Z. R. Dai

Publications (24)42.3 Total impact

• Article: Characterization of Pd Impurities and Finite-Sized Defects in Detector Grade CdZnTe

  M.C. Duff, J.P. Bradley, Z.R. Dai, N. Teslich, A. Burger, M. Groza, V. Buliga
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  ABSTRACT: Synthetic CdZnTe or “CZT” crystals are highly suitable for γ-spectrometers operating at the room temperature. Secondary phases (SP) in CZT are known to inhibit detector performance, particularly when they are present in large numbers or dimensions. These SP may exist as voids or composites of non-cubic phase metallic Te layers with bodies of polycrystalline and amorphous CZT material and voids. Defects associated with crystal twining may also influence detector performance in CZT. Using transmission electron microscopy, we identify two types of defects that are on the nano scale. The first defect consists of 40 nm diameter metallic Pd/Te bodies on the grain boundaries of Te-rich composites. Although the nano-Pd/Te bodies around these composites may be unique to the growth source of this CZT material, noble metal impurities like these may contribute to SP formation in CZT. The second defect type consists of atom-scale grain boundary dislocations. Specifically, these involve inclined “finite-sized” planar defects or interfaces between layers of atoms that are associated with twins. Finite-sized twins may be responsible for the subtle but observable striations that can be seen with optical birefringence imaging and synchrotron X-ray topographic imaging.
  MRS Proceedings. 12/2010; 1341.
• Article: Focused ion beam recovery of hypervelocity impact residue in experimental craters on metallic foils

  G. A. Graham, N. Teslich, Z. R. Dai, J. P. Bradley, A. T. Kearsley, F. Hörz
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  ABSTRACT: Abstract— The Stardust sample return capsule returned to Earth in January 2006 with primitive debris collected from comet 81P/Wild-2 during the flyby encounter in 2004. In addition to the cometary particles embedded in low-density silica aerogel, there are microcraters preserved in the aluminum foils (1100 series; 100 μm thick) that are wrapped around the sample tray assembly. Soda lime spheres (˜49 μm in diameter) have been accelerated with a light gas gun into flight-grade aluminum foils at 6.35 km s−1 to simulate the capture of cometary debris. The experimental craters have been analyzed using scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDX) to locate and characterize remants of the projectile material remaining within the craters. In addition, ion beam-induced secondary electron imaging has proven particularly useful in identifying areas within the craters that contain residue material. Finally, high-precision focused ion beam (FIB) milling has been used to isolate and then extract an individual melt residue droplet from the interior wall of an impact. This has enabled further detailed elemental characterization that is free from the background contamination of the aluminum foil substrate. The ability to recover “pure” melt residues using FIB will significantly extend the interpretations of the residue chemistry preserved in the aluminum foils returned by Stardust.
  Meteoritics & Planetary Science. 01/2010; 41(2):159 - 165.
• Article: Characterization of heterogeneities in detector-grade CdZnTe crystals

  M.C. Duff, D.B. Hunter, A. Burger, M. Groza, V. Buliga, J.P. Bradley, G. Graham, Z.R. Dai, N. Teslich, D.R. Black, A. Lanzirotti
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  ABSTRACT: Synthetic Cd1–x Zn x Te or “CZT” crystals are highly suitable for γ-spectrometers operating at room temperature. Secondary phases (SP) within CZT, presumed to be Te metal, have detrimental impacts on the charge collection efficiency of fabricated device. Using analytical techniques rather than arbitrary theoretical definitions, we identify two SP morphologies: (i) many void, 20-μm “negative” crystals with 65-nm nanoparticle residues of Si, Cd, Zn, and Te and (ii) 20-μm hexagonal-shaped bodies, which are composites of metallic Te layers with cores of amorphous and polycrystalline CZT material that surround the voids.
  Journal of Materials Research. 03/2009; 24(04):1361 - 1367.
• Article: Mechanism of Formation of Glass with Embedded Metal and Sulfides

  J. P. Bradley, Z. R. Dai
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  ABSTRACT: GEMS (glass with embedded metal and sulfides) grains in interplanetary dust particles (IDPs) were examined using 200 keV analytical transmission electron microscopy. The morphologies and crystallography of embedded relict grains reveal that GEMS are pseudomorphs formed by irradiation processing of crystals free-floating in space. Some GEMS retain a compositional and morphological "memory" of the crystal from which they formed. Pseudomorphism may rule out condensation, annealing, flash heating, or shock melting as alternative mechanisms of GEMS formation. A significant and often dominant fraction of the atoms in GEMS were sputter-deposited from other grains. Therefore, a normal (solar) isotopic composition is not a reliable indicator of whether GEMS formed in the solar system or in presolar interstellar or circumstellar environments.
  The Astrophysical Journal 12/2008; 617(1):650. · 6.02 Impact Factor
• Source

