Effect of He-4 pre-plating on third sound in superfluid He-3

We recently reported observation of third sound resonances in superfluid fi lms of pure He-3 on a disk-shaped polished copper substrate. From the obser ved spectra of resonant modes, the third sound speed, the average superflui d density, and information on dissipation wire obtained. The film thickness es studied were larger than or comparable to the superfluid coherence lengt h, which is near 100 nm. We describe preliminary results from efforts aimed at using third sound in thinner films on a substrate which has been coated with a few atomic layers of He-4. (C) 2000 Elsevier Science B.V. All right s reserved.