Figure 2.

The voltage- and current-time responses during the porous alumina assisted anodizing (a) in 0.2 M oxalic electrolyte followed by reanodizing (b) in 0.5 M boric acid and 0.05 M sodium tetraborate electrolyte of an Al (1000 nm)/Nb (50 nm) bilayer system sputter-deposited on a polished glass substrate. The marked stages are: I—nucleation and beginning of a steady-state growth of pores in the alumina layer, II—steady-state pore growth (at 53 V) during the anodizing (Figure 1b), III—aluminum complete oxidation, nucleation, and development of niobia embryos (Figure 1c), IV—galvanostatic reanodizing the Nb underlayer to 230 V (Figure 1d), V—galvanodynamic-potentiostatic polarization at 410 V (current decay). The profiles have been presented in two separate panels, for the sake of clarity.