FRG: Structural Phase Transformations in Polymorphic Nanostructures

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Technical Description: This project aims to understand the underlying mechanisms of crystalline-amorphous and polymorphic crystalline-crystalline phase transformations in phase-change nanostructure materials, particularly In2Se3 nanowires, and to understand the multi-level phase-change memory switching process. Specific tasks include (1) understanding the thermodynamics of phase transformations by constructing the temperature-pressure phase diagram; (2) investigating the phase transformation kinetics; (3) establishing the structure-property relation; and (4) elucidating the multiphysics process that underlies the multi-level memory switching. The approach combines experimental and theoretical investigations. The experimental approach utilizes a combination of transmission electron microscopy, Raman and infrared spectroscopy, x-ray diffraction, and multi-functional scanning probe microscopy techniques, with the capability to adjust the temperature and pressure in situ. Complementing the experimental aspect, the theory component based on first-principles calculations investigates the phase stability and its dependence on temperature and pressure, kinetic pathways of the phase transformation, and phase-specific electronic structures and physical properties.Non-technical Description: This project provides a fundamental insight into the structural phase transformation in a technologically important phase-change material. Compared to current mainstream non-volatile memory technologies, such as the Flash memory, phase-change memory offers faster random access time, higher endurance and scalability to the 10-nm range. The knowledge acquired in this study establishes a fundamental basis for developing next-generation non-volatile phase-change memory with multi-level storage capabilities in a single material system. This project provides training opportunities for undergraduate and graduate students, including those who are members of underrepresented groups. A new seminar course focusing on providing a coherent understanding of phase-change nanomaterials is developed and is team-taught by the PIs. The outreach to the general public is facilitated by developing visual materials, including images and movies, which are posted on YouTube. These materials are a part of the Explore Nano! exhibit in a local science museum.