Chemistry Reference
In-Depth Information
d
n
3
r
4
n
g
|
4
Figure 9.7 Laser-assisted patterned VACNTs for micro-supercapacitor electrodes.
(a) SEM (side view) of Ni-coated VACNTs transferred on a polycarbonate
substrate. (b) Enlarged SEM view of the lateral morphology of VACNTs.
(c) SEM (top view) of Ni-coated VACNTs. (d) SEM (top view) of a line
extremity of a laser-assisted transferred VACNT pattern. (e) Optical
microscopy (top view) of the interdigitated VACNT pattern. (f) Illus-
tration of the micro-supercapacitor device.
r
IOP Publishing.
Reproduced from ref. 42 by permission of IOP Publishing. All rights
reserved.
growth of CNTs on common metallic substrates is challenging since the
growth catalyst can be deactivated by reaction with metals.
17
.
9.3.2.2 Graphene
Graphene is a single layer of planar graphitic carbons that are sp
2
-bonded to
each other in a hexagonal honeycomb configuration. The resistivity of gra-
phene can ideally be as low as 10
6
O cm
1
,
43
and mechanical strength is
over 100 GPa with a very high elastic modulus (
1 TPa).
44
The specific
surface of graphene approaches 1520 m
2
g
1
.
45
In contrast to CNTs, the
2-dimensional structure of graphene enables improved electrical contact.
These outstanding properties prove that graphene is a promising electrode
material, equivalent or possibly superior to CNTs.
Similar to the CVD growth of CNTs, large-area graphene can be produced
by CVD techniques. Copper foils are commonly used as catalytic growth
substrates. A single or a few layers of graphene can grow on the copper
surface with a methane feedstock gas at high temperatures (900-1100 1C).
46
While the CVD method is advantageous in growing large-grained graphene,
the growth domain is restricted by the size of the catalytic copper foil (or the
size of the growth system). Graphene films can be also extracted by exfoli-
ation from a bulk form of graphite such as highly oriented pyrolytic
graphite.
47
Wet exfoliation processes are highly promising and economic
techniques for separating soluble graphene oxide (GO) layers from graphite
B
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