Effects of Grain Size and Concentration of Cl^- in Solution on Properties of Passive Film on Cu

The formation process and mechanism of passive film on Cu with two different grain sizes in solutions with different Cl- concentrations were studied by electrochemical methods and Mott-Schottky theory. The carrier density in the passive film formed at two oxidation potentials (0.2 V, 0.4 V) in the solutions with different Cl- concentrations was calculated. The results indicated that under different conditions, the Mott-Schottky plots of the oxide films on the surface of Cu were linear with a negative slop and showed the behavior of P-type semiconductor. The majority carriers in the passive film were holes. With the increase of the grain size of Cu and the increase of anodic passivation potential, the acceptor density (NA) in the passive film formed on the surface of Cu reduced. When the concentration of Cl- in the medium solution increased, the acceptor density (NA) in the passive film increased.