CAREER: Probing the Thermal Relaxation Dynamics of Nanomaterials with Time-Resolved Calorimetry

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The conversion of energy from one form to another is central to a number of emerging technologies such as solar cells and batteries. Nanoscale materials play a key role in the development of these technologies due to their unique electrical, optical, and thermal properties. However, energy conversion within nanomaterials is a complex and highly dynamic process that remains poorly understood. For example, the transient response of these materials to an external stimulus often results in the generation of heat over very short time scales of nanoseconds or less, which state-of-the-art experimental techniques are not able to fully characterize. In this proposal, a measurement approach will be developed that is capable of resolving these transient heat flow rates with both picowatt resolution and nanosecond response time. The insights obtained from these real-time measurements will not only enable improvements to the conversion efficiency of the devices introduced above, but will also unlock new classes of sensors and computer processors with higher bandwidth and lower power consumption. The proposed research will concurrently promote educational initiatives that will establish a pipeline for future researchers from south-central Wisconsin to become leaders in the field of thermal nanoscience and the larger STEM community. The PI proposes to develop an experimental platform that will enable real-time, room-temperature measurements of transient heat dissipation in nanomaterials as they relax over ultra-fast time scales. Although this measurement is extremely difficult due to the miniscule and rapidly-evolving heat signatures, it represents a crucial supplement to established pump-probe techniques and first-principles modelling approaches that will provide a detailed mapping of the relaxation pathways in these materials for the first time. The PI will leverage extensive technical expertise in nanofabrication, precision instrumentation, and thermal modelling to develop a novel calorimetric approach that is orders-of-magnitude more sensitive and more dynamic than the calorimetric techniques in use today. Using this platform, fundamental and technologically-relevant questions about the thermal relaxation dynamics of nanomaterials will be answered including, but not limited to, the following: What pathways are responsible for non-radiative recombination of excitons in quantum dots? How are structural phase transitions induced in polymorphic 2D materials? What role does magnon-phonon coupling play in the Bose-Einstein condensation of magnons within nanostructures?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.