Environmental Engineering Reference
In-Depth Information
plane have different sound velocity in the longitudinal direction. As
aresult,atomsnearthecore-shellinterfacearestretchedduetothe
different sound velocity. This induces a strong coupling/interaction
between the transverse and longitudinal motions. It is well known
thatwhenthereisaninteractionbetweentwomodes,theoscillation
amplitude will be maximized when the frequencies of these two
modes are close to each other (resonance). Due to the frequency
quantization of the transverse modes, resonance will take place
when the frequency of the longitudinal mode is close to the
eigenfrequency of the transverse mode, giving rise to the enhanced
oscillation amplitude. This coupling picture explains that frequency
quantization of the transverse modes can indeed manifest itself in
HCACFalongthelongitudinaldirectionincore-shellNWs.Moreover,
as the resonance effect of acoustic wave is a coherent process that
requires long-time correlation, the stronger anharmonic phonon-
phonon scattering at high temperature causes phonon to lose
coherence,andleadstothevanishingoftheoscillationeffectathigh
temperature. This study extends the application of EMD simulation,
and provides a coherent resonance mechanism to tune thermal
conductivity of nanomaterials.
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