Influence of Potentiostatic Aging on Nb and W Oxides Formed in 0.1 M HClO[sub 4]

Abstract

The evolution of the electrical properties of and films, at different formation potentials , in , were followed by electrochemical impedance spectroscopy (EIS). During the growth of the oxide films, EIS spectra were acquired every hour, maintaining the potentiostatic pulse during . The and impedance spectra show variations vs potentiostatic aging. However, the Mott–Schottky analysis showed that the density of donors does not depend on the potentiostatic aging but depends on the , while, the flatband potential is almost constant with the potentiostatic aging and , for both oxides. The relationship between the invariability of the semiconductor properties ( and ) with the potentiostatic aging and the variation of the impedance spectra, in the case of the W, can be explained by the formation of an external layer of , which must be very thin; the detachment of this layer causes a very small difference in the thickness, not modifying the semiconductor properties ( and ), but greatly changing the electric properties of the film, since is more resistive. A similar hydration process may occur in the films to a lesser extent.