The Stability of Phases in Thin Multilayered Films

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TECHNICAL SUMMARY:Materials in structures with large surface area-to-volume ratios can exhibit size dependent physical and chemical properties that are different than their bulk form. These changes can be related to crystallographic transformations to new phases called pseudomorphs. This research will elucidate the underpinnings of this phase stability behavior by providing a systemic study using multilayered thin film architectures. Model metallic systems whose length scales and compositions can be controlled with near atomic processing precision will allow the influence of lattice misfit, layer thickness, and composition on pseudomorphic phase formation and stability to be determined. Real-time, in situ thin film growth stresses of these materials will be measured and correlated to the interfacial stress evolution. Molecular Dynamics (MD) simulations will be used to explore the kinetics of pseudomorphic formation during deposition, merging experiments with modeling. These results will be related to post-growth structural and chemical characterization of the phases and interfaces. The program will be able to delineate how intrinsic film stress drives compositional intermixing across interfaces which can thermodynamically promote phase transformations. Classical thermodynamics will be used to predict and explain phase stability criteria. The results will be developed within the framework of a predictive phase diagram, where length scale is a state variable similar to temperature and pressure used in traditional metallurgy phase diagrams, in determining phase transition regions. NON-TECHNICAL SUMMARY:When material sizes become very small, a material can alter how it arranges its atoms within its structure. This atomic rearrangement often results in changes in the materials properties such as its electrical conduction, its optical appearance or its physical strength. Too often these atomic rearrangements are serendipitously discovered. This research aims at developing a predictive diagram to let scientists understand when atomic rearrangements occur as a function of size. The results will provide maps on how to predict and engineer atomic structure for ever decreasing material sizes. Through this grant, the technical workforce of the United States will be grown. This will be achieved through the education of graduate and one post-doctoral students. These individuals will engage industry through their interaction in the multi-disciplinary research center, Materials for Information Technology (MINT) situated on the campus of the University of Alabama (UA). In addition, the program will engage local Alabaman high school students through the Nanoscience and Engineering High School Research Internship Program, successfully initiated during the principle investigator?s NSF Career award. Materials education efforts during this grant will be broadened to include instruction to middle and high school teachers through summer camps held on the campus of UA. By directly educating secondary education teachers on how to incorporate materials examples in their classroom, the impact of materials education will engage a broader and more diverse number of students.