Growth regimes and metal enhanced 6-fold ring clustering of carbon in carbon-nickel composite thin films

Growth regimes of C:Ni (~ 30 at.%) composite thin films grown by ion beam co-sputtering in the temperature range of RT-500◦C are investigated. the combination of elastic recoil detection analysis, X-ray diffraction, transmission electron microscopy and Raman spectroscopy employing two excitation wavelengths was used to characterize the coexisting carbon and nickel constituents of the composite structure. Three growth regimes are identified characterized by different Ni nanoparticle shape (granular, columnar) and crystal structure (Ni3C or fcc Ni). The comparison of the Raman spectroscopy results from a carbon reference and C:Ni (~30 at.%) thin films shows that the presence of Ni enhances significantly the 6-fold ring clustering process at temperatures as low as RT, while at higher temperatures it favors ordering within the 6-fold ring clusters. The enhancement occurs independently on Ni nanoparticle size, shape or phase and is related to processes taking place on the surface of the growing film growth rather than in the bulk.