Thermal Phonon Transport in Complex Structures and across Interfaces

Abstract:  The ever-increasing energy demand and greenhouse gas emissions call for a clean energy economy, and there is a vast amount of untapped thermal energy resources. The continued miniaturization and densification of electronic devices demand innovative solutions to the compelling cooling challenges. Today’s transistors could run much faster if not because they get so hot. A solid grasp of thermal phonon transport processes is essential to designing nanomaterials and devices with desired thermal transport properties for thermal energy conversion and management. Despite the significant progress in thermal transport of perfect crystals with simple structures, our understanding of thermal transport in complex structures and across interfaces remains limited but is required for practical applications. In this talk, I will present my research group’s efforts to fill the gap using both atomic modeling and optical measurements. For complex structures, I will focus on the phonon dynamics in hybrid organic-inorganic perovskites using inelastic x-ray scattering (IXS) and transient thermal grating (TTG) measurements, where we gained useful insights into their ultralow thermal conductivity and discovered record-low anisotropy in thermal conductivity of 2D hybrid among other layered structures. I will then show the unusual thermal diode behavior in tapered bottlebrush polymers using molecular dynamics (MD) simulations. On the interface side, I will highlight our development of rigorous formalism for the anharmonic atomistic Green’s function (AGF), which overcame a persistent challenge to capture the contribution of inelastic scattering at the interfaces. I will also share the first direct evidence of phonon Anderson localization in aperiodic superlattices. The fundamental knowledge gained from these studies will facilitate more efficient renewable energy generation, thermally managed energy-efficient microelectronics, and functional thermal devices. Finally, I will briefly share the new directions my group is heading by leveraging our core phonon expertise, spanning quantum, neuron, enzyme, and space..

Bio: Dr. Zhiting Tian is an Associate Professor, Eugene A. Leinroth Sesquicentennial Faculty Fellow of the Sibley School of Mechanical and Aerospace Engineering at Cornell University. She is currently on her sabbatical and visiting Stanford as a Visiting Associate Professor in the Department of Materials Science and Engineering. Zhiting obtained her Ph.D. in Mechanical Engineering at MIT in 2014. Zhiting’s awards and honors include Fellow of American Society of Mechanical Engineers (ASME), NASA Early-Stage Innovations Award, Air Force of Scientific Research (AFOSR) Young Investigator Award, Office of Naval Research (ONR) Young Investigator Award, National Science Foundation (NSF) CAREER Award, ACS Petroleum Research Fund Doctoral New Investigator Award, 3M Non-Tenured Faculty Award, and ACS Polymeric Materials Science and Engineering (PMSE) Young Investigator Award. Zhiting serves as an Associate Editor of the Journal of Applied Physics.

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