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a strong structural deformation can be viewed as a perturbation
of the transport of most low-frequency phonons in CNTs [48].
We expect similar feature in graphene because of the similar
sp
2
bonding configuration that is well preserved even under severe
deformation. Third, introducing an isolated structural defect (such
as vacancy or substitution) in graphene-like structures almost does
not affect the transport of low-frequency acoustic phonons and
onlyslightlyscattershigh-frequencyopticalphonons[49].Extended
defects or isolated defects of high concentration may significantly
lower thermal conductance of graphene [50]. However, the defect
formation energy is very high in graphene because of the strong
bonding configuration. Last, but not least, interface scattering is
weak in all-graphene transport systems, characterized by the very
low thermal contact resistance [51]. In short summary, benefitting
from unique 2D plane structure and strong
sp
2
bonding configura-
tion,phononsingrapheneexperienceweakmany-bodyinteractions,
structural distortion induced scatterings, defect scatterings and
interface scatterings, all of which are much weaker than in 3D
materials (such as bulk silicon). This gives rise to very long phonon
mean free path in graphene.
3.4.3
Thermal Transport in Graphene-Based Devices
The finding of graphene has inspired enormous research interest
fromfundamentalsciencetoemergingtechnologies.Usinggraphene
as the base material to replace silicon for future nanoeletronics
is one of the most fascinating and promising research directions.
In graphene-based nanoelectronics, there are two major building
blocks to achieve transistor action. One is graphene junctions built
by GNRs. As shown in Fig. 3.12, the patterned GNRs combined
with controlled doping and manipulation of edge termination can
be used for building electronic devices, like metal-semiconductor
junctions,
p
-
n
junctions,heterojunctions,andfieldeffecttransistors
(FETs) [52]. These GNR-based devices are believed to exhibit
superior performance over the conventional silicon-based devices.
Forinstance,first-principlescalculationsrevealthatGNR-FETsshow
outstandingperformance,characterizedbytheirverylargeON/OFF
ratiooftheorderof10
3
10
4
[52]. The other major building block
is graphene quantum dots (QDs) [53]. Using etched QDs (shown in
∼
