Percolative, Multifractal, and Symmetry Properties of the Surface at Nanoscale of Cu-Ni Bimetallic Thin Films Deposited by RF-PECVD

Abstract

We explored the morphological and 3D spatial properties of Cu/Ni thin films obtained by a co-deposition process. The 3D AFM topographic maps analysis indicated that the films displayed different morphologies and rough profiles dictated by their singular directional inhomogeneities. Moreover, Minkowski’s volume showed that the Cu/Ni films deposited after 15 and 20 min had a similar relative distribution of matter as a function of height, which is different from the individual Cu films. The Minkowski boundary and connectivity point out that the percolative properties of the Cu/Ni samples were similar to each other. However, they were distinct from the percolative features of the Cu sample. It was also observed that the surface microtexture of the films showed similar spatial complexity, dominant spatial frequencies, and topographical uniformity. For the Cu/Ni thin films, the Minkowski functionals morphological analysis showed that the type of film dictated the surface percolation. In contrast, clear fingerprints of multifractal behavior in all the samples were also observed, indicating that the multifractality degree increased with the sputtering time, supporting the significant vertical growth of the Cu/Ni thin film deposited after 20 min. Aside from that, the results from a symmetry-based approach indicated that the vertical growth dynamics of individual Cu and Cu/Ni thin films were different in terms of scaling symmetry, where we observed that the sputtering induced the formation of less asymmetric topographies regarding their multiscaling behavior. Finally, our findings suggested that the sputtering process can be employed to tune the percolative properties, multifractality, and scaling symmetry of the films, inducing different vertical growth dynamics, which can be useful in the optimization of the fabrication of bimetallic surfaces for technological purposes.

Keywords

• AFM
• Cu-Ni
• fractal
• multifractal
• scaling symmetry
• thin films