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Gang Chen and Nicolas G. Hadjiconstantinou. Zeng, Lingping Massachusetts Institute of Technology. Department of Mechanical Engineering. Massachusetts Institute of Technology. Department of Mechanical Engineering 2013-06-17T19:51:53Z 2013-06-17T19:51:53Z 2013 2013 http://hdl.handle.net/1721.1/79267 846629386 Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. Cataloged from PDF version of thesis. Includes bibliographical references (p. 99-107). Knowledge of phonon mean free path (MFP) distribution is critically important to engineering size effects. Phenomenological models of phonon relaxation times can give us some sense about the mean free path distribution, but they are not accurate. Further improvement of thermoelectric performance requires the phonon MFP to be known. In this thesis, we improve recently developed thermal conductivity spectroscopy technique to experimentally measure MFPs using ultrafast transient thermoreflectance method. By optically heating lithographically patterned metallic nanodot arrays, we are able to probe heat transfer at length scales down to 100 nm, far below the diffraction limit for visible light. We demonstrate the new implementation by measuring MFPs in sapphire at room temperature. A multidimensional transport model based on the grey phonon Boltzmann equation is developed and solved to study the quasi-ballistic transport occurring in the spectroscopy experiments. To account for the nonlinear dispersion relation, we present a variance reduced Monte Carlo scheme to solve the full Boltzmann transport equation and compare the simulation results with experimental data on silicon. by Lingping Zeng. S.M. 107 p. eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Mechanical Engineering. Experimental and numerical investigation of phonon mean free path distribution Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="b82452f5-3d3a-4aa4-b93c-40b54c8c2232"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Experimental and numerical investigation of phonon mean free path distribution</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2013</PublicationDate> <Authors> <Author> <DisplayName>Zeng, Lingping</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Mechanical Engineering.</Keyword> <Abstract>Knowledge of phonon mean free path (MFP) distribution is critically important to engineering size effects. Phenomenological models of phonon relaxation times can give us some sense about the mean free path distribution, but they are not accurate. Further improvement of thermoelectric performance requires the phonon MFP to be known. In this thesis, we improve recently developed thermal conductivity spectroscopy technique to experimentally measure MFPs using ultrafast transient thermoreflectance method. By optically heating lithographically patterned metallic nanodot arrays, we are able to probe heat transfer at length scales down to 100 nm, far below the diffraction limit for visible light. We demonstrate the new implementation by measuring MFPs in sapphire at room temperature. A multidimensional transport model based on the grey phonon Boltzmann equation is developed and solved to study the quasi-ballistic transport occurring in the spectroscopy experiments. To account for the nonlinear dispersion relation, we present a variance reduced Monte Carlo scheme to solve the full Boltzmann transport equation and compare the simulation results with experimental data on silicon.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>