CAREER: Novel Debye Waller Thermometry of Oxide Interfaces for Reducing Thermal Interface Resistance

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NON-TECHNICAL DESCRIPTION: To control thermal conduction in materials, it is critical to understand heat transport through various interfaces within the material. Interfaces often display thermal interface resistance (TIR), and for a broad range of electronic, photonic, and energy-harvesting materials, TIR can critically affect the materials' performance and stability. However, it is often very challenging to identify the exact origin of TIR, since it would require an exact understanding of 'what really happens' at the interface, including the exact structure of the interface and how the structure affects the thermal transport process. This project develops a novel technique that uses a small electron probe to directly measure the temperature at the interface with near atomic scale resolution and determine TIR with unprecedented precision. This new approach can deliver transformative impact to the thermal engineering of materials in many ways, by providing the new important understanding on how the atomic scale structure and defects at the interface affect TIR, verifying the existing theories and simulation results on how to reduce TIR, and providing new material design rules on how to control TIR by modifying the interface structure and composition. This project integrates the education and outreach activities for underrepresented students to provide them with opportunities to engage with researchers, motivate, and help them potentially pursue advanced degrees or careers in science and engineering. The project also includes the development of the interactive data analysis system that allows people with visual impairment to perceive and process scientific data using their auditory senses.TECHNICAL DETAILS: A new Debye-Waller thermometry under development is based on quantifying Debye-Waller factor, the attenuation of the scattered electron intensity due to thermal vibration, spatially resolved at the atomic scale, using high angle annular dark field signal in scanning transmission electron microscopy that is highly sensitive to thermal vibration. Using this new approach, the temperature profile at the interface at the atomic scale can be measured in situ, and TIR is directly determined from the profile with high precision, beyond the limits of any existing methods. This new experimental capability can validate the existing theories and hypotheses on how to reduce TIR, including the theories involving phonon matching, acoustic matching, epitaxial strain, and defect control. The validation is carried out using carefully designed perovskite oxide interfaces, which are synthesized using different structural parameters, such as the atomic mass, bond strength, strain, defect density, layer thickness, and interface roughness. The error analysis part of this work is assisted by the accommodation technology developed in this project, which allows people with disabilities to efficiently perceive, handle, and analyze the scientific data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.