Molecular Dynamics Simulations for Computing Thermal Conductivity of Nanomaterials - Nanoscale Energy Transport and Harvesting - page 29

Figure 1.12 Thermal conductivity versus 14 C impurity percentage for a
(5,5)SWNT at 300 K.

isotopic doping can lead to increased phonon scattering. From
NEMD simulation, the isotopic effect on thermal conductivity of
SWNT was calculated [48], as shown in Fig. 1.12. It is found that the
thermal conductivity decreases as the percentage of 14 C impurity
increases. With 20% 14 C, the thermal conductivity is reduced to
about50%ofthatoneinapure 12 CSWNT.Thethermalconductivity
decreases more quickly at low percentage range than at higher
range. From this curve, thermal conductivity decreases about 20%
with only 5% 14 C isotope impurity. This result tells us that one can
modulate the thermal conductivity of carbon nanotubes by adding
isotope impurity as it alters only thermal conductivity and has no
effectontheelectronicproperties.ThisMDpredictedisotopiceffect
on thermal conductivity has been verified experimentally by Chang
et al. [50]. In their experiment, they found that 20% isotopic doping
caninduce50%reductioninthermalconductivityofnanotube.This
iswith quantitativeagreement withthe MD calculations.
Veryrecently,interestingthermalconductivitydependenceinSi-
coated Ge nanowire (NW) was found by using NEMD simulation
[51]. The structure of the Ge/Si core-shell NW is shown in
Fig. 1.13a. Here the cross-sectional side length (diameter) of Ge
NW D Ge changes from 2.8 to 11.3 nm. Figure 1.13b shows the
roomtemperaturethermalconductivityofGeNWs( D coating = 0)and

Ge/Si core-shell NWs ( D coating > 0) for different D Ge . It is obvious