29 July 1992 Thermal diffusivity of thin films and surfaces investigated by transient thermal gratings
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Abstract
In this contribution we demonstrate that surface conditions and microstructures of thin films strongly modify the thermal transport in these materials. Our technique is based on the pulsed photothermal deformation technique, refined by utilizing transient thermal gratings. Such gratings introduce a preferred direction in the surface plane for heat conduction. By using a nanosecond pump laser and analyzing the data with an appropriate model, the technique is capable of distinguishing between vertical and lateral channels for heat diffusion. Data are presented for thermally evaporated gold films of different thicknesses (20 - 2500 nm) on BK7 substrates, a commercial Au plate with random surface structure, and a Ni foil with a well oriented texture. The measured thermal diffusivity of the Au plate is about 25% lower than the literature value, due to a random surface roughness. For the Ni foil we find a strongly anisotropic diffusivity, either 0.19 +/- 0.03 or 0.05 +/- 0.002 cm2/s, depending on whether the direction of the grooves is parallel or perpendicular to the grating vector. For the gold films we observe the typical thickness dependent behavior, which most likely originates from disorder in the films that leads to an increased lateral thermal resistance.
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Zhouling Wu, Javier Jauregui, Dieter Schaefer, Eckart Matthias, "Thermal diffusivity of thin films and surfaces investigated by transient thermal gratings", Proc. SPIE 1624, Laser-Induced Damage in Optical Materials: 1991, (29 July 1992); doi: 10.1117/12.60113; https://doi.org/10.1117/12.60113
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