Ion beam synthesis of amorphous carbon thin films containing metallic nanoclusters

We investigated the synthesis of metallic nanoparticles during growth of an amorphous carbon matrix using mass selected ion beam deposition of carbon and metal ions. By varying the carbon-to-metal ion ratio, a-C:Cu and a-C:Ag films with metal concentrations between 0 and 50 at.% were grown at room temperature on Si substrates by co-deposition of low energy mass-selected 12C+, 63Cu+ and 107,109Ag+ ions. X-ray diffraction and transmission electron microscopy reveal metal particles with diameters of a few nanometers. The matrix is diamond-like with mainly sp3-bonded carbon at low metal concentrations and becomes graphitic for metal concentrations exceeding 10 at.%. Whereas a large fraction of the deposited Cu ions are incorporated into the films, most of the deposited Ag ions have disappeared. The residual Ag accumulates at the surface and at the C/Si interface. Furthermore, the interface roughness of a-C:Ag films on Si is high. These observations are discussed in terms of the stability of small Ag clusters and Ag induced interface reactions.