Acoustic wave interference has been observed at frequencies between 18 and 58 GHz in thin films of liquid helium absorbed on surfaces of CaF 2 , SrF 2 , and BaF 2 . The thickness of the films, ranging from 10 to 200 A, could be measured to within a few percent in most cases» The dependence of the van der Waals potential on the film thickness is also discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.