CAREER: Pushing the Lower Limit of Thermal Conductivity in Layered Materials

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Identifying effective strategies to achieve exceptionally low thermal conductivity in solid-state materials can potentially push the extremes in heat conduction. The proposed project seeks to enable novel thermal control functionalities in disordered, layered materials to be applied in sustainable energy infrastructure, such as energy savings by thermal insulation, energy storage in batteries, energy conversion in thermoelectrics, and thermal management in electronics. The integration of research, education, and outreach programs aims to raise the public awareness of challenges in sustainable energy, and motivate students to pursue appropriate education pathways to STEM occupations. Cinematic 360 Virtual Reality lab tours will be developed to "teleport" online K-12 students into the lab to visualize thermal transport research and its applications in sustainable energy. Teachers will be invited to collaborate and pilot educational activities promoting the importance and challenges in sustainable energy infrastructure. The enhancement of students' preparation for a STEM career will be achieved by a summer program with a particular emphasis on reaching out to female and African-American students.The research goal of this CAREER project is to understand how to suppress vibrational energy transport in anisotropic layered materials by disorder. Precise and reversible control of the degree and inhomogeneity of disorder and thus interlayer spacing are achieved by an electrochemistry process, which inserts ions or molecular chains into the van der Waals gaps of layered crystals. The investigations will focus on a model transition metal dichalcogenide crystal, using complementary state-of-the-art theoretical and experimental approaches. The thermal conductivity of bulk crystals with a controllable amount and type of ions or molecular chains inserted into the gaps will be measured by the time-domain thermoreflectance method. The contribution from different types of vibrational modes to the microscopic thermal transport in these disordered crystals will then be analyzed using a combination of lattice dynamics and molecular dynamics methods. The success of this project will enable the first set of experimental and theoretical studies to elucidate the roles of interlayer spacing and bonding environment on suppressing vibrational energy transport, thereby advancing the current understanding on the microscopic thermal transport mechanisms in anisotropic disordered, layered materials.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.