Hydrogen and helium films as model systems of wetting

Optical experiments on the wetting properties of liquid 4He and molecular hydrogen are reviewed. Hydrogen films on noble metal surfaces serve as model systems for studying triple point wetting, a continuous transition between wetting and non-wetting. By means of optically excited surface plasmons, the adsorbed film thickness for temperatures around, and far below, the bulk melting temperature is measured, and the physical mechanisms responsible for the transition are elucidated. Possible applications for other experiments in pure and applied research are discussed. Thin films are droplets of liquid helium are studied on cesium surfaces, on which there is a first order wetting transition. Ou…