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MOLECULAR DYNAMICS SIMULATION OF THE THERMAL PROPERTIES OF Y-JUNCTION CARBON NANOTUBES By ARON

by Aron William Cummings, M.S. Washington State University August 2004 Chair: Mohamed A. Osman Molecular dynamics simulations have been used to investigate the thermal properties of a Y-junction carbon nanotube consisting of a (14,0) trunk splitting into a pair of (7,0) branches. Steady state simulations were used to calculate the thermal conductivity of the Y-junction nanotube over a range of temperatures. It was found that the thermal conductivity of the Yjunction nanotube is less than that of a corresponding straight (14,0) nanotube, due to lattice defects in the form of non-hexagonal carbon rings at the junction. These lattice defects result in a discontinuity in the temperature profile of the Y-junction nanotube. Defects that were introduced to a straight (14,0) nanotube resulted in a similar discontinuity in the temperature profile. Phonon spectra revealed that the presence of lattice defects suppresses the density of certain vibration modes, which in turn impedes the heat flow. Heat pulse simulations were also conducted on the Y-junction nanotube. These revealed that the junction at least partially blocked all propagating modes. Furthermore, some asymmetry in heat flow was observed. Traveling waves passed well from the trunk to the branches, but not vice versa. This was attributed the vibrations in traveling waves in the branches being out of phase when they reach the junction. Finally, the inconsistencies in the magnitude and stability of