The growth of Cu on an O-precovered Ru(0001) surface was studied at va
rious substrate temperatures by Auger electron spectroscopy, thermal d
esorption spectroscopy and sputter profiling. In contrast to the Volme
r-Weber growth mode of Au films on O-precovered Ru(0001) the initial g
rowth of Cu films is layer-by-layer at moderate temperatures (300 K-45
0 K). During the deposition of Cu, O is displaced from the Ru surface
and transported to the top of the surface of the growing film. This ca
n be observed up to Cu coverages of 9 ML and even higher, independentl
y of the evaporation rate and substrate temperature. The thermal depos
ition spectra of Cu and O2 indicate the existence of an oxidized Cu la
yer.