SGER: Electrochemical Effects on Crystal Plasticity in Nanometer-Scale Samples

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TECHNICAL: Recently compression testing of focused ion beam machined (FIB'd) nano-pillars have demonstrated that plastic properties such as yield strength in these large surface to volume ratio structures can approach the theoretical shear strength of a solid. These recently developed techniques offer a new experimental approach for studying environment-induced alterations of the mechanical properties of solids. This high-risk/high-payoff, transformative research program examines surface and electrochemical effects on plasticity (so-called Rehbinder effects) in FIB'd Au, Ag and Cu pillars using fundamental mechanics of materials experimental approaches combined with electrochemistry. If such an effect is discovered, it would be transformative in the sense that a new paradigm for understanding stress-corrosion phenomena would emerge. PI's study uses two experimental protocols. One involves the development of a new technique for examining the compressive behavior of essentially dislocation-free 200 nm diameter metallic pillars in an electrochemical cell. The other involves the use of wafer curvature techniques to ascertain surface stress changes in electrolytes owing to the adsorption of underpotentially deposited ad-layers. The important and practical problems addressed in this research deal with outstanding fundamental issues related to plasticity and environmental effects on mechanics of materials at small length scales. These chemical/mechanical effects have been notoriously difficult to study and consequently many researchers have questioned the very existence of these phenomena. With the advent of nano-technology, these issues are once again at the forefront of interesting and unsolved problems in the mechanics of materials. NON-TECHNICAL: If PI demonstrates that surface stress alterations affect surface dislocation nucleation, this finding would impact broader understanding of the ductile versus brittle response of a crack in a solid. Thus this research would provide researchers a new "knob to turn" in order to control the deformation and fracture properties of a solid. Consequently new classes of structural materials may have the potential to be "tuned" for immunity to stress-corrosion failure. Expertise in chemical effects on the mechanics of materials requires the ability to integrate knowledge in the disciplines of electrochemistry, applied mechanics and materials science. PI is developing a new undergraduate course in this area that will be taught at the senior undergraduate level specifically aimed at providing students with this integrated background. Additionally, the PI will be involving undergraduate students in this research through Arizona State University's NSF funded Minority Graduate Education @ Mountain State Alliance (MGE@MSA) program.