431599_Print.indd

Solving for the bending stiffness,Dm, with the assumption thatuis small so that
sinuuyields:

Dm¼

F

wd

ll 0 sinðK 0 l 0 Þ

K 0

þ

1

K 02

lcosðK 0 l 0 Þlþ

l 0

2



þ

1

K 03

sinð 2 K 0 l 0 Þ

4

sinðK 0 l 0 Þ



ð 2 : 4 Þ

The slope of a representative loading force-deflection curve, yieldsF/d=12nN/
μm(Fig.2.2c), and using Eq. (2.4) the calculated bending stiffness per width
(w=5μm) isDm= 0.358 nN m. For typical 3D macroporous nanoelectronic net-
works the area fraction for both types of elements (i.e., SU-8 and SU-8/metal/SU-8) can
range from 1 to 10%, yielding values of the effective bending stiffness from 0.0038 to
0.0378 nN m.

2.4 Conclusions

We have demonstrated a general strategy combining bottom-up and
mechanics-driven approaches for preparing regular 3D interconnected and
addressable macroporous nanoelectronic networks from 2D nanoelectronic“pre-
cursors”that are fabricated by conventional lithography. The 3D networks have
porosities larger than 99%, contain 100’s of addressable nanowire devices, and
have feature sizes from the 10 micron scale for electrical and structural intercon-
nections to the 10 nm scale for the functional nanowire device elements. The
network is extremelyflexible with the bending stiffness from 0.0038 to 0.0378,
which is the mostflexible electronics reported.

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24 2 Three-Dimensional Macroporous Nanoelectronics Network