+MAO ; To meet the constant challenges of miniaturization in the microelectronics industry, new innovative pathways must be explored to produce nano-objects. Ionic liquids (ILs) can be used to generate and stabilize metallic nanoparticles (MNPs) by several physical and chemical routes. Here, the simultaneous decomposition of Ru and Cu organometallic precursors in IL is shown to yield core-shell Ru@CuNPs with smaller diameters and narrower size distributions than the corresponding monometallic NPs, in a broad range of Ru:Cu compositions. They are probably formed by rapid nucleation of Ru cores followed by decomposition of the Cu precursor on their surface. This effect forces the formation of a bimetallic structure that does not form with the use of purely physical processes such as PVD. These Cu, Ru, and Ru@CuNPs could be used for the formation of seed and barrier layers for the metallization of advanced interconnect structures. (C) 2012 Elsevier B.V. All rights reserved.