Biomedical Engineering Reference
In-Depth Information
5.4 CHARACTERIZATION OF TITANIA NANOTUBES
LAYERS
5.4.1 Scanning Electron Micrograph (SEM) and X-Ray
Difracion (XRD)
SEM pictures of the resulting titanium dioxide nanotubes are
shown in this section. Depending on the electrochemical conditions
during anodization experiments, the obtained nanotube length (or
thickness) differs. From the top-view image, it is possible to observe
the nanotube morphology at different times of anodization. In the
beginning, after 5 min, the presence of F
ions induces the localized
breakdown of the compact oxide layer, probably starting on defect
sites (Fig. 5.6).
SEM investigations show that the breakdown sites are randomly
distributed and there is no sign of self-organization at this stage,
as we mentioned in Section 5.3.2 (Fig. 5.5b). These sites act as
nucleation points of a disordered wormlike structure (Fig. 5.5c).
Highly ordered array of TiO
2
-
nanotubes is observable after 20 min
and 4 h of anodization, as discussed in Section 5.3.2. ntTiO
2
presents
a tube diameter that varies from about 50 nm to about 200 nm and
wall thickness of about 20 nm whatever the time employed during the
experiment (Fig. 5.7a,b). From cross-sectional images, it is possible
to observe that the nanotube length is increased during anodization
for longer times. Thus, the samples obtained after 20 min and 4 h
exhibit about 600 nm and 900 nm length, respectively (Fig. 5.7c,d).
On the other hand, when using Ti thin film onto Silicon substrates
(Fig. 5.8), self-organized TiO
nanotubes layers with thickness
of about 600 nm are obtained after anodization under the same
conditions. Moreover, the nanotube diameter and wall thickness
are in the range 50-200 nm and about 20 nm, respectively. Hence, a
layer of titania nanotubes is successfully fabricated on Ti foils and Ti
thin films. Moreover, the titania nanotubes were heated at 450oC in
air for 3 h and the nanotube morphology remained unmodified, as
we will discuss later.
XRD characterization can be helpful in knowing which TiO
2
phase
or which kind of amorphization is obtained just after anodization
and thermal treatment. For that purpose, X-ray-diffraction (XRD)
2
Search WWH ::
Custom Search