Temperature-fluctuation noise of thin films supported by a substrate

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Abstract
A computation is given of the fluctuations in average temperature of an isolated thin film on a substrate, the noise being due to two causes: (i) fluctuations in blackbody radiation absorbed and emitted by the front surface; (ii) thermal diffusion in the sample and the substrate. The surface source results in a large 1/f range, the level of which decreases with increasing heat conductivity of the substrate; the noise goes over into a 1/f2 spectrum at high frequencies. The noise due to the volume source results in a 1/f1/2 spectrum, going over into a 1/f3/2 spectrum at higher frequencies; the noise also decreases with increasing heat conductivity of the substrate. The integrated total noise is of the order kT20/C . Under most circumstances the spectrum due to the volume source dominates.