Environmental Engineering Reference
In-Depth Information
The phonon LDOS characterizes the distribution of phonons in
real space and can provide more detailed information on thermal
transport. To see the difference in thermal-transport behavior, we
plot phonon LDOS for the three systems at
ω
=
900 cm
−
1
where
their phonon transmission is noticeably different. As shown in
Fig. 3.16c, the atoms with large LDOS is mainly distributed in the
inner part of the two graphene junctions, indicating that phonons
aremorelikelytoappearinthatregion.Therefore,straightchannels
along the transport direction are available for phonons and the
reflection probability is small. Differently, large LDOS appears in
the inner part of the narrow section and the protruding part of
the wide section in the QD. The transport trajectory is not straight,
giving rise to large scattering probability. This rationalizes why the
interfacescatteringismuchstrongerintheQDthaninthejunctions.
3.4.3.3 Edge shape
It is well known that the electronic transport properties of AGNRs
are significantly different from those of ZGNRs [18]. We showed
that the edge shape can also noticeably affect thermal-transport
properties of pristine GNRs [38]. However, its influence on thermal
transportinmorecomplexgraphene-basedtransportsystemsisstill
unknown. To explore edge effects, we further considered graphene
structures composed of AGNRs. Our results show that thermal-
transport characteristics of the graphene structures with armchair
edges are very similar to those with zigzag edges, but the structures
with armchair edges have higher thermal contact resistance and
lower thermal conductance ratio. Thermal contact resistance of the
junctions with armchair edges, which approximately equals to that
betweenAGNRsandgraphene,is0.4
×
10
−
9
m
2
K/Wat300K,about
30% higher than the case of zigzag edge. Thermal conductance
ratios of the single-interface junction, the double-interface junction,
and the QD are 77%, 76%, and 54%, respectively, at 300 K when
the width of the narrow part is about 2 nm. These values are
sizably lower than the corresponding values of structures with
zigzag edges. Our calculations reveal that zigzag edge shows better
thermal-transport ability than armchair edge in graphene-based
nanodevices.
