Session: 14-01: Measurement Techniques and Thermophysical Properties in Micro/Nanoscale

Paper Number: 132134

132134 - Simultaneous Determination of Thermal Conductivity and Heat Capacity in Thin Films With Picosecond Transient Thermoreflectance and Picosecond Laser Flash 

Abstract: 

In-situ thermal properties characterization is critical for a broad range of scientific fields, including but not limited to thermal management, phase transition in solid state physics, as well as Earth and planetary science, etc. Accurate determination of both  and  during a phase transition is crucial for estimating the thermoelectric figure-of-merit and ensuring proper thermal management. In general, high thermal conductivity materials are more efficient at transferring heat away from heat generation area, thus help avoid overheating and improve overall performance and reliability, while high heat capacity helps stabilize the device’s temperature. Thus, adding a layer of material with both high heat conductibility and high heat storage ability would further benefit the thermal management.  In solid state physics, the second-order derivative of the thermodynamic Gibbs free energy, provides information about the nature of phase transition, including the type of phase transition and the critical temperature. For instance,  displays singularity at the critical point for the first-order phase transition which reflects the latent heat -- the absorption of energy without any temperature change. While in certain types of second-order phase transition such as paramagnetic to ferromagnetic transition and superconducting transition,  experiences an anomaly near the critical point. Simultaneous determination of thermal conductivity  and heat capacity can reveal the charge carrier and lattice vibration behaviours near the phase transition.

Combining the picosecond transient thermoreflectance (ps-TTR) and picosecond laser flash (ps-LF) techniques, we have developed a novel method to simultaneously measure the thermal effusivity and the thermal diffusivity of metal thin films, and determine the thermal conductivity and the heat capacity altogether. In order to validate our approach and evaluate the uncertainties, we analyzed five different metal films (Au, Cu, Ni, Pt, and Ti) with thicknesses ranging from 297nm to 1.2µm. Our results on thermal transport properties and heat capacity are consistent with literature values, with the uncertainties for the thermal conductivity and the heat capacity measurements about  and , respectively. Comparing with the ps-TTR technique alone, the combined approach substantially lowers the uncertainty of the thermal conductivity measurement. Uncertainty analyses on various materials show that that this combined approach is capable to measure most of the materials with a wide range of the thicknesses, even down to 43nm for low thermal conductivity materials (e.g. mica). Simultaneous measurement of thermal conductivity and heat capacity enables exploration of thermal physical behaviour of materials under various thermodynamic and mechanical perturbations, with potential applications in thermal management materials, solid state phase transitions, planetary sciences, and beyond.

Presenting Author: Yaguo Wang The University of Texas at Austin

Presenting Author Biography: Dr. Yaguo Wang is currently an Associate Professor with Temple Foundation Endowed Faculty Fellowship No. 1, as well as the Associate Chair for DEI at Walker Department of Mechanical Engineering at University of Texas at Austin. Yaguo Wang received her Bachelor's degree from the University of Science and Technology of China (USTC) in 2005 and her Ph.D. degree from the Department of Mechanical Engineering, Purdue University, Indiana, in 2011. After one-year's postdoctoral experience at Purdue University, she joined the faculty of UT Austin in 2013. Dr. Wang received the NSF Career Award in 2014. Dr. Wang is devoted to promoting an interdisciplinary experimental approach to address fundamental scientific problems in the areas of thermal sciences, ultrafast optics and material science. Dr. Wang’s research interests include developing and utilizing time-resolved laser spectroscopy to study interactions among photons, phonons and electrons, as well as to characterize macroscopic electrical and thermal properties in a wide-range of materials, including metal films, semiconductor nanostructures and 2D materials. Results from her research advance the understanding of fundamental physics of electron/phonon transport in these materials and facilitate the development of high-performance next-generation electronic devices with improved thermal stability. In recent years, Dr. Wang expanded her research endeavor to laser-based additive manufacturing and carbon capture. Dr. Wang has published more than 50 articles in prestigious journals and conference proceedings, including Physical Review Letters, Advanced Materials, ACS Nano, Additive Manufacturing Letters etc.

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