  Available from: Phil A. Bland

  Article: Dust from comet Wild 2: Interpreting particle size, shape, structure, and composition from impact features on the Stardust aluminum foils

  A. T. Kearsley, J. Borg, G. A. Graham, M. J. Burchell, M. J. Cole, H. Leroux, J. C. Bridges, F. Hörz, P. J. Wozniakiewicz, P. A. Bland, [......], N. Teslich, T. See, P. Hoppe, P. R. Heck, J. Huth, F. J. Stadermann, C. Floss, K. Marhas, T. Stephan, J. Leitner
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  ABSTRACT: Abstract— Aluminum foils of the Stardust cometary dust collector are peppered with impact features of a wide range of sizes and shapes. By comparison to laboratory shots of known particle dimensions and density, using the same velocity and incidence geometry as the Stardust Wild 2 encounter, we can derive size and mass of the cometary dust grains. Using scanning electron microscopy (SEM) of foil samples (both flown on the mission and impacted in the laboratory) we have recognized a range of impact feature shapes from which we interpret particle density and internal structure. We have documented composition of crater residues, including stoichiometric material in 3 of 7 larger craters, by energy dispersive X-ray microanalysis. Wild 2 dust grains include coarse (>10 μm) mafic silicate grains, some dominated by a single mineral species of density around 3–4 g cm−3 (such as olivine). Other grains were porous, low-density aggregates from a few nanometers to 100 μm, with an overall density that may be lower than 1 g cm−3, containing mixtures of silicates and sulfides and possibly both alkali-rich and mafic glass. The mineral assemblage is very similar to the most common species reported from aerogel tracks. In one large aggregate crater, the combined diverse residue composition is similar to CI chondrites. The foils are a unique collecting substrate, revealing that the most abundant Wild 2 dust grains were of sub-micrometer size and of complex internal structure. Impact residues in Stardust foil craters will be a valuable resource for future analyses of cometary dust.
  Meteoritics & Planetary Science. 01/2008; 43(1‐2):41 - 73.
• Source

  Available from: arxiv.org

  Article: Analytical scanning and transmission electron microscopy of laboratory impacts on Stardust aluminum foils: interpreting impact crater morphology and the composition of impact residues

  A. T. Kearsley, G. A. Graham, M. J. Burchell, M. J. Cole, Z. R. Dai, N. Teslich, J. P. Bradley, R. Chater, P. A. Wozniakiewicz, J. Spratt, G. Jones
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  ABSTRACT: The known encounter velocity (6.1kms-1) and particle incidence angle (perpendicular) between the Stardust spacecraft and the dust emanating from the nucleus of comet Wild 2 fall within a range that allows simulation in laboratory light gas gun experiments designed to validate analytical methods for the interpretation of dust impacts on the aluminum foil components of the Stardust collector. Buckshot of a wide size, shape and density range of mineral, glass, polymer and metal grains, have been fired to impact perpendicularly upon samples of Stardust Al1100 foil, tightly wrapped onto aluminium alloy plate as an analogue of foil on the spacecraft collector. We have not yet been able to produce laboratory impacts by projectiles with weak and porous aggregate structure, as may occur in some cometary dust grains. In this report we present information on crater gross morphology and its dependence on particle size and density, the pre-existing major and trace element composition of the foil, geometrical issues for energy dispersive X-ray analysis of the impact residues in scanning electron microscopes, and the modification of dust chemical composition during creation of impact craters as revealed by analytical transmission electron microscopy. Together, these observations help to underpin the interpretation of size, density and composition for particles impacted upon the Stardust aluminum foils.
  01/2007;
• Article: Mineralogy and Petrology of Comet Wild 2 Nucleus Samples.

