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Theoretical and Experimental Investigation of Phonon Boundary Scattering in Thin Silicon Membranes


Ravichandran, Navaneetha Krishnan (2017) Theoretical and Experimental Investigation of Phonon Boundary Scattering in Thin Silicon Membranes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9SJ1HK2.


The thermal transport properties of thin semiconductor membranes play an important role in the performance of many technologies like micro-electronics and solid-state energy conversion. The dominant resistance to heat flow in thin membranes is offered by the scattering of thermal phonons at the membrane boundaries. In this dissertation, we examine the nature of microscopic phonon boundary scattering processes and their effect on the thermal conductivity of the thin membranes using a pump-probe experimental technique and computationally efficient solutions of the phonon Boltzmann transport equation (BTE).

First, we investigate the boundary scattering-limited thermal transport in nanostructures using an efficient variance-reduced Monte Carlo (MC) solution of the BTE to elucidate the impact of specular and diffuse phonon boundary scattering events on the thermal conductivity of the nanostructures. To directly measure the relative frequency of these two boundary scattering events, called the phonon specularity parameter, we design, implement and characterize a non-contact laser-based pump-probe experiment called the transient grating (TG) to perform phonon mode-dependent measurements of the specularity parameter in suspended free-standing thin silicon membranes. We describe the phenomenon of quasiballistic heat conduction, which enables the phonon mode-dependent measurements of the specularity parameter, and derive a transfer function based on the BTE with ab-initio phonon properties as inputs, to connect the specularity parameter with the experimentally measured thermal conductivity of the thin membranes.

Finally, we present the methodology adopted to invert the BTE transfer function to extract the phonon specularity parameter from the thermal conductivity measurements in the TG experiment, while rigorously accounting for the experimental uncertainties. We find that the observed magnitudes and trends of the thermal conductivity of the thin membranes cannot be explained by the 50-year old Ziman's model for the phonon specularity parameter and the Fuchs-Sondheimer theory of phonon boundary scattering. We also find that the partially specular boundary scattering picture of phonon boundary interactions works well for one of the membranes, enabling a direct measurement of the mode-dependent phonon specularity parameter for the first time in an experiment. We discuss the possibility of phonon mode conversion at the boundaries of a few membranes for which the partially specular phonon boundary scattering picture fails to explain the observed thermal conductivity trends. Considering the importance of understanding phonon boundary scattering to engineer and improve nanoscale device performance, we expect that the new experimental and computational tools developed in this work will advance a variety of nanoscale energy applications and further our understanding of nanoscale heat transport.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Phonon boundary scattering; silicon membranes; thermal conductivity; Boltzmann transport equation; transient grating; Monte Carlo method
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Minnich, Austin J.
Group:Resnick Sustainability Institute, Kavli Nanoscience Institute
Thesis Committee:
  • Hunt, Melany L. (chair)
  • Minnich, Austin J.
  • Blanquart, Guillaume
  • Faraon, Andrei
Defense Date:15 August 2016
Funding AgencyGrant Number
Dow-Resnick Graduate FellowshipUNSPECIFIED
Record Number:CaltechTHESIS:01172017-145551495
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 5
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10014
Deposited By: Navaneetha Krishnan Ravichandran
Deposited On:09 Mar 2017 22:51
Last Modified:08 Nov 2023 00:34

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