EAGER: Oxide Film Effects on Dislocation Nucleation -- Implications to Structure/Property Relations

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TECHNICAL SUMMARYThis project involves a combination of in situ nanoindentation studies in a Transmission Electron Microsocpe (TEM) with in situ measurements of electrical conductance between tip and sample. It is now possible to measure small conductance changes induced by dislocation nucleation, while simultaneously measuring nanoindentation curves. This powerful measurement capability will address the role of native oxide film formation on nanoscale mechanical properties. This effect is very important because as sizes scale downwards, the oxide role is inadequately understood but of relevance to a large variety of technological issues such as stress corrosion cracking, fretting fatigue, mechanically-assisted dielectric breakdown, fatigue of Micro-Electro-Mechanical Systems (MEMS), fracture toughness of nanostructures, MEMS tribology and wear and yielding in general. Model thin-film systems comprised of metal or semiconductor films coated with oxide overlayers will be used to explore fundamentals of the early stages of dislocation nucleation at or near surfaces, i.e. to establish the critical structure-property relationships at the nanometer scale. In particular, understanding the indentation size effect at very small length scales is unresolved in most metallic systems since the image forces associated with native oxide films have usually been ignored. By measuring conductive contacts during deformation of oxide-covered thin metallic films, simultaneously with load-displacement output, dislocation scale events can be directly monitored.NON-TECHNICAL SUMMARYThe proposed work has the potential to impact an unusually wide range of scientific communities because it is fundamentally inter-disciplinary. It includes instrumental, scientific, and technological advances that will be of interest to the communities doing research on electron microscopy, electronic transport in nanostructures and atomistic simulation of mechanical properties of materials. The proposed research is of very significant value technologically. Oxide film formation affects mechanical properties at small length scales and plays and important role in areas as diverse as stress corrosion cracking, fretting fatigue, mechanically assisted dielectric breakdown, fatigue of MEMS, fracture toughness of nanostructures, MEMS tribology and wear. These are core issues in many areas of nanotechnology that will be immediately impacted by the proposed research. The PIs have an excellent record of inclusion of undergraduate students in their research, an effort that will be aggressively continued during the duration of this award. These students are funded through various programs such as the UMN Undergraduate Research Opportunities Program, NSF REU programs, directed research for credit, etc., and have been involved in all aspects of the activities of the PI?s research groups.