Decoupling of image-potential states from bulk Cu(1 0 0) by Ar spacer layers has been investigated by time-resolved two-photon photoemission. Ordered films with thicknesses of up to five monolayers have been prepared that lead to a lifetime increase of almost three orders of magnitude, It is also demonstrated that continuum models fail to give a satisfactory description of the adlayer electronic structure. (C) 2002 Published by Elsevier Science B.V.