Verification of the Lifshitz Theory of the van der Waals Potential Using Liquid-Helium Films

Accurate measurements are presented of the thickness of helium films on cleaved surfaces of alkaline-earth fluoride crystals at 1.38 $^{\mathrm{o}}\mathrm{K}$. The films were measured between 10 and 250 \AA{} using an acoustic interferometry technique. The data are in excellent agreement with calculations based on the Lifshitz theory of van der Waals forces. Calculations of the film thickness on a variety of other substrates are also given.

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