Thermal transport in superstructured organic-inorganic hybrid materials
Department of Mechanical Engineering and Materials Science Seminar
Thermal transport in superstructured organic-inorganic hybrid materials
Dr. Wee-Liat Ong
Postdoctoral Fellow
Columbia University & Carnegie Mellon University
Superstructured organic-inorganic hybrid materials self-assemble from solutions and are scalable replacements for single crystal semiconductors for many technologies. Although their electrical, electronics, and optoelectronics properties have been investigated, thermal properties in these materials remain relatively unchartered, which inhibits technological adoption where thermal management is requisite to prevent performance and lifetime degradation. In this talk, I will focus on thermal transport in three hybrid material systems – nanocrystal arrays (NCAs), superatom crystals (SACs) and organic-inorganic perovskites (OIPs). NCAs are organized arrays of ligand-stabilized colloidal nanocrystals with size-tunable electronic and optical structure. SACs are periodic self-assemblies of superatoms, which are clusters of atoms that behave as a unit with emergent properties distinct from their elemental atoms. OIPs are hybrid crystals with molecular organic cations embedded in inorganic octahedral scaffolds and have displayed excellent solar energy conversion efficiency. In my presentation, I will explain the mechanisms of thermal transport through these hybrid materials. I have utilized the frequency domain thermoreflectance technique to measure thermal conductivity in NCA thin films, nanoliter sized superatom crystals, and organic-inorganic perovskite single crystals. Complementing these experiments, I have employed molecular dynamics simulations, lattice dynamics calculations, and density functional theory calculations to interpret the experimental measurements and explore experimentally-inaccessible nanoscale phenomena. The thermal conductivity of the NCAs are controlled by the organic-inorganic interface. Room temperature thermal conductivity measurements of various SACs depict a correlation on their group velocities, indicating the importance of cooperative modes. Temperature dependent measurements elucidate the importance of dynamic disorder in SACs and OIPs for thermal transport. The low thermal conductivity measured in the NCAs and OIPs presents a challenge for thermal management but a boon for thermoelectric waste heat scavenging. The SACs exhibit tunable amorphous to crystalline thermal conductivity temperature behavior suggesting the possibility using SACs for phononic and active thermal transport control.
Bio: Wee-Liat graduated with a B.Eng in Mechanical Engineering from the National University of Singapore (NUS) and was the valedictorian of his class and recipient of the IES gold medal and Lee Kuan Yew gold medal in 2002. He also received a M.Eng from NUS in 2004 where he developed a robot for performing experiments used in drug discovery. He joined the Institute of Microelectronics, Singapore and worked in the fields of bioMEMS and microfluidics. In 2015 he received his Ph.D. in Mechanical Engineering at Carnegie Mellon University under Prof. Jonathan Malen and Prof. Alan McGaughey, where he studied nanoscale heat transfer focusing on organic-inorganic nanostructured materials using both experimental and simulation techniques. He received several faculty/departmental awards in CMU including the Steinbrenner, the Northrop-Grumman, and the Bushnell graduate fellowships. Currently, he is a joint post-doctoral fellow at Columbia University and Carnegie Mellon University working with chemists to characterize novel hybrid materials.
Host: Udo Schwarz Monday,
February 6, 2017
Mason Lab 107
2:30pm - 3:30pm
Refreshments 2:15pm