Regensburg 2002 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
O: Oberflächenphysik
O 13: Postersitzung (Adsorption an Oberfl
ächen, Elektronische Struktur, Magnetismus in reduzierten Dimensionen, Epitaxie und Wachstum, Halbleiteroberfl
ächen und -grenzfl
ächen, Organische Dünnschichten)
O 13.19: Poster
Montag, 11. März 2002, 18:00–21:00, Bereich C
Non-Wetting and Thin-Film State of Liquid 4He on Cs and Rb — •Jürgen Klier1,2, Valentin Iov1, Paul Leiderer1, and Adrian Wyatt2 — 1Universität Konstanz, Fachbereich Physik, Fach M676, 78457 Konstanz; Germany — 2Department of Physics, University of Exeter, Exeter, EX4 4QL, UK
It was theoretically predicted that the alkali metals Cs and Rb are the only surfaces non-wetted by superfluid 4He below a certain temperature. This was experimentally proven for the He-Cs system. Using the photoelectron tunneling method we have sensitively measured the growth of the non-wetting thin-film state of 4He on a quench-condensed Cs surface. It turns out that far from coexistence there is little adsorption of helium. In contrast, close to coexistence a rapid growth up to two monolayers of helium is observed, but the surface is still non-wet under the usual convention. We interpret this behaviour on the basis of 2-dimensional gas-liquid film and discuss the phase diagram in the non-wetting regime. After Cs, Rb is the next weakest binding substrate for 4He. The wetting temperature has been found to be close to zero or pre-wetting continues down to T = 0. However, theory predicts Tw = 1.3K. We have measured the flow of liquid 4He over a pure Rb and oxidised Rb surface. For the pure Rb non-wetting of 4He is observed and the non-wetting thin-film state is about 0.3 monolayer thick and superfluid. We show that Tw is greater than 300mK. For the oxidised Rb complete wetting is observed.
This work is supported by the DFG under grant Kl 1186/1.