The micro- and nanomorphology of surface enhanced Raman scattering (SERS) active rough substrates obtained by plasma oxidation-reduction cycles onto original flat silver surfaces have been investigated by means of a dual technique approach. Scanning force microscopy and low-frequency Raman spectroscopy give complementary results when applied on very rough systems. Almost spherical silver colloids have been used as well-defined systems to model, by their stacking over flat silicon wafers, the plasma roughening process inducing SERS activity. The SERS activity results are strongly related to the micromorphology of the nanoparticles assembly, rather than to the silver cluster size. In particular an electromagnetic enhancement factor of 10(3) for the breathing mode of the polystyrene aromatic rings was found to be related to the vertical stacking of tens of clusters about 10 nm in diameter.