(a)
(b)
(c)
(d)
(e)

Figure 4: SEM images of titanium oxides that are anodically prepared under different anodizing conditions: (a) chemical etch in 0.5 wt% HF for 30s, (b) aqueous 0.3 wt% HF + 1 M H3PO4 at 20 V, (c) aqueous 0.5 wt% HF + 1 M H3PO4 at 20 V, (d) aqueous 0.5 wt% HF + 1 M H3PO4 at 10 V, and (e) aqueous 0.5 wt% HF + 1 M H3PO4 at 150 V [42].