observed [28], the pores grow toward the substrate and the current remains constant, which is similar to the pore growth stage in Al foils since there is no change in electrode surface area. And then comes the next stage (30 to 40 s), as

anodization is about to be completed, the current falls off rapidly. This drop is due to the increase in sheet resistance owing to the diminishing amount of aluminum remaining in the film. The remaining aluminum is oxidized, leaving behind a barrier layer. And Repotrectinib mw finally, in the last stage (after 40 s), the current density increases slowly and slightly and then is kept to a fixed value. However, the fixed value is lower than the current density of bare ITO, indicating that AAO is stuck to the ITO substrate. YM155 The tiny increase in this stage may be due to the upturned and broken barrier layer, as shown in Figure 2c,d, in which the holes open up a little and the exposed area of the ITO substrate to the

electrolyte is increased. Chemical dissolution and field-assisted dissolution of the barrier layer can also happen during this stage; however, the process is too slow to be observed. Figure 1 Current-time curves of high-field anodization of bare ITO glass and sputtered aluminum. Bare ITO glass (120 s) and sputtered aluminum for different times (30, 40, 60, 90, and 150 s). Figure 2 Schematic diagram illustrating the pore formation mechanism in anodic alumina. (a) Original aluminum sputtered on ITO glass; (b) the pore progress through the aluminum film and their tending towards an ordered hexagonal Saracatinib price arrangement; (c) barrier layer reaching the substrate, (d) fully formed AAO film with barrier layer; and (e) the disappearance of the barrier layer. Figure 3 shows SEM images of the cross-sectional morphology of the AAO films formed from the anodization of aluminum

samples at 195 V for different times. Barrier layers could be observed clearly in each Fossariinae image. Figure 3a,b,c has anodizing times of 30, 90, and 150 s, separately, and from these three images, we can see that the barrier layer became thinner with the increase of anodization time. This may be generated by the chemical dissolution and field-assisted dissolution of the barrier layer. The same phenomenon has been observed in the AAO walls. Figure 3d shows the anodization of the specimen sputtered in two steps and the ‘Y’ branches are obtained in the middle of the AAO walls. It can be seen clearly that the pores from the underlayer are denser than that of the upper layer. It is obvious that this phenomenon is quite different from the above three specimens whose aluminum were sputtered only in one step and shows that the ‘Y’ branches could only be developed from specimens sputtered in more than one step under high current density. Moreover, as observed by Chu et al. [23], the samples sputtered in multi-cycles and anodized under 130 V have transverse holes, which is also quite different from what we have observed in our study.