Structure thermal domain size in sapphire single crystal

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2023-12
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Bai, John Jianyu
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Wang, Xinwei
Bai, Xianglan
Wang, Jigang
Yu, Chenxu
Sippel, Travis
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Mechanical Engineering
Abstract
The structure thermal domain (STD) size is a structure characteristic size determined by the thermal reffusivity theory and reflects the grain boundary-energy carrier scattering at the 0 K limit. The relation of this size with the crystallite size determined by x-ray diffraction (XRD) has not be studied well, partly due to structure complexity of many studied materials. In this work, a single crystalline sapphire wafer is studied for its XRD crystallite and STD sizes, and the comparison between them is conducted. The thermal reffusivity of a 1×5 mm sapphire wafer (25 m thick) is measured from room temperature down to 13 K, and the residual thermal reffusivity at the 0 K limit is determined. The STD size is found to be 72.5 nm in the in-plane direction while the XRD analysis uncovers crystallite sizes of 283 nm in the thickness direction, and 34.4 nm in the in-plane direction. These two characteristic sizes are compared and explained based on the underneath scattering physics.
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