Equilibrium helium film in the thick film limit

For the thickness 0 5 a liquid or solid quantum f i lm, like liquid helium or solid hydrogen, there exist still open questions about how the film thickness develops in certain limits. One of these is the thick film limit, i.e., the crossover from the thick film to bulk. We have performed rneasurements in this range using the surface plasmon resonance technique and an evaporated h g film deposited on glass as substrate. The thickness of the adsorhed helium film is varied by changing the distance h of the bulk reservoir to the surface of the substrate. In the limiting case, when h 4 0, the film thickness approaches about 100 n m following the wan der Waals law in thc retarded regime. The film thickness and its dependence on h is precisely determined and theoretically modeled. The equilibrium fiIm thickness behavimzr js discussed in detail. The agreement between theory and experiment is very good.