Author : Max S. Aubain
Publisher :
ISBN 13 : 9781303145773
Total Pages : 95 pages
Book Rating : 4.1/5 (457 download)
Book Synopsis Determination of the Thermal Conductivity of Dielectric Thin Films Through Experimental Measurement and Crystallographic Analysis by : Max S. Aubain
Download or read book Determination of the Thermal Conductivity of Dielectric Thin Films Through Experimental Measurement and Crystallographic Analysis written by Max S. Aubain and published by . This book was released on 2013 with total page 95 pages. Available in PDF, EPUB and Kindle. Book excerpt: The prediction and measurement of the thermal conductivity, k, of crystalline materials, particularly in those with nano-scaled structural features, continues to pose a challenge to the heat transfer community. One difficulty arises in the correlation of experimental data with the theoretically calculated, direction-specific phonon dispersion characteristics that determine thermal conductivity, such as heat capacity and group velocity. k is often considered a scalar quantity, which implicitly assumes three-dimensional isotropic behavior, e.g., k of wurtzite (hexagonal) aluminum nitride at room temperature is considered to be 320 W/m.K. Although, simultaneously, it is acknowledged that the phonon transport characteristics within crystalline materials varies non-negligibly with direction; we calculate the a-axis and c-axis heat capacity and group velocity at room temperature to be different by approximately a factor of 10 and 2.5, respectively, favoring basal-plane heat conduction. Experimental measurements may elucidate these phenomena, but fabrication of large single crystals in multiple orientations is impractical for most materials, and in those samples which are commonly single crystal, such as thin films, nanowires, or nanodots, it is difficult to measure the full thermal conductivity tensor. This dissertation then develops two experimental techniques to measure k anisotropy of two substrate-supported thin film systems. An optical technique called thermoreflectance thermometry was utilized to measure the heat transport that takes place only within the plane of Si films, ranging in thickness from 70 nm to 255 nm, atop thermally insulating substrates. The use of an optical method was deployed to preclude possible heat losses from contacted thermometer structures and enabled temperature measurements with sub-miliKelvin resolution, with 4 um spatial resolution. Additionally, heater/thermometer structures, in a 3w measurement configuration, were used to simultaneously probe the cross-plane and in-plane heat transport characteristics of aluminum nitride thin films, between 500 nm and 750 nm thick, deposited by molecular beam epitaxy on sapphire substrates. Finite element models were applied to fit the measured data, using the thin film thermal conductivity as a free parameter. Finally, the results are discussed with respect to calculations of the heat capacity and group velocity based on phonon dispersion relations, and scattering mechanisms specific to the thin film samples.
