Penanen, KonstantinFukuto, MasafumiHeilmann, Ralf K.Silvera, IsaacPershan, Peter2010-09-082000Penanen, Konstantin, Masafumi Fukuto, Ralf K. Heilmann, Isaac F. Silvera, and Peter S. Pershan. 2000. 4He liquid-vapor interface below 1 K studied using x-ray reflectivity. Physical Review B 62(14): 9621-9640.1098-0121http://nrs.harvard.edu/urn-3:HUL.InstRepos:4428798The free surface of thin films of liquid helium adsorbed on a solid substrate has been studied using x-ray reflectivity. The film thickness and interfacial profile are extracted from the angular dependence of measured interference between signals reflected from the liquid-vapor and liquid-substrate interfaces. Polished silicon wafers, chemically cleaned and passivated, were used as substrates. Results are reported for measurements for 4He films 35 to 130 Å thick in the temperature range 0.44 to 1.3 K. The 10%/90% interfacial width for temperature T=0.45 K varies from 5.3±0.5 Å for 36±1.5 Å thick films to 6.5±0.5 Å for 125±1.5 Å thick films. The profile width at zero temperature should not differ significantly from that measured at T=0.45 K. For T=1.22 K, the width is 7.8±1.0 Å.en-USJournal Article10.1103/PhysRevB.62.9621