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SUMMARY:The Behaviour of Grain Boundaries in Nanocrystalline Metal Films. 
 - Professor John Boland\, Centre for Research on Adaptive Nanostructures a
 nd Nanodevices (CRANN)\, Trinity College\, Dublin
DTSTART:20190607T090000Z
DTEND:20190607T100000Z
UID:TALK125605@talks.cam.ac.uk
CONTACT:Kirsty Shepherd
DESCRIPTION:This talk discusses on the properties of nanocrystalline metal
  films\, with a particular emphasis on copper.  Scanning tunneling microsc
 opy and simulations are used to visualize for the first time the 3D struct
 ure of grain boundaries (GBs) that emerge at the surface of nearly coplana
 r copper nanocrystalline (111) films. Remarkably\, we observe that low ang
 le dissociated GBs are found exclusively at valley and ridge locations.  T
 his behavior is the result of a GB energy minimization phenomenon that inv
 olves the formation of wide kink-free stacking fault ribbons\, made possib
 le by the rotation of dislocation lines along the boundary and the commens
 urate tilting of the adjoining grains (Science 357\, 397-400 (2017)).  In 
 the case of high angle boundaries the GB core is expected to be perpendicu
 lar to the film surface and comprised of so-called structural units.  Howe
 ver\, both experiment and simulation support the reconstruction of the GBs
  as it approaches the surface to form a dissociated structure\, reminiscen
 ce of lowangle behavior.  In contrast\, high angle GBs shows the presence 
 of both local and global curvature\, the local behavior mapping closely on
 to that seen for lower angles.  We show that this behavior is in part due 
 to the influence of the triple junction and leads to surface and size effe
 cts that should have implications for corrosion\, transport and other GB m
 ediated processes. 
LOCATION:Maxwell Centre\, Rayleigh Seminar Room
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