Biomedical Engineering Reference
In-Depth Information
17.2
Fabrication of NTs on Ti
Uniform and highly ordered NT arrays can be readily fabricated by anodization of a Ti foil in
F-containing electrolytes. The as-anodized NTs, which grow in situ on the Ti substrate, are highly
oriented perpendicular to the Ti surface
[21]
. The NTs are generally fabricated in the aqueous
hydrofluoric acid (HF) electrolyte in a two-electrode electrochemical cell at a constant potential
between 5 and 35 V
[4,8,10]
. At a low anodization voltage of 5 V, the morphology of the anodized
film is sponge-like with a typical pore size of 25 nm. At 20 V, hollow and cylindrical tube-like fea-
tures with an inner diameter of 80 nm form (
Figure 17.1
). Besides the HF/H
2
O electrolyte, many
other aqueous electrolytes have also been developed to fabricate NTs, for example, H
2
SO
4
/NaF/
(A)
(B)
(C)
(D)
FIGURE 17.1
(A and B) NTs formed at 5 and 20 V in 0.5 wt% aqueous HF solution with tube diameters of 25 and 80 nm,
respectively. (C and D) NTs formed at 10 and 40 V in an EG solution with 0.5 wt% NH
4
F,
5 vol% CH
3
OH, and 5 vol% H
2
O with tube diameters of 30 and 80 nm, respectively.
Reprinted with permission from Ref.
[4]
.
