Environmental Engineering Reference
In-Depth Information
Figure 1.22
ThermalconductivityofSiNWsandSiNTsversuscross-section
area at 300 K. The dot and triangle denote SiNWs and SiNTs, respectively.
The cross-section areas for these two SiNWs are 7.37 nm
2
and 4.72 nm
2
,
respectively.
phonons has been probed by the HCACF in Si/Ge core-shell NWs
in EMD simulations [69]. The schematic picture for core-shell NWs
is shown in Fig. 1.23. The canonical ensemble molecular dynamics
simulations with Langevin heat reservoir first run for 10
5
steps to
equilibrate the NWs at a given temperature, during which the free
boundary condition isapplied to allthe atoms on the surface.
After structure relaxation, all atoms are assigned with a random
velocity according to Gaussian distribution. The periodic boundary
condition is applied in the longitudinal direction, and the free
boundary condition is applied in the other two directions. Then
microcanonical ensemble EMD runs for 3
×
10
6
time steps (2.4 ns)
and heat current is recorded at each step. Finally, the heat current
(in longitudinal direction) autocorrelation function is calculated.
The whole procedure is repeated six times with different initial
conditionsofthe velocity distribution.