  M. E. Zolensky, T. J. Zega, H Yano, S. Wirick, A. J. Westphal, M. K. Weisberg, I. Weber, J. L. Warren, M. A. Velbel, A. Tsuchiyama, [......], M. Chi, A. L. Butterworth, D. E. Brownlee, John C. Bridges, S Brennan, A. Brearley, J. P. Bradley, P. Bleuet, P. A. Bland, R. Bastien
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  ABSTRACT: The bulk of the Wild 2 samples appear to be weakly-constructed mixtures of nanometerscale grains with occasional much larger (>1{micro}m) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in Wild 2 require a wide range of formation conditions, probably reflecting different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and absence of hydrous phases indicate that Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require large-scale radial transport in the early protoplanetary disk. The nature of cometary solids is of fundamental importance to our understanding of the early solar nebula and protoplanetary history. Until now we have had to study comets from afar using spectroscopy, or settle for analyses of interplanetary dust particles (IDPs) of uncertain provenance. We report here mineralogical and petrographic analyses of particles derived directly from Comet Wild 2. All of the Wild 2 particles we have thus far examined have been modified in various ways by the capture process. All particles that may have been loose aggregates, ''traveling sand piles'', disaggregated into individual components with the larger, denser components penetrating more deeply into the aerogel. Individual grains experienced a wide range of heating effects that range from excellent preservation to melting (Fig. 1); such behavior was expected (1, 2 ,3). What is remarkable is the extreme variability of these modifications and the fact that severely modified and unmodified materials can be found within a micrometer of each other, requiring tremendous local temperature gradients. Fortunately, we have an internal gauge of impact collection heating. Fe-Ni sulfides are ubiquitous in the Wild 2 samples, are very sensitive indicators of heating, and accurate chemical analyses can reveal which have lost S, and which have not (and are therefore stoichiometric) (Fig. 2). Our surveys show that crystalline grains are found along the entire lengths of tracks, not just at track termini.
  10/2006;
• Source

  Available from: adsabs.harvard.edu

  Article: Origin and properties of GEMS (Glass with Embedded Metal and Sulfides)

  Z. R. Dai, J. P. Bradley
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  ABSTRACT: GEMS are to the outer solar system what chondrules are to the inner solar system. Ten years after it was first proposed that GEMS are the long-sought interstellar amorphous silicates, ion microprobe measurements have confirmed that some of them are indeed interstellar amorphous silicates. The new challenges are to obtain even higher precision isotope measurements from these submicrometer-sized objects and to clarify how and where they originally formed. Individual GEMS exhibit a strikingly narrow (0.1-0.5 μm diameter) size distribution and they are systematically depleted from solar abundances in S/Si, Mg/Si, Ca/Si and Fe/Si, implying that they formed by a common mechanism. Mineralogical and petrographic evidence suggest that irradiation processing may be that mechanism. Recent nanometer-scale compositional mapping using new-generation transmission electron microscopes reveals that truly pristine GEMS may be relatively rare and new metrics need to be developed to distinguish the primordial properties of GEMS from more recent secondary alteration effects.
  11/2005; 341:668.
• Article: Electron Beam Analysis of Micrometeoroids Captured in Aerogel as Stardust Analogues

  G. A. Graham, J. Sheffield-Parker, P. Bradley, A. T. Kearsley, Z. R. Dai, S. C. Mayo, N. Teslich, C. Snead, A. J. Westphal, H Ishii
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  ABSTRACT: In January 2004, NASA s Stardust spacecraft passed through the tail of Comet 81P/Wild-2. The on-board dust flux monitor instrument indicated that numerous micro- and nano-meter sized cometary dust particles were captured by the dedicated silica aerogel capture cell. The collected cometary particles will be returned to Earth in January 2006. Current Stardust analogues are: (i) Light-gas-gun accelerated individual mineral grains and carbonaceous meteoritic material in aerogels at the Stardust encounter velocity ca.approximately 6 kilometers per second. (ii) Aerogels exposed in low-Earth orbit (LEO) containing preserved cosmic dust grains. Studies of these impacts offer insight into the potential state of the captured cometary dust by Stardust and the suitability of various analytical techniques. A number of papers have discussed the application of sophisticated synchrotron analytical techniques to analyze Stardust particles. Yet much of the understanding gained on the composition and mineralogy of interplanetary dust particles (IDPs) has come from electron microscopy studies. Here we discuss the application of scanning electron microscopy (SEM) for Stardust during the preliminary phase of post-return investigations.
  02/2005;
• Source

