Interfacial wetting and percolation threshold in ultrathin Ni/C multilayer films

Abstract

Magnetron sputtered Ni/C graded multilayers with bilayer periods between 3.5 and 4.5 nm are investigated by cross-sectional transmission electron microscopy. The multilayers consist of amorphous C layers and close packed hexagonal Ni layers. A percolation threshold of 2.0 nm at which Ni forms coalescent layers is observed for the given deposition conditions. This percolation threshold can be explained by island growth of Ni on amorphous C owing to the higher surface energy of Ni compared with C, explaining the sharp decrease in X-ray reflectivity observed for periods below 4 nm.