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Chapter Events

March Chapter Meeting - An Approach to Reliability Assessment of Cold Spray Sputter Targets in PV Manufacturing

February 28 - March 07, 2017 | Michael's at Shoreline

Cold spray has been used to manufacture more than 800 Cu-In-Ga (CIG) sputter targets for deposition of high efficiency photovoltaic (PV) thin films. It is a preferred technique since it enables high deposit purity and transfer of non-equilibrium alloy states to the target material. In this work an integrated approach to reliability assessment of such targets with deposit weight in excess of 50 lb. is undertaken, involving thermal-mechanical characterization of the material in as-deposited condition, characterization of the interface adhesion on cylindrical substrate in as-deposited condition, and developing means to assess target integrity under thermal-mechanical loads during the physical vapor deposition (PVD) sputtering process. Mechanical characterization of cold spray deposited CIG alloy is accomplished through the use of indentation testing and adaptation of Brazilian disc test. A custom lever test was developed to characterize adhesion along the cylindrical interface between the CIG deposit and cylindrical substrate, overcoming limitations of current standards. A cohesive zone model for crack initiation and propagation at the deposit interface is developed and validated using the lever test and later used to simulate potential catastrophic target failure in the PVD process. It is shown that this approach enables reliability assessment of sputter targets and improves robustness

Chapter events

Jan Chapter Meeting – Mechanical Properties of Lithiated Silicon: A Candidate Electrode for Lithium Ion Batteries

January 11, 2017 | Michael's at Shoreline

Understanding the insertion of lithium into silicon electrodes for high capacity lithium-ion batteries is likely to have benefits for mobile energy storage, for both electronics and transportation. Silicon nanostructures have proven to be attractive candidates for electrodes because they provide more resistance to fracture during lithium insertion. But still, facture can occur even in nanostructured silicon. Here, we consider the fracture of Si nanopillars during lithiation and find surprising results. In situ transmission electron microscopy observations of initially crystalline Si nanoparticles shows that lithiation occurs by the growth of an amorphous lithiated shell, subjected to tension and leading to fracture. We show that the expansion of the nanopillars is highly anisotropic and that the fracture locations are also anisotropic. Also, we show that initially amorphous Si nanopillars are much more resistant to failure, having much larger critical fracture diameters. For sufficiently big amorphous Si nanopillars, cracking is expected to be initiated in the interior based on diffusion-induced stresses, but we have not yet observed that kind of fracture. The modeling we, and others, have done has been based largely on estimates or guesses about the mechanical properties of lithiated Si. Recent nanoindentation experiments show that the elastic modulus and hardness of lithiated amorphous Si depend strongly on the lithium content. When these more subtle effects are included in the modeling they may be helpful in the design of silicon electrodes for advanced battery systems

Chapter events

February Chapter Meeting: Nanoporosity and the Welcome Guest: Developing Metal-Organic Frameworks for Catalysis, Hydrogen Storage, and Electronic Devices

February 01, 2017 | Michael's at Shoreline 2960 Shoreline Blvd

Metal-Organic Frameworks (MOF)s are crystalline materials in which metal ions or metal-ion clusters are linked by rigid organic molecules, creating a supramolecular network that has permanent nanoporosity. Unwanted "guest" species, which can be solvent molecules or residual reactant, can be removed without pore collapse. Once a MOF is activated, it provides a highly ordered, chemically tailorable structure that can function as a nanoscale catalytic reactor, store gases such as hydrogen, or serve as an active component of electronic devices.

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