Deformation mechanisms and size-dependent mechanical response at the nanoscale

Daniel S. Gianola
Skirkanich Assistant Professor
Department of Materials Science and Engineering
University of Pennsylvania

Metal nanostructures proposed as the fundamental building blocks for emerging nanotechnological devices will often be subject to extreme duress during operation, particularly high mechanical stresses.  Investigations of size-dependent deformation have shown that “smaller is stronger” in metals, yet the underlying mechanisms that give rise to this departure from bulk behavior are still elusive.  The emerging picture is that plasticity in extremely small volumes is fundamentally different than in large materials; the law of averages gives way to discrete processes that dominate the response.  Systematically probing the mechanical response and uncovering the underlying deformation mechanisms of diminishingly small structures at the micro- and nanoscale requires new strategies and approaches that circumvent difficulties associated with handling, gripping, loading, and measuring small specimens.  The need for in situ experiments that give a one-to-one correlation between mechanical response and deformation morphology is exacerbated by the fact that electron optics are needed to image and manipulate nanostructures.

In this talk, I will describe quantitative in situ tensile experiments on quasi-1D metallic nanostructures using electron and ion beam microscopies.  In particular, the intimate link between pre-existing defects and flaws, which is critically tied to the materials synthesis route, and mechanical response will be discussed.