Thin Cu layers have been evaporated at room temperature on Cr films (similar to 10 monolayers) deposited on a Cu(001) single crystal. The crystallographic structure of these sandwiches is analysed by means of low-energy electron diffraction (LEED), angle-resolved ultra-violet photoemission spectroscopy (ARUPS) and X-ray photoemission spectroscopy. The data show that the attenuation of the Cr signal versus Cu deposition is much lower than expected for a uniform film growth. Moreover, the LEED pattern characteristic of the Cr film (made of Cr(110) domains with four different orientations) is visible for Cu coverages as high as 23 ML. This indicates a strong diffusion of the Cu atoms on the Cr film surface and the formation of Cu three-dimensional islands which present, according to ARUPS and X-ray photoelectron diffraction measurements, a highly disordered fee crystallographic structure. However the low reactivity of the sandwiches towards oxygen suggests that the whole Cr surface is wetted by at least 1 ML of Cu.