Self-Organization in Network Glasses-Beyond Selenides

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Technical abstractCovalent network glasses are usually composed of the group IV and/or V selenides, and exist in three basic types of elastic phases- flexible, intermediate and stressed-rigid. Flexible phases are made up of weakly cross-linked structures and possess "floppy" modes, while stressed-rigid phases consist of heavily cross-linked structures that have stress creating "redundant" bonds. Intermediate phases (IPs) are optimally cross-linked structures that are marginally rigid but stress-free features that lead to unforeseen functionalities, such as thermal reversibility of the glass transition, absence of aging, liquid-like configurational entropies, and network adaptability to expel stress and lower their free energies. This individual investigator award supports a project to extend investigations of IPs from selenides to sulfides and oxides. Modulated DSC, Raman, IR reflectance and Molar volume measurements will be undertaken as a function of glass composition to establish IPs. These measurements will permit elucidating the role of chemical bonding and structure on IPs as fractional ionicity of bonding increases. Possible applications include optimization of thin-film gate dielectrics in 3-terminal devices, flat panel displays, programmable cell metallization memory devices, protein folding and drug design. Research on amorphous semiconductors and insulators has proven to be an outstanding training ground for young physicists and electrical engineers seeking jobs in industry and academia.Non-Technical abstractAdvances in synthesis, purification of starting materials and detailed compositional studies have led to the recognition that physical properties of amorphous semiconductors including glasses can change abruptly with chemical composition. These developments have permitted probing the rigidity transition (between flexible and intermediate phase glasses) and the stress transition (between intermediate and stressed-rigid phases) in network glasses. This individual investigator award supports a project to investigate Intermediate phases (IPs) in select sulfides and oxides, extending present results of IPs from selenides to systems that are more ionic. Thermal, optical, mechanical and electrical measurements will be undertaken to establish IPs and their aging behavior. The goal of the project is to establish IPs of these technologically important materials and to understand them in terms of glass sub-structure. These findings will also serve as bounds for numerical simulations of these phases using first principles methods that are currently ongoing in the US and Europe. Students will be trained in state-of the art techniques and semiconducting materials growth, which will open jobs in Science and Engineering infrastructure of the US.