  Available from: Sasa Bajt

  Article: Nitrogen Isotopic Anomalies in a Hydrous Interplanetary Dust Particle

  J. B. Smith, Z. R. Dai, P. K. Weber, G. A. Graham, I. D. Hutcheon, S. Bajt, H Ishii, J. P. Bradley
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  ABSTRACT: Interplanetary dust particles (IDPs) collected in the stratosphere are the fine-grained end member (5 - 50 microns in size) of the meteoritic material available for investigation in the laboratory. IDPs are derived from either cometary or asteroidal sources. Some IDPs contain cosmically primitive materials with isotopic signatures reflecting presolar origins. Recent detailed studies using the NanoSIMS have shown there is a wide variation of isotopic signatures within individual IDPs; grains with a presolar signature have been observed surrounded by material with a solar isotopic composition. The majority of IDPs studied have been anhydrous. We report here results from integrated NanoSIMS/FIB/TEM/Synchrotron IR studies of a hydrous IDP, focused on understanding the correlations between the isotopic, mineralogical and chemical compositions of IDPs.
  02/2005;
• Article: Focused Ion Beam Recovery and Analysis of Interplanetary Dust Particles (IDPs) and Stardust Analogues

  G. A. Graham, J. P. Bradley, M. Bernas, R. M. Stroud, Z. R. Dai, C. Floss, F. J. Stadermann, C. J. Snead, A. J. Westphal
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  ABSTRACT: Meteoritics research is a major beneficiary of recent developments in analytical instrumentation [1,2]. Integrated studies in which multiple analytical techniques are applied to the same specimen are providing new insight about the nature of IDPs [1]. Such studies are dependent on the ability to prepare specimens that can be analyzed in multiple instruments. Focused ion beam (FIB) microscopy has revolutionized specimen preparation in materials science [3]. Although FIB has successfully been used for a few IDP and meteorite studies [1,4-6], it has yet to be widely utilized in meteoritics. We are using FIB for integrated TEM/NanoSIMS/synchrotron infrared (IR) studies [1].
  02/2004;
• Article: The Petrography of Meteoritic Nano-Diamonds

  Z. R. Dai, J. P. Bradley, D. E. Brownlee, D. J. Joswiak
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  ABSTRACT: At least some meteoritic nanodiamonds are likely of presolar origin because of their association with anomalous Xe-HL and Te isotopic components indicative of a supernova (SN) origin. But the abundance of Xe is such that only approx. 1 in 10(exp 6) nano-diamonds contains a Xe atom, and the bulk C-13/C-12 composition of nano-diamond acid residues is chondritic (solar). Therefore, it is possible that a significant fraction of meteoritic nano-diamonds formed within the solar nebula. Nano-diamonds have recently been detected for the first time within the accretion discs of young stars by the Infrared Space Observatory (ISO). No comparable evidence of nanodiamonds in the interstellar medium has yet been found. We have identified nano-diamonds in acid etched thin-sections of meteorites, polar micrometeorites, and interplanetary dust particles (IDPs) with the goal of determining their distribution as a function of heliocentric distance. (It is assumed the meteorites and the polar micrometeorites are from asteroids at 2-4 AU and at least some of the IDPs are from comets at >50AU). We found that nano-diamonds are heterogeneously distributed throughout carbon-rich meteoritic materials (we identified them in some IDPs and not in others), and that their abundance may actually decrease with heliocentric distance, consistent with the hypothesis that some of them formed within the inner solar system and not in a presolar (SN) environment. In order to gain further insight about the origins of meteoritic nano-diamonds we are currently investigating their distribution in unetched thin-sections. We have examined a chondritic cluster IDP (U220GCA), fragments of the Tagish Lake (CM1) meteorite, and a SN graphite spherule (KE3d8) isolated from the Murchison (CM) meteorite. We selected U220GCA because its nano-diamond abundance (in acid etched thin-sections) appears to be as much as approx. 10X higher than in Murchison matrix, Tagish Lake because it has a higher reported nano-diamond abundance than other carbonaceous chondrites (approx. 3650-4330 ppm), and KE3d8 because it is a carbon spherule with an isotopic composition suggesting that it is a bone fide presolar SN grain.
  02/2003;
• Source

  Available from: imperial.ac.uk

  Article: Possible in situ formation of meteoritic nanodiamonds in the early Solar System.

