Roughness and surface potential in physisorption

The surface potential due to physical adsorption of xenon on iron, copper and sodium films has been investigated as a function of annealing temperature using the diode method. As iron and copper films are annealed, the surface potential falls to low values. On sodium films the surface potential is always zero despite finite uptakes of xenon. The falling surface potentials on iron and copper may be due to contamination, changes in the crystal plane exposure of the film, a rise in the metallic work function, or variations in the roughness of the surface. Surface roughness appears to be the vital factor, smoother films giving lower surface potentials because they lack the electric field enhancement which occurs on rough surfaces.