Biased magnetron sputter deposition of corrosion resistant Al–Zn alloy thin films

The reason for the high corrosion resistance of Al–Zn films is unclear. To relate this behavior to the structure and fabrication we have studied films deposited by dc biased magnetron sputtering onto Fe–Cr substrates. Changes of composition, structure, and electrochemical polarization behavior of resultant films were measured as a function of experimental parameters, including on‐axis and off‐axis substrate positions. The films, 1.6–4 μm thick, were deposited with a chamber Ar pressure of 10 mTorr (1.33 Pa), substrate temperature of 22–90 °C, and substrate bias of −60 to −380 V. Transmission electron photomicrographs of thin alloy films exhibited polycrystalline structure comprising one or two phases depending on film composition. Lower bias (−60 V) tends to produce two phases. Reflection high‐energy electron diffraction photomicrographs also presented polycrystal ring patterns. Energy‐dispersive x‐ray spectroscopy analysis of as‐deposited films revealed that Al vapor flux was more likely than Zn to go ax...