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Advanced Characterization: 3D chemistry and structure at sub-nm resolution

Kotula, Paul G.; Rye, Michael J.

This work has started the process of extending nanometer-scale comprehensive microanalysis to the 3rd dimension by combining full x-ray spectral imaging with previously developed computed tomography techniques whereby we acquire a series of spectral images for a large number of projections of the same specimen in the transmission electron microscope and then analyze the composite computed tomographic spectral image data prior to application of existing tomographic reconstruction software. We have demonstrated a needle-shaped specimen geometry (shape/size and preparation method) by focused ion beam preparation and acquisition and analysis of a complete tomographic spectral image on a test material consisting of fine-grained Ni with sub-10 nm alumina particles.

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TYPE Other Report YEAR 2014
DOIOSTI

Deformation behavior of sub-micron and micron sized alumina particles in compression

Sarobol, Pylin; Chandross, Michael E.; Carroll, J.D.; Mook, William M.; Boyce, Brad L.; Kotula, Paul G.; Mckenzie, Bonnie; Bufford, Daniel C.; Hall, Aaron

The ability to integrate ceramics with other materials has been limited due to high temperature (>800°C) ceramic processing. Recently, researchers demonstrated a novel process, aerosol deposition (AD), to fabricate ceramic films at room temperature (RT). In this process, sub-micron sized ceramic particles are accelerated by pressurized gas, impacted on the substrate, plastically deformed, and form a dense film under vacuum. This AD process eliminates high temperature processing thereby enabling new coatings and device integration, in which ceramics can be deposited on metals, plastics, and glass. However, knowledge in fundamental mechanisms for ceramic particles to deform and form a dense ceramic film is still needed and is essential in advancing this novel RT technology. In this work, a combination of experimentation and atomistic simulation was used to determine the deformation behavior of sub-micron sized ceramic particles; this is the first fundamental step needed to explain coating formation in the AD process. High purity, single crystal, alpha alumina particles with nominal sizes of 0.3 µm and 3.0 µm were examined. Particle characterization, using transmission electron microscopy (TEM), showed that the 0.3 µm particles were relatively defect-free single crystals whereas 3.0 µm particles were highly defective single crystals or particles contained low angle grain boundaries. Sub-micron sized Al2O3 particles exhibited ductile failure in compression. In situ compression experiments showed 0.3µm particles deformed plastically, fractured, and became polycrystalline. Moreover, dislocation activity was observed within these particles during compression. These sub-micron sized Al2O3 particles exhibited large accumulated strain (2-3 times those of micron-sized particles) before first fracture. In agreement with the findings from experimentation, atomistic simulations of nano-Al2O3 particles showed dislocation slip and significant plastic deformation during compression. On the other hand, the micron sized Al2O3 particles exhibited brittle fracture in compression. In situ compression experiments showed 3µm Al2O3 particles fractured into pieces without observable plastic deformation in compression. Particle deformation behaviors will be used to inform Al2O3 coating deposition parameters and particle-particle bonding in the consolidated Al2O3 coatings.

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TYPE SAND Report YEAR 2014
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Template-free electrochemical synthesis of tin nanostructures

Journal of Materials Science

Mackay, David T.; Janish, Matthew T.; Sahaym, Uttara; Kotula, Paul G.; Jungjohann, Katherine L.; Carter, C.B.; Norton, M.G.

One-dimensional (1D) nanostructures, often referred to as nanowires, have attracted considerable attention due to their unique mechanical, chemical, and electrical properties. Although numerous novel technological applications are being proposed for these structures, many of the processes used to synthesize these materials involve a vapor phase and require high temperatures and long growth times. Potentially faster methods requiring templates, such as anodized aluminum oxide, involve multiple fabrication steps, which would add significantly to the cost of the final material and may preclude their widespread use. In the present study, it is shown that template-free electrodeposition from an alkaline solution can produce arrays of Sn nanoneedles directly onto Cu foil substrates. This electrodeposition process occurs at 55 C; it is proposed that the nanoneedles grow via a catalyst-mediated mechanism. In such a process, the growth is controlled at the substrate/nanostructure interface rather than resulting from random plating-induced defects such as dendrites or aging defects such as tin whiskers. There are multiple potential applications for 1D Sn nanostructures - these include anodes in lithium-ion and magnesium-ion batteries and as thermal interface materials. To test this potential, type 2032 lithium-ion battery button cells were fabricated using the electrodeposited Sn. These cells showed initial capacities as high as 850 mAh/g and cycling stability for over 200 cycles. © 2013 Springer Science+Business Media New York.

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TYPE Journal Article YEAR 2014
DOIOSTIScopus
Results 151–175 of 371
Results 151–175 of 371
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