Molecular dynamics simulation of heat pulse propagation in single-wall carbon nanotubes

The propagation of heat pulses in single-wall carbon nanotubes has been investigated using molecular dynamics simulations. It is found that heat pulses of picosecond duration in (10,0), (7,0), and (5,5) single-wall carbon nanotubes induce several wave packets that propagate at different propagation speeds. The leading wave packets move at the speed of sound corresponding to that of longitudinal acoustic (LA) phonons, followed by wave packets with speeds corresponding to twisted phonon mode (TW), second sound wave, and diffusive components. The waves corresponding to ballistic LA and TW phonon modes in (10,0) and (7,0) zig-zag nanotubes carry more heat energy than in (5,5) armchair nanotubes. The energy carried by wave packets corresponding to the speed of second sound waves is larger than those carried by TW and LA modes. These are used to explain the higher thermal conductivity of zig-zag nanotubes as compared to armchair nanotubes reported recently.

Figure 1

Temporal and spatial distribution of kinetic temperature along the (10,0) SWNT.

Figure 2

Spatial distribution of kinetic temperature along the (10,0) SWNT at times 4 and $5\mathrm{ps}$ after application of the pulse.

Figure 3

Shape of the leading LA mode in (10,0), (7,0), and (5,5) nanotubes at $\text{time}=4\mathrm{ps}$. The peaks are shifted to have all of them centered at slab 10. The line through the data points represents the best Gaussian fit.

Figure 4

Time dependence of the peak kinetic temperature of (a) TW mode wave packets (the line represents the best exponential decay fit), (b) LA mode wave packets.

Figure 5

Time dependence of the peak kinetic temperature of the second sound waves. The lines through data points represent best exponential decay fit.

Figure 6

Temporal and spatial distribution of kinetic temperature along the (5,5) SWNT.

Figure 7

Spatial distribution of kinetic temperature along the (5,5) SWNT at times 3 and $4\mathrm{ps}$ after application of the pulse.

Figure 8

Temporal and spatial distribution of kinetic temperature along the (7,0) SWNT.