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Mar. 27 2013

RREP Fellows Conference - Gilberto Casillas: "In situ TEM studies of nanostructures at the nanoscale"

Gilberto is a Ph.D. candidate in Physics at University of Texas at San Antonio. He was awarded a RREP Fellowship in 2011.

There is a strong interest in studying changes of mechanical properties with reducing grain size. The rational is that consequent dislocation glide cannot be sustained resulting in an increase of material strength. However this comes with the cost of a reduction in ductility. On the other hand, it has been shown that coherent twin boundaries in nanostructured Cu improve the ductility to 14%; therefore, by introducing certain grain boundaries in a controlled fashion it should be possible to increase the ductility of the materials without losing strength. In this talk I will be discussing properties of individual nanoparticles under 100 nm as measured by In situ TEM experiments. Three nanoparticles were tested, two with twin boundaries (decahedra and icosahedra) and one free of defects (octahedral). Our results indicate the yield strength of the twinned nanoparticles is between 0.5-2.0 GPa. The total malleability for the twinned particles ranges from 80% to 100%. In addition, experimental results were reproduced by MD simulations of the compression phenomena.

Also, cold-welding of individual gold nanoparticles was done by the same technique. A liquid-like grain boundary behavior is observed between the two nanoparticles, as well as grain boundary rotation of 90 degrees. Finally, surface diffusion coefficient is estimated from experimental observations.

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