  Z R Dai, J P Bradley, D J Joswiak, D E Brownlee, H G M Hill, M J Genge
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  ABSTRACT: Grains of dust that pre-date the Sun provide insights into their formation around other stars and into the early evolution of the Solar System. Nanodiamonds recovered from meteorites, which originate in asteroids, have been thought to be the most abundant type of presolar grain. If that is true, then nanodiamonds should be at least as abundant in comets, because they are thought to have formed further out in the early Solar System than the asteroid parent bodies, and because they should be more pristine. Here we report that nanodiamonds are absent or very depleted in fragile, carbon-rich interplanetary dust particles, some of which enter the atmosphere at speeds within the range of cometary meteors. One interpretation of the results is that some (perhaps most) nanodiamonds formed within the inner Solar System and are not presolar at all, consistent with the recent detection of nanodiamonds within the accretion discs of other young stars. An alternative explanation is that all meteoritic nanodiamonds are indeed presolar, but that their abundance decreases with heliocentric distance, in which case our understanding of large-scale transport and circulation within the early Solar System is incomplete.
  Nature 08/2002; 418(6894):157-9. · 36.28 Impact Factor
• Source

  Available from: articles.adsabs.harvard.edu

  Article: Some Diamonds May Not be Forever

  J. P. Bradley, Z. R. Dai, D. J. Joswiak, D. E. Brownlee, H. G. M. Hill, M. M. Genge
  Meteoritics and Planetary Science Supplement. 06/2002; 37:21.
• Article: Nano-Diamonds in Interplanetary Dust Particles (IDPs), Micrometeorites, and Meteorites

  Z. R. Dai, J. P. Bradley, D. J. Joswiak, D. E. Brownlee, M. J. Genge
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  ABSTRACT: Nano-diamonds have been identified in IDPs (Interplanetary Dust Particles), micrometeorites, and meteorites. They appear to be depleted in non-cluster IDPs suggesting that some nano-diamonds are not presolar. Additional information is contained in the original extended abstract.
  05/2002;
• Article: Nano-Diamonds in Chondritic Interplanetary Dust Particles

  Z. R. Dai, D. J. Joswiak, J. P. Bradley, D. E. Brownlee, H. G. M. Hill
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  ABSTRACT: In-situ acid etching of ultramicrotomed thin sections has lead to the identification of nano-diamonds in interplanetary dust particles. Additional information is contained in the original extended abstract.
  02/2001;
• Article: Research article - Comet 81P/Wild 2 under a microscope

  D. Brownlee, P. Tsou, J. Aleon, C. M. O. Alexander, T Araki, S. Bajt, G. A. Baratta, R. Bastien, P. Bland, P. Bleuet, [......], I. Wright, H. Yabuta, H Yano, E. D. Young, R N Zare, T. Zega, K. Ziegler, L. Zimmerman, E. Zinner, M. Zolensky
  Science, v.314, 1711-1716 (2006).
• Source

  Available from: open.ac.uk

  Article: Microcraters in aluminum foils exposed by Stardust

  F. Hörz, J. Borg, J. P. Bradley, John Bridges, D. E. Brownlee, M. J. Burchell, M. J. Cole, Z. R. Dai, Z. Djouadi, C. Floss, [......], N. Teslich, K. K. Marhas, C. S. Schwandt, T. H. See, F. J. Stadermann, T. Stephan, D. Troadec, P. Tsou, M. E. Zolensky, The Stardust Cratering Team
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  ABSTRACT: We will present preliminary results on the nature and size frequency distribution of microcraters that formed in aluminum foils during the flyby of comet Wild 2 by the Stardust spacecraft.
• Article: Report - Mineralogy and petrology of comet 81P/Wild 2 nucleus samples

  M. E. Zolensky, T. J. Zega, H Yano, S. Wirick, A. J. Westphal, M. K. Weisberg, I. Weber, J. L. Warren, M. A. Velbel, A. Tsuchiyama, [......], M. F. Chi, A. L. Butterworth, D. E. Brownlee, J. C. Bridges, S Brennan, A. Brearley, J. P. Bradley, P. Bleuet, P. A. Bland, R. Bastien
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  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.
• Article: Comet 81P/Wild 2 under a microscope

  D. Brownlee, P. Tsou, J. Aleon, C. M. O. Alexander, T Araki, S. Bajt, G. A. Baratta, R. Bastien, P. Bland, P. Bleuet, [......], I. Wright, H. Yabuta, H Yano, E. D. Young, R N Zare, T. Zega, K. Ziegler, L. Zimmerman, E. Zinner, M. Zolensky
  Science, v.314, 1711-1716 (2006).