SGER: Exploring Thermal Interfacial Transport Using Molecular Dynamics and Transient Thermal Reflectance

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REVIEW AND ANALYSISProposal Number: CTS-0536744Principal Investigator: Norris, PamelaAffiliation: University of VirginiaProposal Title: SGER: Exploring Thermal Interfacial Transport Using Molecular Dynamics and Transient Thermal ReflectanceContext:The proposal was received as an unsolicited submission to the Chemical and Transport Systems Division in the Small Grants for Exploratory Research (SGER) category and was subsequently assigned to the Thermal Transport and Thermal Processing Sub-element of the Thermal Systems Program for review. TTTP Program Director Alfonso Ortega handled the proposal. No formal external reviews were sought, as they are not required for SGER grants.The recommendation for action is based on current NSF and program priorities, budget constraints, the balance of project topics in the program, the likely contribution of the work to the thermal systems research and education infrastructure, and the appropriateness of the proposal as a SGER activity. Analysis and rationale for recommendation:The proposed one-year study will use a combined theoretical and experimental approach to study thermal interfacial transport, specifically to measure the thermal boundary resistance (TBR) and compare it with Molecular Dynamic Simulations to extract the same. Although thermal interfaces were one of the first areas of thermal engineering that were studied utilizing newly evolving non-continuum approaches, their physics remain elusive. There has been little definitive experimental work to directly measure the TBR at or near room temperature. The PI has conducted preliminary unfunded work to demonstrate the ability to use a novel transient thermo-reflectance technique (TTR) developed initially for characterization of thin film properties. They have shown that it has good sensitivity for measurements of the thermal boundary resistance. Through preliminary MD simulations of crystal/crystal interfaces, the PI's group have hypothesized, based on simulations, that in the classical limit, thermal transport is best described using a Thermal Boundary Resistance with a term accounting for both elastic and inelastic phonon scattering. In the limit, the inelastic scattering is dominant. These are surprising results, first recorded by the PI, and they form the basis for the promising work proposed. The primary goal of the exploratory work is to experimentally verify the temperature dependence of the interface thermal conductance observed using MD simulations. It has never been shown experimentally, and if proven, will be the first direct evidence of elastic and inelastic phonon interaction contributions at interfaces. The interface thermal conductance can vary by an order of magnitude with temperature excursions seen by many practical devices, such as VLSI chips. Modeling these interfaces has become critical in several technologies.The Principle Investigator's team has steadily contributed to research in this area, and has perfected a technique (the transient thermo-reflectance technique) that has not been widely utilized in the U.S. This exploratory grant will allow a short-term, highly focused experimental inquiry using this technique (previously used for characterizing thin films), to demonstrate that it can indeed be used for measuring TBR at room temperature. If successful, the project will answer important questions related to fundamental phonon interaction mechanisms at room temperature, that heretofore have only been speculative, and have been inferred from less refined measurements. Furthermore, it will establish the TTR technique as a new important tool for characterizing interfaces below continuum scales. Finally, the concurrent MD modeling that will be performed will serve as an example of highly coupled non-continuum modeling and experiments that will accelerate the overall progress in understanding nano-scale interface physics.With respect to the Broader Impacts of the proposed work, the PI has an excellent history of inclusion and impact on people in her research. Although the proposal is not specific in detailing a plan to involve undergraduate students, there is a general plan to continue the approach of integrating undergraduate students and minority students in laboratory research that has been previously demonstrated. The direct costs are minimal, because the laboratory is well established.Recommendation: AWARD