Observations of anomalies in the anodic behaviour of microcrystalline aluminium

The anodic behaviour of sputtered microcrystalline Al (mc-Al) was investigated in neutral Na2SO4 electrolyte under varied conditions. Our results revealed that Cl− addition led to a reduction in the anodic current density, which we considered unusual. Mott–Schottky analysis showed that Cl− introduction altered the semiconducting property of the passive film from n-type to p-type, implying that the p-type film can possessed a relative higher stability. Immersion of mc-Al in other electrolytes yielded films with n-type, p-type and positive p–n junction structure. The results also indicate that the p-type film was most stable and the positive p–n junction film least stable.