SURFACE REFLECTION OF SUBMILLIKELVIN ATOMIC-HYDROGEN FROM THIN SUPERFLUID HE-4 FILMS - SUBSTRATE EFFECTS

We present the results of experiments measuring the film thickness dep endence of the sticking probability for H on thin films of superfluid He-4 for H atom temperatures of 0.3 - 4.0 mK. Data is presented for 0. 6 nm to 1 mm thick films on a silver sinter substrate. For the 0.3 mK H atoms, the sticking probability varies from 0.7 for a film 0.6 nm th ick to 2 x 10(-2) for films thicker than 1 mum. Our data are in reason able agreement with recent theoretical calculations.