Collaborative Research: Spectroscopy of Phonon Scattering Cross-Sections in Nanomaterials from Time-Resolved Surface Wave Fields

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The transfer of heat from one body to another has a fundamental role in contemporary technology. Advancements in energy, transportation, manufacturing, biomedical devices, information processing and communication often rely on improvements in engineering heat transfer between a system and its environment. For instance, increasing the energy efficiency of data centers, in part requires improved heat management of their electronic components. The impact of heat transfer technology, though not often visible is nevertheless ubiquitous in modern society. An important new problem arises when the heat flow is between a (typical) material that exists in three dimensions and a novel material that spans space in only two dimensions. Recent success in fabricating such two-dimensional materials paves the way for investigating this important system. However, current tools for investigating heat transport run into problems when probing such complex transport phenomena. This project develops specialized experimental tools in conjunction with simulations to probe such heat transfer that bridges three- and two-dimensional materials. Further, simplified models of the transport process aid the design and development of future electronics, sensors and energy technologies. The project also trains future undergraduate and graduate engineers, including those underrepresented in the technical workforce, in advanced metrology and simulations and helps maintain the technical edge of the US industrial workforce. Data and models developed in the project are disseminated through peer-reviewed publications, technical conferences, and specialized online databases. Elementary concepts associated with the research are demonstrated in outreach efforts to K-12 schools and through university open houses to the general public. The scientific goal of the project is to elucidate the microscopic physics of phonon transport across junctions between materials of dissimilar composition and dimensionality and develop simplified models to be used in design. Specifically, the project develops a semi-empirical approach for directly measuring the phonon scattering cross-section at the junction between a two-dimensional material such as graphene and a three-dimensional material such as silicon or silicon oxide, without any requirement for interpreting conductivity or conductance. This advances the state of art of experimental nanoscale thermal transport beyond the prevalent thermal conductivity/conductance measurement approaches.