Structure-dependent adhesion and friction on highly ordered metallic nanopore membranes

Highly ordered metallic nanopore membranes are fabricated by direct deposition of nickel on typical porous anodic alumina (PAA) templates. The large-area uniform nanopore arrays of the PAA templates are accurately transferred to the metallic nanopore replicas, depending on the thickness of the deposited metal and the pore size of the base template. We demonstrate the ready tunability of the pore size and reproducibility of the metallic nanopore structure in a wide range of pore sizes. The adhesion and friction characteristics of the metallic replicas are studied according to the pore size using atomic force microscopy (AFM). As the pore diameter increases, the friction coefficients increase nonlinearly, and the adhesive forces scarcely change. These characteristics are understood in terms of the structural properties of the replicas, specifically the surface morphology and the real contact area. Initial pore formation from a flat thin film reduces the adhesive force by up to four times.