Surface state electrons on quench-condensed hydrogen films as a surface probe

The surface of quench-condensed hydrogen films was studied employing conductivity measurements of surface state electrons (SSE). The surface quality of the films could be drastically improved by thermal annealing. The absence of any residual gas above the surface was found to be essential for an effective annealing process. The SSE conductivity reached values comparable to those obtained on bulk hydrogen crystals. Adsorbing small amounts of helium onto the surface led to pronounced conductivity oscillations, which are ascribed to a layering of the helium film. This has previously been observed only on bulk hydrogen. The positions of the conductivity maxima agree with those expected from previously published values of the binding energy of helium on bulk solid hydrogen