Effect of Implanted Cl and Deposited Oxides on the Pitting Behavior of Aluminum

Insight into the influence of Cl on the pitting behavior of aluminum has been gained using a combination of ion implantation and oxide deposition. High-purity Al thin-film samples were implanted with 35 keV Cl+ followed by plasma deposition of an aluminum oxide (Al2O3). The pitting potential of unimplanted areas in 50 mM NaCl increased with increasing deposited oxide thickness (0, 80, 140 A). For implanted areas, polarization in 50 mM NaCl resulted in pitting that was insensitive to oxide thickness and implant fluence above a critical level. By comparison, polarization in 50 mM K2SO4 resulted in pitting which exhibited a dependence on both deposited oxide thickness and implant fluence. Finally, the effect of the Cl source (solution, implantation, or both) on the pitting behavior of Al with a deposited oxide was examined. These results are used to support the hypothesis that both a critical chlorine distribution and oxide modification are contributing factors to pit nucleation.