega}, T., {Keane}, J., {Becerra}, P., , S. (2015, mar). The Oxidation State of Fe Nanoparticles in Lunar Soil: Implications for Space Weathering Processes. In Lunar and Planetary Science Conference, 46.
• {Thompson}, M., {Zega}, T., {Keane}, J., {Becerra}, P., , S. (2015, nov). The Oxidation State of Nanophase Fe Particles in Lunar Soil: Implications for Space Weathering. In Space Weathering of Airless Bodies: An Integration of Remote Sensing Data, Laboratory Experiments and Sample Analysis Workshop, 1878.
• {Zega}, T., {Haenecour}, P., {Floss}, C., , R. (2015, jul). Circumstellar Magnetite Identified in the LAP 031117 CO3.0 Chondrite. In 78th Annual Meeting of the Meteoritical Society, 1856.
• {Zega}, T., {Haenecour}, P., {Floss}, C., , R. (2015, mar). Identification of Circumstellar Magnetite in the LAP 031117 CO3.0 Chondrite. In Lunar and Planetary Science Conference, 46.
• {Haenecour}, P., {Floss}, C., , T. (2014, sep). Spatial Variation of Presolar Silicate Abundances in CO3 Chondrites: Correlation with Aqueous Alteration?. In 77th Annual Meeting of the Meteoritical Society, 1800.

Poster Presentations

• Asaduzzaman, A., Zega, T., Runge, K., & Muralidharan, K. (2014, March). Synthesis and Delivery of Amino Acids to the Early Earth via Surface Catalysis: A Computational Study. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1777; Page: 1647
• Haenecour, P., Floss, C., Jolliff, B., Zega, T., Bose, M., & Carpenter, P. (2014, March). Presolar Silicates as Tracers of the Formation of Fine-Grained Chondrule Rims in CO3 Chondrites. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1777; Page: 1316
• Miller, K., Thompson, M., Lauretta, D., & Zega, T. (2014, March). Conditions for Formation of Chalcopyrite in the Rumuruti Chondrites. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1777; Page: 1461
• Thompson, M., & Zega, T. (2014, March). Determining the Oxidation State of Iron Nanoparticles in Mature Lunar Soil Through Electron Energy-Loss Spectroscopy. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1777; Page: 2834
• Thompson, M., Christoffersen, R., Zega, T., & Keller, L. (2014, March). Nanoscale Analysis of Space-Weathering Features in Soils from Itokawa. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1777; Page: 2121
• Zega, T. (2014, June). Coordinated analysis of planetary materials at the nanoscale. 2014 Goldschmidt Conference.
• Zega, T., Haenecour, P., Floss, C., & Stroud, R. (2014, March). Extraction and Analysis of Presolar Grains from the LAP 031117 CO3.0 Chondrite. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1777; Page: 2256
• Asaduzzaman, A., Muralidharan, K., Runge, K., & Zega, T. (2013, March). A Computational Exploration on the Attachment of Organics to Minerals: Implications for the Delivery of Organics to Meteorite Parent Bodies and the Early Earth. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1719; Page: 2884
• Berger, E., Lauretta, D., Zega, T., & Keller, L. (2013, March). FIB-TEM Investigations of Fe-Ni-Sulfides in the CI Chondrites Alais and Orgueil. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1719; Page: 1615
• Bolser, D., Zega, T., Simon, S., & Grossman, L. (2013, July). Analysis of Refractory Inclusions in the Allende and Axtell CV3 Chondrites via Electron-Backscatter Diffraction. 76th Annual Meeting of the Meteoritical Society. Edmonton, Canada.
• Bose, M., Zega, T., & Williams, P. (2013, March). Effects of Secondary Processes on the Circumstellar and Interstellar Grains in QUE 97416. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1719; Page: 2718
• Bose, M., Zega, T., Andronokov, A., & Williams, P. (2013, March). A Large Presolar Oxide Grain Identified in Allende CV3 Chondrite. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1719; Page: 3024
• Thompson, M., & Zega, T. (2013, March). Microstructural and Chemical Analysis of Soils from Itokawa: Evidence for Space Weathering. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1719; Page: 2593
• Zega, T. (2013, March). From the bottom up: Decoding the physical and chemical history of the early solar system and ancient stars through nanoscale characterization. 2013 Arizona Imaging and Microanalysis Society Conference. Tucson, AZ.
• Zega, T. (2013, May). Decoding the thermodynamics of ancient circumstellar envelopes via nanoscale analysis of presolar stardust grains. NOT PROVIDED.
• Zega, T. (2013, October). Structural, chemical, and isotopic analysis of (presolar) dust grains from ancient stars. Guest Lecture for Chemistry 529 Methods of Surface and Materials Analysis. Tucson, AZ.
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  Instructor: Armstrong, N
• Zega, T. (2013, September). Laboratory-based astronomy at the nanometer scale. Nanoscale Science Seminar. Tempe, AZ: LeRoy Eyring Center for Sold State Science, Arizona State University.
• Zega, T., & Floss, C. (2013, March). Extraction and Analysis of a Presolar Oxide Grain from the Adelaide Ungrouped C2 Chondrite. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1719; Page: 1287
• Asaduzzaman, A., Muralidharan, K., Runge, K., & Zega, T. (2012, August). First Principles Investigation of Adsorption of Organic Molecules on Planetary Materials. 75th Annual Meeting of the Meteoritical Society. Cairns, Australia.
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  Published in: Meteoritics and Planetary Science Supplement; ID: 5397
• Zega, T. (2012, November). Laboratory analysis of refractory oxides from the early solar system and ancient stars. University of Arizona, Materials Science and Engineering Department Colloquium. Tucson, AZ.
• Zega, T. (2012, October). Characterization of condensed matter from the early solar system: The need for integrated computational materials science and engineering. The integrated computational materials science and engineering workshop. Tucson, AZ.
• Zega, T., Nittler, L., Stroud, R., Alexander, C., & Kilcoyne, A. (2012, March). Measurement of the Oxidation State of Ti in Solar and Presolar Hibonite. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  LPI Contribution No. 1659; ID: 2338