Fabrication of nanoporous thin films via radio-frequency magnetron sputtering and O ₂ plasma ashing

In this study, we report a new method for fabricating nanoporous thin films. In the first step, metal–carbon thin films were prepared by radio-frequency reactive magnetron sputtering, using Cu, Ni, and Ti targets as the metal sources and CH ₄ gas as the carbon source during the co-deposition process. In the second step, the metal–carbon films were then oxidized by an oxygen plasma generated with a flowing a gas mixture of Ar and O ₂ , and nanoporous metal–oxide films were obtained by removing carbon atoms from the metal–carbon thin films. The pores in the films varied with the amount of carbon in the film surface, and mesopores grew to lager macropores as the flow rate of CH ₄ was increased. Depending on the film composition, the calculated porosity varied from 50% to 90%. With advantages such as a wide range of suitable raw materials and good reproducibility, this fabrication method is expected to offer a new approach to the commercial production of nanoporous materials.