Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 100000

100000 - Two-Temperature Time-Fractional Model for Electron-Phonon Coupled Interfacial Thermal Transport 

This research aims to investigate thermal transport in the multi-layer metal-nonmetal thin films under the femtosecond laser pulses. In particular, a two-temperature time-fractional (2T-TF) model based on the Caputo fractional derivative is presented. The results of the 2T-TF model have been validated against the available experimental data and the Boltzmann transport equation (BTE) results. The 2T-TF model is demonstrated to be much more accurate than the conventional two-temperature model based on the Fourier’s law, while its complexity can be much lower than the BTE simulations. Moreover, various forms of thermal resistances can be readily implemented to the 2T-TF model, in order to characterize the electron and phonon transmissions at the interface of metal and nonmetal thin films. Notably, our 2T-TF simulations further confirm the effectiveness of inserting a metallic interlayer with high electron-phonon coupling factor to expedite the electron cooling in the top metallic layer for a metal-nonmetal heterojunction structure, which was previously demonstrated through BTE simulations. In fact, inserting an interlayer can create additional heat dissipation paths, meaning that the electron-electron and phonon-phonon interactions would be considerable, and thus the thermal energy can be transmitted from the top layer to the substrate more quickly. The 2T-TF model can serve as a convenient and reliable tool for simulating electron-phonon coupled thermal transport in the multilayered systems, particularly when there are fast thermal transient processes or the system size is smaller than or comparable to carrier mean-free-paths. For such cases, the heat conduction equation based on the Fourier's law is no longer valid, because it shows a significant deviation from the experimental data and also the BTE results, although the fractional form of heat conduction equation is capable of describing the thermal transport in short spatial and temporal scales, the electron-phonon interactions and the finite time required for the electrons to transmit the thermal energy absorbed from the laser heating source to the phonons. It has been demonstrated that for the thin films with great thickness, the heat transfer mechanism is diffusive-like, but for the films with small thickness comparable to the mean-free-path of heat carriers, the heat transfer mechanism would change and the non-Fourier effects can be observed in the thermal transport of thin films under the femtosecond laser heating pulses. The 2T-TF model developed can accurately describe a wide range of thermal behaviors, from diffusive to ballistic ones which is due to the presence of time derivative term with non-integer order.

Presenting Author: Milad Mozafarifard University of Nevada Reno

Presenting Author Biography: He is pursuing his Ph.D. degree in the Department of Mechanical Engineering and working on the thermal transport in materials under femtosecond repetitious laser pulses at the Nano-Thermal-Mechanical Engineering (NTME) Lab. He received his B.Sc. degree in Mechanical Engineering, Heat and Fluids, from IAU, and M.Sc. degree in Energy Conversion from SCU in 2011 and 2017 respectively. His research interests include fractional calculus, laser-matter interactions and micro-scale heat transfer.

Authors:

Milad Mozafarifard University of Nevada Reno
Yan Wang University of Nevada Reno