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The first experimental study measured thermal conductivity
of suspended graphene exfoliated from highly oriented pyrolytic
graphite (HOPG) using the optothermal Raman technique [29, 30].
There, extremely high thermal conductivity in the range from
3000 W/m/K to 5000 W/m/K at room temperature is reported.
Moreover, phonon mean free path in graphene is estimated to be
around 775 nm at room temperature [30]. Another experiment,
using similar Raman technique but with an additional power meter
under suspended graphene, reported thermal conductivity of sus-
pended graphene grown by CVD exceeding (2500
+
1100/-1050)
W/m/K near 350 K. The other experiment, using a combination of
Raman spectroscopy and electrical current heating, found thermal
conductivity of suspended graphene grown by CVD in the range
from 1500 W/m/K to 5000 W/m/K near 350 K [33]. All
these experiments consistently show that thermal conductivity of
suspended graphene is extremely high, exceeding that of diamond
which possesses the highest bulk thermal conductivity. Contacting
graphene with a substrate significantly affects thermal-transport
properties of graphene. A recent experiment found that the room
temperature thermal conductivity of exfoliated graphene on a
silicon dioxide support is only around 600 W/m/K, which is still
higher than those of metals such as cooper [34]. This value is
significantly lower than that of suspended graphene. The support-
induced thermal conductivity reduction was attributed to strong
interface scattering of flexural modes and phonon leaking across
the interface [34]. A comprehensive review on thermal-transport
properties ofgraphene-related materials can befound in Ref. [28].
3.4 Thermal Conduction of Graphene: Theory
Inthischapter,wewillpresentrecenttheoreticalstudiesonthermal
conduction of graphene. A complete review on the progress of
the whole research field is obviously beyond the scope of the
present chapter. Instead, we place extra emphasis on fundamental
aspects of thermal transport in graphene, which could help readers
understand the more complex and exciting cutting-edge research
and development of the field. On the other hand, we have already
 
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