FRG: Nanoscale Structural Order in Amorphous Materials and its Relation to Diffusion and Electronic Defects

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TECHNICAL: This research offers new insights into nanoscale atomic ordering, its connection to defects and defect clustering in amorphous materials, and the influence of nanoscale order and defects on properties. The project is a collaborative focused research project (FRG), and addresses: (1) nanoscale structure as a function of composition in chalcogenide glasses with the goal of building a detailed model of intermediate phases; (2) optically-driven, nanoscale structural transformations that cause photodarkening and photomelting in chalcogenide glasses; (3) influence of nanoscale order on thermal stability and phase transformations of amorphous transition metal diboride thin films; and (4) connection between impurity diffusion and nanoscale order in amorphous diborides, which may be mediated by a spatially non-uniform defect distribution caused by nanoscale order. The chalcogenides have important applications in photonics in addition to being prototypical glass-forming networks. Several glasses in the intermediate phase composition region exhibit extremely high Kerr optical non-linearities that are being investigated for all-optical switching. Photodarkening enables easy fabrication of waveguides and diffraction gratings. The metal diborides are candidate diffusion barriers for silicon microelectronic metallizations, for which low impurity diffusion and high thermal stability in extremely thin films are essential. Research on the four problems above will lay basic materials science groundwork for these applications. NONTECHNICAL: A primary impact of this research collaboration is establishment of a new paradigm for the structural analysis of amorphous materials, in which one uses scattering probes to characterize the structure and chemistry of a sample from nearest-neighbors to a few nanometers, then uses modeling techniques to synthesize an atomistic structural model consistent with what is known about the particular material. That model is then studied to further elucidate the structure and properties of the material. Key innovations are nanoscale structural information from fluctuation electron microscopy included in synthesis of experimental data and ab initio energetics with experimentally constrained molecular relaxation. The project will provide downloadable manuals, computer code and make use of technical meetings to disseminate these tools broadly in the scientific community, where they will eventually be used to address a wide range of materials science problems. The effort also provides an exceptional opportunity for the training of students and post-docs in a multidisciplinary, collaborative environment that is at the forefront of the integration of experimental and computational tools in materials. The project also includes activities designed to enhance participation of underrepresented groups in science and engineering.