Theoretical Studies of Non-Crystalline Solids

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New methods are developed to reliably model complex and technologically important glasses and amorphous materials. The focus is on structural modeling, atomic diffusion in the materials, and electronic properties including hopping and transport in non-crystalline environments. This work impacts a broad and important range of materials with applications ranging from computer memories (solid glassy chalcogenide-silver electrolytes), digital x-ray radiography (amorphous chalcogenides) to solar photovoltaics (amorphous silicon hydride). This award addresses fundamental questions concerning structure, diffusive atomic dynamics, and electron states and their dynamics in non-crystalline semiconductors. Among these issues are: methods for creating new structural models for complex glasses, and thorough analysis of these models (the nature of topological and chemical ordering, electronic and dynamical properties). Using novel techniques, we will determine non-diffusive dynamics in these glasses (this is an important area with many phenomenological models of the diffusive dynamics, but few atomistic calculations with "realistic" interatomic interactions). The techniques for modeling diffusive dynamics are quite new, and expected to develop from the experience obtained from the complex materials studied in this grant (in a general way, such methods are relevant to problems in biophysics like protein folding and dynamics in polymers). Finally, the work on electron dynamics will give new insight into hopping-based carrier transport in glasses, and other disordered materials. Also we will explore the phenomenon of thermally driven electron hopping by direct simulation: this will add important new insights to the finite-temperature Anderson problem.The research conducted here will be incorporated into courses taught by the PI and students, including those from underrepresented groups, will participate in the research. Results of the research, atomic coordinates in particular, will be available through the internet. There are also links to a small, startup company, Axon Technologies, in Tempe, AZ. %%%New methods are developed to reliably model complex and technologically important glasses and amorphous materials. The focus is on structural modeling, atomic diffusion in the materials, and electronic properties including hopping and transport in non-crystalline environments. This work impacts a broad and important range of materials with applications ranging from computer memories (solid glassy chalcogenide-silver electrolytes), digital x-ray radiography (amorphous chalcogenides) to solar photovoltaics (amorphous silicon hydride). The research conducted here will be incorporated into courses taught by the PI and students, including those from underrepresented groups, will participate in the research. Results of the research, atomic coordinates in particular, will be available through the internet. There are also links to a small, startup company, Axon Technologies, in Tempe, AZ. ***