1997 Volume 46 Issue 3 Pages 169-175
The dielectric and semiconductive properties of the passive film on titanium were investigated under potentiostatic polarization in neutral phosphate and borate solutions by using the impedance technique. Further topographic change of the passivated surface with potential was observed by AFM. From comparison between the film thickness and the capacitance of the space charge layer, the dielectric constant of the passive film was estimated at about 40 in the potential region lower than 3V and about 85 in the potential region higher than 3V. From the Mott-Schottky plot the donor density of the passive film was calculated, which is in the order of 1026m-3, and decreased with an increase of the film formation potential. The decrease may correspond to a change of film structure from amorphous to crystalline. At potential higher than 7.5V, breakdown of the passive film was observed, probably due to influence of very high electric field in the film. The breakdown brings about the increase of donor density, and a roughening surface due to micro-crystallization.