Surface excitations in thin helium films on silica aerogel

First measurements are reported on pure surface excitations in thin superfluid 4He films on silica aerogel. The ripplon dispersion curve is found to be the same for helium on graphite and silica aerogel substrates. However, the layered roton line width in helium films on aerogel shows a pronounced broadening with respect to that found in helium films on graphite.