Herein, we report on the interplay between structural and electronic properties in the dynamical screening processes and the excitation of collective modes in Ag/Cu(111). For the (9 × 9)-Ag/Cu(111) structure, the excitation of the two-dimensional plasmon, observed in Ag/Si(111), is forbidden by both the high corrugation of the Ag layer and the presence of the underlying metal substrate. The increase of the sp density of states at the Fermi energy induces the appearance of a broad peak at 7–8 eV assigned to a free-electron collective excitation.