Publications
57 results found
Conroy M, Moore K, O'Connell E, et al., 2020, Probing the Dynamics of Topologically Protected Charged Ferroelectric Domain Walls with the Electron Beam at the Atomic Scale, ISSN: 1431-9276
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- Citations: 2
Schwantes JM, Conroy M, Lach TG, et al., 2019, Changing the rules of the game: used fuel studies outside of a remote handling facility, Journal of Radioanalytical and Nuclear Chemistry, Vol: 322, Pages: 1267-1272, ISSN: 0236-5731
Pacific Northwest National Laboratory (PNNL) has leveraged focused ion beam capability at their Category II Nuclear Facility to facilitate nuclear materials analysis and experimentation at the micron scale. For this particular study, micron-size specimens of un-irradiated UO2 fuel pellets of various enrichments were prepared and irradiated to a burnup equivalent of 8–3700 MWd/MTU. This represents first of its kind study of used fuel investigations outside of a hot cell facility, dramatically minimizing resource requirements through reduction in scale. Results of this study provide insight into the initial production of noble metal phase particles in used nuclear fuel at extremely low burnup levels.
Lu H, Tan Y, McConville JPV, et al., 2019, Electrical Tunability of Domain Wall Conductivity in LiNbO3 Thin Films., Adv Mater, Vol: 31
Domain wall nanoelectronics is a rapidly evolving field, which explores the diverse electronic properties of the ferroelectric domain walls for application in low-dimensional electronic systems. One of the most prominent features of the ferroelectric domain walls is their electrical conductivity. Here, using a combination of scanning probe and scanning transmission electron microscopy, the mechanism of the tunable conducting behavior of the domain walls in the sub-micrometer thick films of the technologically important ferroelectric LiNbO3 is explored. It is found that the electric bias generates stable domains with strongly inclined domain boundaries with the inclination angle reaching 20° with respect to the polar axis. The head-to-head domain boundaries exhibit high conductance, which can be modulated by application of the sub-coercive voltage. Electron microscopy visualization of the electrically written domains and piezoresponse force microscopy imaging of the very same domains reveals that the gradual and reversible transition between the conducting and insulating states of the domain walls results from the electrically induced wall bending near the sample surface. The observed modulation of the wall conductance is corroborated by the phase-field modeling. The results open a possibility for exploiting the conducting domain walls as the electrically controllable functional elements in the multilevel logic nanoelectronics devices.
Devanathan R, Jiang W, Kruska K, et al., 2019, Hexagonal close-packed high-entropy alloy formation under extreme processing conditions, Journal of Materials Research, Vol: 34, Pages: 709-719, ISSN: 0884-2914
We assess the validity of criteria based on size mismatch and thermodynamics in predicting the stability of the rare class of high-entropy alloys (HEAs) that form in the hexagonal close-packed crystal structure. We focus on nanocrystalline HEA particles composed predominantly of Mo, Tc, Ru, Rh, and Pd along with Ag, Cd, and Te, which are produced in uranium dioxide fuel under the extreme conditions of nuclear reactor operation. The constituent elements are fission products that aggregate under the combined effects of irradiation and elevated temperature as high as 1200 °C. We present the recent results on alloy nanoparticle formation in irradiated ceria, which was selected as a surrogate for uranium dioxide, to show that radiation-enhanced diffusion plays an important role in the process. This work sheds light on the initial stages of alloy nanoparticle formation from a uniform dispersion of individual metals. The remarkable chemical durability of such multiple principal element alloys presents a solution, namely, an alloy waste form, to the challenge of immobilizing Tc.
