Pore structure, barrier layer topography and matrix alumina structure of porous anodic alumina film

Different anodic voltages and methods were adopted to produce porous anodic alumina films (PAAF) in an aqueous solution of oxalic acid. Carbon tube growth by chemical vapor deposition (CVD) in the films was used to copy the internal pore structure and was recorded by transmission electron microscopy (TEM) photos. Atomic force microscope (AFM) was employed to obtain the topography of the barrier layer of the corresponding films. When the anodic voltage was 40 V and the two-step method adopted, the barrier layer of the film had domains with highly ordered hexagonal cell distribution, and the corresponding pores were straight. When the anodic voltage increased to 60 V, the barrier layer showed random cell distribution with an obvious difference in cell size and form, and the corresponding pores exhibited multi-branch features. When the anodic voltage increased further to 110 V, the barrier layer also showed a random cell distribution. Additionally, smaller protrusions connected to bigger cells were found, which can be correlated to the formation of branches with smaller diameters. Most of the branches of carbon tubes grown in the film anodized at 110 V have a saw-tooth like feature. X-Ray diffraction analysis shows that all the anodic films are amorphous, regardless of the anodic voltage. However, unoxidized aluminum particles in the film anodized at 110 V was observed by TEM.