John Boland – “A Scanning Tunneling Microscopy Perspective on the Behavior of Grain Boundaries in Nanocrystalline Metals”

John Boland (CRANN, Trinity College Dublin) – “A Scanning Tunneling Microscopy Perspective on the Behavior of Grain Boundaries in Nanocrystalline Metals”

ABSTRACT
This talk focuses on the properties of nanocrystalline metal films. Scanning tunneling microscopy and simulations are used to visualize for the first time the 3D structure of grain boundaries (GBs) that emerge at the surface of nearly coplanar copper nanocrystalline (111) films. Remarkably, we find that low angle dissociated GBs are always found at valley and ridge locations, so that flat films are impossible to fabricate. This behavior is due to a previously unrecognized phenomenon that involves the rotation of the dislocation line, which minimizes the GB energy, and which has significant implication for materials properties (Science 357, 397-400 (2017)). In the case of high angle boundaries the GB core is predominantly perpendicular to the film surface and comprised of so-called structural units. However, the core reconstructs as it approaches the surface to form a dissociated GB structure, reminiscence of low-angle behavior. This surface reconstruction of GBs is expected to have significant implications for corrosion and other GB mediated process.

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Friday
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