A direct indication for specular reflection of conduction electrons at the vacuum boundary of metal films

Highly disordered films of Al, Cu, Ag and Au are deposited at low temperatures on top of an annealed layer of the same metal. Although two electric conductors are connected in parallel, the total conductance of the sandwich first decreases, then passes through a minimum, and finally increases with increasing thickness of the disordered overlayer. Such curves of the total conductance versus thickness of the second film are interpreted within the Fuchs-Sondheimer model of the geometrical size effect. This model is used to calculate the fraction of specularly scattered conduction electrons at the uncovered surface, and the mean free path of the conduction electrons in the quench condensed overlayer.