Jiang W, Conroy MA, Kruska K, et al., 2019, In Situ Study of Particle Precipitation in Metal-Doped CeO<inf>2</inf> during Thermal Treatment and Ion Irradiation for Emulation of Irradiating Fuels, Journal of Physical Chemistry C, Vol: 123, Pages: 2591-2601, ISSN: 1932-7447
Metallic particles formed in oxide fuels (e.g., UO2) during neutron irradiation have an adverse impact on fuel performance. A fundamental investigation of particle precipitation is needed to predict the fuel performance and potentially improve fuel designs and operations. This study reports on the precipitation of Mo-dominant β-phase particles in polycrystalline CeO2 (surrogate for UO2) films doped with Mo, Pd, Rh, Ru, and Re (surrogate for Tc). In situ heating scanning transmission electron microscopy indicates that particle precipitation starts at ∼1073 K with a limited particle growth to ∼10 nm. While particle concentration increases with increasing temperature, particle size remains largely unchanged up to 1273 K. There is a dramatic change in the microstructure following vacuum annealing at 1373 K, probably due to phase transition of reduced cerium oxide. At the high temperature, particles grow up to 75 nm or larger with distinctive facets. The particles are predominantly composed of Mo with a body-centered cubic structure (β phase). An oxide layer was observed after storage at ambient conditions. In situ heating X-ray photoelectron spectroscopy reveals an increasing reduction of Ce charge state from 4+ to 3+ in the doped CeO2 film at temperatures from 673 to 1273 K. In situ ion irradiation transmission electron microscopy with 2 MeV Al2+ ions up to a dose of ∼20 displacements per atom at nominally room temperature does not lead to precipitation of visible particles. However, irradiation with 1.7 MeV Au3+ ions to ∼10 dpa at 973 K produces ∼2 nm sized pure Pd particles; Au3+ irradiation at 1173 K appears to result in precipitates of ∼6 nm in size. Some of the defects produced by ion irradiation could be nucleation sites for precipitation, leading to generation of smaller particles with a higher concentration. ©
Chatterjee S, Fujimoto MS, Canfield NL, et al., 2019, An electrochemical technique for controlled dissolution of zirconium based components of light water reactors, RSC Advances, Vol: 9, Pages: 1869-1881
Zircaloy-4 (Zr-4) based liners and getters are the principle functional components of Tritium-Producing Burnable Absorber Rods (TPBARs) in light water nuclear reactors where they reduce tritiated water into tritium gas. Upon tritium exposure, zirconium tritide is formed, which changes the chemical composition, structure and morphology of these materials. Their thermodynamic properties are affected by (i) the hydride phase identity, (ii) radial and spatial tritide/hydride (T/H) distribution, and (iii) the changes in structure and morphology of the material upon T/H-migration, and their comprehensive knowledge is needed to predict performance of these materials. This work demonstrates that controlled potential electrochemistry techniques to be highly efficient for controlled oxidative radial dissolution of Zr-4 based liners (both unloaded and loaded with hydride/deuteride as chemical surrogates for tritium). The electrodissolution is further combined with microscopic techniques to accurately determine the distribution of hydride phases. This work demonstrates a reliable technique for radially etching the liners after irradiation to provide insight into the radial and spatial distribution of tritium within the TPBAR, improving the fundamental understanding of tritium transport and providing a basis for validating predictive models.
Weaver JL, Pearce CI, Sjoblom R, et al., 2018, Pre-Viking Swedish hillfort glass: A prospective long-term alteration analogue for vitrified nuclear waste, INTERNATIONAL JOURNAL OF APPLIED GLASS SCIENCE, Vol: 9, Pages: 540-554, ISSN: 2041-1286
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- Citations: 13
Soltis JA, Isley WC, Conroy M, et al., 2018, <i>In situ</i> microscopy across scales for the characterization of crystal growth mechanisms: the case of europium oxalate, CRYSTENGCOMM, Vol: 20, Pages: 2822-2833, ISSN: 1466-8033
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- Citations: 7
Johnson IE, Chatterjee S, Hall GB, et al., 2018, Inorganic Ba-Sn nanocomposite materials for sulfate sequestration from complex aqueous solutions, ENVIRONMENTAL SCIENCE-NANO, Vol: 5, Pages: 890-903, ISSN: 2051-8153
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- Citations: 5
Kusch G, Conroy M, Li H, et al., 2018, Multi-wavelength emission from a single InGaN/GaN nanorod analyzed by cathodoluminescence hyperspectral imaging, Scientific Reports, Vol: 8, Pages: 1-8, ISSN: 2045-2322
Multiple luminescence peaks emitted by a single InGaN/GaN quantum-well(QW) nanorod, extending from the blue to the red, were analysed by a combination of electron microscope based imaging techniques. Utilizing the capability of cathodoluminescence hyperspectral imaging it was possible to investigate spatial variations in the luminescence properties on a nanoscale. The high optical quality of a single GaN nanorod was demonstrated, evidenced by a narrow band-edge peak and the absence of any luminescence associated with the yellow defect band. Additionally two spatially confined broad luminescence bands were observed, consisting of multiple peaks ranging from 395 nm to 480 nm and 490 nm to 650 nm. The lower energy band originates from broad c-plane QWs located at the apex of the nanorod and the higher energy band from the semipolar QWs on the pyramidal nanorod tip. Comparing the experimentally observed peak positions with peak positions obtained from plane wave modelling and 3D finite difference time domain(FDTD) modelling shows modulation of the nanorod luminescence by cavity modes. By studying the influence of these modes we demonstrate that this can be exploited as an additional parameter in engineering the emission profile of LEDs.
Schwantes J, Peterson R, Reilly D, et al., 2018, A new paradigm in actinide research: Nuclear materials science at the micron-scale, Pages: 145-147
Conroy M, Soltis JA, Wittman RS, et al., 2017, Importance of interlayer H bonding structure to the stability of layered minerals, Scientific Reports, Vol: 7, Pages: 1-10, ISSN: 2045-2322
Layered (oxy) hydroxide minerals often possess out-of-plane hydrogen atoms that form hydrogen bonding networks which stabilize the layered structure. However, less is known about how the ordering of these bonds affects the structural stability and solubility of these minerals. Here, we report a new strategy that uses the focused electron beam to probe the effect of differences in hydrogen bonding networks on mineral solubility. In this regard, the dissolution behavior of boehmite (γ-AlOOH) and gibbsite (γ-Al(OH)3) were compared and contrasted in real time via liquid cell electron microscopy. Under identical such conditions, 2D-nanosheets of boehmite (γ-AlOOH) exfoliated from the bulk and then rapidly dissolved, whereas gibbsite was stable. Further, substitution of only 1% Fe(III) for Al(III) in the structure of boehmite inhibited delamination and dissolution. Factors such as pH, radiolytic species, and knock on damage were systematically studied and eliminated as proximal causes for boehmite dissolution. Instead, the creation of electron/hole pairs was considered to be the mechanism that drove dissolution. The widely disparate behaviors of boehmite, gibbsite, and Fe-doped boehmite are discussed in the context of differences in the OH bond strengths, hydrogen bonding networks, and the presence or absence of electron/hole recombination centers.
