Gas-tight alumina films on nanoporous substrates through oxidation of sputtered metal films

The fabrication of ultrathin oxide films without gas leakage was investigated for the application to low-temperature solid oxide fuel cells (SOFCs). Aluminum thin films were deposited onto two types of anodic nanoporous alumina substrates with pore diameter of 20 and 200 nm, respectively, using dc-magnetron sputter at room temperature. By subsequent oxidation at temperatures over 500 °C, the metal films were successfully transformed into oxide films with thickness of about 35 and 410 nm. Volume expansion induced from oxidation of metal resulted in dense thin films that are free from hydrogen permeation.