Nanoporous thin films obtained by oblique angle deposition of aluminum on porous surfaces

Abstract

The oblique angle deposition (OAD) is a versatile and easily controllable method appropriate for the production of nanoporous structures with pores in nanometric range and high surface area. In this study, aluminum thin films were deposited by sputtering on both commercial and homemade porous aluminum oxide substrates, tilted 85° and 89°. The morphology of substrates and the shadowing effect created by the OAD led to the deposition of densely packed columnar Al thin films with surface pores which sizes range between 19 and 75 nm depending on the substrate, tilt angle, time of deposition and power density. Focused ion beam (FIB) nanotomography allowed the 3D reconstruction of the whole nanoporous structures, in which the substrate, the thin film and the interface could be easily observed. Moreover, these results showed the hourglass-like shape of pores in the Al thin films, as well as the pores interconnectivity and the existence of open porosity that ensures the passage of the gas/liquid flow through the nanoporous structure. This study provides further insights into the production patterns of nanoporous structures by OAD, with a potential application in nanofiltration systems able to filter nanoparticles, which are often found in industrial environments and can represent a risk for human health and environment.