Jiang W, Conroy MA, Kruska K, et al., 2017, Nanoparticle Precipitation in Irradiated and Annealed Ceria Doped with Metals for Emulation of Spent Fuels, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 121, Pages: 22465-22477, ISSN: 1932-7447
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- Citations: 6
Jiang W, Conroy MA, Devanathan R, et al., 2017, Precipitation of epsilon particles in metal doped ceria irradiated with energetic ions, Pages: 431-434, ISSN: 0003-018X
Conroy M, Buck EC, Balooch M, et al., 2017, Microanalysis of irradiated metallic hydride nuclear fuel (U<inf>0.17</inf>ZrH<inf>1.6</inf>), Pages: 349-351, ISSN: 0003-018X
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- Citations: 1
Pearce CI, Weaver JL, Vicenzi EP, et al., 2017, Investigating alteration of pre-viking hillfort glasses from the broborg Hillfort Site, Sweden, Pages: 957-959
Conroy M, Li H, Zubialevich VZ, et al., 2016, Self-Healing Thermal Annealing: Surface Morphological Restructuring Control of GaN Nanorods, CRYSTAL GROWTH & DESIGN, Vol: 16, Pages: 6769-6775, ISSN: 1528-7483
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- Citations: 9
Conroy M, Zubialevich VZ, Li H, et al., 2016, Ultra-High-Density Arrays of Defect-Free AIN Nanorods: A "Space-Filling" Approach, ACS NANO, Vol: 10, Pages: 1988-1994, ISSN: 1936-0851
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- Citations: 17
Conroy M, Li H, Kusch G, et al., 2016, Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods, NANOSCALE, Vol: 8, Pages: 11019-11026, ISSN: 2040-3364
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- Citations: 18
Chatterjee S, Conroy MA, Smith FN, et al., 2016, Can Cr(III) substitute for Al(III) in the structure of boehmite?, RSC ADVANCES, Vol: 6, Pages: 107628-107637
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- Citations: 5
Smith MD, O'Mahony D, Conroy M, et al., 2015, InAlN high electron mobility transistor Ti/Al/Ni/Au Ohmic contact optimisation assisted by <i>in</i>-<i>situ</i> high temperature transmission electron microscopy, APPLIED PHYSICS LETTERS, Vol: 107, ISSN: 0003-6951
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- Citations: 5
Biswas S, Doherty J, Majumdar D, et al., 2015, Diameter-Controlled Germanium Nanowires with Lamellar Twinning and Polytypes, CHEMISTRY OF MATERIALS, Vol: 27, Pages: 3408-3416, ISSN: 0897-4756
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- Citations: 19
Dinh DV, Conroy M, Zubialevich VZ, et al., 2015, Single phase (11(2)over-bar2) AIN grown on (10(1)over-bar0) sapphire by metalorganic vapour phase epitaxy, JOURNAL OF CRYSTAL GROWTH, Vol: 414, Pages: 94-99, ISSN: 0022-0248
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- Citations: 24
Conroy M, Zubialevich VZ, Li H, et al., 2015, Epitaxial lateral overgrowth of AlN on self-assembled patterned nanorods, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 431-437, ISSN: 2050-7526
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- Citations: 54
Zhao C, Ng TK, Prabaswara A, et al., 2015, An enhanced surface passivation effect in InGaN/GaN disk-in-nanowire light emitting diodes for mitigating Shockley-Read-Hall recombination, NANOSCALE, Vol: 7, Pages: 16658-16665, ISSN: 2040-3364
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- Citations: 79
Conroy MA, Petkov N, Li HN, et al., 2013, Preparation of Substrates Intended for the Growth of Lower Threading Dislocation Densities within Nitride Based UV Multiple Quantum Wells, 14th Symposium on Wide-Bandgap Semiconductor Materials and Devices held during the 223rd Meeting of the Electrochemical-Society, Publisher: ELECTROCHEMICAL SOC INC, Pages: 39-42, ISSN: 1938-5862
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- Citations: 2
Morris V, Fleming P, Conroy M, et al., 2012, The formation of surface stable anion vacancy states at CeO<sub>2</sub> ultra-small crystallite dimensions, CHEMICAL PHYSICS LETTERS, Vol: 536, Pages: 109-112, ISSN: 0009-2614
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- Citations: 2
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