Vapor-Deposition Techniques - Engineered Biomimicry - page 384

The modified CEFR technique is one of the two
main steps of the Nano4Bio technique devised to
fabricate multiple high-fidelity replicas of a single
biotemplate [22] . As depicted schematically in
Figure 15.7 , in the first step of this technique, the
modified CEFR technique is used to deposit a
∼ 250-nm-thick conformal coating of nickel on the
biotemplate. In the second step, a roughly
60- μ m-thick structural layer of nickel is electro-
formed onto the thin layer to give it the structural
integrity needed for casting or stamping. The
biotemplate is then plucked off and plasma ash-
ing is carried out to completely remove all organic
material in the third step. What is left behind is a
master negative made of nickel. This can be used
in the fourth step as either a die for stamping or
a mold for casting multiple replicas. Casting pro-
duces high fidelity at the 2- μ m length scale [22] ,
but stamping will improve the reproduction
fidelity at lower length scales [1, 23] . Because the
Nano4Bio technique can simultaneously produce
multiple replicas of multiple biotemplates, it is
suitable for industrial bioreplication.

400 nm is separated from template, the coating
becomes a high-fidelity replica.
To date, this technique has been applied for
replicating the compound eyes of tephritid flies
[18] , as shown in Figure 15.5 , and the wings of
butterflies [19, 20] , as shown in Figure 15.6 ,
without compromising their optical characteris-
tics that are due to nanoscale (<100 nm) struc-
tural features. The CEFR technique is particularly
well suited for bioreplication because the tem-
peratures involved during deposition are suffi-
ciently low and the replication process occurs in
a non-corrosive environment, thereby avoiding
damage to the underlying biotemplate.
The CEFR technique has been modified to
improve the uniform thickness of the replica by
introducing a second degree of freedom to the
biotemplate motion during deposition [21] . The
first degree, as in the original CEFR technique,
is the rotation of the biotemplate about a central
normal axis. The second degree is the rocking of
the biotemplate so as to continuously vary χ v
during deposition.

FIGURE 15.5 SEM of the eye of a tephritid fly (common fruit fly) coated with GeSbSe chalcogenide glass using the CEFR

technique [18] .