Biomedical Engineering Reference
In-Depth Information
The thickness of electrochemically grown Titania gyroid arrays
is limited by mechanical stability during high temperature
processing. Macroscopic signs of cracking appear for templates
around 900 nm and thicker. Kavan
reported cracking of
nonstructured electrodeposited Ti(IV) oxide layers above 250 nm
[92]. Eventually the films crack and buckle from the substrate,
as shown in Fig. 2.25, and complete delamination begins above
this thickness. Conceptually, stable thick layers would be possible
by increasing the density of electrodeposited material, ideally
synthesizing a fully crystalline material, such that volume contraction
is reduced or completely eliminated.
et al.
(a)
(c)
100
µ
m
(b)
2
µ
m
50
µ
m
Film failure by cracking during high temperature annealing.
(a,b) Low and high magnification SEM cross section views of 4 μm thick
TiO
Figure 2.25
°
C annealing for 2 h. Lateral stress is relieved by
cracking and buckling of ∼50−100 μm pieces of the array which delaminate
from the substrate. The failure plane is at the interface with the substrate.
(c) Cracking and partial delamination of a 1.5 μm thick array after annealing.
gyroid arrays after 500
2
2.5 APPLICATIONS: THE BULK
HETEROJUNCTION SOLAR CELL
The ability to pattern ordered nanometer-scale structures into
semiconducting composite materials is of great interest for emerging
solar energy technologies based on so-called excitonic photovoltaic
systems [76]. These multicomponent devices rely on a donor-
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